Science and technology Geoff Talbot

Science and technology
of enrobed and filled
chocolate, confectionery
and bakery products
Edited by
Geoff Talbot
CRC Press
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First published 2009, Woodhead Publishing Limited and CRC Press LLC
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Contents
Contributor contact details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
G. Talbot, The Fat Consultant, UK
1.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2
Enrobed and filled products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3
Scope of the book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.4
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.5
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Part I
2
3
1
1
3
6
7
7
Formulation
Chocolate manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
S. Beckett, formerly of Nestlé Product Technology Centre, UK
2.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2
Raw materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3
Basic recipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4
Grinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5
Conching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6
Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.8
Sources of further information and advice . . . . . . . . . . . . . . . . . .
2.9
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Formulation of chocolate for industrial applications . . . . . . . . . . . . .
P. Yates, Barry Callebaut (UK) Ltd, UK
3.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2
Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3
Ingredients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
11
12
16
16
21
26
27
27
28
29
29
30
34
vi
Contents
3.4
3.5
3.6
3.7
3.8
3.9
4
5
6
7
Formulations for industry sectors . . . . . . . . . . . . . . . . . . . . . . . . .
Speciality products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Health aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sources of further information and advice . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
40
45
49
51
52
52
Fats for confectionery coatings and fillings . . . . . . . . . . . . . . . . . . . . .
G. Talbot, The Fat Consultant, UK
4.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2
Crystal structure and polymorphism of fats . . . . . . . . . . . . . . . . .
4.3
Range of coating and filling fats . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4
Effects of fat on quality and processing . . . . . . . . . . . . . . . . . . . .
4.5
Selecting the correct fat for application type . . . . . . . . . . . . . . . .
4.6
Trans fats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.7
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.8
Sources of further information and advice . . . . . . . . . . . . . . . . . .
4.9
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
Compound coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
G. Talbot, The Fat Consultant, UK
5.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2
Cocoa butter alternatives in compound coatings . . . . . . . . . . . . .
5.3
Recipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4
Flavourings and colourings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5
Effects of formulation on sensory and functional properties . . . .
5.6
Effect of fat choice on manufacturing process . . . . . . . . . . . . . . .
5.7
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8
Sources of further information and advice . . . . . . . . . . . . . . . . . .
5.9
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fat-based centres and fillings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
J. Birkett, AarhusKarlshamn Denmark A/S, Denmark
6.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2
Effects of ingredients on quality . . . . . . . . . . . . . . . . . . . . . . . . .
6.3
Recipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4
Manufacturing processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.5
Stability and shelf-life issues . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.6
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.7
Sources of further information and advice . . . . . . . . . . . . . . . . .
6.8
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
57
61
69
71
73
76
78
78
80
80
82
87
89
90
93
98
99
99
101
101
102
112
116
119
121
121
121
Caramels, fondants and jellies as centres and fillings . . . . . . . . . . . . 123
W. P. (Bill) Edwards, Bardfield Consultants, UK
7.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
7.2
Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Contents
vii
Ingredients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gelled products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
127
138
142
147
149
150
151
Biscuits and bakery products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M. Brown, Burtons Foods Ltd, UK
8.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.2
Chocolate formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3
Emulsifiers in chocolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4
Moisture barriers for caramel- and jam-containing biscuits . . . .
8.5
Non-hydrogenated coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6
Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.7
Quality issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.8
Fillings for bakery products . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.9
Future trends in chocolate enrobing . . . . . . . . . . . . . . . . . . . . . .
8.10 Sources of further information and advice . . . . . . . . . . . . . . . . .
152
7.3
7.4
7.5
7.6
7.7
7.8
7.9
8
9
Chocolate and couvertures: applications in ice cream . . . . . . . . . . .
D. J. Cebula and A. Hoddle, Unilever R&D, UK
9.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2
Features of ice cream and chocolate . . . . . . . . . . . . . . . . . . . . . .
9.3
Application processes, formats, requirements, defects . . . . . . . .
9.4
Inclusions in ice cream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.5
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.6
Sources of further information and advice . . . . . . . . . . . . . . . . .
9.7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Part II
152
153
155
155
156
157
159
161
162
162
163
163
164
171
178
180
181
182
Product design
10 Product design and shelf-life issues: oil migration and fat bloom . .
G. Ziegler, Penn State University, USA
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2 Mechanisms of oil migration and fat bloom . . . . . . . . . . . . . . . .
10.3 Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4 Optimizing product quality in relation to oil migration
and fat bloom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.6 Sources of further information . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
185
185
186
195
204
206
206
207
viii
Contents
11 Product design and shelf-life issues: moisture and ethanol
migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
G. Talbot, The Fat Consultant, UK
11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.2 Mechanism of moisture migration . . . . . . . . . . . . . . . . . . . . . . .
11.3 Measurement of permeability . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.4 Reducing moisture migration . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.5 Alcohol (ethanol) migration . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.6 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.7 Sources of further information and advice . . . . . . . . . . . . . . . . .
11.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12 Shelf-life prediction and testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
P. J. Subramaniam, Leatherhead Food International, UK
12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.2 Shelf-life testing methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3 Sensory changes during storage of chocolate confectionery . . .
12.4 Shelf-life prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.5 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.6 Sources of further information and advice . . . . . . . . . . . . . . . . .
12.7 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13 Controlling the rheology of chocolate and fillings . . . . . . . . . . . . . . .
M. Wells, formerly of Cadbury Trebor Bassett, UK
13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2 Defining rheological terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3 How to measure the rheology of chocolate and fillings . . . . . . .
13.4 Typical chocolate flow curves . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.5 Factors affecting chocolate rheology . . . . . . . . . . . . . . . . . . . . .
13.6 The rheology of fillings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.7 Issues with shell moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.8 Issues with enrobing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.9 Issues with one-shot depositing . . . . . . . . . . . . . . . . . . . . . . . . . .
13.10 Dealing with viscoelasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.11 Sources of further information and advice . . . . . . . . . . . . . . . . .
13.12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
211
211
212
214
216
229
231
231
231
233
233
234
243
249
251
252
253
253
255
255
256
259
263
265
273
278
280
281
282
282
283
14 Using microscopy to understand the properties of confectionery
products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
K. Groves, Leatherhead Food International, UK
14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
14.2 Microscopy techniques and their uses . . . . . . . . . . . . . . . . . . . . . 286
14.3 Relationships between the microstructure of chocolate and
14.4
14.5
14.6
Part III
Contents
ix
coatings and their properties . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
298
307
307
307
Processing, packaging and storage
15 Ingredient preparation: the science of tempering . . . . . . . . . . . . . . .
K. Smith, Unilever R&D, UK
15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.2 Effects of tempering on quality . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3 Polymorphism and phase behaviour of triacylglycerols . . . . . . .
15.4 Cocoa butter polymorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5 Changes during tempering . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.6 Factors affecting tempering . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.7 Measurement of temper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.8 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.9 Sources of further information and advice . . . . . . . . . . . . . . . . .
15.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16 Tempering process technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
K. Richter, Sollich KG, Germany
16.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.2 Characteristics of cocoa butter . . . . . . . . . . . . . . . . . . . . . . . . . .
16.3 Chocolate tempering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4 Chocolate coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.5 Chocolate moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6 Aerated chocolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.7 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17 Manufacturing processes: enrobing . . . . . . . . . . . . . . . . . . . . . . . . . .
M. J. Bean, Baker Perkins Ltd, UK
17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.2 Types of enrobing machines . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3 Centre preparation and presentation to the enrober . . . . . . . . . .
17.4 Chocolate application case study . . . . . . . . . . . . . . . . . . . . . . . .
17.5 Chocolate handling systems within the enrober . . . . . . . . . . . . .
17.6 Environmental and hygiene issues . . . . . . . . . . . . . . . . . . . . . . .
17.7 Ancillary equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.8 Typical operating parameters . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.9 Faults and remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.10 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.11 Sources of further information and advice . . . . . . . . . . . . . . . . .
313
313
314
315
322
324
330
333
337
338
339
344
344
344
346
355
359
359
361
361
362
362
363
376
377
379
385
388
390
390
394
396
x
Contents
17.12 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396
18 Manufacturing processes: chocolate panning and inclusions . . . . .
G. Geschwindner and H. Drouven, Drouven & Fabry GmbH, Germany
18.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.2 Centres and raw materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3 Preparation of the centres: precoating . . . . . . . . . . . . . . . . . . . . .
18.4 Panning process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.5 Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.6 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.7 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8 Sources of further information and advice . . . . . . . . . . . . . . . . .
397
397
398
400
403
405
406
412
412
19 Manufacturing processes: production of chocolate shells . . . . . . . .
J. Meyer, Bühler Bindler GmbH, Germany
19.1 Fundamentals of chocolate shell production methods . . . . . . . .
19.2 Cold stamping technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3 Depositing, vibrating, cooling and demoulding . . . . . . . . . . . . .
19.4 Process conditions and product quality . . . . . . . . . . . . . . . . . . . .
19.5 Faults, causes and solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.6 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.7 Sources of further information and advice . . . . . . . . . . . . . . . . .
19.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
414
20 Manufacturing processes: deposition of fillings . . . . . . . . . . . . . . . .
J. Meyer, Bühler Bindler GmbH, Germany
20.1 Modern processes for depositing fillings into premade
shells: One-Shot technology . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.2 One-Shot process conditions and product quality . . . . . . . . . . . .
20.3 Faults, causes and solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.4 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.5 Sources of further information and advice . . . . . . . . . . . . . . . . .
20.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
427
415
416
418
422
423
423
425
426
428
428
436
438
438
439
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
Contributor contact details
(* = main contact)
Chapters 1, 4, 5, 11
Geoff Talbot
The Fat Consultant
Suite 250
St Loyes House
20 St Loyes Street
Bedford
MK40 1ZL
UK
Email: [email protected]
Chapter 2
Dr S. T. Beckett
Formerly of Nestlé Product
Technology Centre
Haxby Road
York
YO91 1XY
UK
Email: [email protected]
Chapter 3
Philip Yates
UK Product Manager
Barry Callebaut (UK) Ltd
Wildmere Road
Banbury
OX16 3UU
UK
Email: [email protected]
Chapter 6
J. Birkett
AarhusKarlshamn Denmark A/S
DK-8000 Aarhus C
Denmark
Email: [email protected]
Chapter 7
Dr Bill Edwards
Bardfield Consultants
14 Durham Close
Gt. Bardfield
Braintree
Essex
CM7 4UA
UK
Email: BillEdwards@bardfield
consultants.co.uk
xii
Contributor contact details
Chapter 8
M. Brown
Technical Operations Manager
Burtons Foods Ltd
Pasture Road
Moreton
Merseyside
CH46 8SE
UK
Email
[email protected];
[email protected]
Chapter 9
D. J. Cebula* and A. Hoddle
Unilever R&D
Colworth Science Park
Sharnbrook
Bedford
MK44 1LQ
UK
Email: [email protected];
[email protected]
Leatherhead Food International
Randalls Road
Leatherhead
Surrey
KT22 7RY
UK
Email: psubramaniam@leatherhead
food.com
Chapter 13
Martin Wells
106 Golden Cross Lane
Catshill
Bromsgrove
Worcs
B61 0LA
UK
Email: [email protected]
Formerly of Cadbury Trebor Bassett
Bournville
Birmingham
UK
Chapter 14
Chapter 10
Professor G. R. Ziegler
Department of Food Science
Penn State University
341 Food Science Building
State College
PA 16801
USA
Kathy Groves
Food Innovation
Leatherhead Food International
Randalls Road
Leatherhead, Surrey
KT22 7RY
UK
Email: [email protected]
Email:
[email protected]
Chapter 12
Chapter 15
Persis Subramaniam
Food Innovation
K. W. Smith
Unilever R&D
Contributor contact details
Colworth Science Park
Sharnbrook
Beds
MK44 1LQ
UK
xiii
Peterborough
PE4 7AP
UK
Email:
[email protected]
Email: [email protected]
Chapter 18
Chapter 16
K. Richter
Process-Engineering
SOLLICH KG
Siemensstraße 17–23
32105 Bad-Salzuflen
Germany
Email: [email protected]
G. Geschwindner and H. Drouven*
Drouven & Fabry GmbH
Hirzenrott 6
52076 Aachen
Germany
Email: [email protected]
Chapters 19, 20
Chapter 17
M. J. Bean
Baker Perkins Ltd
Manor Drive
Paston Parkway
Joerg Meyer
Technologist/Manager Pilot Plant
Bühler Bindler GmbH
Germany
Email: [email protected]
1
Introduction
Geoff Talbot, The Fat Consultant, UK
Abstract: Multi-component confectionery products with a chocolate coating are not
new, the first ones having been developed during the early part of the 20th century. Their
complexity has, however, increased tremendously during the past hundred years or so.
One of the reasons for this has been the continual consumer demand for new taste and
textural sensations. This means that, despite the well-established nature of this sector of
the food industry and also despite the fact that many of the leading products were
developed over 70 years ago, it is still a sector that is growing. This book is divided into
three parts. Part I covers the main component parts of these multi-component products –
chocolate, compound coatings, fat-based fillings, caramels, fondants, biscuits, bakery
products and ice cream. Part II then goes on to discuss some of the product design issues
related to enrobed and filled confectionery including fat and moisture migration, fat
bloom, as well as the shelf-life, rheology and microstructure of chocolate. Part III deals
with the processing and production of these products – tempering, enrobing, moulding,
panning and cooling,.
Key words: biscuits, caramels, chocolate, compound coatings, cooling, enrobed
confectionery, enrobing, fat bloom, fats, filled confectionery, fillings, fondants, ice
cream, market trends, microstructure, moisture migration, moulding, oil migration,
panning, rheology, storage, tempering.
1.1
Introduction
The basis of all chocolate-enrobed and filled confectionery products is, of course,
chocolate. To look at the way in which these products have developed means going
back many centuries to central America where first the Mayans and then the Aztecs
prized the cocoa bean for the drink that it produced. The Aztecs called this drink
‘chocolatl’ which means ‘warm liquid’. They called the cocoa bean, ‘the food of
the gods’, a name which continues to this day in the Latin botanical name for the
2
Enrobed and filled chocolate, confectionery and bakery products
cocoa tree, Theobroma cacao. According to legends, Montezuma II, the emperor
of the Aztecs, consumed 50 cups of chocolatl each day. Not only were cocoa beans
used as the basis of this drink, they were also used as a form of currency amongst
the Aztecs.
The beans were first brought to Europe by Columbus and were one of the many
things he brought back from his journeys to be presented to King Ferdinand and
Queen Isabella of Spain. They were, however, largely ignored until the Spanish
explorer Cortez arrived in Mexico in 1519. Thinking that he was a long-lost godking, the Aztecs greeted him and his crew with cups of chocolatl. This was the start
of the downfall of the Aztec empire and the Spanish overpowered them. It took
Cortez, though, to realise the potential of these beans and he introduced the drink
to the Spanish aristocracy, after having added sugar to make it more to their taste.
Its popularity spread across Europe and by the mid-17th century chocolate
drinking houses had sprung up across England.
It was not until 1828, when van Houten in The Netherlands found a way of
pressing the fat from cocoa beans and then adding this back to a mixture of
powdered bean and sugar that the first solid chocolate bars were produced. Further
processing developments included the introduction in 1847 by Fry in Bristol of
steam presses to separate out the fat more easily and thereby produce the first bars
of plain chocolate. Milk chocolate came along some 30 years or so later having
been developed by Daniel Peter in Vevey in Switzerland.
Even in these early days, plain chocolate was used to coat centres such as
fondants and nuts and the first ‘chocolate box’ is generally attributed to Cadbury.
It is said (National Confectioners’ Association) that in 1868 Richard Cadbury
decorated a box with a painting of his young daughter holding a kitten in her arms.
Filled chocolates were mainly sold from trays (much like the luxury hand-made
products of today). This was reflected in the names of two new Cadbury products
launched in 1914 (Plain Tray) and in 1915 (Milk Tray, a chocolate box assortment
still produced today). Other British chocolate box assortments that are still
available, such as Terry’s All Gold and Rowntree’s (now Nestlé’s) Black Magic,
were launched in the 1930s.
Filled countlines (i.e products that were sold as an individual product, often in
the form of a bar) were first produced in the United States in the early 20th century
but some would say that the 1930s were the golden era of development for such
products. Certainly many products still available today were first developed and
launched in that decade in the United Kingdom (Opie, 1988):
•
•
•
•
•
•
•
1932
1935
1935
1935
1936
1937
1937
Mars
Milky Way
Aero
Chocolate Crisp (renamed KitKat in 1937)
Maltesers
Rolo
Smarties.
Many of these are now global brands.
Introduction
1.2
3
Enrobed and filled products
It is clear from this historical background that it didn’t take long after plain and then
milk chocolate in a solid form were developed for manufacturers to start to make
chocolate a part of a whole product and to use it to encase other components. This
was partly to extend existing product lines by, for example, coating already
commercially successful biscuit products with chocolate, partly to protect the
centres from deterioration such as, for example, preventing the drying out and
hardening of caramel by putting a coating of chocolate around it. The main
impetus, though, was the ability to produce totally new products by combining
cereal-based biscuits and wafers, fruits and nuts, aqueous-based systems such as
caramels, jams and fondants and fat-based pralines in a chocolate wrapper. These
developments gave new combinations of tastes and textures to satisfy consumers’
hunger for new sensations.
In recent years cross-over and leveraging of brands from one product sector into
another has been a major factor in developing new products. One of the most
successful of these cross-over developments was the launch in 1989 of the Mars ice
cream bar which was soon followed by many other ice cream products coated in
‘real’ chocolate (until then most ice cream bars had been coated in a chocolateflavoured compound coating). This has since been followed by the translation of
other chocolate confectionery products into cake bars, biscuits, drinks, desserts
and so on.
It is useful, perhaps, at this stage to say exactly what is meant by ‘enrobing’ and
‘filling’. Enrobing means to apply a coating of, usually, chocolate (although it
could also be a chocolate-flavoured coating or, indeed, a coating of any other
flavour) to the outside of a product. Typical examples are coated biscuits, coated
ice cream bars, coated cakes, coated fruits and nuts. The coating is usually applied
by means of an enrober. This is a machine in which the products to be coated pass
through a continuous ‘curtain’ of the coating. As they pass through, they are coated
on the top, sides and bottom. Excess coating is removed and the remaining coating
is crystallised by passing the coated product through a cooling tunnel.
Some products are dipped into the coating and removed before again allowing
the coating to crystallise and harden. Products that are typically dipped are ice
creams on a stick (where the coldness of the ice cream begins to harden the coating
even before passing into a blast freezer) and some hand-made confectionery
products. Other products, particularly small items such as nuts and raisins are
coated by panning. In this process the centres are continually moving in a rotating
‘pan’ (similar to a cement mixer) and the coating is sprayed on to them gradually
building up in a number of layers. In other products, particularly where a thin
coating is needed, the coating will be sprayed on to the surface of the centre. This
is often used to apply thin barriers to reduce moisture and alcohol migration.
On the other hand, there is ‘filled’ confectionery. Rather than start with the
centre and put the coating around it, in filled confectionery we start with the
coating and put the centre inside it. This is usually achieved by first making a shell
of chocolate into which is deposited the filling. Since, in most applications, this
4
Enrobed and filled chocolate, confectionery and bakery products
leaves an incomplete coating on the product it is then finished by ‘backing off’ with
further coating. For example, a praline centre can be deposited into a chocolate
shell which, at that stage, consists of the top and sides of the eventual end product.
Once the shell has been filled with the praline centre a further quantity of fluid
chocolate is deposited on top of the praline centre to seal the whole product. This
final ‘backing-off’ layer will be the base of the end product.
Chocolate shells are usually produced in one of two ways. Either the moulds are
filled with a surplus of chocolate and are then inverted and rotated both to coat the
insides of the mould and allow excess chocolate to drain back for further use, or a
small surplus of chocolate is deposited into the mould and a cold former is plunged
into the chocolate to produce a shell with very accurately defined dimensions. In
some instances, the centre is pressed down into the still liquid chocolate in the
mould, allowing this to squeeze up the sides and over the top of the centre. This
method is used where, for example, chocolate-coated biscuits are produced in a
mould to allow the name of the product to be moulded into the top surface.
1.2.1 Definitions
The fact that individual nations can be very protective about what constitutes
‘chocolate’ means that there is no single compositional standard or definition of
chocolate across the world. For example, it took some 30 years or so for an EUwide definition of chocolate composition to be agreed, finally culminating in the
Directive which came into force in August 2003. One of the main stumbling blocks
(although, by no means, the only one) in global acceptance of a single compositional
standard for chocolate has been whether or not non-cocoa vegetable fat can be
added. For many years some EU countries permitted the use of vegetable fat up to
a level of 5% in chocolate, while others did not. The 2003 EU Directive permits the
use of up to 5% vegetable fat in chocolate but only under well-defined circumstances. The United States, on the other hand, does not permit the use of vegetable
fat. In some ways, Codex Alimentarius could be seen as a global standard but even
Codex has recently amended its standard to include now the use of vegetable fat.
These different legislations will be discussed in more detail in Chapter 3, but it is
perhaps instructive, even here, to compare the standards for milk chocolate in the
EU, the USA and Codex (Table 1.1).
If compositions move outside these definitions this does not mean that they are
unsuitable for consumption and cannot be used. It simply means that they cannot
be called ‘chocolate’ and need to be labelled in some other way. The most common
form of labelling, in the United Kingdom at least, is to call them ‘chocolateflavoured coatings’. Other countries will have other forms of wording.
Within the food industry, however, these ‘chocolate-flavoured coatings’ are
often called compound coatings and, if non-cocoa butter fats are used they are
referred to as compound coating fats (or, also, as cocoa butter alternatives). This
book covers the use of both chocolate and compound coatings. Where it is
unnecessary to distinguish one from the other, the term ‘chocolate’ will usually be
used for simplicity. Where remarks apply solely to chocolate containing cocoa
Introduction
5
Table 1.1 Comparison of milk chocolate compositions in EU, USA and Codex
(extracted from Yates, Tables 3.1, 3.2 and 3.3 of this book)
Total cocoa solids (dry)
Non-fat cocoa solids (dry)
Total milk solids (dry)
Milk fat
Total cocoa butter + milk fat
Vegetable fat
Cocoa butter
EU (%)
USA (%)
Codex (%)
25 min
2.5 min
14 min
3.5 min
25 min
5 max
10 min
25 min
2.5 min
12–14 min
2.5–3.5 min
12 min
3.39 min
Not permitted
5 max
20 min
butter (for example, those coatings which require tempering to create a stable
crystal form) this will be made clear in the text. Where remarks apply solely to
compounds or compound coatings these will be referred to as such.
While on the subject of components in chocolate, it should also be made clear
that, unless otherwise stated, milk fat is taken to be the fat obtained specifically
from cows’ milk. It may also be interchangeably referred to as anhydrous milk fat
(AMF) or anhydrous butter. Butter itself is an emulsion of water droplets within a
milk fat matrix, typically containing about 80% fat and 16% water. Although
butter can be directly used in some enrobed centres (as an ingredient in caramels
or biscuits, for example) it is more generally used in its anhydrous form.
Many of the various phases of multi-component enrobed or filled products
contain fat. Fat will be referred to in this volume in various ways. While the terms
‘oil’ and ‘fat’ will often be used interchangeably there will be occasions when ‘oil’
is used to denote the liquid form and ‘fat’ the solid form. Oils and fats are,
chemically, tri-esters of three fatty acid groups on a backbone of glycerol. The food
industry usually refers to these as ‘triglycerides’ or TG; the scientific and academic
communities, however, call them ‘triacylglycerols’ or TAG. These terms will be
used interchangeably in this book as will the corresponding terms for diglycerides/
diacylglycerols (DG/DAG) and monoglycerides/monoacylglycerols (MG/MAG).
1.2.2 Market trends
Although chocolate has been around for a long time, EU production statistics still
show a rising trend (Table 1.2), although consumption patterns are fairly static.
According to CAOBISCO (Association of chocolate, biscuit and confectionery
industries of the European Union) the greatest consumers of chocolate confectionery are the Swiss with, in 2006, a per capita consumption of 10.05 kg, closely
followed by the United Kingdom with a per capita consumption of 9.97 kg. Indeed,
in general, northern European countries are the greatest consumers of chocolate
confectionery, occupying all of the top ten places in 2006. The United States ranks
12th in the CAOBISCO list with a consumption of 5.45 kg per head. Southern
European countries have lower levels of consumption and this is related to the fact
that it is more difficult to keep chocolate in a hard, solid, bloom-free condition in
Mediterranean climates than it is in northern Europe.
6
Enrobed and filled chocolate, confectionery and bakery products
Table 1.2 EU production and consumption of chocolate confectionery (2004–6) (from
CAOBISCO)
2004
2005
2006
Production (103 tonnes)
Consumption (103 tonnes)
2510
2766
2814
2381
2367
2382
Since many biscuits and wafers are chocolate coated it is useful just to mention
the statistics for 2006 for these products (although these are not necessarily all
chocolate coated). The Netherlands are by far the largest consumers of these
products, at 18.72 kg per head, followed in second place by the United Kingdom
with a consumption of less than half of that (9.22 kg per head).
1.3
Scope of the book
It is the intention of this book to be both one that can be read as a whole by taking
the reader logically through the various aspects and processes of producing
chocolate-enrobed and filled chocolate products, and also one that can be used as
a reference text for specific aspects of the whole enrobing process.
Logically, the production of chocolate is described beginning with a brief
overview of the raw materials used and the mixing, refining and conching processes
necessary to get chocolate in a form suitable for subsequent processing in tempering,
enrobing and moulding equipment. The various formulations that can be used to
produce chocolate, particularly chocolate for industrial use are also described. Legislation has already been referred to and a more detailed comparison of the legislation
relating to chocolate composition in the main producing countries is made.
Although chocolate is rich in both fat and sugar, it has a number of health
benefits within its composition. Of these, perhaps the ones that make the headlines
the most are the flavanols that are found in high cocoa-solids dark chocolate and
which have been shown to help reduce the risk of cardiovascular disease as well as
act as antioxidants. Even though the fat in chocolate is rich in saturates there is
some evidence to suggest that some of the saturated fatty acids in cocoa butter may
well be neutral in terms of blood cholesterol levels.
As has already been mentioned, fats are present in many of the components of
enrobed and filled confectionery and so an introduction is given to confectionery
fat technology and to the use of fats in these products. To complement the chapters
on chocolate production and composition there is also a chapter on compound
coatings which describes the differences between the different types of compound
fat and how they are used in place of chocolate.
We then move on to look in more detail at the different types of centre that are
either coated in chocolate or compound or which are used to fill shells of these
materials. These chapters consider not only the more conventional ‘chocolate-box
assortment’ types of centres based on fat-continuous fillings, caramels and fondants
Introduction
7
but also the more generic product sectors of biscuit and bakery products and ice
cream.
Part II of the book deals with various aspects of product design looking first at
the major problems that can arise as a result of having multi-component systems.
These are oil migration and fat bloom which are often inexorably linked together,
and the analogous problems of moisture and alcohol migration. It is often necessary to take these into account when designing a new enrobed or filled product and
the factors associated with both promoting and minimising them are described.
There then follows three chapters relating to the chocolate itself which are also
of importance in product design but more related to the process that the product
will need to undergo or the storage of the product than to the actual product itself.
These are the shelf life, rheology and the microstructure of the chocolate, coating
or filling being used.
Part III covers the all-important aspects of processing beginning with two
chapters on tempering. The first looks at the science of tempering and, in particular, at what happens to the fat phase of chocolate during the different stages of
tempering and temper measurement. The second considers the industrial methods
available for tempering chocolate and how these are used in practice.
Having tempered the chocolate (or not, in the case of compound coatings) it can
then be used either to enrobe centres or to be formed into shells for subsequent
filling. Both of these processes and the necessary equipment are described. In the
case of a shell-moulded product it then, of course, has to be filled and so both the
processes for filling pre-made chocolate shells and the process of forming both
shell and filling in one operation (one-shot technology) are considered. After
enrobing or production of a chocolate shell it is necessary to cool and crystallise the
chocolate ready for packing. In this part of the book there is also a chapter on
panning inclusions and small components such as nuts and fruits.
1.4
Acknowledgements
I would like to thank all the authors who have contributed chapters to this book. It
is never easy fitting such things in with everything else that needs to be done,
especially when facts need to be checked to ensure that in this fast-moving world
they are still up to date, but they have all approached the task with professionalism
and dedication. I would also like to thank the editors at Woodhead Publishing for
their support and advice.
1.5
References
CAOBISCO.
Consumption Trends (2004–2006). http://www.caobisco.com/doc_uploads/
Charts/consumption_trends.pdf.
CAOBISCO. Production Trends (2004–2006). http://www.caobisco.com/doc_uploads/Charts/
production_trends.pdf.
NATIONAL CONFECTIONERS’ ASSOCIATION. ‘Facts and Trivia’. http://www.chocolateusa.org/
Story-of-Chocolate/how-america-loves-chocolate.asp
OPIE R (1988). Sweet Memories, Pavilion Books Ltd, London.
Part I
Formulation
2
Chocolate manufacture
S. Beckett, formerly of Nestlé Product Technology Centre, UK
Abstract: This chapter describes the processes and ingredients involved in the large
scale manufacture of liquid chocolate to give it the correct taste and flow properties. The
quality criteria of the cocoa and its initial processing are particularly important. For the
chocolate to be smooth tasting, the solid particles must be ground to less than 0.03 mm
and this can be carried out in several different ways. The ground material is normally in
the form of a powder or thick paste which is converted into a liquid in a machine called a
conche. This machine is also able to modify the taste and remove unwanted acidic
flavours from the chocolate.
Key words: chocolate conche, cocoa beans, flow properties, grinding, liquefying.
2.1
Introduction
Most people think of chocolate as a solid material, which when eaten melts in the
mouth, whereas to the confectioner it is a liquid that is poured into a mould or over
the sweet centre. This chapter describes the processes and ingredients involved in
the large scale manufacturing of this liquid chocolate.
The final taste and texture depend strongly upon the ingredients being used.
Their quality criteria and initial processing, where applicable, are the subject of the
second section of this chapter, followed by some very basic recipes. More detailed
recipes are given in a later chapter of this book.
The particles of the non-fat ingredients themselves are relatively large, often
greater than 1 mm in diameter. For the chocolate to be smooth this must be reduced
to less than 0.03 mm. The way this is done is described and is very important for
the final chocolate taste and texture. At this stage the chocolate is often in powder
form and a machine, unique to the industry, called a conche is then used to turn it
into a liquid. At the same time the taste is modified, in particular by the removal of
12
Enrobed and filled chocolate, confectionery and bakery products
acids contained in the cocoa beans. This chapter concludes by looking at quality
characteristics followed by possible future developments in chocolate manufacture.
2.2
Raw materials
2.2.1
Cocoa based
Growing areas and conditions
All commercial cocoa is grown within 20o of the equator. Although the cocoa trees
originated in the north of southern and central America, the majority of the world’s
cocoa is now grown in Africa, with 40% coming from the Ivory Coast alone.
Significant amounts are now also produced in south east Asia.
There are four types of cocoa or cacao tree (Theobroma cacao, L.) namely
Criollo, Forastero, Trinitario and Nacional. These grow in areas of high rainfall
that is evenly distributed throughout the year and prefer a high humidity, typically
70–80% during the day and up to 100% at night. The mean monthly temperatures
should be between 18 °C and 32 °C with an absolute minimum of about 10 °C.
About 90% of the world’s cocoa is grown by smallholders (Fowler, 2009), usually
on farms with mixed cropping systems.
The flavour of the bean depends not only upon the cocoa type, but also upon the
soil and weather conditions and many other factors, especially the harvesting and
fermentation. These different flavours can be experienced by tasting dark chocolates made from cocoa from single origins which are currently available as tablets.
In many other products, beans from several sources are often blended in order to
get a consistent flavour.
Harvesting
The flowers on the cacao tree develop from flower cushions on the trunk and
branches. Some trees flower almost continuously, whereas others have welldefined periods of flowering (often twice a year). The flowers are pollinated by
small insects such as midges. After five to six months, the fully developed pods are
between 100 and 350 mm long and weigh between 200 g and 1 kg. When they
ripen, most pods change colour – usually from green or red to yellow or orange.
They are then cut by hand from the trunks and branches. The pods that are low on
the trunk are cut with a machete (cutlass). The upper branches are harvested using
a special knife fixed on a long pole. The crop does not all ripen at the same time so
that harvesting has to be carried out over a period of several months. Pods are
normally harvested every two to four weeks. In West Africa the main harvest
period is from the beginning of October until December.
The pods are opened to release the beans, either by cutting with a machete or
cracking with a simple wooden club. There are about 30 to 45 beans in the pod
covered in a sweet, white mucilaginous pulp and attached to a central core or
placenta (Fig. 2.1). At this stage the beans do not contain the correct chemicals to
Chocolate manufacture
Fig. 2.1
13
Cocoa beans in pods (Fowler, 2009: 18) reproduced with the permission of
Wiley-Blackwell.
give a chocolate flavour. The precursor flavours are mainly formed and developed
during the subsequent fermentation and roasting processes.
Fermentation
In the fermentation stage the fresh beans are usually heaped in a pile or in a wooden
box, typically for five days. In West Africa the beans are normally covered with
banana leaves. The white pulp contains natural yeasts and bacteria which multiply
causing the breakdown of the sugars and mucilage. This kills the bean and forms
some of the flavour precursors. The whole fermentation process is critical for the
final bean quality and is often monitored by purchasers using a cut-test (Fowler,
2009). This test involves cutting up to 300 beans into half lengthways to determine
the proportion that are visibly mouldy, slaty, infested, germinated or flat (i.e.
containing no nib or cotyledon). Slaty beans (more than 50% grey or slaty in
colour) have not undergone fermentation, giving them a low level of cocoa flavour
coupled with high levels of astringency. Fully fermented beans are brown, brown/
purple and purple in colour.
Drying
The fermented beans are then dried either in the sun or by artificial heating. It is
very important that the moisture level is about 7–8%. At higher moisture levels the
beans are very likely to become mouldy. This imparts an unpleasant flavour and so
the beans cannot be used for chocolate making. If the beans are dried below about
6% they become very brittle and difficult to process.
When drying beans with artificial heating, care must be taken to ensure that the
14
Enrobed and filled chocolate, confectionery and bakery products
smoke does not come into contact with the beans, otherwise it too will impart a
flavour that will be present in the final chocolate and cannot be removed by
subsequent processing.
Roasting and winnowing
The cocoa bean consists mainly of an outer shell surrounding two cotyledons. This
shell is very hard and will damage processing machinery. It is also often encrusted
with dirt and does not have a good cocoa taste and so must be removed. Traditionally the beans are roasted to produce more chocolate flavour and also to kill any
microbiological contamination that may have arisen during the growing, fermentation, drying or transport. This loosens the shell from the cotyledon and once the
beans have been broken in a cracker, the light shell can be removed in an air stream
(winnowed) from the heavier centre, known as the cocoa nib.
An alternative procedure is to heat the surface of the bean to release the shell,
then break and winnow, before roasting the cotyledons. This process, known as nib
roasting, is said to give a more even roast and to save energy, because the shell,
which is being thrown away, is no longer being taken to a very high temperature.
Roasting itself is normally at a temperature of between 110 oC and 140 oC and takes
about 45 minutes to 1 hour.
Grinding cocoa
The nib contains approximately 55% of a fat known as cocoa butter. This is mainly
solid at 20 oC, but is liquid at body temperature. The fat is contained in cells within
the cotyledons and must be released by grinding to break up the cells and produce
an ingredient called cocoa liquor or cocoa mass. It is normally best to grind it finer
than 0.03 mm so that the cocoa liquor feels smooth in the mouth and most of the fat
is released. Unlike chocolate, the finer the liquor is ground, the more easily it flows.
The nib pieces are often bigger than 1 mm, so a large amount of size reduction is
required and this is normally done in two or more stages. The first stage is often in
an impact mill, where the cocoa nibs are broken by hammers or pins. The cocoa
liquor produced is then made finer in a disc mill or one or more ball mills and is now
ready for chocolate or cocoa butter production. The production of cocoa liquor is
increasingly being carried out in the country of origin of the beans.
Cocoa butter
As was noted earlier, the cocoa liquor contains about 55% cocoa butter. The
highest quality fat is obtained by pressing it out directly, leaving a hard cake
material which is milled into cocoa powder for use in drinks and cakes and similar
products. Cocoa butter can also be extracted chemically and/or treated to remove
flavour and manufacture a deodorised fat.
2.2.2 Sugar
Standard granulated sugar (sucrose) is normally used to make chocolate, although
icing sugar or larger particle size sugar are sometimes preferred. Ideally the sugar
Chocolate manufacture
15
should have a narrow particle size distribution and have a low moisture content.
Unlike in many other applications colour is not usually an important quality
criteria.
Low calorie, tooth-friendly and sucrose-free chocolates use sugar alcohols,
often with other bulking agents such as polydextrose and artificial sweeteners, to
replace the sucrose. These sometime require lower temperature conching and
should be eaten in moderation because of their laxative nature.
2.2.3
Milk based
Full cream milk powder
Chocolate contains a lot of small sugar particles and any moisture that is present
will bind the particles together and stop the chocolate flowing properly. It is
therefore important to remove all the water from the milk before it is used to make
chocolate. The EU, Codex Alimentarius and some other legislation states that all
the solid components of the milk, for example lactose and whey protein, must be
in their natural proportions. This means that although lactose (milk sugar) is
sometimes used in chocolate to reduce its sweetness (lactose is less sweet than
sucrose) it is not part of the milk component for regulatory and labelling purposes.
Milk can be dried in several ways, but the majority of the milk powder used in the
chocolate industry has been spray dried. It is possible to dry the whole milk so that the
powder includes the milk fat and this is said to have a better flavour than when
skimmed milk is used. Roller dried full cream milk powder is considered better by
some manufactures as the chocolate produced tends to have a lower viscosity.
Skimmed milk powder and butter oil
Many manufacturers prefer to use skimmed milk powder and then add in the milk
fat (butter oil) during the processing. This tends to give the liquid chocolate better
flow properties than when full cream milk powder is used.
Chocolate crumb
In the United Kingdom, United States and some other countries, chocolate crumb
is used. This was developed in the early part of the 20th century, when milk
powders had poor keeping qualities, and is an ingredient that can be stored and
used over a period of more than a year. It is normally made by drying condensed
milk and adding cocoa liquor during the later stages of this process. The sugar and
the natural antioxidants in the cocoa liquor give the long shelf-life, but the
Browning reaction, which takes place during the drying stage, gives it a cooked
flavour. The actual crumb processes are often highly kept secrets, as they provide
the means by which several manufacturers obtain their house flavours.
2.2.4 Emulsifiers
Part of the enjoyment of eating chocolate is the way it melts and flows in the mouth.
16
Enrobed and filled chocolate, confectionery and bakery products
This is in part due to the way in which the cocoa butter coats the solid particles. To
help it do so, an emulsifier (surface active agent) is often added to the chocolate at
a low level, normally less than 0.5%. Traditionally this is lecithin produced from
soya or sunflower and is claimed to have beneficial health effects at higher levels.
Other emulsifiers are used, sometimes to produce special shaped sweets or to
reduce the formation of the white mould-like spots on chocolate known as
chocolate bloom (see later chapters).
2.3
Basic recipes
2.3.1 Dark chocolate
Dark chocolate is made from cocoa liquor, sugar and cocoa butter. Many contain
a small amount of milk fat to reduce the formation of chocolate bloom. High cocoa
content chocolates do not contain any added cocoa butter (all the cocoa butter
present comes from the cocoa liquor).
2.3.2 Milk chocolate
Milk chocolate is the same as dark chocolate, but with milk solids and fat replacing
some of the cocoa liquor. Legislation is very strict about how much cocoa liquor
and milk must be present. In some countries a high level of milk content must be
labelled as household milk chocolate or its equivalent.
When using chocolate crumb, the milk, sugar and most, if not all the cocoa
liquor are already together as a single ingredient, which only needs grinding,
followed by the addition of cocoa butter and emulsifiers at the conching stage.
2.3.3 White chocolate
White chocolate is made from milk powder, sugar and cocoa butter. Deodorised
cocoa butter is usually preferred to avoid the off-flavours present in pressed cocoa
butter.
2.4
Grinding
2.4.1 Importance of particle size
Most of the solid ingredients are about 1 mm or more in diameter. The tongue will
detect particles larger than 0.03 mm and the chocolate will appear to be gritty. The
finer a milk chocolate is milled, the smoother and creamier it becomes. Dark
chocolates on the other hand increase in cocoa flavour as they are made finer.
Often, milling produces a lot of very fine particles of less than 0.005 mm in size.
The surface of these particles needs to be coated with fat to make them flow, so that
unless extra fat is added the chocolate has a high viscosity and tends to melt less
Chocolate manufacture
Fig. 2.2
17
A five-roll refiner.
easily, often remaining in the mouth with a slightly clay-like texture. Chocolate is
therefore the opposite to cocoa, which normally gets much thinner when it is milled
to be smaller.
Good grinding therefore involves breaking the bigger particles without producing too many very small ones, in other words having a narrow particle size
distribution. This is often best achieved by having a series of milling events each
of about 4- or 5-fold reduction, rather than one very big breaking procedure.
2.4.2 Two- and five-roll refining
Five-roll refiners (Fig. 2.2) have been used for very many years to grind chocolate
and other industrial products such as paints and pigments. For many years the sugar
or crumb was dry milled in a hammer mill and the powdered product added to some
of the fat and remaining ingredients before being milled on the five-roll refiner.
More recently it has become more common to mix all the ingredients (apart from
some of the fat and emulsifiers) and pre-mill on a two-roll refiner to about 0.120
mm, before feeding the product directly into a series of five-roll refiners operating
in parallel (Fig. 2.3).
The initial mixing is critical because the refiners need a liquid/pasty texture to
operate. Failure to do so may result in separation of the ingredients or in extreme
cases the material being thrown off one of the rolls into the room.
The two-roll refiner consists of two cylinders, placed horizontally side by side,
which turn in opposite directions so as to pull the paste into the gap between them.
The pressure and shear in the gap mainly breaks the bigger particles and also coats
18
Enrobed and filled chocolate, confectionery and bakery products
Fig. 2.3 Diagram of two- and five-roll refiner chocolate making plant
(Beckett, 2008: 64) reproduced with the permission of the RSC.
some of the newly formed surfaces with fat. Shear is related to the difference in
speed between the two moving surfaces divided by the distance between them.
This means that if two surfaces are travelling at very different speeds and are very
close together, there is a very high shearing action, which will pull the particles
apart. This is the operating principle of both types of roll refiner. The paste
produced by the two-roll refiner is fed along moving belts into the feed hoppers of
several five-roll refiners (Fig. 2.3).
As its name suggests, the five-roll refiner consists of five slightly barrel-shaped
horizontal cylinders, with four of the cylinders placed one above the other. The
first roll or feed cylinder is placed below the others, but on the side so that a feed
‘hopper’ is formed between it and the second cylinder (Fig. 2.4). The five-roll
refiner has a much smaller throughput than the two-roll one, as it has four crushing
gaps, compared with one, and also as the chocolate is finer at this stage, it has many
more particles to break, especially when producing a fine chocolate with a
maximum particle size of less than 0.02 mm.
The cylinders are hollow and are temperature controlled by flowing water
through them. They are also pressed so closely together that the pressure bends the
barrel shape so that there is a uniform straight gap between the cylinders. A knife
blade scrapes the back of the fifth cylinder removing the chocolate in the form of
flakes or a powder.
Each successive roller is faster than the previous one which makes the chocolate
form a continuous film proceeding up the refiner rather than keeping going round
and round the bottom one. The thickness of this film depends on the gap between
that particular roller and the one below it. The actual final particle size depends
upon the gaps between the rolls and their relative speeds. In modern roll refiners
the speed of the individual rolls is fixed and the size is mainly controlled by
adjusting the gap between the first two rolls, that is, the ‘hopper’. The texture of the
feed is continually changing so this gap keeps requiring adjustment. Refiner
manufacturers have automated this by measuring the thickness of the chocolate
film just before the knife removes it and then using this to control the feed gap.
The temperature of the rolls alters the texture/viscosity of the film of chocolate
Chocolate manufacture
19
2
1
4
1
3
Fig. 2.4 Diagram of a five-roll refiner. 1, chocolate film; 2, thickness monitor; 3,
chocolate feed hopper; 4, chocolate flake from scraper.
by changing the flow properties of the fat present. Because the roller surfaces are
turning at a high speed, there is a centrifugal force on the individual particles trying
to throw the chocolate from the roll. The film however holds it on, as long as it
remains intact. Good temperature control is therefore needed when grinding
chocolate.
As the rollers press against the particles, they not only cause breakage but they
also rub some fat onto the newly broken surfaces. In addition, newly formed sugar
surfaces are chemically very reactive and able to adsorb the volatile flavours given
off by cocoa, which is being crushed close by. This means that chocolate made
using roll refiners will taste different to one made with the same ingredients, but
where these ingredients are milled individually.
2.4.3 Dry grinding
In the roll refiner the different ingredients are all milled together. Sugar breaks very
differently from milk powder, but it is necessary to mill so that the biggest particles
are of the required size. This results in the sugar, which breaks very easily being
over-milled relative to the milk, which is much more rubbery and harder to break.
As a consequence there is a relatively large number of small particles, giving the
liquid chocolate a higher viscosity. This can be overcome by grinding the ingredients separately. The cocoa liquor should already be fine enough so in essence this
means having a sugar mill and a milk powder mill. Both can be milled by hammer
mills, without any fat being present. Having two mills is industrially unsatisfactory. A single air classifier mill can process them together and still minimise the
production of very fine particles.
The sugar and dried milk particles are fed together onto a milling disc. The
metal hammers, wedges or pins at the edge of the disc rotate at very high speed
hitting the particles, breaking some and chipping pieces off others. At the same
time air is blown through the milling chamber. This carries the particles with it as
20
Enrobed and filled chocolate, confectionery and bakery products
it passes through the classifier. This is usually a rotating hollow cylinder with slits
cut into the side. The smaller particles can travel at almost the same speed as the air
and so pass through the classifier. Larger ones, however, travel much slower
because of their weight and size, and are hit by the rotating bars of the classifier and
knocked back into the milling chamber for further breakage. The smaller ones
continue moving with the air until they reach the cyclones and filter bags where
they are collected for further processing in the conche.
The larger particles will recirculate through the classifier and milling chamber
as many times as is necessary for them to be broken into pieces small enough to
pass through into the cyclone. This means that any small sugar particles which are
chipped or smashed off the larger crystals pass straight out of the mill, but some of
the sugar and most of the milk will recirculate through the mill several times.
The size of the particles can be controlled in two ways. One is to adjust the speed
of the classifier. The faster it rotates the more particles are recirculated and the finer
the final product. Alternatively the air flow can be changed. Faster moving air will
carry more particles with it and thereby increase the particle size.
Chocolate crumb can also be milled in this type of machine, although fat
contents above about 12% may require the circulating air to be cooled. This is
because milling generates heat, melting the fat and making the product sticky. This
may eventually block up the pipe-work, stopping production.
2.4.4 Batch systems
The above processes are often carried out at several tonnes per hour by large scale
chocolate manufacturers, who often supply other small and even large scale
companies, who manufacture confectionery products. Some smaller scale manufacturers use batch processes to process perhaps a few tonnes per day. This type of
machinery is particularly popular when making chocolate flavoured coatings, for
example a recipe where the cocoa butter is partially or wholly replaced by some
form of vegetable fat. Most include the liquefying/taste changing processes that
take place in the conche during large scale chocolate manufacture. There are many
types of device, perhaps the most common being based upon ball mills or on a drum
with internal scraping/breaking elements commonly known as a Macintyre refiner
conche, manufactured, amongst others, by Low and Duff (Developments) Ltd
(LADCO) UK and Lloveras (Spain).
Ball mills
The mills contain a large number of balls which hit each other as they tumble in a
rotating container or by central turning agitators. The balls impact and rotate,
breaking any particles that are caught between them and then pushing the smashed
particles away. Smaller particles can move away faster and are less likely to be
broken. This type of machine therefore tends to produce a relatively narrow
particle size distribution. Several passes through the ball mill are likely to be
needed in order to reach the required fineness for chocolate. Usually as the
chocolate gets finer, smaller balls are used, coupled with a higher agitation speed.
Chocolate manufacture
21
These mills tend to be more efficient at smaller particle sizes.
This type of mill has three problems:
1) It requires a liquid feed material and so needs a relatively high fat pre-mix and
some pre-milling.
2) It is not able to coat the newly broken surfaces properly with fat. For this
reason it is common to pass the milled material through a high shearing in-line
liquefier before returning it to the input of the same or another ball mill.
3) It is completely enclosed, which is good because the chocolate remains free
from external contaminants, but means that unwanted acidic flavours are not
removed. Some systems incorporate taste changers. These can take the form of
pouring the liquid chocolate over a spinning disc and blowing air over it.
Macintyre refiner conches
This machine has a temperature controlled jacketed drum with a serrated inner
surface (Fig. 2.5). Particles are broken by spring loaded scrapers that rotate inside
it. Air blown through it provides a forced ventilation which removes moisture and
some flavour volatiles. Between 50 kg and 5 tonnes can be processed in a period
of 12 hours or more depending upon the final required particle size.
Unlike the ball mill, this type of machine is more efficient with larger particle
sizes, as with smaller ones the particles can move out of the way rather than be
broken, especially in lower viscosity chocolates. In order to reduce processing
time, therefore, it can be useful to do the initial breakage in this type of machine,
but then produce the final fineness in a ball mill. An alternative combination feeds
the Macintyre with material from a two-roll refiner. These refiner/conches can
operate with powdery/pasty feed material.
2.5
Conching
2.5.1 Flavour changes
The cocoa fermentation and roasting processes produce the precursors and some
final components of the chocolate flavour, which are modified in the conche. In
addition certain acids are present in the cocoa, which give an unpleasant ‘vinegar’
flavour that needs to be removed from most chocolates.
Recent studies (Ziegleder, 2004) have shown that conching also redistributes
the flavour chemicals within the chocolate. As the ingredients enter the conche,
about half of these flavours are associated with the cocoa and most of the rest are
within the fat phase. Less than 5% are associated with the sugar. At the end of
conching, an equilibrium is almost reached with about a third of the chemicals
attached to each of these three components. It must also be remembered that it is
possible to over conche and produce a very bland chocolate. There is still very
much an art in combining the ingredients, recipe and processing to get the best
tasting chocolate for a particular product.
22
Enrobed and filled chocolate, confectionery and bakery products
(a)
(b)
Fig. 2.5 Schematic diagram (a) and photograph (b) of Macintyre type refiner/conches.
The conche does this by stirring and mixing and allowing air to remove some of the
volatiles. In addition the chocolate masse may be heated up to 100 oC or even
higher, to cause the Maillard reaction and introduce cooked notes. However, at this
stage, the moisture is low (<1%) and so this reaction is slow. These flavours can be
more easily introduced at the milk drying stage. In some chocolates, a milky rather
than a cooked flavour is desired, so the chocolate is maintained at a much lower
temperature. This is normally about 50 oC, as the cocoa butter must also be kept in
a liquid state for the liquefying to take place. The actual temperature used will
depend both on the original ingredients and the final flavour and is normally
between these two extremes.
Chocolate manufacture
23
2.5.2 Liquefying
The grinding procedure usually results in a powdery material with uncoated
surfaces of solid material. Liquefying is largely a process to coat these surfaces as
well as to break up agglomerates of solid particles that may be formed during
previous grinding processing. With the separate grinding procedures very little fat
is present, whereas with the roll refiners a significant amount of the surface is
already coated and the majority of fat is already in the mixture. The conching time
and procedure therefore need to be adjusted according to the feed material.
Traditionally there are three phases during conching:
1) dry phase
2) pasty phase
3) liquid phase.
Dry phase
At this stage the material in the conche is in a powdery form. The shafts turn and
the mixing elements push it against the sides to coat some of the particles with the
fat, which is kept liquid by the conche temperature controlled jacket and the heat
developed by the mixing action. In addition, the powder is thrown into the air to
enable moisture and other volatiles to escape. Once the particles are coated in fat
and the moisture evaporated, it is much harder for flavour changes to take place. In
addition any remaining moisture will tend to make the small sugar particles sticky
and thereby raise the chocolate viscosity. If the moisture is removed too quickly
however, it will be unable to leave the conche and may condense into droplets. This
will then fall back into the conche and stick the particles together and make the
final chocolate taste gritty. The first dry phase is therefore critical for the flavour,
viscosity and texture of the chocolate.
Pasty phase
As more solid particles become coated, the powder turns into a paste and the power
needed to turn the conche shafts increases greatly. This stage is very important
from a liquefying point of view. When the paste is thick, the conche mixing
elements are able to press it against the wall and so coat more particles. Once the
paste becomes thin the uncoated particles can move out of the way of the elements
and remain uncoated. The eventual viscosity of the chocolate relates to the
proportion of solid particles that are coated, so it is important to retain a thick paste
for as long as possible. The actual thickness and time will depend upon the conche
design and its motor power. In general it is better not to have all the fat and
emulsifier present at this stage. This is especially true of lecithin, as if this is added
early in the conching it not only thins the paste, but also holds in the moisture,
which is detrimental to the final chocolate viscosity.
Liquid phase
This is the final point at which the viscosity can be adjusted. Enrobing often
requires a different viscosity to moulding plants whilst chocolate for lentils can be
24
Enrobed and filled chocolate, confectionery and bakery products
(a)
(b)
(b)
Fig. 2.6 Schematic diagram (a) and photograph (b) of a conche manufactured by
Frisse, Germany (Beckett, 2008: 76) reproduced with the permission of the RSC.
very different again. It is therefore important to know the viscosity required and to
add the appropriate amount of fat and emulsifier into the conche at this stage. This
process only needs to be long enough to ensure the fat/emulsifier additions are
thoroughly mixed in, as no further flavour or viscosity changes are likely to take
place.
Chocolate manufacture
Fig. 2.7
25
Mixing elements of an Elk conche (Richard Frisse GmbH, Germany).
2.5.3 The conche
The conche was invented by Rodolphe Lindt at his factory in Berne in Switzerland
in 1880. It consisted of a granite roller going backwards and forwards in a granite
trough. This made the chocolate taste a lot smoother by its coating action and
perhaps at that period some breakage of particles. This type of conche could not
carry out dry conching. It often took a day or more to process a tonne of chocolate
and is known as a long conche. It has been almost entirely superseded by jacketed
vessels with one or more central rotating shafts attached to which are arms and
mixing elements. The latter are able to squash the chocolate against the sides of the
vessel. Figure 2.6 illustrates a typical three-shafted conche capable of processing
between 3 and 10 tonnes of chocolate in less than 12 hours.
Sometimes the ends of the arms are wedge shaped. This moves point first when
the chocolate is thick and pasty and is therefore able to cut into it. Once the
chocolate has become thinner the direction of rotation is reversed so the flat end
hits the chocolate and more movement/liquefying takes place.
Recently there has been a lot of development related to the design of these
mixing elements to reduce processing time and produce lower viscosity chocolate
for the same fat content. The mixing elements are often used with single shaft
vessels. Figure 2.7 shows the shaft especially designed for the Frisse Elk conche.
Ventilation from the conche is important, especially during the dry conching
stage. Some conches have a forced air ventilation system, whereas others have
louvers that can be opened or shut depending upon the condition of the chocolate
within the conche.
A wide variety of conches exist including some that operate in a continuous
manner. This can be achieved, amongst other ways, by a series of weirs, where the
chocolate flows over the weirs from one tank into another. Each tank contains
different mixing conditions appropriate to that part of the conching cycle.
26
Enrobed and filled chocolate, confectionery and bakery products
2.6
Quality
2.6.1 Flow properties
The viscosity of chocolate is very important. Too thin or too thick chocolate will
give rise to the wrong weight and/or misshapen products. It also affects the taste.
Two chocolates made with the same ingredients but with different viscosities will
appear to be very different when eaten.
Chocolate viscosity measurement is rather complex however, mainly because,
like non-drip paint and tomato ketchup, it cannot be represented by a single figure.
It is what is called a non-Newtonian fluid and its viscosity depends upon the rate
at which it is flowing, fast moving chocolate being much thinner than when it is
running slowly down the side of a sweet. Ideally the viscosity should be measured
at the flow (shear) rate at which it is being used, but this will vary greatly
throughout the moulding or enrobing processes. To simplify this therefore, the
chocolate manufacturer will make a chocolate with two quality control points. For
example, one control point should be at low shear, which corresponds to the yield
value and relates to starting the chocolate moving. The other is at a high shear rate,
which corresponds to the plastic viscosity and is the ‘viscosity’ when the chocolate
is flowing quickly. Very careful laboratory procedures are required when carrying
out this measurement (Aeschlimann and Beckett, 2000). Ideally the chocolate
from every conche should be checked before discharging, to ensure that both flow
parameters are correct.
A chocolate may be too thick for a variety of reasons, the chief ones being:
• the moisture has not been removed (check by laboratory measurement)
• the chocolate has been milled too finely (measure using a laser-based instrument)
• the chocolate has not been conched correctly – often too much fat/emulsifier has
been added at the start of conching (stir at high speed and the chocolate viscosity
drops).
If any of these happens then the manufacture must correct the cause and modify
that batch by adding extra cocoa butter or lecithin. If the high shear rate (plastic
viscosity) measurement is correct, but the low shear rate (yield value) is too high
then an emulsifier called PGPR (polyglycerol polyricinoleate) can be used to
correct this defect. It must, of course, be declared on the label of any chocolate
product made with this batch. Too thin a chocolate is very rare and if necessary can
be blended with an extra thick batch.
2.6.2 Sensory properties
Off-flavours in the initial ingredients cannot be removed by chocolate processing
and taste tests should therefore be carried out on cocoa liquor and milk components. Lactose and whey powders are sometimes used in chocolate to reduce
sweetness or for economic reasons. Poor quality powders however can introduce
metallic flavours and reduce shelf-life.
Chocolate manufacture
27
Using an analytical GC/MS (gas chromatography/mass spectrometry) method
to study conching Dr Ziegleder of the Fraunhofer IVLV in Munich, Germany
(Ziegleder, 2004) evaluated samples from 6-tonne conches, which he correlated
with sensory results obtained by 14 panels consisting of 150 trained panellists all
together. The main factors affecting chocolate flavour change were found to be:
• dry conching time (70% preferred a long dry conching compared with 30% for
long liquid conching)
• total energy/average power consumed by the conche
• speed and type of shafts/mixing elements in the conche
• free fat level at the start of conching
• flavour of the cocoa liquor
• temperature of conching
• ventilation system from the conche
• humidity within the conche
• particle size distribution of the milled ingredients.
All these factors must be considered when optimising the flavour of a chocolate for
use in a product. A single chocolate flavour is seldom suitable for a wide variety of
sweet centres. For example, a peppermint flavour might need stronger acidic notes
so that the chocolate flavour is not overwhelmed, whereas a nut praline would
probably need a very mild milky chocolate coating.
2.7
Future trends
In recent years many chocolate manufacturers have stopped producing their own
cocoa liquor, but obtain this from a few very large cocoa bean processing
companies. In a similar way there are fewer larger chocolate processors and this
trend may continue. Technical machinery developments are likely to be in the
direction of increased automation and shorter processing times.
The development of new ingredients is likely to continue especially with regard
to increasing nutritional or health benefits. Sugar and sucrose-free chocolate are
already on the market, but many have limited consumption because of their
laxative effect. Improved products are likely to be developed together with low
calorie or low fat chocolates that have the taste and texture of the traditional higher
fat products. The higher polyphenol content chocolates, with their positive health
benefits, are likely to become more common as methods are developed to prevent
the destruction of this type of chemical during cocoa processing.
2.8
Sources of further information and advice
This chapter can only give an outline of chocolate manufacture. Detailed information on the technical aspects are given in Minifie (1980), Cook (1984) and Beckett
(2009). A more general scientific approach is given in Beckett (2008).
28
Enrobed and filled chocolate, confectionery and bakery products
Although chocolate manufacture has become much more automated with a
consequent large reduction in workforce, the current very large throughputs mean
that the remaining operatives need considerable skill and knowledge of the
processes involved. Training in these areas is provided by, amongst others, The
German Confectionery School (ZDS), Solingen, Germany, Leatherhead Food
International, Leatherhead, UK, William Angliss Institute, Melbourne, Australia
and PMCA, Bethlehem, PA 18017 in the USA.
2.9
References
AESCHLIMANN, J.-M. AND BECKETT, S.T.
(2000), ‘International inter-laboratory trials to
determine the factors affecting the measurement of chocolate viscosity’, Journal of
Texture Studies, 31, 541–76.
BECKETT, S.T. (2009), ‘Non-conventional machines and processes’, in Industrial Chocolate
Manufacture and Use, 4th edition, Beckett, S.T. (ed.), Wiley-Blackwell, UK.
BECKETT, S.T. (2008), The Science of Chocolate, 2nd edition, RSC, UK.
COOK, L.R. (revised by E.H. Meursing) (1984), Chocolate Production and Use, Harcourt
Brace, New York.
FOWLER, M.S. (2008), ‘Cocoa beans: from tree to factory’, in Industrial Chocolate Manufacture and Use, 4th edition, Beckett, S.T. (ed.), Wiley-Blackwell, UK.
MINIFIE, B.W. (1980), Chocolate, Cocoa and Confectionery, 2nd edition, Avi Publishing,
Westport, Connecticut, USA.
ZIEGLEDER, G. (2004), ‘A greater understanding of your conching process’, ZDS Chocolate
Technology Conference, 14–15 December, Cologne, Germany. Zentralfachschule der
Deutschen Süsswarenwirtschaft (German Confectionery School), Solingen.
3
Formulation of chocolate for industrial
applications
Philip Yates, Barry Callebaut (UK) Ltd, UK
Abstract: This chapter provides a short overview of current legislation relating to the
composition of different types of chocolate. Information is provided about raw materials
and their impact on taste and performance, and formulations are given for various
industrial applications. Speciality products such as origin, organic, fair-trade and without
added sugar are discussed along with developments relating to health aspects.
Key words: applications, chocolate, fairtrade, flavanols, health, legislation, milk
chocolate, organic chocolate, origin chocolate, probiotic, recipes, white chocolate.
3.1
Introduction
Chocolate is relatively simple in terms of the number of ingredients used, but few
other foods evoke such universal pleasure and have such a mysterious and
intriguing history. The cocoa bean, the origin of all chocolate products, originated
in Latin America. The bean, originally made into a chocolate drink called Xocoatl
(or chocolatl), played an important role in the ancient cultures of the Mayans,
Toltecs and later, the Aztecs. According to Aztec legend, their feathered god
Quetzalcoatl, first gave us the cocoa tree, Theobroma cacao, meaning ‘food of the
gods’. In the 16th century, cocoa was brought to Europe by the Spanish explorers,
where this luxury product was consumed as a drink by those who could afford it,
the Royal courts and privileged classes. In the 19th century, new machines and
processes were invented, such as the cocoa press, which allowed separation of
cocoa butter, the conche, for flavour development, and the refiner mill, to achieve
much lower particle size. These, coupled with the idea of adding milk powder,
started to create the types of products that we know today.
30
Enrobed and filled chocolate, confectionery and bakery products
Starting from the cocoa bean, the process of making chocolate is complex,
involving the selection of ingredients, process parameters, time and temperature.
So where do we start? Whether the chocolate is to be used in large industrial
applications or by the individual artisan chocolatier, the basic production process
remains the same. The source and type of ingredients, the devised formulation and
the manufacturing process conditions will determine the taste profile and technical
properties of products for the many different applications.
3.2
Legislation
Legislation relating to cocoa and chocolate products is not consistent throughout
the world. Some legislation is quite complex and in this chapter it is not possible to
cover all items of legislation. The following is an overview of the key points
specific to chocolate products in different areas of the world, highlighting the
similarities and differences in the main product groups.
3.2.1 European Union
Within the European Union, chocolate is one of a small number of foods that is
covered by ‘vertical’ legislation, specific to a food category. The legislation gives
compositional standards for various types of products under the reserved description and also states some specific labelling requirements for a particular product.
Reserved descriptions are given for a number of products, including chocolate,
milk chocolate and white chocolate.
The first directive in 1973 was introduced because new member states had
different standards in relation to the existing members. The main contentious
issues were:
• the minimum amounts of milk and cocoa solids and how these were labelled;
• the use of non-cocoa vegetable fats and the labelling implications.
It was agreed that a review should be undertaken to simplify, harmonise and to
‘bring into line’ the legislation for each of the then nine member states. The
intention was to create a single market for chocolate in Europe, whilst recognising
the different traditions of making chocolate in the different member states. This
review process became very political and, after many years of discussion, a new
directive, EC Directive, 2000/36, was introduced in 2000. Each member state then
had three years to transpose the directive into national law. On 3 August 2003, the
Directive came into force applicable in each member country. For example, in
England, the Directive was implemented as The Cocoa and Chocolate Products
(England) Regulations 2003.
In order to ensure products meet the legislation it is important to understand the
basics of compositional requirements. In calculations to check legality, it is
fundamental to understand the concept of the ‘chocolate’ part of a formulation, the
so-called ‘noble’ ingredients and other permitted edible substances.
Formulation of chocolate for industrial applications
31
Noble ingredients
These include all the cocoa ingredients, milk ingredients (as defined in the
regulations) and sugar (all kinds of sugars).
Optional ingredients/other edible substances
These include other edible substances, emulsifiers and flavourings to a maximum
of 40%, but exclude flour or starch, animal fats other than milk fat and flavourings
that mimic the taste of chocolate or milk fat. Examples of ingredients permitted in
this category would include nuts, whey powder, soya lecithin and vanilla.
Cocoa solids
Cocoa solids are calculated on a dry basis (after the deduction of moisture) and
include cocoa mass, cocoa powder and cocoa butter. The total dry cocoa solids are
the sum of the dry non-fat cocoa solids (NFCS) and cocoa butter, expressed as a
percentage of the noble ingredients (the total recipe minus the edible substances)
(see Table 3.1).
Milk solids
Milk solids are calculated using a similar method. The total dry milk solids are the
sum of the dry non-fat milk solids (NFMS) and milk fat, expressed as a percentage
of the noble ingredients (see Table 3.1).
Labelling requirements
General labelling legislation now also applies to chocolate products, for example,
a list of ingredients in descending order is needed. Other specific labelling rules
apply. The level of cocoa solids must appear on the label for chocolate and milk
chocolate. A 25:14 (total cocoa solids:total milk solids) milk chocolate can be
labelled as milk chocolate in all member states. A 20:20 (total cocoa solids:total
milk solids) milk chocolate can still be called milk chocolate on an English only
label, for products sold in the United Kingdom and Ireland. A statement of the milk
solids content is required, either the minimum needed or the actual level. Elsewhere in the EU this product would need to be labelled Family milk chocolate.
Quality criteria
The reserved description for chocolate and milk chocolate can be supplemented by
additional words of description relating to quality criteria if certain additional
compositional requirements are met. For example, the word ‘dark’ could be used
with chocolate, as long as it contained not less than 43% total dry cocoa solids, and
not less than 26% cocoa butter. For milk chocolate it must contain not less than
30% total dry cocoa solids, not less than 18% dry milk solids and not less than 4.5%
milk fat.
The use of vegetable fat
Until 2003, only certain countries within the EU allowed the use of vegetable fats
other than cocoa butter in chocolate products. In the 2003 regulations this changed
Table 3.1
Summary of composition to meet EU reserved descriptions
Reserved description
Chocolate
Chocolate
(with ‘quality’ description)
Milk chocolate
Milk chocolate
Family milk chocolate
Milk chocolate
(with ‘quality’description)
White chocolate
Total cocoa
solids (dry)
(%) (min)
35
43
Non-fat cocoa
solids (dry)
(%) (min)
14
14
25
20
2.5
2.5
30
2.5
Cocoa
butter
(%) (min)
Total milk
solids (dry)
(%) (min)
Milk fat
(%) (min)
Total fat (cocoa
butter & milk fat)
(%) (min)
18
26
20
Vegetable fat
(%) (max)
5
5
14
20
3.5
5
25
25
5
5
18
14
4.5
3.5
25
23.5
5
5
Formulation of chocolate for industrial applications
33
and vegetable fats are now permitted, subject to specific requirements and labelling, in all member states. The vegetable fat must be a cocoa butter equivalent
(CBE) and must comply with certain criteria. The vegetable fat must be:
• non-lauric, rich in symmetrical monounsaturated triglycerides.
• miscible in any proportion with cocoa butter and compatible with its physical
properties.
• obtained only by the processes of refining or fractionation or both.
In addition, the fats can only be from six plant sources. The vegetable fats that can be
used are illipé butter, palm oil, sal fat, shea butter, kokum gurgi and mango kernel oil.
The vegetable fat can be added to chocolate, milk chocolate and white chocolate, to a maximum of 5%. The labelling on the product packaging is also
important. The product name, for example, ‘milk chocolate’, has to be supplemented by a conspicuous and clearly legible statement, ‘contains vegetable fat in
addition to cocoa butter’. This statement should be in the same field of vision as the
ingredient list, clearly separated from the list, in lettering at least as large and in
bold, with the sales name near by. If the chocolate that contains vegetable fat is
used as an ingredient to make another product, for example, coating a biscuit, it is
recommended that the presence of vegetable fat in the chocolate is made clear in
the ingredients list.
3.2.2 United States of America
Legislation (or Standards of Identity) for chocolate products is administered by the
US Food and Drug Administration, in the Code of Federal Regulations. This code
is divided into 50 titles that represent broad areas subject to federal regulation. Title
21 is for Food and Drugs, and Part 163 of this title covers cacao (chocolate)
products. It is updated annually in April.
Definitions exist for a number of cocoa and chocolate products, the main ones
being chocolate liquor, sweet and bitter-sweet chocolate, milk chocolate and in
April 2004, a new Standard of Identity was introduced for white chocolate (see
Table 3.2).
Table 3.2
Summary of composition to meet USA chocolate standards
Total cocoa
Cocoa
Total milk Milk fat
solids (dry)* butter
solids (dry)
(%) (min) (%) (min)
(%)
(%) (min)
Sweet chocolate
Semisweet
(bittersweet)
chocolate
Milk chocolate
White chocolate
Milk chocolate &
vegetable fat coating
*as chocolate liquor
15
35
(%)
12 (max)
12 (max)
10
20
10
Vegetable fat
12 (min)
14 (min)
12 (min)
3.39
3.5
3.39
Not limited
34
Enrobed and filled chocolate, confectionery and bakery products
The main differences in the USA chocolate standards compared to EU regulations can be summarised as follows:
• Whey powder is only permitted in white chocolate in the United States. It is not
permitted in the other chocolate products.
• Vegetable fats, other than cocoa butter are not permitted.
• Separate standards exist for chocolate products that contain vegetable fats, for
example, milk chocolate with vegetable fat coating.
• In milk chocolate, the minimum level of milk solids and milk fat are slightly
lower and the total cocoa solids are also lower than in the EU.
3.2.3 Codex
The Codex Alimentarius Commission (Codex) is the highest international body for
food standards. It was established in the early 1960s and is a subsidiary of the UN
Food and Agriculture Organization (FAO) and the World Health Organization
(WHO). It was set up to ensure fair trade, protect consumers and create global
standards for foods. CODEX STAN 87-1981, Rev. 1 – 2003, is the Codex standard
for chocolate and chocolate products. The Codex standard could be used as a
reference for products sold to countries where specific legislation does not exist
(see Table 3.3).
The EU and Codex allow the use of whey in standard chocolate products, but
the United States does not. The EU, Codex and the United States allow whey to be
used in white chocolate. Both the EU and Codex allow the use of up to 5%
vegetable fat in chocolate products, but again the United States does not.
3.3
Ingredients
The quality, quantity and type of ingredients used in chocolate manufacture all
affect the fundamental basic flavour of the end chocolate. This flavour can then be
fine-tuned during processing, through roasting of the cocoa beans and the conching
conditions, particularly time and temperature.
In terms of cost, the raw materials used are crucial. For most chocolate
formulations, raw materials typically make up over 80% of the direct cost of the
product. However, in order to achieve a high quality chocolate flavour, high
quality ingredients are needed.
3.3.1 Cocoa
Cocoa is the most important ingredient in the manufacture of chocolate and dark
chocolate. Typically, a chocolate recipe is a balance of cocoa mass and sugar with
vanilla used to round the flavour. Emulsifier and added cocoa butter are used to
alter the rheology of the chocolate, dependent on its application. Cocoa powder is
sometimes added, both to increase total cocoa solids without significantly increasing overall fat percentage and to influence the intensity of the cocoa flavour.
Table 3.3
Summary of composition to meet Codex standards
Chocolate
Sweet chocolate
Milk chocolate
Family milk chocolate
White chocolate
Total cocoa
solids (dry)
(%) (min)
Non-fat
cocoa solids (dry)
(%) (min)
35
30
25
20
14
12
2.5
2.5
Cocoa butter
(%) (min)
18
18
20
20
Total milk
solids (dry)
(%) (min)
12–14
20
14
Milk fat
Vegetable fat
(%) (min)
(%) (max)
2.5–3.5
5
2.5–3.5
5
5
5
5
5
36
Enrobed and filled chocolate, confectionery and bakery products
Table 3.4
Chocolate formulations with different levels of cocoa solids
Cocoa mass (%)
Sugar (%)
Cocoa butter (%)
Lecithin (%)
Natural vanilla (%)
Total cocoa solids* (%)
Particle size (µm)
Total fat content (%)
A
B
C
32.5
51.38
15.5
0.6
0.02
47.5 (min)
23–25
33.4
42.6
46.18
10.6
0.6
0.02
52 (min)
23–25
34
59.3
36.77
3.3
0.6
0.03
62 (min)
23–25
35.8
* Figures will vary dependent on tolerances allowed
Cocoa flavour is influenced by the variety of cocoa used, the climate and soil
conditions where it is grown. These factors also affect the cocoa butter content of
the beans and the relative hardness of the cocoa butter. Further cocoa flavour
development occurs during roasting and conching. For the majority of industrial
applications, a consistent cocoa flavour is preferred. In order to achieve this,
quality cocoa beans are blended to attain the desired taste profile. For the European
market for example, West African bean blends are normally used, in particular
from Ivory Coast, Ghana, Nigeria and Cameroon.
Blends of fermented, dried cocoa beans are selected and roasted. The shell is
removed by winnowing and the roasted nibs are ground using pin mills and ball
mills to produce cocoa mass (also called cocoa liquor). Cocoa mass is then either
pressed to produce cocoa butter and cocoa cake (which is kibbled and then further
processed into cocoa powder), or it is used as the base ingredient for chocolate
manufacture. The pressed cocoa butter is also used as an ingredient, and for some
formulations, cocoa powder or fat-reduced cocoa powder can be added.
The most important considerations at this stage are the flavour, the fat content
and the particle size of the cocoa mass. Cocoa grinding creates a lot of machine
wear, but if a particle size close to that of the end chocolate specification is
achieved during grinding, wear on the five-roll refiners used later in the process is
significantly reduced. These are important factors in the determination of the
overall formulation economics (Table 3.4).
3.3.2 Sugar
Sugar used for chocolate manufacturing is sucrose in its crystalline form, derived
from either sugar cane or sugar beet. The main function of sugar in chocolate is to
provide sweetness. Industrial granulated sugar is normally used, but how it is
processed may vary according to the machinery used to reduce the particle size.
Sugar can be milled prior to addition in the mixer and then further reduced in
particle size in a single stage refining process. Alternatively, granulated sugar can
be added to the mixer and particle size reduction achieved through a two-stage
refining process, a pre-refiner followed by a second stage five-roll refiner. Particle
Formulation of chocolate for industrial applications
37
size distribution is an important factor and the amount of very small particles will
influence final product rheology, particularly the yield value.
3.3.3 Milk
Milk in different forms is used in combination with cocoa and sugar to make milk
chocolate and white chocolate. Starting from liquid milk, a number of different
ingredients can be made. It is necessary to understand what is available, the
characteristics of each and their composition in order to meet the legal requirements when formulating milk and white chocolate recipes.
Milk chocolate crumb
Crumb is a raw material used to achieve the unique caramelised flavour profile
typical of UK milk chocolate. The process was developed as a method to improve
the shelf life of milk, to overcome the variation and availability of milk throughout
the year and to achieve consistent flavour. During the crumb manufacturing
process liquid milk is condensed to remove water, mixed with sugar and cocoa
mass, then cooked, dried and milled to create a fine powder.
Milk chocolate manufactured from crumb is essentially a UK product and is
perceived to be more creamy and caramelised in flavour when compared to
European milk powder-based products. Flavour development during the process
centres around Maillard browning reactions and caramelisation and is dependent
upon the crumb formulation, for example the amount and quality of the cocoa
mass, the process time and temperature and the method of drying. The actual
composition of crumb can vary, as can the level of crumb added to the milk
chocolate recipe. Crumb with a higher cocoa mass content (13.5%) can be used in
very high crumb milk chocolates, usually only with addition of cocoa butter,
emulsifier and flavours. Milk chocolate manufactured with crumb with lower
cocoa mass level (6.8%) needs the addition of other ingredients to ensure the recipe
meets legislation requirements.
Because crumb is not a recognised legal entity, it is not listed as an individual
ingredient. However, as it consists wholly of noble ingredients it is split into its
component parts for all declaration purpose (see Table 3.5).
Whole milk powder or full cream milk powder
This is dehydrated whole milk and is usually produced in one of two ways: spray
drying or roller drying. The water in the milk is evaporated using heat, either heated
air in a spray tower or on heated rolls. Each process results in a powder of similar
composition but with differences in flavour characteristics and process performance.
The approximate composition is 26–27% milk fat, 70% non-fat milk solids and
3.5% water. Whole milk powder gives a flavour influence that provides creamy
and milky notes; roller dried powder is usually preferred owing to the slight
caramelisation that occurs on the heated rollers. Roller drying powder also results
in significantly higher levels of free fat compared to spray dried powder. Milk fat
38
Enrobed and filled chocolate, confectionery and bakery products
Table 3.5
Milk chocolate formulations with different levels of crumb
A
Crumb (6.8% mass) (%)
Crumb (13.5% mass) (%)
Cocoa butter (%)
Sugar (%)
Skimmed milk powder (%)
Milk fat (%)
Lecithin (%)
Natural vanilla (%)
Particle size (µm)
Total fat (%)
B
20
60
22.7
33.19
13.5
3
0.6
0.01
23–27
32.5
22
10.88
0.6
0.02
23–27
33.8
C
79
20.38
0.6
0.02
23–27
33.5
tends to be bound in the particles of spray dried powder. The free fat content
influences the mixing and refining stages of chocolate manufacture and ultimately
the rheology achieved for a specified fat content. The moisture content of powders
can also influence process parameters and rheology, as most of this moisture needs
to be removed during the conching phase of production.
More and more powder is now dried in spray drying towers with apparently less
investment occurring in roller drying. This affects the relative availability of the
different powders and their price. Thus choosing which powder to use in a
formulation becomes a trade-off in terms of flavour, fat contribution to rheology at
the same fat content, and cost.
Whole milk powder is a noble ingredient in chocolate and contributes to both
non-fat milk solids and milk fat.
Skimmed milk powder
This is liquid whole milk which is skimmed to remove nearly all the fat prior to
drying. A small amount of fat, less than 1%, still remains in the powder. Skimmed
milk powder offers milky flavours. It can be added in recipes to increase milk
solids levels, without impact on the overall fat level, or in conjunction with butter
oil to give a softer product, instead of whole milk powder.
Milk fat or butter oil
This is the natural fat in milk and is almost liquid at room temperature, having a
solid fat content, typically, of about 11% (Shukla, 1994). It is manufactured from
either butter or cream. There are minimum levels of milk fat legally required in
milk and white chocolate and this can come from full cream milk powder, added
milk fat or a combination of both. Milk fat in combination with cocoa butter can
result in a eutectic effect at high levels and this can be used to give a softer texture.
Milk fat can also be added to chocolate at low levels to help inhibit bloom
formation.
Whey powder
Whey powder is produced as a by-product from cheese making, and is usually
Formulation of chocolate for industrial applications
Table 3.6
39
Milk and white chocolate formulations
Sugar (%)
Cocoa butter (%)
Cocoa mass (%)
Whole milk powder (roller) (%)
Whole milk powder (spray) (%)
Skimmed milk powder (%)
Milk fat (%)
Whey powder (%)
Lactose powder (%)
Lecithin (%)
Natural vanilla (%)
Particle size (µm)
Total fat (%)
Milk
chocolate
White
chocolate
Milk
chocolate
Milk
chocolate
45.99
21.4
12
9
11
49.19
27.2
48.68
22.7
12
40.09
22.9
12
7.2
7.2
9
14
12
4
0.6
0.01
22–27
33.5
0.6
0.01
22–27
33.5
0.6
0.02
22–27
33.5
5
5
0.6
0.01
22–27
33.5
spray dried. It can be used in milk chocolate to replace sugar, as it is less sweet, and
is often used to reduce cost. Different types of whey powder are available and it is
important to consider the level of minerals they contain, as they can pass on salty
flavours above certain levels. Whey powder is classified as an edible substance and
legally does not contribute to the total milk solids.
Lactose powder or milk sugar
Lactose or milk sugar is also available as an ingredient. Typically it has been used
for cost reduction, but has the benefit of being significantly less sweet than sugar
so can be used when reduced sweetness is needed in a recipe. Although it is derived
from milk, lactose is classified as a sugar for declaration purposes (see Table 3.6).
3.3.4
Emulsifiers
Lecithin E322
The main emulsifier used in chocolate is soya lecithin. It has had a major impact for
chocolate manufacturers as the addition of relatively small amounts has a significant effect on rheology. Lecithin addition reduces both viscosity and yield value,
resulting in less cocoa butter being needed, thus saving on cost. It is important to
understand however, that although lecithin quality is stable, there is still variation
in the extent of viscosity reduction from batch to batch.
The amount of lecithin needed to optimise rheology increases as the fineness
(particle size) of the chocolate decreases. Also, the ability of lecithin to influence
rheology decreases as the fat content of the chocolate increases. An important
feature of lecithin is that above a certain optimum quantity, the impact on yield
value is reversed. There is an optimum level for every formulation in relation to fat
content, moisture content and particle size distribution.
40
Enrobed and filled chocolate, confectionery and bakery products
Ammonium phosphatide E442
An alternative emulsifier to lecithin is ammonium phosphatide, derived from
glycerol and rapeseed oil. It works in a similar way to lecithin, but can give more
consistent and repeatable viscosity reduction. Another reason for its use may be
that it has a bland neutral taste.
PGPR E476
PGPR (polyglycerol polyricinoleate) can also be used in chocolate. It is not
normally used as the sole emulsifier, but in combination with lecithin or ammonium phosphatide. The impact of PGPR on viscosity is quite small but it has a
significant effect on yield value.
3.3.5 Flavours
In the EU chocolate legislation, certain flavours, such as those which mimic the
taste of chocolate or of milk fat, are not permitted. The main flavours that are used
are vanillin, a nature-identical flavour and natural vanilla.
3.4
Formulations for industry sectors
When we start to look at a formulation for a chocolate product, there are a number
of factors that should be considered:
•
•
•
•
•
•
•
•
•
•
Chocolate: milk chocolate or white chocolate?
What type of product is to be made, confectionery, bakery, ice cream?
How will the chocolate be used – moulded, dipped, enrobed?
What flow characteristics are needed for the application?
What particle size is required?
What level of cocoa solids (and milk solids)?
What is the target flavour and market?
Is it a premium, indulgent product?
What ingredients should be used?
What is the price point?
Each of these points needs to be answered if we are to make a successful costeffective product and, having devised a formulation, a check must be done to
ensure that the relevant legislation is met.
One of the key areas to consider when creating a recipe is to ensure that the
product works in the application. In order to do this we need to have an understanding of some of the important, interrelated factors that influence the performance of
a product for a particular application.
Rheology
Rheology is ‘flow theory’, and when applied to chocolate, in very simple terms,
describes how fluid the chocolate is when fully melted. We can measure the
Formulation of chocolate for industrial applications
41
viscosity and yield value. The viscosity is how the product spreads and the yield
value is the force needed to move the product. Various factors can influence the
rheology of chocolate and can be manipulated to achieve the correct flow characteristics to suit the application. Rheology is discussed in detail in Chapter 13.
Fat content
Chocolate is a suspension of solid particles in a fat phase. The solid particles can
be sugar, cocoa and milk powder. We can make the product ‘thinner’ (more fluid)
by adding more fat. This lowers the rheology and makes the chocolate flow more
easily. However, cocoa butter is the most expensive ingredient so it is important to
optimise the other influencing factors too.
Emulsifier
Emulsifiers also influence rheology. As mentioned earlier, different emulsifiers
can be used to reduce viscosity and yield value to achieve an acceptable rheology
at a lower fat content. Typically soya lecithin is used. A simple ‘rule of thumb’ is
for every 0.1% lecithin added there is a saving of approximately 1% cocoa butter.
Emulsifiers are normally used at around 0.5–0.7%, to give the maximum benefit of
lowering both viscosity and yield value. At levels above this, depending on other
ingredients used, lecithin can have the opposite effect on yield value. Chocolate
can be made without emulsifiers, but a higher fat content is needed to achieve an
acceptable flow.
Moisture content: conching
Moisture can have a large impact on flow characteristics of chocolate. The
moisture content of ingredients is carefully managed and is an important criterion
for setting specifications for raw materials. Most chocolates have an end moisture
content of less than 1%. During the conching phase, moisture is removed and, at
the same time, the flavour is improved by the removal of unwanted acidity.
Particle size distribution
The size of the largest particles is important, because above a certain size the
particles can be detected in the mouth when the product melts. The particle size
distribution and the proportion of very fine particles influence the final rheology,
particularly the yield value. A very smooth product will use more cocoa butter to
achieve the required rheology.
3.4.1
Bakery applications
Biscuits
There are numerous kinds of biscuits that use chocolate. Biscuits can be coated
with chocolate by enrobing, either full or half coated, or by moulding the chocolate
and adding the biscuit into the mould. Chocolate inclusions such as chips or chunks
are also often found in biscuits or cookies.
42
Enrobed and filled chocolate, confectionery and bakery products
Table 3.7
Milk chocolate formulations for biscuits
Sugar (%)
Cocoa butter (%)
Cocoa mass (%)
Crumb (%)
Whole milk powder (spray) (%)
Skimmed milk powder (%)
Whey powder (%)
CBE (%)
Milk fat (%)
Lecithin (%)
Natural vanilla (%)
Particle size (µm)
Total fat (%)
Standard
Premium
47.44
12.8
14
29.59
19.3
7.5
25
13
10
7
4.6
3.5
0.65
0.01
35– 40
28.9
5
0.6
0.01
33–36
30.5
For enrobing applications, the required rheology of the chocolate will depend
on the shape of the biscuit to be covered and will determine the amount of
chocolate used per biscuit. A more fluid formulation will result in less chocolate on
the biscuit, with a more viscous chocolate leading to higher pick up weights.
It is usual to find that the particle size of chocolate products used on biscuits is
higher than confectionery products. Particle size is critical in influencing the
amount of cocoa butter that is used in the recipe for a specified rheology and the
actual texture of the biscuit means that larger particles in the chocolate are
undetected.
In the United Kingdom, the largest proportion of biscuit products are coated
with milk chocolate, however, for certain biscuits using dark chocolate, butter oil
can be added for its anti-bloom properties. It helps prevent the appearance of white
fat crystals caused by fat migration from the biscuit (Table 3.7).
Cakes
Milk chocolate is used in a variety of ways in the cake market, from a thin coating
on an individual mini-roll, to a thick covering on premium celebration cakes.
Formulations are designed to optimise flavour and tend to have a low viscosity to
achieve a thin coating. Milk chocolate designed for cakes that need to be cut with
a knife often have a higher milk fat content, resulting in a softer texture to prevent
cracking and make it easier to cut. Higher cocoa mass content can be used to
achieve a darker colour and stronger cocoa flavour to counteract the sweetness of
the cake if required (Table 3.8).
3.4.2 Confectionery
Chocolate is used in a huge array of confectionery products, from simple moulded
bars to ‘high class’ hand-crafted assortments of individual chocolates. Formulations can vary extensively with applications including moulding, enrobing, dipping,
panning and spinning, each requiring its own specific rheology.
Formulation of chocolate for industrial applications
Table 3.8
43
Milk chocolate formulation for mini rolls
Milk chocolate
Sugar (%)
Cocoa butter (%)
Cocoa mass (%)
Skimmed milk powder (%)
Whey powder (%)
CBE (%)
Milk fat (%)
Lecithin (%)
Natural vanilla (%)
Particle size (µm)
Total fat (%)
Table 3.9
39.58
15.2
19
8
6
4.6
7
0.6
0.02
27–33
37.5
Formulations for confectionery applications
Sugar (%)
Cocoa butter (%)
Cocoa mass (%)
Whole milk powder (roller) (%)
Whole milk powder (spray) (%)
Crumb (%)
Skimmed milk powder (%)
Lactose powder
Milk fat (%)
Lecithin (%)
Natural vanilla (%)
Particle size (µm)
Total fat (%)
Milk chocolate
for bars
Milk chocolate
for spinning
Dark chocolate
for bars
45.78
18.6
12
9
14
21.38
24.5
10.5
27.37
72
30
7
5
1
0.6
0.02
20–24
35.5
0.6
0.03
18–22
39.2
0.6
0.02
18–22
31.5
For dark chocolate products, it is generally accepted that the level of cocoa
solids is an important quality criterion. A high level of cocoa solids means less
sugar and subsequently a more intense cocoa flavour so the choice of cocoa bean
blends or origin can be significant. For all chocolate types, formulations are often
market driven in terms of flavour preference, permitted ingredients and cost (Table
3.9).
3.4.3 Ice Cream
The market for chocolate use with ice cream has changed considerably in the last
few years, with a move from chocolate flavoured coatings used on simple choc-ice
type products to premium ‘real’ chocolate items. Chocolate flavoured coatings still
have their place for certain products and applications but there has been a huge
growth in volume of the dipped, individual products on a stick.
44
Enrobed and filled chocolate, confectionery and bakery products
Table 3.10 Formulations for ice cream dipping or enrobing
Cocoa butter (%)
Sugar (%)
Milk fat (%)
Whole milk powder (roller) (%)
Whole milk powder (spray) (%)
Cocoa mass (%)
Lecithin (%)
Natural vanilla (%)
Particle size (µm)
Total fat content (%)
Milk chocolate
Chocolate
White chocolate
28.5
40.9
5
8.5
5
11.5
0.58
0.02
20–22
43.4
20.5
41.4
5
32.4
40
5
13
9
32.5
0.58
0.02
20–22
43.4
0.58
0.02
20–22
43.5
Chocolate used in ‘frozen’ applications still has to meet the same cocoa and
chocolate regulations as other product sectors, however, applying chocolate to
products below freezing temperature (approximately –18 °C) is very different.
The ice cream is typically dipped into untempered chocolate which then hardens
owing to the low temperature. To achieve the correct weight of chocolate on the
product, adequate flow is needed, which is why the fat content of the chocolate is
normally higher than in other applications. If a moulding rheology chocolate were
used for example, you would get a very thick, uneven covering (Table 3.10).
Yield value is a dominant factor in dipping so it can be very beneficial to use the
emulsifier PGPR to reduce the yield value of the chocolate. In this way, PGPR in
a formulation can help achieve a ‘thin’ coating on an ice cream. PGPR can also help
prevent changes in the rheology of the chocolate in the dipping tank, caused by
moisture from the ice cream. This is because PGPR has greater water-binding
properties than either lecithin or ammonium phosphatide.
The legislation regarding the use of vegetable fats other than cocoa butter in
chocolate used for the manufacture of ice cream and similar frozen products
permits the use of coconut oil or CBEs. The use of coconut oil is specific to this
product category and can give significant cost savings. As with CBEs in other
chocolate products, a maximum addition of 5% is permitted and the method of
calculation is the same.
3.4.4 Inclusions
Chocolate is moulded or deposited into different size and shape pieces to be
included in other products such as biscuits, cakes and ice cream. The majority of
inclusions are chunks, moulded and specified by their dimensions, and chips
which are deposited and specified by count per kilogram. Chip sizes can range
from the largest at approximately 1750 per kg to very small at 22 000 per kg.
Chocolate inclusions can be used in a number of applications but they are most
often used in bakery products, for example, cookies and muffins. For this reason
the formulations are designed to withstand the baking process. Obviously, the
high oven temperatures used cause the chocolate pieces to melt, but choosing a
Formulation of chocolate for industrial applications
45
Table 3.11 Formulations for chips or chunks
Milk
White
Chocolate
chocolate chocolate
Sugar (%)
Cocoa butter (%)
Cocoa mass (%)
Whole milk powder (spray) (%)
Skimmed milk powder (%)
Milk fat (%)
Fat reduced cocoa powder (%)
Lecithin (%)
Natural vanilla (%)
Particle size (µm)
Total fat (%)
52.43
14.4
11.5
21
0.65
0.02
22–27
26.5
55.33
21
Chocolate with
higher cocoa solids
57.55
7.8
34
47.15
1.7
48.5
0.65
2
0.65
22–27
26.5
22–27
28.5
9
11
3
0.65
0.02
22–27
26.7
chocolate with a low fat percentage will help the inclusion to retain its shape better
during baking. Another consideration is not to use inclusions immediately after
moulding. Time is needed to allow for full crystallisation of the cocoa butter to
achieve the most stable product. Pieces of chocolate are also used for decoration
purposes, for example, curls, shavings and vermicelli (Table 3.11).
3.5
Speciality products
3.5.1 Origin chocolate
Alongside standard products, consumers also want unique, premium flavours.
This is true in many markets as can be seen, for example, from the explosion in the
number of coffee outlets, serving many different styles and sources of coffee.
Cocoa beans are not all the same. It is possible to create some unique highly
flavoured products from different origin countries. There is no clear legal definition of origin chocolate, but it is important to ensure that the products do not
mislead the consumer. The source of the cocoa is the most important factor. Origin
chocolates are made from cocoa mass produced from cocoa beans from a single
geographical area and the products made owe their unique flavour to the specific
conditions in the area that the cocoa is grown. Usually there is limited availability
of the cocoa beans and this makes them even more desirable. The market for origin
products is currently expanding more quickly than the market for standard
chocolate products. It is important to remember that the origin does not refer to
where the chocolate is produced but to the geographical origin of the cocoa.
As was mentioned earlier, cocoa trees originated in the tropical rain forests of
Central and South America. Cocoa trees need a hot and humid environment but
also prefer to grow in the shade of larger trees, protected from direct sunlight and
strong winds. The region of cultivation, the soil and climatic conditions play a
major role in determining the flavour and aroma of the cocoa. The trees grow in the
46
Enrobed and filled chocolate, confectionery and bakery products
tropical zone approximately 10 degrees north or south of the equator. Africa is now
the leading area of cultivation, and grows about 70% of the world crop.
The variety of cocoa is also important for development of unique flavours and
aromas. There are two original botanical varieties of cocoa, Criollo and Forestaro.
As a result of cross fertilisation and experimentation it is now unlikely that the pure
original varieties can be found, although the names are still used. Criollo beans
have exceptional flavour and give delicate and sought-after flavours to the
chocolate made from them. The total Criollo crop is only around 5% of the of world
production, making this type of cocoa very exclusive. Criollo is a delicate type of
tree and only survives in specific conditions in certain South American and Asian
regions. The other original variety, Forestaro, is a much more robust tree, with
better resistance to disease and gives beans that are dark in colour with a
recognisable basic taste. In some areas the Forestaro beans give unique aromatic
aromas. A third variety, Trinitario, combines the best of Criollo and Forestaro,
having been developed by cross-breeding. The type of beans that are used are not
normally mentioned, as there is no guarantee of botanical purity, but are important
in identifying unique flavour opportunities.
The production of origin chocolates does not require any special machinery.
The expertise in manufacture is in identifying the fine flavours and ensuring that
these are developed and not lost during the process. The process develops and
brings out the natural taste and aromas. In contrast to traditional chocolate made
from blends, it is not possible to give guarantees about consistent flavour as this
may vary from year to year depending on the harvest. Each product made should
comply with the description given and must reflect the true situation. The cocoa
mass used to make the chocolate must come from beans grown in the region
specified.
3.5.2 Organic products
The growth in market size for organic products is increasing each year and more
and more products are available. In recent years growth has been even more
noticeable with an even greater diversity of products. This is also true for cocoa and
chocolate products. This is all part of a general tendency of consumers to be aware
of what is happening around them and to search for products that have a reduced
impact on the environment and offer some sort of guarantee of authenticity and
purity. The consumer is looking for products that have certification from a reliable
and competent authority. These are government accredited organisations which
carry out practical checks to ensure consistency and that the appropriate agreed
standards are met. In terms of chocolate products this means little in terms of
changes to manufacturing processes, but has an impact on the source and availability of raw materials. Compositionally, organic or BIO chocolates, do not differ
much from standard chocolate products, but the ingredients have been checked and
certified from organic sources.
The starting point for organic chocolate products is organic ingredients. The
finished chocolate product must contain organically produced ingredients to a
Formulation of chocolate for industrial applications
47
minimum of 95%. If organic ingredients are available they must be used, assuming
they meet the required composition and quality specification. Non-organic ingredients can therefore be used where no organic alternative exists but only to a
maximum of 5%.
The actual detail of specific criteria laid down for organic production may vary
from country to country, but certain basic principles are applicable everywhere.
For vegetable cultivation, the following principles apply:
•
•
•
•
•
•
•
No pesticides, artificial fertilisers and soil improvers may be used.
Natural and environmentally friendly cultivation must be used.
Natural crop rotation is used to avoid soil exhaustion.
Green manures and composting must be used to maximise soil production
capacity.
No genetic modification is permitted.
Pests, weeds and disease are controlled using nature.
The land must be cultivated to organic standards for at least three years before
produce can be claimed as organic.
For animal and dairy products, the following principles apply:
• Agricultural business must comply for at least three years to organic standards
covering feed, grazing and equipment.
• Dairy products can be considered for certification after the animals have been
fed and cared for organically for at least six months.
• Animal feed, grazing land, veterinary treatment and animal housing must all
comply with organic requirements.
Organic chocolate products are typically manufactured using organically grown
cocoa, organic cane sugar and, in the case of organic milk or white chocolate,
organic milk powders. As manufacturing may take place on the same lines as
standard products, strict clean down procedures are adopted and agreed and
monitored by the certification body.
In terms of compositional requirements, the various products made must also
comply with the relevant chocolate legislation and all other appropriate legislation.
The chocolate products made can be processed in the same way as standard
products in terms of melting, tempering and cooling conditions. Various chocolate
recipes are available across the range of milk, white and dark chocolate to suit
different customer applications and each is certified organic by a proper authority.
3.5.3 Fairtrade
Along with the growth in organic products and premium, unique flavoured
products, another area of growth in recent years has been in Fairtrade products
such as cocoa, chocolate, coffee, tea and bananas. Fairtrade focuses in particular on
exports from developing countries to developed countries.
Fairtrade is a trading partnership, based on dialogue, transparency and respect,
that seeks greater equity in international trade. It is not just about paying a fair
48
Enrobed and filled chocolate, confectionery and bakery products
price. It contributes to sustainable development by offering better trading conditions to, and securing the rights of, disadvantaged producers and workers. Fairtrade
organisations are actively engaged in supporting producers in raising awareness
and campaigning for changes in the rules and practices of conventional trade. It is
a strategy for poverty alleviation and involves transparent management and
commercial relations to deal fairly and respectfully with trading partners. It
provides fair pay to the producers and not only covers the costs of production but
also enables production that is socially just and environmentally friendly. It means
a safe and healthy environment for producers and ensures that the work of men and
women is properly valued and rewarded. The strategic intent of Fairtrade is
deliberately to work with marginalised producers and workers in order to help
them move from a position of vulnerability to security and economic selfsufficiency. It aims to empower people to become stakeholders in their own
organisations and to actively play a wider role in the global arena to achieve greater
equity in international trade.
Fairtrade is regulated by a worldwide non-profit-making organisation, The
Fairtrade Labelling Organization (FLO). This was created in 1997 and marked a
tremendous step forward. The FLO labelling system is the largest and most widely
recognised standard setting and certification body. It is responsible for defining
product standards. Producers, manufacturers and traders must comply with the
standards in order to obtain their certification and the standards monitor the entire
trade chain through to the end consumer. FLO-Cert is the certification body; by
issuing certification the FLO is able to guarantee to consumers that the agreed
standards have been met throughout the entire trade chain. By use of an internationally recognised Certification Mark, consumers can easily recognise products
that meet the agreed standards.
The cost of the minimum price and Fairtrade premium is borne by the consumer.
Retailers and wholesalers pay a license fee that entitles them to use the certification
mark and producers and traders pay a certification fee that covers the cost of
inspection work carried out by FLO-Cert.
For chocolate products, the standards apply to the cocoa ingredients, sugar and
vanilla. Other ingredients used, such as milk and lecithin, are not subject to
Fairtrade standards. Fairtrade certified raw materials are used to manufacture
Fairtrade chocolate products to the same formulations and in the same way as the
traditional chocolate production process. Each manufacturing run is registered
with the FLO, so that checks can be done on the quantities of raw materials
purchased and the quantities of the products processed and sold. Customers who
buy and use Fairtrade chocolate can sell them under a Fairtrade label once they
have signed a licensing agreement with the corresponding labelling initiative. All
Fairtrade labels are registered and cannot be used without prior written permission
from the labelling initiatives.
3.5.4 Without added sugar
Depending on the formulation, chocolates typically contain around 30–55%
Formulation of chocolate for industrial applications
49
sugars, principally sucrose obtained from sugar beet or sugar cane. Lactose, or
milk sugar is naturally present in milk powders and hence is also present in milk
and white chocolate. The main reason for the addition of sugar is for taste. Sugar
gives chocolate its sweetness and, therefore, it is an integral part of the chocolate
taste experience. The other role of sugar is as a bulking agent, allowing the product
to be more easily processed.
An increasing number of consumers today want to avoid sugar for lifestyle or
health reasons, particularly those concerned about their weight. This has led to the
development of products without added sugar, using various alternative sweeteners instead of sucrose. The best results have been achieved using maltitol. Maltitol
offers various advantages over other polyols, because its chemical structure and
properties have much in common with those of sugar. It is not hygroscopic (an
important factor for processing) and it is temperature stable. The flavour and
composition of maltitol remain constant over the temperature range needed in
production. This is not the case for all sweeteners. The mass to volume ratio is
comparable to sucrose and so it can be used as a direct replacement. The taste of
maltitol-based chocolate is virtually identical to that of normal chocolate products
and can be used in exactly the same way. Production should be made on a separate
line or carried out on a thoroughly cleaned line.
Excessive use of maltitol can have a laxative effect. Tolerance varies from
individual to individual. The Scientific Committee of the European Commission
states that a daily consumption of maltitol of 30–50 g (equating to 60–100 g of
maltitol chocolate) should cause no problems for the majority of consumers.
Where a product contains more than 10% polyols by weight, the packaging must
carry the following statement ‘Excessive use may have a laxative effect’.
Chocolate based on maltitol and without added sugar must be described for
food legislation purposes as ‘chocolate with sweetener’ or ‘chocolate with maltitol’
and may bear the statement ‘without added sugar’. In the EU, nutrition labelling is
mandatory when a claim ‘without added sugar’ is made.
3.6
Health aspects
The nutritional and health aspects of chocolate have been the subject of debate for
many years. Historically, when chocolate arrived into Europe is was considered
medicinal and was regularly prescribed for a number of different ailments in the
17th and 18th centuries. Since then it has remained an important source of energy,
used by sportspeople and labourers to replenish calories and can still be found as
a component of modern army ration packs. However, with the rise in obesity,
diabetes and cardiovascular diseases, chocolate tends to find itself labelled as
unhealthy and indulgent. Governments and international bodies are taking action
to promote a healthier lifestyle and some individuals are becoming more health
conscious and demanding about their personal diet. Now that health, nutrition, diet
and lifestyle are becoming more important to consumers, manufacturers are
looking in greater detail at the raw materials used and how processes can be
50
Enrobed and filled chocolate, confectionery and bakery products
adapted to create innovative chocolate products that meet these new positive
demands.
3.6.1 Flavanols
Recent studies, (Lee et al., 2003), revealed that cocoa beans contain a considerably
larger amount of flavanols than red wine and other commonly known sources of
antioxidants, such as green tea and grapes. In addition, cocoa contains more
complex flavanols, the so-called procyanidins. These are powerful antioxidants
which may have positive cardiovascular effects and strengthen the natural defences in case of oxidative stress.
There is an increasing amount of evidence to suggest that the antioxidant
activity of flavanols can protect the body against the negative effects of the free
radicals that cause damage to our cells. The presence of these free radicals, highly
unstable molecules, in the body can be triggered by a number of things such as
stress, pollution, direct exposure to sunlight and smoking. Cocoa flavanols appear
to be special owing to their high availability and extreme effectiveness in neutralising free radical activity (Baba et al., 2000; Corder, 2008; Engler and Engler,
2006; Hooper et al., 2008; Vinson et al., 2006).
Barry Callebaut has developed a special process, the ActicoaTM process, in
which the flavanols naturally present in the cocoa bean are retained at higher levels
during the process of making chocolate. During traditional chocolate processing,
especially during fermentation of the beans the quantity of flavanols is reduced.
Using this innovative process, the positive effects of the cocoa flavanols on the
body and the authentic taste of the chocolate are preserved.
3.6.2 Nutritionally improved products
Chocolate products have been developed with a better balance of nutritious
ingredients using unique technologies and specific ingredients, such as more
dietary fibre and less sugar or fat. Consumers still want the same delicious taste and
texture that they are used to, but with better balanced nutrition.
Chocolates are now available in which the amount of sugar has been reduced by
30%, compared to the traditional counterpart. By replacing sugar with dietary
fibre, a natural end result is obtained that contains no artificial sweeteners or
polyols and does not have an increased fat content. Furthermore, the special
selection of dietary fibres is well tolerated by our digestive system and offers
prebiotic and bifidogenic benefits. This type of chocolate product can be used by
food manufacturers in many applications to create new product concepts offering
important nutritional and health benefits.
3.6.3 Probiotic
Natural functional foods exist in virtually every food group and now manufacturers can fortify and enhance products to give health benefits. New food
Formulation of chocolate for industrial applications
51
products are being developed with beneficial components that are attracting a
significant share in many segments of the food market. Probiotics fit perfectly
into this expanding market. Historically, much of the emphasis on probiotics
has been found in dairy products. Barry Callebaut has now developed a process
to incorporate probiotics, Lactobacillus and Bifidobacterium, into chocolate.
Numerous stability and clinical studies have been conducted or are under way.
The probiotics have no influence on the taste, texture or mouthfeel of the end
product. Chocolate is a stable environment and so the products do not need to
be refrigerated, with a shelf life of up to one year being achieved. Only a small
quantity, 13.5 g per day, of this probiotic chocolate is required for optimal
activity.
3.6.4 Stearic acid in cocoa butter
Extensive work is going on in many countries to reduce the levels of saturated fats
in the diet. Chocolate, because of its cocoa butter content, is rich in saturated fatty
acids. However, a significant proportion of these is stearic acid and there is
increasing evidence in the literature that stearic acid may not have the adverse
effect on blood cholesterol levels seen with shorter-chain saturated fatty acids.
German and Dillard (2004), in their review of the dietary effects of saturated fats
state that stearic acid is not thought to increase cholesterol concentrations. Furthermore they go on to discuss the importance of the position of the stearic acid group
on the triglyceride molecule. If it is esterified in the 1- or 3-position (as it is in cocoa
butter) then, when the fat is digested, it is released as free stearic acid. In the
presence of calcium it is then poorly absorbed. Calcium will be present to some
extent from milk powders in milk chocolate. Sanders and Berry (2005) have
specifically evaluated stearic acid as present in cocoa butter and found that its
effects on blood lipids and other indicators of cardiovascular disease risk were
comparable to those seen after consuming a similar meal containing high-oleic
sunflower oil.
3.7
Future trends
New products will be developed that respond to the evolving nutritional needs or
changing eating habits of the modern consumer. The shift towards natural ingredients will continue, and this is clearly seen in the area of added flavourings. Natural
vanilla is now replacing the nature identical flavour vanillin in a large number of
chocolate products. Consumers want to know where the ingredients used have
come from. The demand for natural, authentic, traceable ingredients that give
distinctive flavours will continue to grow to produce exciting, indulgent products.
Fundamental research will continue to identify opportunities to develop new
nutritionally improved products and products that can help with certain aspects of
health.
52
Enrobed and filled chocolate, confectionery and bakery products
3.8
Sources of further information and advice
For further information, the following websites can help:
•
•
•
•
•
www.acticoa.com
www.barry-callebaut.com
www.soilassociation.org
www.ecocert.com
www.fairtrade.org
3.9
References
BABA S., OSAKABE N., NATSUME M., YASUDA A., TAKIZAWA T., NAKAMURA T. AND TERAO
J. (2000). ‘Cocoa powder enhances the level of antioxidative activity in rat plasma’. Br J
Nutr, 84, 673–80.
CORDER R. (2008). ‘Red wine, chocolate and vascular health : developing the evidence base’.
Heart, 94, 821–3.
ENGLER M. B. AND ENGLER M. M.
(2006). ‘The emerging role of flavonoid-rich cocoa and
chocolate in cardiovascular health and disease’. Nutr Rev, 64, 109–18.
GERMAN J. B. AND DILLARD C. J. (2004). ‘Saturated fats: what dietary intake?’. Am J Clin
Nutr, 80(3), 550–9.
HOOPER L., KROON P. A., RIMM E. B., COHN J. S., HARVEY I., LE CORNU K. A., RYDER J. J., HALL
W. L. AND CASSIDY A. (2008). ‘Flavonoids, flavonoid-rich foods, and cardiovascular risk:
a meta-analysis of randomized controlled trials’. Am J Clin Nutr, 88, 38–50.
LEE K. W., KIM Y. J., LEE H. J. AND LEE C. Y. (2003). ‘Cocoa has more phenolic phytochemicals
and a higher antioxidant capacity than teas and red wine’. J Agric Food Chem, 7292–5.
SANDERS T. A. B AND BERRY S. E. E. (2005). ‘Influence of stearic acid on postprandial lipemia
and hemostatic function’ Lipids, 40(12), 1221–7.
SHUKLA V. K. S. (1994). ‘Milkfat in sugar and chocolate confectionery’. In Fats in Food
Products, Moran D. P. J. and Rajah K. K. (eds), Blackie Academic & Professional,
London, p 260.
VINSON J. A., PROCH J., BOSE P., MUCHLER S., TAFFERA P., SHUTA D., SAMMAN N. AND AGBOR
G.A. (2006). ‘Chocolate is a powerful ex vivo and in vivo antioxidant, an antiatherosclerotic
agent in an animal model, and a significant contributor to antioxidants in the European and
American diets’. J Agric Food Chem, 54, 8071–6.
4
Fats for confectionery coatings and
fillings
Geoff Talbot, The Fat Consultant, UK
Abstract: Fats form an integral part of both confectionery coatings and fillings and, in
many cases, are the continuous phase of these components, meaning that much of the
functionality of coatings and fillings is defined by the nature of the fat phase. This
functionality includes production constraints (whether the coating or filling needs to be
tempered and how it should be cooled), storage constraints (including the likelihood of
migration occurring and fat bloom forming) and sensory characteristics (hardness, speed
of melt, coolness during eating). The different types of fats used in coatings and fillings
are described in this chapter as well as the effects they have on processing, recipe and
quality. To have good structure in such products it is necessary to use fats which are
solid at ambient temperatures and above, but which still melt at mouth temperature. This
often means using fats that are rich in either saturated or trans fatty acids. The nutritional
issues surrounding these fatty acids are also discussed.
Key words: coating fats, cocoa butter alternatives, cocoa butter equivalents, cocoa
butter replacers, filling fats, polymorphism, trans fats.
4.1
Introduction
Without denying the obvious functional and sensory benefits of the other ingredients in confectionery coatings, it may be argued that many of the properties of these
products stem from the attributes of the fat phase. In most cases the fat is the
continuous phase within which the other ingredients (sugars, milk powders, cocoa
powders, nuts, flavours etc) are distributed. The same thing can be said about many
confectionery fillings, certainly those of a praline nature, although some fillings,
notably those which are predominantly sugar-based (fondants, high-boiled sugar
confectionery and, to some extent, toffees and caramels) are exceptions to this.
54
Enrobed and filled chocolate, confectionery and bakery products
H
H
C
O
O
C
O
H
C
O
C
O
H
C
O
C
Three
fatty
acid
groups
H
Glycerol backbone
Fig. 4.1 Schematic structure of a triacylglycerol (triglyceride) molecule.
This does mean, however, that the nature of the fat in a coating or filling is
extremely important in defining product design, processing and sensory properties. It also plays a major role in some of the problems seen in enrobed confectionery
(the formation of fat bloom, oil migration between components) while also being
part of the solution to other problems such as moisture and alcohol migration. On
this basis, the structure of fats and fatty acids is a good place to start in discussing
the range of fats used in coatings and fillings.
4.1.1 Fats and fatty acids
In chemical terms, fats are esters of glycerol (a trihydric alcohol) and three fatty
acid groups. Scientifically they are known as triacylglycerols (TAG); commonly
they are termed triglycerides (TG). Their structure is shown schematically in Fig.
4.1 and will be discussed in more detail in Section 4.2.
Two factors are important in defining the properties of triglycerides: (a) the
nature of the three fatty acids found on the molecule and (b) the position of these
three acids relative to each other. Fatty acids fall into four major groupings:
• Saturated fatty acids. These are long carbon-carbon chains with a methyl (CH3)
group at one end and a carboxylic (fatty) acid group (COOH) at the other. In
between is a long chain of methylene (CH2) groups. In the types of vegetable oil
commonly used in confectionery products, the carbon chains contain an even
number of carbon atoms ranging from 8 to 10 carbon atoms in fatty acids in
coconut oil up to 18 carbon atoms in cocoa butter and shea butter. Milk fat
contains a wider range of saturated fatty acids, some with much shorter chain
lengths (as short as four carbon atoms – butyric acid) and some with an odd
number of carbon atoms. Saturated fatty acids are essentially straight chain in
nature (Fig. 4.2a)
Fats for confectionery coatings and fillings
55
• cis-mono-unsaturated fatty acids. These differ from saturates in that between
•
•
one pair of carbon atoms there is a double bond instead of the (saturated) single
bond. The most common cis-mono-unsaturate is oleic acid which has 18 carbon
atoms in the chain with the double bond being found between the 9th and 10th
carbon atoms (counting the methyl end group as the first carbon atom). Unlike
saturated fatty acids, cis-unsaturates have a bend in the chain where the double
bond lies (Fig. 4.2b). This has implications when it comes to seeing how fatty
acids in adjacent triglyceride molecules pack together.
cis-polyunsaturated fatty acids. As their name suggests, these contain more than
one double bond in the fatty acid chain. In terms of the oils used in confectionery, the most commonly encountered cis-polyunsaturates are linoleic acid and
linolenic acid. Linoleic acid contains two double bonds – one between the 6th
and 7th carbon atoms and the other between the 9th and 10th carbon atoms.
Linolenic acid contains three double bonds – two are in the same position as in
linoleic acid, the third one is between the 3rd and 4th carbon atoms (all counting
the methyl end group as the first carbon atom). The position of the first of these
double bonds defines the type of cis-polyunsaturate. In linoleic acid the first
double bond starts with the 6th carbon atom and acids like this are called n-6 or
omega-6 polyunsaturates. In linolenic acid, the first double bond starts with the
3rd carbon atom and such acids are called n-3 or omega-3 polyunsaturates. cisPolyunsaturates have a bend in the carbon chain at each of the double bond
positions (Fig. 4.2c)
trans-unsaturated fatty acids. In the two types of cis-unsaturate the carbon
chains emerging from the double bonds are on the same side of the chain as each
other. In trans-unsaturates, however, the carbon chains are on opposite sides of
the double bond. This is best seen by comparing the structure of oleic acid (a cismono-unsaturate) with elaidic acid (the corresponding trans-mono-unsaturate)
in Figs 4.2b and 4.2d. Comparing the structures of stearic acid (Fig. 4.2a) and
elaidic acid (Fig. 4.2d) it is also clear that there are great similarities between the
two. This similarity is not only seen in their physical characteristics (e.g.
melting point) but also in some of their nutritional aspects.
The degree and type of unsaturation found in a fatty acid has a great effect on its
physical characteristics, especially its melting point. Saturated fatty acids found in
vegetable oils are usually solid at room temperature, in fact most have melting
points well above mouth temperature. Unsaturated fatty acids, on the other hand,
are usually liquid at room temperature. The exceptions to this are the trans fatty
acids which, because their structure is more similar to that of a saturated fatty acid
(see Fig. 4.2) are also solid at room temperatures. The melting points of the fatty
acids most commonly found in confectionery are shown in Table 4.1. This table
also lists the common names of these acids as well as their chemical names and
shows the two types of abbreviation commonly applied. The first way of abbreviating these acids is to use two numbers separated by a colon (:). The first of these
numbers is the number of carbon atoms in the chain, the second is the number of
double bonds. So, for example linolenic acid with 18 carbon atoms and 2 double
56
Enrobed and filled chocolate, confectionery and bakery products
COOH
(a)
CH3
CH3
COOH (b)
COOH
(c)
CH3
CH 3
COOH
(d)
Fig 4.2 Fatty acid structures. (a) Saturated fatty acid: stearic acid; (b) cis-mono-unsaturated fatty acid: oleic acid; (c) cis-polyunsaturated fatty acid: linoleic acid;
(d) trans-mono-unsaturated fatty acid: elaidic acid.
bonds is abbreviated to C18:2. This type abbreviation is most commonly used to
describe the acids themselves.
The second type of abbreviation is to use, where possible, the first letter of the
acid’s common name. So, for example, oleic acid is abbreviated to ‘O’. There are
two areas where this can be confusing: (i) some acids start with the same letter, for
example, ‘L’, so lauric acid is abbreviated to ‘L’ but linoleic and linolenic are
abbreviated to ‘Li’ and ‘Ln’ respectively, (ii) it is often useful to group saturates
and unsaturates together – unsaturates as a group are abbreviated to ‘U’ and
saturates to ‘S’ but this then means that stearic acid needs to be abbreviated to ‘St’
to avoid confusion with saturates as a whole! This type of abbreviation is most
commonly used to describe the composition of the triglycerides (see below).
The physical properties of the fatty acids found on a triglyceride molecule carry
through to define the physical properties of the triglyceride itself. So, for example,
a triglyceride which contains three saturated fatty acids will have a higher melting
point than one which has two saturated and one cis-unsaturated fatty acid group. In
turn this will have a higher melting point than one with two or three cis-unsaturated
fatty acid groups. As with the acids themselves, triglycerides containing transunsaturates are higher melting. This means that in defining the physical
characteristics of a triglyceride molecule it is the fatty acids that are present that are
the most important parameter.
However, the position of these acids on the triglyceride molecule also plays a
part in defining the physical characteristics. This is particularly the case in
triglycerides with, say, two saturated groups and one unsaturated group. The
unsaturated group can be in the middle or 2-position with the saturates in the
outside, 1- and 3-positions. Such structures are known as symmetrical triglycerides.
Fats for confectionery coatings and fillings
Table 4.1
57
Melting points, names and abbreviations of common fatty acids
Chemical name
Common name
Numeric
abbreviation
Alphabetic
abbreviation
Melting
point (°C)
Decanoic acid
Dodecanoic acid
Tetradecanoic acid
Hexadecanoic acid
Octadecanoic acid
Eicosanoic acid
Octadec-cis, 9-enoic acid
Octadec-trans, 9-enoic acid
Octadec-cis 9, cis 12dienoic acid
Octadec-cis 9, cis 12,
cis 15-trienoic acid
Capric acid
Lauric acid
Myristic acid
Palmitic acid
Stearic acid
Arachidic acid
Oleic acid
Elaidic acid
Linoleic acid
C10:0
C12:0
C14:0
C16:0
C18:0
C20:0
C18:1c
C18:1t
C18:2cc
C
L
M
P
St
A
O
E
Li
31.6
44.8
54.4
62.9
70.1
76.1
16
44
–6.5
Linolenic acid
C18:3ccc
Ln
–12.8
Source: Loders Croklaan Speciality Fat Technology Handbook (1989).
Alternatively the unsaturated group can be on one of the outside (1- or 3-positions)
giving an asymmetrical triglyceride. These different types of structure are important, particularly in cocoa butter and cocoa butter equivalents, and will be discussed
in more detail in the next section.
The alphabetic abbreviation of fatty acid names is often used to give a shorthand
description of the triglyceride composition in terms of both fatty acid composition
and position. So, for example, ABC would denote a triglyceride with fatty acid A
in the 1-position, fatty acid B in the 2-position and fatty acid C in the 3-position.
One of the main triglycerides in cocoa butter has a palmitic acid group in the 1position, an oleic acid group in the 2-position and a stearic acid group in the
3-position and so is abbreviated to POSt. Although there is a difference between
POSt and StOP – these being optical isomers of the same molecule – for most
purposes they can be taken as being interchangeable because triglycerides such as
these in fats are present as racemic mixtures.
4.2
Crystal structure and polymorphism of fats
Although the structure or a triglyceride molecule was shown schematically in Fig.
4.1, the actual structure is more like the one depicted in Fig. 4.3.
This depiction of the structure makes it much clearer that the fatty acid in the 2position (in this case, oleic acid) is quite different from those in the 1- and
3-positions in that it appears out of the glycerol backbone from the opposite side.
This structure is of great importance when it comes to defining how molecules of
triglyceride pack together in a crystal.
Essentially there are three main forms in which fats crystallise, known as
polymorphic forms. Polymorphism is the ability of a substance to crystallise in
more than one crystal structure. In this sense all fats are polymorphic. Some,
58
Enrobed and filled chocolate, confectionery and bakery products
Palmitic acid groups
Glycerol backbone
Oleic acid
group
Fig. 4.3 Structure of POP (1,3-dipalmitoyl, 2-oleoylglyceol) (from K W Smith,
Unilever Research, Colworth, UK).
however, very quickly and easily attain a stable crystal form and, in this sense, are
often considered to be ‘non-polymorphic’. Others, such as cocoa butter, have a
large number of polymorphic forms and need to be processed in very specific ways
to get them to crystallise in a stable form. The three main polymorphic forms are,
in order of increasing stability:
• alpha (α)
• beta-prime (β')
• beta (β)
Many fats are stable in the β' form and do not go on to the β form; others (cocoa
butter being the prime example) need to crystallise in the β form for full stability. The
structures of each of these polymorphic forms are shown in Fig. 4.4. Here we see each
of the three forms both side-on and end-on. The α form has its fatty acid chains
perpendicular to the end view but when viewed end-on has an hexagonal conformation in which each molecule is at a point on a hexagon. The β' form, however, is
significantly different in that firstly the fatty acid chains are now at an angle to the
end-plane and secondly, looking end-on, they pack in what is known as an
orthorhombic sub-cell in which adjacent fatty acid chains are mutually perpendicular when viewed from this angle. This allows a closer packing of molecules than with
the α form and gives the β' form a greater stability. Closer packing still is found in the
β form where the angle of the fatty acid chains is tilted slightly further away from the
perpendicular and where now the end chains are packed in a triclinic sub-cell. In this
sub-cell all the fatty acid chains lie parallel to each other.
The side views in Fig. 4.4 show how the fatty acid chains in adjacent molecules
can pack together. The triglycerides pack in a ‘chair’ or ‘tuning fork’ structure. In
the β' and β examples in Fig. 4.4, the fatty acid in the 2-position of one molecule
lies adjacent to the fatty acid chains in the 1- and 3-positions of the next molecule.
The length of the sub-cell is two fatty acid chains long and this type of crystal
packing is known as double chain length packing. Many fats crystallise in this way.
Some triglycerides, however crystallise with a sub-cell that is three fatty acid
Fats for confectionery coatings and fillings
β'-form
α-form
Side
view
59
β-form
Glycerol
end
plane
Methyl
end
plane
Glycerol
end
plane
End
view
Fig. 4.4 Crystal structures of the main polymorphic forms.
(a)
Fig. 4.5
(b)
Double (a) and triple (b) chain length structures of POP. (a) β-3; (b) β-2 (from
K W Smith, Unilever Research, Colworth, UK).
chains long – known as triple chain length packing. This is especially the case with
the kind of symmetrical triglycerides referred to earlier in which saturated fatty
acids are at the 1- and 3-positions and oleic acid at the 2-position. The most
important of these are POP, POSt and StOSt, the main triglycerides in cocoa butter.
If, for example, POP packed in a double chain length configuration then the
oleic acid of one molecule would lie next to the saturated acid groups of the next
molecule. As we see in Fig. 4.2b, oleic acid has a bend in the chain where the
double bond is and so this bent chain would be trying to fit next to the straight
saturated group on the next molecule. The result would be a thermodynamically
unstable crystal (Fig. 4.5b).
By moving to a triple chain length configuration the oleic acid groups on
adjacent molecules are next to each other allowing a much closer fit together in the
60
Enrobed and filled chocolate, confectionery and bakery products
Table 4.2
Traditional view of cocoa butter polymorphism
Wille and Lutton
(1966)
Form I
Form II
Form III
Form IV
Form V
Form VI
Larssona
(1966)
Melting point (°C)
Chain packing
sub-α
α
β'2
β'1
β2
β1
16–18
21–22
25.5
27–29
34–35
36
Double
Double
Double
Double
Triple
Triple
a
The suffixes 1 and 2 are used to denote different degrees of stability with forms with suffix
‘1’ having a greater stability than forms with suffix ‘2’.
crystal and a much more stable system (Fig. 4.5a). For this reason cocoa butter
which is rich in these triglycerides has a triple chain length structure.
Having said earlier that cocoa butter shows a large degree of polymorphism,
exactly how many different crystal forms does it have? For a long time, this was
considered to be fairly easy to answer but more recent work on the polymorphism
of cocoa butter has shifted these ideas. Historically, cocoa butter was considered to
have six different polymorphic forms. This view was based on the work of both
Wille and Lutton (1966) and Larsson (1966). Larsson defined six variants and subsets of the three main polymorphic forms, whereas Wille and Lutton described the
six forms simply as Form I through to Form VI in order of increasing stability. The
long-held traditional understanding (which is still the understanding of many
confectioners) of these forms is summarised in Table 4.2.
More recently, however, it has been found (van Malssen et al., 1999) that (i)
Form I is a sub-α form but that its melting point is considerably lower than first
thought, (ii) Form II/α also melts at a lower temperature than first thought and (iii)
Forms III and IV, instead of being two distinct forms of β' are in fact two members
of a continuously varying spectrum of β' crystals. The result of this is to change the
traditional view of cocoa butter polymorphism in Table 4.2 to the current understanding of this as described by Smith (2003) in Table 4.3.
Both views of the polymorphism of cocoa butter agree that there are two ‘stable’
forms, both in the β configuration. To combine the current understanding, as
Table 4.3
2003)
Current view of cocoa butter polymorphism (from Smith,
Basic polymorpha
Sub-α
α
β'
βV
βVI
Melting point (°C)
0
17
21–28
31.5
33.5
Stability
Least stable
Meta-stable
Meta-stable
Stable
Most stable
a
The suffixes V and VI are used to denote that these two β forms are the same as Forms
V and VI as defined by Wille and Lutton (1966).
Fats for confectionery coatings and fillings
61
described by Smith (2003) with the traditional understanding as described by Wille
and Lutton (1966) the subscripts V and VI are often used in conjunction with ‘β’
to distinguish between these two stable forms. Thus Wille and Lutton’s form V is
now more often referred to as βV and form VI is now more often referred to as βVI.
Because cocoa butter exhibits such a high degree of polymorphism it is
necessary to temper any coatings or fillings which have cocoa butter as their
predominant fat. The scientific aspects of tempering are dealt with in Chapter 15
and the tempering process is described in Chapter 16.
4.3
Range of coating and filling fats
In many ways the fats which are used in confectionery fillings can be considered
to be simply softer versions of those used in confectionery coatings. By thinking of
them in this way some of the interactions that occur when coating fats and filling
fats intermix by, for example, oil migration can be better understood. It is also
possible to divide them into three main groupings (and these groupings apply to
both coating and filling fats).
1. Polymorphic non-lauric fats. These are fats which are (a) based on non-lauric
oils (essentially any oil other than palm kernel oil or coconut oil) and (b)
exhibit the kind of complex polymorphism described in the previous section.
The most common of these fats is cocoa butter itself, but the group also
includes cocoa butter equivalents (CBE), fats with a similar composition to
cocoa butter which are used in place of some of the cocoa butter in coatings.
2. Non-polymorphic, non-lauric fats. These are fats which traditionally have
been based on partially hydrogenated and often fractionated oils such as palm
oil, soyabean oil, rapeseed oil and cottonseed oil. These types of fats are
generally referred to as cocoa butter replacers (CBR).
3. Lauric fats. These are fats based on either palm kernel oil or coconut oil. These
oils may be used in some applications in their basic state, although in most
ambient coating use they are usually fractionated or hydrogenated, or both.
These types of fat are generally termed cocoa butter substitutes (CBS).
The whole collection of CBE, CBR and CBS is given the generic name of cocoa
butter alternatives (CBA). When these fats have a high solid fat content at 20 °C
(e.g. greater than 60%) they are usually used as coating fats; when they have a
lower solid fat content at 20 °C (e.g. less than 50%) they are generally used as
filling fats.
4.3.1 Cocoa butter and cocoa butter equivalents (CBE)
Cocoa butter can be considered to be the fundamental confectionery fat on which
the properties of all other cocoa butter alternatives are based. Cocoa butter has a
very simple and very specific fatty acid and triglyceride composition. It is mainly
composed of three fatty acids: palmitic, stearic and oleic acids. This also gives it a
62
Enrobed and filled chocolate, confectionery and bakery products
Table 4.4 Fatty acid compositions of cocoa butter of different origins (taken from Lipp
and Anklam, 1998)
Origin
Brazil
Ivory Coast
Malaysia
C16:0
C18:0
C18:1
C18:2
C18:3
C20:0
C22:0
25.1
25.8
24.9
33.3
36.9
37.4
36.5
32.9
33.5
3.5
2.8
2.6
0.2
0.2
0.2
1.2
1.2
1.2
0.2
0.2
0.2
Table 4.5 Triglyceride compositions of cocoa butter of different origins (taken from
Chaiseri and Dimick, 1989)
Origin
POP
POSt
StOSt
StOA
SLiS
SOO
South America
Africa
Asia
19.0
18.4
18.6
38.0
39.1
40.0
26.0
28.2
30.8
0.5
0.6
0.8
7.4
6.7
5.9
9.1
6.9
4.1
P = palmitic acid, St = stearic acid, A = arachidic acid, S = total saturated acids (mainly palmitic and
stearic), O = oleic acid, Li = linoleic acid.
very simple triglyceride composition in which POP, POSt and StOSt predominate.
Having said that, there are subtle distinctions between cocoa butters from different
countries of origin (Tables 4.4 and 4.5).
While the differences are small in terms of fatty acid composition it can be seen
from Table 4.4 that Brazilian cocoa butter contains more of the unsaturated oleic
and linoleic acids than cocoa butter from Ivory Coast or Malaysia. Malaysian
cocoa butter also contains slightly less palmitic acid than does Ivory Coast cocoa
butter. These small differences are then translated into slightly greater differences
in the triglyceride compositions with south American cocoa butters (of which
Brazilian may be representative) containing significantly higher levels of the more
unsaturated (and softer) triglycerides such as SLiS and SOO. Asian cocoa butters
(of which Malaysian can be representative) generally have higher levels of the
harder POSt and StOSt triglycerides. Subtle though these differences may be, they
result in a gradation of hardnesses and solid fat contents in cocoa butters in which
Malaysian cocoa butter is ‘harder’ than Ivory Coast cocoa butter which, in turn, is
‘harder’ than Brazilian cocoa butter.
Although the main use of cocoa butter in confectionery applications is as a
coating fat, it is sometimes used as a component in fillings, either as a means of
structuring a nut-oil rich filling or in ‘ganache’ which is a combination of chocolate
and dairy cream used in short shelf life, chilled confectionery.
Cocoa butter can also be fractionated. This is a process in which higher melting
triglycerides are separated from lower melting triglycerides. The higher melting
(SOS-rich) triglycerides concentrate more into the stearine fraction while the
lower melting (SOO- and SLiS-rich) triglycerides concentrate more into the oleine
fraction (Weyland, 1992). The stearine fraction can be used in chocolates that
require a greater degree of heat resistance. Because it is softer, the oleine fraction
can be used in fillings and ice cream coatings.
Fats for confectionery coatings and fillings
Table 4.6
63
Typical fatty acid compositions of the main CBE base oils
Fatty acid
Palma
C14:0
C16:0
C18:0
C18:1
C18:2
C18:3
C20:0
Others
1.1
44.0
4.5
39.2
10.1
0.4
0.4
0.3
Illipéb
Salc
Shead
19.3
43.5
35.3
1.0
6.3
44.6
41.6
1.7
3.3
44.3
45.6
5.5
1.3
5.7
1.3
Kokum gurgib
1
4
53
40
2
Mango kernele
10
40
44
5
1
a
Tan and Oh (1981), bBracco et al. (1970), cBhattacharyya and Bhattacharyya (1991), dSawadogo and
Bezard (1982), eSridhar and Lakshminarayana (1991).
Table 4.7
Typical triglyceride compositions of the main CBE base oils
Triglyceride
POP
POSt
StOSt
Total SOS
Cocoa
buttera
16
37
26
79
Palmb
26
3
<1
29
Illipéb
7
34
45
80
Salc
Sheaa
5
16
36
67*
<1
6
30
36
Kokum gurgia Mango kernela
<1
6
72
78
6
13
18
37
*includes 9% StOA and 1% AOA, aTalbot (2006), bJurriens (196) cSridhar and Lakshminarayana
(1991).
P = palmitic acid, St = stearic acid, S = total saturated acids (mainly palmitic and stearic), O = oleic acid.
Cocoa butter equivalents (CBE) are sourced from vegetable fats which contain
the three main triglycerides that are found in cocoa butter: POP, POSt and StOSt.
No single fat contains all three triglycerides in the same levels and proportions as
are found in cocoa butter and so it is often necessary to use a combination of two
or more fats in producing CBEs.
Cocoa butter equivalents component fats
Although there are a number of seed fats that are rich in SOS triglycerides, most of
them are uncultivated and so available only in small and commercially uncertain
quantities. Six oils, however, are produced in quantities significant enough to
make them viable as components of CBEs. They are:
•
•
•
•
•
•
palm oil
illipé
sal
shea
kokum gurgi
mango kernel
Elaeis guineensis and Elaeis olifera
Shorea stenoptera
Shorea robusta
Butyrospermum parkii
Garcinia indica
Mangifera indica
Typical fatty acid compositions of each of these base oils are shown in Table 4.6
and typical triglyceride compositions are shown in Table 4.7.
64
Enrobed and filled chocolate, confectionery and bakery products
Table 4.8
Typical triglyceride distribution in palm oil (from Berger, 2005)
Glyceride type
Trisaturated
Mono-unsaturated
Di-unsaturated
More highly unsaturated
%
Major components
8.5
37.8
35.1
18.6
PPP
POP, PPO
POO, PPLi
OOO, PLiO, OOLi
P = palmitic acid, O = oleic acid, Li = linoleic acid.
Palm oil is now the most widely traded vegetable oil globally, having recently
overtaken soyabean oil in this regard. Although grown in many parts of the world
the major tonnage comes from Malaysia and Indonesia. The fruit of the oil palm
consist of two main parts, an outer fleshy mesocarp from which palm oil is obtained
and a harder kernel where palm kernel oil is found.
Palm oil has three main fatty acids: palmitic, oleic and linoleic acids (Table 4.6).
Although relatively simple in its fatty acid composition, palm oil is extremely
complex in terms of its triglyceride composition although these do fall into four
main groups based on degree of unsaturation (Table 4.8). The type of triglyceride
which is needed for use in CBE compositions is the mono-unsaturated group
consisting mainly of POP with some POSt. These triglycerides are separated by
fractionation in a two-stage process. The di-unsaturated and more highly unsaturated triglycerides are separated out in a low-melting oleine fraction. The trisaturated
triglycerides are then removed in a high-melting stearine or ‘top’ fraction leaving
the desired POP/POSt triglycerides in a middle-melting or ‘mid’ fraction. Almost
all CBEs contain some proportion of palm mid-fraction and it is this component
that contributes most of the POP to the blend.
Illipé butter, also known as Borneo tallow or tenkgawang tallow is obtained
from the kernels of seeds of trees which grow in South East Asia, notably Borneo,
Malaysia and Java. Over the years there has been some confusion about the naming
of illipé, with mowrah fat from the Madhuca species also having been given this
name. As far as CBE components are now concerned it is fat from the Shorea
stenoptera species which is commercially traded as illipé.
In terms of its fatty acid and triglyceride composition, it is the closest of all the
six main component fats to that of cocoa butter, being rich in palmitic, stearic and
oleic acids, although with less palmitic and more stearic acid than cocoa butter
(Table 4.6). It also contains as much total SOS as does cocoa butter. This means
that illipé is generally used directly in CBE compositions without further
fractionation and contributes both POSt and StOSt to the blend. Indeed, typically
containing about 34% POSt it is the main contributor of this triglyceride to CBE
blends.
Sal fat is obtained from trees which grow in northern India and, like illipé, is a
member of Shorea species. There, to a large extent, the similarity stops. The oil
extracted from the seeds has a deep green colour which is often difficult to bleach
out by conventional oil refining techniques and has, in the past, somewhat limited
the amount of sal used in a CBE blend. It also contains a couple of unusual fatty
Fats for confectionery coatings and fillings
65
acids: 9.10 epoxystearic acid (in which an epoxy group replaces the double bond
in oleic acid) and 9,10-dihydroxystearic acid (in which two hydroxyl groups are
found on the carbon atoms normally associated with the double bond in oleic acid).
Both of these fatty acids can adversely affect the physical properties of sal oil.
Apart from these, the typical fatty acid composition of sal oil is shown in Table 4.6.
Although sal fat can be used directly in CBE compositions, its unsaturated fatty
acid content is such that it is often fractionated and the higher melting stearine
fraction is used.
Shea butter is sourced from trees growing in those parts of Africa between the
equator and a latitude of 15°N. The shea fruit is like a plum with the oil being found
in the kernel. As well as being used in confectionery applications, it has widespread use in cosmetics (both under the name ‘shea butter’ and its French name
‘beurre du karité’). It is also used locally in Africa as a bakery fat and for soap
making. Although shea butter is not a plantation crop (it takes about 15 years
before the tree begins to fruit), it is important both to the economy of this part of
Africa and as a component of CBEs. Indeed, it is true to say that, after palm oil, shea
is the most common component of CBEs. Its fairly high unsaturated fatty acid
content means that it needs to be fractionated with the higher melting stearine
fraction used in CBE blends. This fraction is very rich in StOSt.
Kokum gurgi like sal, also grows in India and has a fatty acid composition that
is rich in stearic acid with an oleic acid content low enough to allow it to be used
in CBEs without further fractionation. Fractionation is, however, sometimes used
to give an even harder stearine.
Mango kernel oil is the third of the main CBE component oils to be sourced
from India. Because the main fatty acids present in mango kernel oil are stearic and
oleic acids, its main SOS-type of triglyceride is StOSt. However, like shea butter
and sal oil, the level of oleic acid is such that the oil needs to be fractionated to give
mango kernel stearine. This is then used in CBE blends.
Production processes
Apart from conventional oil refining to remove free fatty acids, oxidation byproducts, pigments and other impurities, the only processes which are generally
used for CBE production are fractionation and enzyme-catalysed interesterification.
Under the EU chocolate regulations (see section on Legislative constraints later in
this chapter) only fractionation is permitted.
Fractionation is a separation process in which high-melting triglycerides crystallise out and are separated as a ‘stearine’ while the lower melting triglycerides
remain in a liquid phase known as the ‘oleine’. There are two main types of
fractionation process. The simplest of these is ‘dry’ fractionation in which the oil
is cooled to a temperature at which it will be partially solid. Crystallisation is
allowed to take place and the resulting crystals are separated from the supernatant
liquid. Dry fractionation produces excellent quality oleine fractions. However, for
CBEs we need good quality stearine fractions and, historically, one of the drawbacks of this process was that there could be a significant degree of entrainment
(inclusion of liquid oil within the solid crystals) which meant that the hardness of
66
Enrobed and filled chocolate, confectionery and bakery products
Table 4.9 Typical triglyceride composition of CBE component fats and fractions
(Talbot, 2006)
Cocoa
butter
POP
POSt
StOSt
Total SOS
16
37
26
79
Palm
Shea
mid-fraction stearine
66
12
3
81
1
7
74
82
Illipé
butter
Sal
stearine
7
34
45
86
<1
10
60
81*
Kokum Mango kernel
fat
stearine
<1
6
72
78
1
16
59
76
*includes 11% StOA
the stearine was not as high as it could have been. Dry fractionation processes have
developed considerably over recent decades to such an extent that most palm
fractions, for example, are now produced in this way.
Usually, though, shea butter and sal oil are still fractionated using the other type
of fractionation, solvent fractionation. In this process the oil is dissolved in an
organic solvent (usually acetone or hexane) and is cooled to a low temperature to
allow the SOS-rich stearine fraction to crystallise out. The crystals are separated by
filtration and washed with chilled solvent to remove any entrained oil. Solvent is
removed from both the crystals and the liquid oleine fraction. The extra cost of
solvent, of the need to operate in flameproof areas and of the cost of solvent
recovery makes this a more expensive process than dry fractionation. This extra
cost can be offset, however, by the higher quality stearine fraction which results.
Shea butter, sal oil, mango kernel oil and, when fractionated, kokum gurgi all
undergo single-stage fractionation. This produces a stearine for use in CBEs and a
softer oleine fraction which can, among other applications, often be used as the
basis of confectionery filling fats. Palm oil, however, is usually doubly fractionated.
This is because it contains high-melting almost fully saturated triglycerides, midmelting triglycerides such as POP and POSt, and more unsaturated triglycerides
(see Table 4.8). Fractionation separates each group. The mid-fraction, rich in SOStype triglycerides, is used in CBEs.
Table 4.7 showed the typical triglyceride compositions of the main CBE base
oils. Table 4.9 shows the typical triglyceride compositions of those fractions of
these oils that are then used in CBE compositions.
Cocoa butter equivalents are then produced by blending some of these components together in different proportions to obtain different properties. Very rarely do
CBE blends contain more than three of these components and almost all blends
contain some palm mid-fraction. The more palm mid-fraction the blend contains,
the less tolerant the CBE will be to higher levels of milk fat in the chocolate. This
means that the CBE being used in any application is often chosen first on the basis
of the milk fat content of the chocolate. But this is not the only criterion by any
means. Other factors to be taken into account are heat and bloom resistance and the
rheology of the chocolate, particularly at temper and hardness of the chocolate.
Sometimes the palm mid-fraction is a fairly minor component of the blend with oils
such as shea stearine, illipé and sal stearine predominating. These compositions are
Fats for confectionery coatings and fillings
67
known as cocoa butter improvers (CBIs) because they have physical characteristics ‘better’ than those of cocoa butter in the sense of giving greater hardness and
heat resistance to the chocolate.
Enzyme-catalysed interesterification is not permitted in the EU as a process to
make the vegetable oils permitted to be used in chocolate. It may, however, be
permitted in other countries (although it is advisable to check local regulations
first!) and it can be used in coatings which are not going to be declared as
‘chocolate’. It was developed by Unilever initially as a means of producing the
SOS-type of triglycerides to be used in CBEs because of the limited availability of
such triglycerides from illipé, shea and so on, but has since broadened its scope into
being a much milder alternative to chemically catalysed interesterification.
Interesterification is a process whereby the fatty acids on the starting triglycerides
are rearranged in terms of their position on the glycerol backbone. In chemically
catalysed interesterification, their positions are completely randomised and, because
of this, are highly predictable. This does mean, though, that saturated fatty acids
which may have started on the 1- or 3- positions can end up in the 2-position
making the end product unsuitable for use in CBEs. Enzyme catalysed
interesterification is, however, much more specific. Some enzymes, for example
Mucor miehei, do not touch any fatty acids in the 2-position and only randomise
acids in the 1- and 3-positions. This means that any fat or oil which is rich in oleic
acid in the 2-position can be interesterified with, say, stearic acid to produce
significant levels of StOSt. Other triglycerides are also produced which need to be
removed by fractionation but essentially this is a process which extends the
availability of SOS-rich triglycerides.
Legislative constraints
For many years, the only countries in the EU which allowed the use of vegetable
fats in chocolate were the United Kingdom, Ireland, Denmark, Sweden, Austria,
Finland and Portugal. After many years of debate the EU finally agreed to the use
of vegetable fats in chocolate throughout the EU in 2000 with the publication of
Directive 2000/36/EC. This Directive became law on 3 August 2003. Since that
time all members states have been allowed to use vegetable fats in chocolate, but
with a number of tight restrictions.
First, only vegetable fats based on the six oils described in the section on CBE
component fats above were permitted. Since these were the main oils being used
commercially anyway it was not too much of an imposition. There were a couple
of areas, though, where it did or could cause problems. One was the area of antibloom fats that had been developed, which, for functional reasons, contained
vegetable oils other than these six. These were no longer permitted for use in
chocolate (although they could still be used in chocolate fillings). The second was
the area of ice cream coatings where softer oils are sometimes used to reduce the
brittleness of the ice cream coating. The EU gave some recognition to this problem
and permitted the use of coconut oil in chocolate for use on frozen confectionery.
The level of use was limited to 5% of the chocolate. Even here, there are other
constraints in the regulations which mean that in some formulations (particularly
68
Enrobed and filled chocolate, confectionery and bakery products
those in which the total fat content is less than 30%) the permitted level is less than
5%. As already indicated, the only processes permitted were refining and
fractionation. There were also physical constraints placed on the choice of the
vegetable fat in that it must be miscible in any proportion with cocoa butter and be
compatible with its physical properties.
The composition of chocolate in the United States is defined by Title 21 of the
Code of Federal Regulations Part 163. This does not permit the use of vegetable
fats in chocolate but does define a category ‘vegetable fat coatings’ which can
contain vegetable fats of any type with no limits to incorporation levels. There have
been suggestions recently that the Food and Drug Administration in the United
States may relax the chocolate regulations and allow the use of vegetable fats
without any of the EU type of constraints. This has caused a considerable backlash
from both consumers and the chocolate industry.
A number of other countries permit the use of vegetable fats in chocolate with
different levels of incorporation being permitted and different constraints on the
types being defined. Since it is impossible in a book of this nature to define the
regulations in each country, the reader is advised to check what these are for any
particular countries of interest. It is worth, though, commenting on the Codex
Alimentarius standards for chocolate and chocolate products. The original standard, STAN 87-1981 did not allow the use of vegetable fat in chocolate. It has,
however, recently undergone a revision (CODEX STAN 87-1981, Rev. 1 – 2003)
and now permits the addition of vegetable fats other than cocoa butter at levels not
exceeding 5% of the finished product. While it places no restrictions on the type of
vegetable fat, the revised standard does say ‘where required by the authorities
having jurisdiction, the nature of the vegetable fats permitted for this purpose may
be prescribed in applicable legislation’.
It should be noted that these comments describe the legislative positions at the
time of writing. Legislation can change and so it is recommended that the current
position is checked in any countries of interest before proceeding with the use of
vegetable fats in chocolate.
4.3.2 Supercoatings
Because CBEs have excellent compatibility with cocoa butter in any ratio they can,
in functional terms, be used in coatings at levels higher than 5%. As far as the EU
and many other countries are concerned, this puts them outside the use in anything
that is to be labelled ‘chocolate’. They can, though, still be used at these higher
levels in products labelled, for example, ‘chocolate flavoured coatings’ (actual
nomenclature can vary from country to country). Supercoatings will be considered
in more detail in Chapter 5
4.3.3 Non-lauric cocoa butter replacers
Moving away from chocolate into the area of ‘chocolate-flavoured coatings’
brings us to non-lauric cocoa butter replacers (CBRs). These are fats based on non-
Fats for confectionery coatings and fillings
69
lauric oils such as palm oil, soyabean oil, rapeseed oil and cottonseed oil. None of
these oils has sufficient solidity and structure to be suitable for use as a coating (or
even a filling) fat without some form of further processing. The production and use
of non-lauric CBRs will be considered in more detail in Chapter 5.
4.3.4 Lauric cocoa butter substitutes
Lauric-based cocoa butter alternatives are generally known as cocoa butter substitutes (CBS). These are based on oils rich in lauric acid (C12:0). In terms of
coatings, this generally means oils based on palm kernel oil (lauric fillings can also
be based on coconut oil). These too will be discussed in more detail in Chapter 5.
4.4
Effects of fat on quality and processing
Some of the effects the different fat phases can have on quality and processing have
already been touched on in describing the various types of fat, and some will also
be dealt with in more detail in later chapters. These different effects will have a
bearing on the selection of the correct choice of fat for a specific application.
4.4.1 Effects on recipe
The first effect to consider is the effect different fats have on the coating recipe.
This really boils down to the interactions each type of fat has with cocoa butter and
what its compatibility with cocoa butter is. Cocoa butter equivalents have the same
chemical composition as cocoa butter, the same physical characteristics and are
stable in the same (β) polymorphic form. Therefore they exhibit full compatibility
with cocoa butter. This can be shown by means of an iso-solids diagram (Fig. 4.6).
An iso-solids diagram connects compositions with the same solid fat content.
For example, in Fig. 4.6, every blend of cocoa butter and Coberine™ contains 60%
solid fat at temperatures between about 25.5 °C and 26.5 °C. Indeed, the lines
joining almost all solid fat content levels are horizontal indicating that there are no
interactions between cocoa butter and Coberine™ that are likely to cause any
softening. This, coupled with the observation that all blends are stable in the β
polymorphic form, indicates the full compatibility between Coberine™ and cocoa
butter.
Coberine™ is the brand name of the first cocoa butter equivalent to be sold and
is still produced as the flagship CBE by Loders Croklaan, The Netherlands.
Although Fig. 4.6 shows the interaction between cocoa butter and Coberine™,
similar interactions will be found between cocoa butter and other CBEs. The
interactions between non-lauric CBR and cocoa butter and lauric CBS and cocoa
butter are more complex and place considerable restrictions on how much cocoa
butter can be used in recipes containing these fats. These aspects will be discussed
in more detail in Chapter 5.
All of these different interactions with cocoa butter have an effect on the coating
70
Enrobed and filled chocolate, confectionery and bakery products
5% solids
10
20
30
40
34
30
Temperature (°C)
50
ALL β
26
60
70
22
18
80
14
10
0
10
20
30
40
50
60
70
80
90
100
Coberine (%)
Fig. 4.6 Iso-solids diagram of cocoa butter and CBE (Coberine) (from Gordon et al.,
1979. Copyright Wiley-VCH, reproduced with permission).
recipes that can be used, details of which are found in other chapters (Chapters 3
and 5).
4.4.2 Effects on processing
Coating compositions based on cocoa butter with or without vegetable fat (chocolate) or based on CBEs (supercoatings) are stable in the β-3 crystal form which
means that they do need to be tempered. The science and practice of tempering will
be discussed in Chapters 15 and 16.
4.4.3 Effects on quality
The interactions that are seen between cocoa butter and the three main types of
cocoa butter alternative also have implications for product quality and stability of
filled products.
On storage, softer fats in a filling can migrate with time into the harder outer
coating. This results in a change in overall product texture with the centre
becoming harder and the coating softer, so there is a loss of textural difference
between the two phases and a greater likelihood of fat bloom occurring on the
surface of the coating. Although these effects can be seen even when there is good
compatibility between coating and filling fat they are likely to be much greater
when one fat is incompatible with the other.
The phenomena of oil migration and its effects and of bloom formation will be
dealt with in later chapters so it is perhaps sufficient at this stage just to point out
Fats for confectionery coatings and fillings
71
80
70
Solid fat (%)
60
50
40
30
20
10
0
0
20
40
60
80
100
Filling fat (%)
Fig. 4.7 Interaction of compatible (—) and incompatible (---) filling fats with a coating fat.
the importance of ensuring compatibility where possible of coating fat and filling fat.
This is best explained with reference to Fig. 4.7. This shows the effect of migration
of two filling fats into a coating fat. The coating fat has a solid fat content of 70%;
both filling fats have a solid fat content of 50%. When the compatible filling fat
migrates into the coating, the solid fat content of the coating decreases, following the
solid line. It is not unusual to find degrees of migration as high as 50% in filled
confectionery. At 50% migration, the solid fat content of the coating will be 60%.
This is a 10% softening but still high enough to have an acceptable product. When
an incompatible filling fat migrates into the coating, however, softening of the
coating follows the dotted line. Now at 50% migration, the solid fat content of the
coating is only 33%, much too low for the product to be acceptable. This makes the
selection of filling fat for use with a particular coating fat of great importance.
4.5
Selecting the correct fat for application type
Although from a total fat technology point of view, especially with regard to
maintaining as much compatibility between coating and fillings, it is preferable to
make the selection of coating and filling fat together, there may be requirements
which mean that the selection is led by one or other of these phases. In many cases
the choice of coating fat ‘leads the way’ in this.
4.5.1 Coatings
The main aspects which will define whether one coating fat is to be preferred over
another one in a particular application are:
72
Enrobed and filled chocolate, confectionery and bakery products
• processing capabilities
• nutritional requirements
• flavour
Processing requirements
If no tempering equipment is available then it will not be possible to use coatings
based on cocoa butter (i.e. chocolate) or cocoa butter equivalents (for example,
supercoatings) because these are polymorphic fats and therefore need to be
tempered to obtain a stable coating that will not immediately begin to bloom.
Coatings based on non-lauric CBR or lauric CBS fats, however, do not need to be
tempered in this way.
Nutritional requirements
There has been increasing concern in recent years about the use of partially
hydrogenated vegetable oils in food because of the trans fatty acids they contain.
Alternatives may result in higher levels of saturated fatty acids which, in some
instances, may also be a nutritional concern. A compromise often needs to be made
in terms of the fatty acid contents of the various alternatives. The whole area of
trans fatty acids and alternatives is considered in Section 4.6.
Flavour
Most of the flavour in a chocolate coating comes from the cocoa components. In a
normal cocoa butter-based chocolate, both cocoa butter and cocoa mass are usually
present. Cocoa mass is composed of cocoa butter and cocoa powder, so the main
flavour comes from these two components (particularly if the cocoa butter has not
been deodorised). The combination gives the well-balanced flavour expected of a
good quality chocolate. In most chocolate flavoured coatings, however, the cocoa
butter levels are reduced and this can affect the flavour balance. This is most
noticeable in coatings based on lauric CBS because their intolerance to cocoa
butter means that the only cocoa flavour component present is a low-fat cocoa
powder.
4.5.2 Fillings
When it comes to the choice of filling fat, in an ideal situation, the filling fat should
be chosen to be as similar to the coating fat as possible. In other words, if the
coating fat is real chocolate or a supercoating then the filling fat should be rich in
SOS and/or SOO types of triglycerides to maintain as good a compatibility with the
coating as possible. If, however, the coating fat is based on a lauric CBS, then the
filling fat should ideally be based on palm kernel oil or coconut oil, again to
maintain as good a compatibility as possible.
There are, however, often other requirements that need to be taken into account
in selecting a filling fat. These can be related to sensory requirements (coolness,
softness), to the presence of other components in the filling (nut pastes, butter), to
processing methods (shell moulding, one-shot depositing) and to shelf life and the
Fats for confectionery coatings and fillings
73
limitations placed on this by, for example, migration or bloom formation. All of
these aspects will be dealt with in much greater detail in other chapters.
4.6
Trans fats
Partially hydrogenated vegetable oils have been used in a variety of applications in
enrobed confectionery – in non-lauric CBR-based coatings, in toffees and caramels, in some filling fats, in biscuit dough fats and cream fats, in moisture
migration barriers, and so on. They have often imparted significant functional
benefits to the product. For example, such fats give good, long-lasting gloss to nonlauric coatings; they have excellent aeration characteristics producing light
confectionery fillings; they crystallise quickly when used in boiled toffees and
caramels allowing these to be cut to size and shape quickly after depositing. There
are plenty of reasons for using them but one, overwhelming reason to stop using
them is that they contain significant levels of trans fatty acids.
Trans fatty acids have been shown to have adverse effects on blood cholesterol
levels (Mensink et al., 2003). Cholesterol is carried through the blood in a number
of ways, primarily associated with lipoproteins. The two main lipoproteins associated with blood cholesterol are high density lipoproteins (HDL) and low density
lipoproteins (LDL).
LDL cholesterol is considered by cardiologists and clinical nutritionists to be
‘bad’ cholesterol because any excess causes arterial plaques to be produced which
can eventually result in heart attack or stroke. HDL cholesterol, on the other hand,
is less of a problem and considered to be the ‘good’ kind of cholesterol because the
body has mechanisms to excrete any excess.
For these reasons various bans or regulations of trans fatty acids have come into
force across the world. Denmark led the way in 2003 by putting a limit of 2% on
any artificially produced trans fatty acid in oils and fats used in food. This was
followed on January 1, 2006 by regulations in the United States requiring the
labelling of trans contents of more than 0.5 g per serving. Early in 2007, the British
Retail Consortium, whose members include the major UK retailers, pledged to
remove industrially added trans fats from all of their own brand products by the
end of that year. It should be noted that these bans and regulations only apply to
‘artificially produced’ or ‘industrially added’ trans fats. The reason for this is that
trans fatty acids are also found naturally in the milk and meat of ruminant animals,
so that dairy products, including milk fat, also contain trans fatty acids, typically
at levels of about 5%. If a milk chocolate or a milk coating contains, say, 20% milk
fat in the fat phase then, typically, there will be about 1% naturally occurring trans
in the fat phase of that coating.
Non-lauric CBR from partially hydrogenated vegetable fats can have trans fat
levels as high as 50–55%. Toffee fats and filling fats based on similar oils have
typical trans fat levels of 25–30%. Biscuit dough fats have lower trans contents but
even here 10% trans was typical. Clearly, these levels are now becoming somewhat historical because there is great pressure on oils and fats processors and food
74
Enrobed and filled chocolate, confectionery and bakery products
manufacturers to remove partially hydrogenated oils completely and so reduce
trans from non-natural origins from food to less than 1%. Moving from such high
levels to less than 1% is obviously not easy, so how can it be achieved?
4.6.1 Alternatives to partially hydrogenated vegetable oils.
It would have been simpler to have headed this section ‘zero-trans alternatives’
except that it is all but impossible actually to obtain a truly zero-trans-fat. The
reason for this is that holding fats at a high temperature for a period of time will also
start to convert some of the cis fatty acids into trans fatty acids. Most oils and fats
used in confectionery are deodorised prior to use (the exceptions being cocoa
butter and butter(fat)). The deodorisation process involves vacuum steam distillation at a high temperature (180–220 °C being typical). During this process low
levels of trans fatty acids are produced but these are generally well below 1%.
The alternatives available to manufacturers depend to a large extent on the
application. If a manufacturer has been using these high-trans non-lauric CBR
coatings then he has a limited number of options in terms of alternatives. These are:
• Move to real chocolate. This has major cost implications because the price of
•
•
•
cocoa butter can be up to double that of the hydrogenated non-lauric CBRs.
Chocolate also needs to be tempered so such a move may also necessitate
investment in tempering equipment.
Move to a supercoating. This is a less expensive option but one which will still
necessitate using a higher priced fat and investment in tempering equipment
Move to a lauric CBS. This also can give problems in terms of reduced flavour
impact, possible off-flavour formation and incompatibility with cocoa butter.
These issues are discussed in more detail in Chapter 5. Such a move does,
however, have the advantages of potentially lower costs of the fat phase and no
need to invest in tempering equipment.
Move to a low or ‘no’-trans non-lauric CBR. The issues surrounding trans have
led CBR manufacturers to develop new generations of non-lauric CBRs. In
some cases these have much lower trans contents (8–15% being typical). These
do, however, still need to be declared as ‘hydrogenated’. More recently, the first
non-hydrogenated, non-temper non-lauric CBR has been launched which addresses all of the requirements of this product group.
As far as toffee and caramel fats are concerned these can, to a large extent, be
replaced by non-hydrogenated fats based on fractions of palm oil, albeit with
changes needing to be made to crystallisation and cooling conditions. Biscuit
dough fats were often based on palm oil with some (10–25%) partially hydrogenated palm, rapeseed or soyabean oil added. In many cases, this blend has simply
been replaced by palm oil itself.
4.6.2 Effect on saturates level
Most confectionery products require a certain degree of structure. This degree will
Fats for confectionery coatings and fillings
75
Table 4.10 Fatty acid compositions of alternative coating fats (from Slager et al.,
2007)
Fatty acid type
Saturates
Cis-monounsaturates
Cis-polyunsaturates
Trans-unsaturates
Saturates + trans
Hydrogenated Non-hydrogenated Cocoa butter Lauric CBS
non-lauric CBR non-lauric CBRa
34
13
<1
53
87
65
29
7
<1
65
62
35
3
<1
62
91
8
1
<1
91
a
Composition of Couva™ 850 NH (from Loders Croklaan)
vary from ‘hard’ in coatings to perhaps ‘soft’ in some fillings. The only way in
which this structure can be achieved is by the use of some solid fats – more in hard
structures, less in soft structures. Table 4.1 gave the melting points of the common
fatty acids found in confectionery – the only ones with melting points above
ambient temperatures are saturated fatty acids and trans fatty acids. The implication, therefore, of removing trans fatty acids from confectionery fats is that, in
many instances, the saturates level will rise.
Coating fats
The options, as already stated in the previous section, are cocoa butter (or cocoa
butter equivalents which are very similar in their level of saturates), lauric CBS or
the new generation of non-hydrogenated, non-lauric CBR fats. The fatty acid
composition of these options are compared in Table 4.10.
All of the non-hydrogenated options have saturates levels higher than those
found with the original hydrogenated non-lauric CBR. However, when saturated+
trans are compared, cocoa butter and the new generation of non-hydrogenated
non-lauric CBR are both lower in total, as well as being quite comparable with each
other. The lauric CBS, however, has very high levels of saturates, even higher than
the total of saturates and trans fatty acids in the original hydrogenated fat.
Filling fats
In many instances, partially hydrogenated filling fats have been replaced by blends
of palm fractions. There are pros and cons to making such a change. On the positive
side, as well as nutritional improvements, the fats are generally steeper melting
giving them some cool-melting characteristics. On the less positive side, aeration
and crystallisation conditions may need to be changed to obtain similar endproducts. The fatty acid compositions and melting profiles of a hydrogenated and
fractionated non-lauric filling fat are shown in Table 4.11.
Once again the saturates level increases moving from a hydrogenated to a
fractionated filling fat but the important ‘saturates+trans’ level is 21% lower with
the non-hydrogenated alternative.
Biscuit dough fats
One of the traditional biscuit dough fats, palm oil+15% hydrogenated rapeseed oil
76
Enrobed and filled chocolate, confectionery and bakery products
Table 4.11 Fatty acid compositions and melting profiles of alternative filling fats (from
Talbot, 2004)
Hydrogenated
non-lauric filling fat (%)
Saturates
Cis-monounsaturates
Cis-polyunsaturates
Trans-unsaturates
Saturates + trans
Solid fat at 20 °C
Solid fat at 30 °C
Solid fat at 35 °C
Table 4.12
2004)
Fractionated
non-lauric filling fat (%)
20
24
<1
56
76
51
12
1
55
38
7
<1
55
47
4
1
Fatty acid compositions of alternative biscuit dough fats (from Talbot,
Fatty acid type
Palm oil + 15% hydrogenated rapeseed oil (%)
Saturates
Cis-monounsaturates
Cis-polyunsaturates
Trans-unsaturates
Saturates + trans
45
36
8
11
56
Palm oil-based
dough fat (%)
51
40
9
<1
51
Fractionated palmbased dough fat (%)
55
37
8
<1
55
is compared in Table 4.12 with non-hydrogenated alternatives based on palm oil
and palm fractions.
Using palm oil as a dough fat gives a 5% reduction in total saturates+trans
compared with the original composition. The increase in saturates when a
fractionated palm-based dough fat is used almost exactly balances the decrease in
trans fats. The potential benefit of these dough fats, however, is that, in certain
circumstances, they can be used at lower total fat levels in the dough. This not only
gives a reduction in total fat but also allows a reduction of saturates in the biscuit
itself.
4.7
Future trends
The main trends that we are likely to see in the future in relation to the oils and fats
used in enrobed products will probably fall into two broad areas: nutritional and
functional. In the nutritional area, the removal of partially hydrogenated oils and
hence the reduction of trans fatty acids to levels below 1% has broadly been
achieved in countries such as the United Kingdom and Denmark. This is a trend
which will undoubtedly spread and, indeed, already is spreading to other countries.
The experiences gained in this area in the United Kingdom and Denmark can be
Fats for confectionery coatings and fillings
77
easily transferred to products in other countries and so further developments in this
area are likely to be limited.
There are already moves to reduce the level of saturates in many foods. For
example, the UK Food Standards Agency has proposed a target of reducing the
intake of saturated fatty acids from a current level of about 13.5% of food
energy down to 11% of food energy by the end of 2010. The kinds of product
covered in this book are all fairly high in saturates. For example, chocolate
contains about 65% saturates in the fat phase. This high level is needed for
functional reasons – it is very difficult to make a coating with a good hardness
which does not contain appreciable levels of either trans or saturated fatty acids.
Nevertheless there will be pressure on the confectionery industry to reduce
saturated fat contents.
In chocolate, apart from any functionality issues, the legislation defining its
composition will limit any reductions that can be made. Slightly less saturated
cocoa butters can be sourced from countries such as Brazil or could be achieved by
taking a softer fraction of cocoa butter. Less saturated vegetable fats could also be
used in chocolate (for example, the oleine fractions of palm oil and shea butter
would be acceptable in terms of both base oil and process in the EU Chocolate
Regulations). Both of these routes will, however, soften the chocolate. If hardness
is to be maintained, then the only option would then be to reduce the level of milk
fat used in the chocolate. The end result would be a very different chocolate both
in terms of appearance and flavour and, even then, the reduction in saturates that
could be achieved would be quite limited.
There is more scope for reduction in saturates in the centres of enrobed products
be they truffle/praline-type centres, biscuits or ice cream and this, perhaps, is
where research should be focused.
The third area of nutritional development is likely to be in the total fat content,
with this being seen as a way of reducing both saturates and calories. Because
much of the functionality of confectionery products comes from the fat, other ways
of obtaining this would need to be found if the fat content were to be reduced. This
may mean a greater use of additives such as emulsifiers so, in many cases, there
would be a trade-off between fat reduction and a greater proliferation of additives
on the ingredients label.
In the functional arena, there will continue to be developments in oils and fats
to solve some of the problems that still exist in enrobed products. Many of these are
associated with movement within a multi-component product: fat migration,
moisture migration and fat bloom formation. Although ‘solutions’ are available to
each of these problem areas they are, by and large, ways of slowing down the
problem rather than removing it altogether. Ways of stabilising cocoa butter in
form βV, or even better, ways of tempering chocolate so that the cocoa butter
crystallised directly into form βVI would solve the problem of fat bloom once and
for all. Similarly, ways of holding fats in place in fat-based fillings and ways of
holding moisture in place in water-containing phases would help in minimising
migration of fat and water into other parts of the product.
78
Enrobed and filled chocolate, confectionery and bakery products
4.8
Sources of further information and advice
A number of textbooks cover the use of fats in confectionery:
• Talbot G, Application of Fats in Confectionery, published by Kennedy’s
Publications, London, 2006.
• Beckett ST Industrial Chocolate Manufacture and Use, 4th edition, published
by Wiley-Blackwell, Oxford, 2009.
• Timms RE Confectionery Fats Handbook, published by The Oily Press,
Bridgewater, 2003.
The major suppliers of oils and fats to the confectionery industry also produce
literature and will give advice although, to a large extent, this is restricted to their
own customers. For example, Loders Croklaan publish numerous articles each
year in both the trade and scientific press that are written by their staff and
consultancy associates, and AAK have a Handbook – vegetable oils and fats which
is given to customers who attend their oils and fats academy.
4.9
References
BERGER KG (2005). The Use of Palm Oil in Frying. Malaysian Palm Oil Promotion Council,
Selangor, Malaysia.
BHATTACHARYYA S AND BHATTACHARYYA DK (1991). ‘Enzymatic acidolysis of sal fat and
its fractions’, Oléagineux, 46, 509–13.
(1970). ‘A study of cocoa butter – illipé butter
mixtures’, International Chocolate Review, 25, 41–8.
CHAISERI S AND DIMICK PS (1989) ‘Lipid and hardness characteristics of cocoa butter from
different geographical areas’, Journal American Oil Chemists Society, 66, 1771–6.
GORDON MH, PADLEY FB AND TIMMS RE (1979) ‘Factors influencing the use of vegetable fats
in chocolate’, Fette Seifen Anstrichmittel, 81, 116–21.
JURRIENS G (1968). ‘Analysis of triglycerides’, in Analysis and Characterisation of Oils and
Fats and Fat Products, Vol. 2, Boekenoogen H.A (ed). Interscience Publishers, London.
LARSSON K (1966). ‘Classification of glyceride crystal forms’, Acta Chemica Scandinavica
20, 2255–60.
LIPP M AND ANKLAM E (1998). ‘Review of cocoa butter and alternative fats for use in
chocolate – Part A. Compositional data’, Food Chemistry, 62, 73–97.
LODERS CROKLAAN (1989). Loders Croklaan Specialty Fat Technology Handbook, Talbot,
G (ed.), Loders Croklaan, Wormerveer, The Netherlands.
MENSINK RP, ZOCK PL, KESTER AD AND KATAN MB (2003). ‘Effects of dietary fatty acids and
carbohydrates on the ratio of total to HDL cholesterol and on serum lipids and
apolipoproteins: a meta-analysis of 60 controlled trials’, American Journal Clinical
Nutrition, 77, 1146–55.
SAWADOGO K AND BÉZARD J (1982). ‘Étude de la structure glyceridique du beurre de karité’
Oléagineux, 37, 69–74.
SLAGER H, FAVRE L AND TALBOT G (2007). ‘The ultimate confectionery coating’, Food
Marketing and Technology, December, 12–14.
SMITH KW (2003). ‘Cocoa butter crystallisation’. Lecture at Biscuit, Cake, Chocolate and
Confectionery Association 50th Technology Conference, London, 3–4 April. The proceedings are available from BCCCA on a CD-ROM.
SRIDHAR R AND LAKSHMINARAYANA G (1991). ‘Triacylglycerol compositions of some
BRACCO U, ROSTAGNO W AND EGLI EH
Fats for confectionery coatings and fillings
79
vegetable fats with potential for preparation of cocoa butter equivalents by high performance liquid chromatography’, Journal Oil Technology Association of India, 23, 42–3.
TALBOT G (2004). ‘Trans fats – the means and effects of eliminating them’. Lecture given
at Biscuit, Cake, Chocolate, Confectionery Association Technology Conference, Birmingham, 23–24 April 2004. Available on CD-ROM from BCCCA (part of UK Food and
Drink Federation).
TALBOT G (2006). Application of Fats in Confectionery, Kennedy’s Publications, London.
TAN BK AND OH FCH (1981). ‘Malaysian palm oil: chemical and physical characteristics’,
PORIM Technology, No. 3.
US TITLE 21 OF THE CODE OF FEDERAL REGULATIONS PART 163 (2003). http://
www.access.gpo.gov/nara/cfr/waisidx_03/21cfr163_03.html.
VAN MALSSEN KF, VAN LANGEVELD AJ, PESCHAR R AND SCHENK H (1999). ‘Phase behaviour
and extended phase scheme of static cocoa butter investigated with real-time X-ray
powder diffraction’. Journal American Oil Chemists Society, 76, 669–76.
WEYLAND M (1992). ‘Cocoabutter fractions: a novel way of optimising chocolate performance’, Lecture given at the Pennsylvania Manufacturing Confectioners’ Association 46th
Annual Production Conference, Hershey, PA, April 28.
WILLE RL AND LUTTON ES (1966). ‘Polymorphism of cocoa butter’, Journal American Oil
Chemists Society, 43, 491–496.
5
Compound coatings
Geoff Talbot, The Fat Consultant, UK
Abstract: Although chocolate is the benchmark by which all other coatings are judged,
there are times when it is beneficial to use compound coatings instead. Compound
coatings are coatings in which some or all of the cocoa butter has been replaced by a
vegetable fat. These fall into three main categories: (i) supercoatings based on cocoa
butter equivalent (CBE) type vegetable fats, (ii) coatings based on hydrogenated and/or
fractionated non-lauric oils (CBR), and (iii) coatings based on hydrogenated and/or
fractionated lauric oils (CBS). Reasons for choosing one of these coatings instead of
chocolate can range from economics (the fats used are generally cheaper than cocoa
butter) and ease of processing (CBR and CBS coatings do not need tempering) to greater
suitability for the product being enrobed (CBR coatings are easier to cut on soft products
such as cakes).
Example recipes for coatings using each of these types of compound fat are given as
well as recommendations for processing conditions. The recipes are usually defined and
constrained by the compatibility of the compound fat with cocoa butter. Specific issues
associated with lauric CBS coatings (e.g. incompatibility with cocoa butter, risk of
hydrolysis releasing soapy off-flavours) are also discussed.
Key words: cocoa butter equivalent, cocoa butter replacer, cocoa butter substitute,
compatibility, compound coating, hydrolysis, processing conditions, recipes.
5.1
Introduction
Chocolate, as has already been described in Chapters 2 and 3, is based on cocoa
butter and has a composition that is usually well-defined by local legislation. This
gives manufacturers little scope for introducing fats other than milk fat (in milk
chocolate) and a limited amount of vegetable fat, where this is permitted. To move
outside these well-regulated compositions means losing the ability to call the
product ‘chocolate’. In many cases, the coating needs to be relabelled as ‘chocolate
Compound coatings
81
2300
2200
2100
US $ per tonne
2000
1900
1800
1700
1600
1500
1400
Fig. 5.1
.
.
.
.
.
07
nJa
.
.
06
.
nJa
.
.
.
05
nJa
.
.
.
04
nJa
.
.
.
03
n-
.
Ja
Ja
n-
02
1300
Commodity prices of cocoa (Jan 2002–Dec 2007) (from International Cocoa
Organization).
flavoured coating’, ‘vegetable fat coating’ or something similar. From a technical
point of view they are all given the name ‘compound coatings’ or ‘couvertures’.
The fats that are used in place of cocoa butter in these coatings are the types of
cocoa butter alternative discussed in Chapter 4 and are given the generic name of
‘compound coating fats’. Despite the inability to label the product ‘chocolate’,
there are many reasons for moving away from a strict chocolate composition.
Cocoa butter is not only an expensive commodity but also one which fluctuates
widely in price. Figure 5.1 shows the variations in the commodity prices of cocoa
(International Cocoa Organization, 2008). Depending on the markets, these fluctuating cocoa prices can then cause greater or lesser fluctuations in the price of cocoa
butter depending on the ‘ratio’. This is the ratio between cocoa butter and cocoa
powder. If the cocoa ratio is high then a greater proportion of the price of the beans
is allocated to the cocoa butter. These variations in cocoa butter prices obviously
have an effect on the cost of chocolate. For the most part, these variations in price
are absorbed by the manufacturer. In some instances, though, a manufacturer will
want to make something that looks and tastes like chocolate but contains less cocoa
butter than ‘real’ chocolate. This is where compound coatings come in.
Economics are not the only reason to use a compound coating rather than
chocolate. Many of these coatings are easier to process than chocolate because they
use ‘non-polymorphic’ fats which do not need to be tempered. This not only
removes a process stage, it also removes the need to invest in expensive tempering
equipment. The exceptions to this are the supercoatings (see Section 5.2.1) which
have a similar composition to that of cocoa butter and therefore do need to be
tempered.
It may be desirable, particularly on bakery and biscuit products, to move away
82
Enrobed and filled chocolate, confectionery and bakery products
from a chocolate type of coating and flavour and include fruit colours and flavours.
It may also be desirable to have a coating on bakery products which can be cut
without shattering. All of these can be better achieved by using a compound
coating rather than chocolate.
5.2
Cocoa butter alternatives in compound coatings
There are three basic types of fat used in compounds coatings. First there are cocoa
butter equivalents. These are described in some detail in Chapter 4 but are,
essentially, blends of vegetable fats and fractions of vegetable fats which, together
have a triglyceride composition similar to that of cocoa butter. They are the
components that are used as ‘vegetable fat’, where this is permitted for use in
chocolate. Then there are non-lauric cocoa butter replacers (CBR) that are based on
hydrogenated and/or fractionated oils such as palm oil, rapeseed oil, soyabean oil
and cottonseed oil. Finally there are fats based on hydrogenated and/or fractionated
lauric oils (i.e. palm kernel oil and coconut oil). These are called lauric cocoa butter
substitutes (CBS).
5.2.1 Supercoatings
The cocoa component in chocolate is often made up of a combination of cocoa mass
and added cocoa butter. Since cocoa mass contains about 55% cocoa butter, the fat
phase of chocolate is obtained from both components. Cocoa butter equivalents
(CBE) can be used to replace all of the added cocoa butter, thus retaining much of
the original cocoa flavour because the cocoa mass element is retained. The amount
of added cocoa butter used in chocolate is much higher than the level of vegetable
fat that may be permitted and so replacing all the added cocoa butter with CBE takes
the coating outside the area where the product can still be called chocolate. This kind
of use of CBEs is, therefore, termed a ‘supercoating’ because it has a much better
quality than coatings based on non-lauric CBRs and lauric CBSs. Because CBEs
have almost identical physical and chemical characteristics to those of cocoa butter
it is often difficult to distinguish a supercoating from real chocolate.
Historically, supercoatings were developed for use at times of high cocoa butter
prices to provide economic but still high quality coatings for biscuit and cake
products. Now, they are much more likely to be used as non-hydrogenated,
effectively trans-free alternatives to hydrogenated non-lauric or lauric coating
fats. Unlike these fats, however, they do need to be tempered.
5.2.2 Non-lauric cocoa butter replacers
Non-lauric CBRs are produced from commodity oils such as palm oil, soyabean
oil, rapeseed oil and cottonseed oil. In their native form all of these oils are either
liquid or semi-liquid, making them most unsuitable for use in coatings. To increase
their solid fat content a combination of hydrogenation and fractionation is used.
Compound coatings
83
Hydrogenation is a process in which an oil is treated with hydrogen in the
presence of a catalyst in order to increase the amounts of solid fatty acids present
in the oil. Two competing processes take place during hydrogenation. In the first
process a molecule of hydrogen combines with an unsaturated double bond on the
fatty acid chains of the triglyceride to give a saturated single bond. So, for example,
one of the double bonds on linoleic acid in, say, soyabean oil, may be converted to
a single bond thus changing the linoleic acid into oleic acid. Or, the double bond
on oleic acid in, say, rapeseed oil may be converted to a single bond thus changing
the oleic acid into stearic acid. This latter change will increase the melting point of
the fat considerably (see the melting points of these acids in Table 4.1 of
Chapter 4).
The other process which takes place during hydrogenation is that of isomerisation, in which the cis double bonds naturally present in these oils isomerise in the
presence of hydrogen and catalyst into trans double bonds. The overall degree of
unsaturation does not change but its nature does. Trans fatty acids have a higher
melting point than their corresponding cis fatty acids so, again, the melting point
of the fat is increased.
Both processes will allow a fat with considerable levels of solid fat to be
produced from what are essentially liquid oils. This, then, makes them suitable for
use as replacers of cocoa butter in coatings. Because the trans fatty acids formed
have melting points more appropriate for use in products that need to melt in the
mouth than do acids such as stearic acid, the hydrogenation process conditions
have been optimised to maximise the trans fatty acid content. Even so, the resulting
hydrogenated fat often has significant levels of solid fat above mouth temperature,
giving a degree of waxiness to any coating made from it. By adding a fractionation
stage to remove the higher melting triglycerides after the hydrogenation process,
a much more palatable coating fat is produced.
Fractionation is a crystallisation process in which fats are held at specific
temperatures, either as the fats themselves or in solution in acetone or hexane. The
crystallisation temperatures are chosen such that either unwanted high-melting
triglycerides or unwanted low-melting triglycerides can be removed by filtration.
If it is necessary to remove both high- and low-melting material then two
fractionations are carried out. The result is a steep-melting fat with a melting
profile similar to that of cocoa butter.
Although these coatings have been used successfully for many years and have
given a high degree of functionality to products, there is one major drawback to their
use and that is the high amounts of trans fatty acids that they contain. In some
instances, the trans content has been as high as 50%. The reason for this being a
problem is that it has been demonstrated that trans fatty acids raise low density
lipoproteins (LDL) cholesterol levels in the blood and lower high density lipoproteins
(HDL) cholesterol levels (Mensink et al., 2003). The issues raised by the presence of
trans fatty acids are considered in greater detail in Chapter 4, Section 4.6.
This has led the manufacturers of non-lauric CBR fats to develop low-trans and
virtually no-trans alternatives to these products. The low-trans products generally
contain between 5% and 15% trans fatty acids and are produced by either blending
84
Enrobed and filled chocolate, confectionery and bakery products
conventional non-lauric CBRs with materials such as palm fractions or by hydrogenating the product differently such that less trans fatty acid is produced. One
drawback with this approach is that the product still needs to be labelled as
‘hydrogenated’. Many consumers now associate this label with trans fatty acids
and avoid foods containing hydrogenated fats wherever possible.
For this reason non-lauric CBRs are being developed which are based on nonhydrogenated fats. In some instances these are based on blends of fractions of
non-lauric oils with lauric fats. In others they are made of blends of different
fractions of palm oil such that β'-stable compounds are produced that have a good
meltdown without the need for tempering (Slager et al., 2007).
5.2.3 Lauric cocoa butter replacers
Unlike the traditional non-lauric CBRs which used a combination of hydrogenation and fractionation, lauric CBS fats are produced by either process alone or by
a combination.
Fractionation of palm kernel oil gives stearine and oleine fractions. The stearine
can be used directly in a lauric coating. It can also be fully hydrogenated to give an
even harder coating fat. Because it has been fully hydrogenated, all of the
unsaturated fatty acids (including any trans) have been converted to saturated fatty
acids. This makes it effectively free from trans but almost 100% saturated. It does
still need to be labelled ‘hydrogenated’.
The alternative to fractionation is simply to hydrogenate the oil. In some cases
the oleine fraction can also be recombined with the oil before hydrogenation or just
hydrogenated on its own. All of these methods can produce a fat suitable for use as
a lauric CBS, albeit of lower quality than those produced by fractionation. The
level of unsaturation in palm kernel oil is quite low in comparison to those levels
found in non-lauric oils. This means that even in a partially hydrogenated fat, the
trans levels are nowhere near as high as those in the hydrogenated non-lauric
CBRs.
Lauric CBS fats – particularly those based on palm kernel stearine – can give
good quality coatings with a good ‘snap’ and hardness and a good initial gloss.
There are, however, two main drawbacks to these coatings. First, they have
effectively no compatibility with cocoa butter. Second, if they come into contact
with moisture there is a risk that soapy-tasting off-flavours can be generated. Both
of these issues will be discussed in greater detail in later sections of this chapter.
5.2.4 Formulation constraints
The concept of the iso-solids phase diagram was introduced in Chapter 4 with an
example being given in Fig. 4.5 of the iso-solids diagram of cocoa butter and
Coberine™ (a cocoa butter equivalent produced by Loders Croklaan, the Netherlands). This diagram joined points of equal solid fat content on a diagram in which
blend composition varied along the x-axis and temperature varied along the y-axis.
Generally speaking the lines were all horizontal and parallel to each other,
Compound coatings
85
40
0% solids
10
20
30
40
Temperature (°C)
50
60
20
70
β–3
β' – 2
β – 3 + β' – 2
80
0
0
50
100
Hardened fat fraction (%)
Fig. 5.2 Iso-solids diagram of cocoa butter and non-lauric CBR (hardened fat fraction)
(from Gordon et al., 1979. Copyright Wiley-VCH, reproduced with permission).
indicating that no significant eutectics were formed between cocoa butter and
Coberine™. This further indicated that the melting profile of any blend of cocoa
butter and Coberine™ would be roughly the same.
CBEs like Coberine™ contain the same triglycerides as cocoa butter. They
exhibit the same polymorphism as cocoa butter and every composition in Fig. 4.5
crystallises in the β-3 form, that is in a β polymorphic form with a triple-chain
length packing system. This complete compatibility between cocoa butter and
CBEs means that when CBEs are used in supercoatings they can, from a functional
point of view, be used at any level, even to the extent of fully replacing cocoa
butter. In practice, this is unlikely to happen because the great strength of CBEs in
terms of their use in compound coatings is their compatibility with cocoa butter,
meaning that it is possible to use CBEs to replace all of the added cocoa butter in
a chocolate recipe without having to worry about any compatibility issues relating
to cocoa butter in the remaining cocoa mass. This, then, allows a full chocolate
flavour to be retained in the coating because both cocoa butter and cocoa powder
are still present in the cocoa mass that is used.
Non-lauric CBRs, however, show a different interaction with cocoa butter (Fig.
5.2). Instead of horizontal lines there are now lines with a number of ‘kinks’ in
them; instead of all the compositions being stable in the β polymorphic form, there
are now three distinctly defined areas on the diagram. This is because, at the lefthand end, cocoa butter is β-stable in a triple chain length form, while at the righthand end, the non-lauric CBR is β'-stable in a double chain length form. In the
middle both fats and types of crystal structure vie for position and the result is a
86
Enrobed and filled chocolate, confectionery and bakery products
34
5% solids
10
Temperature (°C)
30
20
30
26
β–3
40
22
β'–2
50
β – 3 + β' – 2
60
18
70
14
0
10
20
30
40
50
60
70
80
90
100
Lauric stearine (%)
Fig. 5.3 Iso-solids diagram of cocoa butter and lauric CBS (lauric stearine) (from
Gordon et al., 1979. Copyright Wiley-VCH, reproduced with permission).
mixed crystallisation, ‘loose’ crystal structure and instability. The broad vertical
lines indicate phase boundaries. To the left of the left-hand phase boundary, cocoa
butter is dominant and all compositions are stable in the β-3 crystal structure. To
the right of the right-hand boundary, the non-lauric CBR is dominant and all
compositions are stable in the β'-2 crystal structure. This area is fairly large,
indicating that there should be stability in any composition containing between
65% and 100% non-lauric CBR. The lower limit of this range is dependent on a
number of factors (type of non-lauric CBR, any milk fat present, quality of cocoa
butter etc) and so, for safety, should be increased to about 80%. In other words, up
to 20% cocoa butter can be safely added to the fat phase of a non-lauric CBR
without any undue softening or phase instability occurring.
So, while not having the same degree of compatibility with cocoa butter that
CBEs have, the non-lauric CBRs have enough compatibility to allow the incorporation of limited quantities of cocoa butter in the coating recipe. ‘Limited’ in this
context means a maximum of 15–20% cocoa butter in the fat phase of the coating.
This is sufficient to allow some cocoa mass to be used in the recipe, giving a
rounded chocolate flavour. If higher levels are used, then there is a greater risk of
softer coatings that may also be more susceptible to bloom formation on storage.
If milk fat is also used in the coating, it should also be included in this 15–20%. It
is, of course, possible to make coatings from non-lauric CBRs without any cocoa
component at all but using pastel colours and fruit flavours instead, for example.
The situation is different again with cocoa butter and lauric CBS fats (Fig. 5.3).
The deviations away from the horizontal lines seen in Fig. 4.5 with CBEs are now
even greater, indicating a very poor compatibility between cocoa butter and a
lauric stearine. The two phase boundaries are still present (as in Fig. 5.2) but the
right-hand boundary has now shifted such that the area of stability at the high lauric
Compound coatings
87
stearine end is now much smaller, having been reduced to about 92–100% lauric
stearine. Again, this needs to be reduced for safety reasons to 95–100% lauric
stearine. In other words, the maximum amount of cocoa butter that can be included
in the fat phase of a lauric CBS coating is 5%.
This means that any cocoa component used in the recipe must be limited to a
low-fat cocoa powder. Since a part of the flavour of chocolate comes from the
cocoa butter in the recipe as well as from the cocoa powder, eliminating cocoa
butter means removing some of the flavour components. The result is that lauric
coatings lack some of the full ‘rounded’ flavour associated with chocolate.
5.3
Recipes
A discussion of the constraints that need to be placed on formulations leads well
into what kinds of recipes can actually be used to produce coatings based on these
three different groups of fats.
Supercoatings
The best place to start in terms of developing supercoating recipes is with chocolate
itself. Table 5.1 shows typical recipes for dark chocolate and milk chocolates with
both low and high levels of milk fat (Talbot, 2006a). Alongside these are shown the
corresponding recipes using CBEs as supercoatings. It is even possible to replace
all of the added cocoa mass by a combination of CBE and cocoa powder or even
in a white supercoating to replace all of the cocoa components completely as
shown in Table 5.2 (adapted from Loders Croklaan Facts About Fats 1).
Table 5.1
Typical chocolate and supercoating recipesa
Plain (%)
b
Chocolate
Cocoa mass
40.0
Cocoa butter
11.0
CBE
Full-cream milk powder
Milk fat
Sugar
49.0
Fat composition:
Cocoa butter
33.0
CBE
Milk fat
Expressed as % of fat phase
Cocoa butter
100.0
CBE
Milk fat
a
Low-milk (%)
Super- Chocolate
coating
40.0
20.0
17.0
11.0
b
High-milk (%)
Super- Chocolateb Supercoating
coating
20.0
10.0
19.3
20.0
17.0
20.0
49.0
43.0
43.0
22.0
11.0
28.0
11.0
17.0
5.0
24.8
33.3
51.5
15.2
75.2
5.0
66.7
33.3
84.8
15.2
20.0
3.2
47.5
8.2
24.8
10.0
19.3
20.0
3.2
47.5
5.5
19.3
8.2
16.7
58.5
24.8
0.4% lecithin is also added to all of these formulations. bChocolate recipes from Talbot (2006a).
88
Enrobed and filled chocolate, confectionery and bakery products
Table 5.2
Examples of high cocoa butter equivalent containing supercoatingsa,b
Milk (%)
Cocoa mass
Cocoa powder 10/12
Full cream milk powder
Skimmed milk powder
CBE
Sugar
Fat composition:
Cocoa butter
CBE
Milk fat:
Expressed as % of fat phase
Cocoa butter
CBE
Milk fat
A
B
10
10
White (%)
C
A
B
20
5
27
48
20
32
48
6
20
15
27
48
15
32
47
5.5
22.0
5.0
5.5
27.0
0.6
32.0
16.9
67.7
15.4
16.9
83.1
1.8
98.2
22
48
27.0
5.0
32.0
84.4
15.6
100.0
a
0.4% lecithin is added to each of these compositions. bAdapted from Loders Croklaan Facts About Fats
1, page 6, Customer information, Loders Croklaan, Wormerveer, The Netherlands.
Non-lauric cocoa butter replacer coatings
Because of the limited compatibility between cocoa butter and non-lauric CBRs,
cocoa components are limited to either low levels of cocoa mass or the use of a lowfat cocoa powder. The use of cocoa mass gives a more rounded chocolate flavour
to the coating because of the presence in this of cocoa butter. There are also
limitations to the levels of milk fat that can be used, meaning that either skimmed
Table 5.3
Examples of typical recipes using non-lauric cocoa butter replacersa, b
Dark (%)
A
Cocoa mass
Cocoa powder 10/12
Full cream milk powder
Skimmed milk powder
Non-lauric CBR
Sugar
Fat composition:
Cocoa butter
Non-lauric CBR
Milk fat
Expressed as % of fat phase
Cocoa butter
Non-lauric CBR
Milk fat
10
15
B
Milk (%)
A
B
White (%)
A
B
10
20
5
6
12
28
44
17
34
44
28
47
33
47
7.0
28.0
2.0
33.0
5.5
28.0
1.5
0.5
34.0
20.0
80.0
5.7
94.3
15.7
80.0
4.3
1.4
98.6
20
5
30
45
20
35
45
30.0
5.0
35.0
85.7
14.3
100.0
a
0.4% lecithin is added to all of these compositions. bAdapted from Loders Croklaan Facts About Fats
1, page 6, Customer information, Loders Croklaan, Wormerveer, The Netherlands.
Compound coatings
Table 5.4
89
Examples of typical recipes using lauric cocoa butter substitutesa, b
Dark (%)
Milk (%)
A
Cocoa powder 10/12
Full cream milk powder
Skimmed milk powder
Lauric CBS
Sugar
Fat composition:
Cocoa butter
Lauric CBS
Milk fat
Expressed as % of fat phase
Cocoa butter
Lauric CBS
Milk fat
14
7
31
48
5
10
10
29
46
White (%)
B
5
17.5
31.5
46
20
32
48
1.4
31.0
0.5
29.0
2.5
0.5
31.5
32.0
4.3
95.7
1.6
90.6
7.8
1.6
98.4
100.0
a
0.4% lecithin is added to all of these compositions. bAdapted from Loders Croklaan Facts About Fats
1, page 7, Customer information, Loders Croklaan, Wormerveer, The Netherlands.
milk powder should be used or low levels of full-cream milk powder. In white
coatings where there need be no cocoa component, higher levels of full-cream milk
powder can be tolerated. Example recipes of coatings made using non-lauric CBRs
are shown in Table 5.3 (taken from Loders Croklaan Facts About Fats 1).
This table shows pairs of recipes for each type of coating. One of each of these
pairs has a composition close to the limits that would be placed on cocoa butter and/
or milk fat incorporation (i.e. maximum 20%). The other recipe for each pair has
much lower levels of cocoa butter and/or milk fat, but correspondingly lower or
less-rounded flavour levels.
Lauric cocoa butter equivalent coatings
The almost total incompatibility between lauric CBS fats and cocoa butter limits
any cocoa component in these coatings to a low-fat cocoa powder. Example
recipes (taken from Loders Croklaan Facts About Fats 1) are shown in Table 5.4.
In all recipes the level of cocoa butter present is less than 5% which from the phase
diagram in Fig. 5.3 would be the maximum tolerable without crossing the phase
boundary into an unacceptable formulation region.
5.4
Flavourings and colourings
There is generally more scope for adding flavourings and colourings to compound
coatings, particularly white compound coatings, than there is to chocolate. In terms
of dark and milk coatings then clearly added flavours are used more than added
colours since the colour of the coating comes almost exclusively from the cocoa
component. Flavours which complement the cocoa flavour are mainly used, such
90
Enrobed and filled chocolate, confectionery and bakery products
as mint or orange. Of particular importance when it comes to white coatings are the
use of fruit flavours with pastel colours, although caramel flavours and colours
have been used in commercially successful products.
The range of flavours and colours available for use in confectionery is discussed
in Chapter 7 and the reader is referred to that chapter for tables showing natural and
synthetic colours. The main differences in terms of choice between flavours and
colours for use in compound coatings and those used in sugar-based centres is that
those used in compound coatings should, ideally, be fat-soluble because of the fatcontinuous nature of coatings. In some circumstances it is possible to use ‘lake’
colours. These are aluminium salts of normal food colours on a carrier which
makes them dispersible in the fat, if not necessarily soluble.
Care should be taken over conching (see below) if colours are added as this
could affect the nature of the colour. Strictly speaking it should not be necessary to
conch a pastel coating other than to remove excess moisture.
5.5
Effects of formulation on sensory and functional
properties
The three different types of compound coating fat can give varying differences in
sensory and functional properties compared with a cocoa butter-based chocolate.
Some of these differences are due to their melting profiles being slightly different
from those of cocoa butter; others are due more to differences in crystallisation and
post-crystallisation.
5.5.1 Effect on melting profile and meltdown in the mouth
Typical melting profiles, as defined by solid fat contents, of the various kinds of
compound coating fat are shown in Table 5.5.
Various sensory attributes such as hardness, coolness and waxiness can be
defined by the melting profile of a fat. An example of this is shown in Fig. 5.4. High
solid fat contents at temperatures of 15–25 °C equate to harder, possibly more
brittle coatings (although brittleness can also be related to the way the fats in the
coating crystallise). Lauric CBS products, particularly fully hydrogenated palm
kernel stearine, usually have the highest solid fat contents at 20 °C of all of the
compound coating fats and also produce coatings that have a brittle snap when
broken.
The more solid fat that is present at 25–30 °C the greater is the heat resistance
of a coating based on that fat. This makes this type of coating more suitable for use
in climates with higher ambient temperatures. Particularly useful in this respect are
cocoa butter improvers (CBIs). These are a sub-category of CBEs in which the
palm fraction component is significantly reduced. This means that the higher
melting POSt and, particularly, StOSt predominate, giving the fat higher solid fat
contents at 30 °C and a higher melting point. These can be used both as vegetable
fats in chocolate (where permitted) or as part of a supercoating formulation to
Compound coatings
Table 5.5
Solid fat contentsa of compound coating fats
Solid fat
Cocoa
CBE Non-lauric Palm kernel
CBR (%) stearine (%)
content butterb (%) (%)
N20
N25
N30
N35
N40
91
76.4
67.2
41.5
0.4
0.1
74
64
47
3
0
88
71
40
6
0
Fully
Hydrogenated
hydrogenated palm kernel
palm kernel
oil (%)
stearine (%)
82
67
28
1
0
95
89
48
5
0
84
63
35
14
6
a
Solid fat contents of cocoa butter and CBE measured following IUPAC method 2.150(b); solid fats
contents on other coating fats measured following IUPAC method 2.150(a). See IUPAC Standard
Methods for the Analysis of Oils, Fats and Derivatives, 8th edition, 2.150 Solid content determination
in fats by NMR. bGhana cocoa butter (from Wong Soon, 1991).
100
90
80
Hardness
Solid fat (%)
70
Heat
resistance
60
Coolness
and
flavour
release
50
40
30
20
10
Waxiness
0
10
15
20
25
30
35
40
45
Temperature (°C)
Fig. 5.4 Melting profile of coating fats (redrawn from Loders Croklaan Facts about
Fats 1, page 5, Customer information, Loders Croklaan, Wormerveer, The Netherlands).
enhance heat resistance. POSt (1-palmitoyl, 2-oleoyl, 3-stearoylglycerol) and
StOSt (1,3-distearoyl, 2-oleoylglycerol) are two of the main triglycerides to be
found in cocoa butter. More details relating to their structure and properties are
given in Chapter 4.
The steepness of the melting profile, especially between 25 and 35 °C defines
whether or not there will be a cooling sensation when the fat melts. The more rapid
92
Enrobed and filled chocolate, confectionery and bakery products
this meltdown is, particularly if it is combined with quite a high initial solid fat
content, the more fat will melt from the coating in a short space of time. This rapid
meltdown removes latent heat from the mouth giving a cooling sensation. Reference to Table 5.5 shows, for example, that there is a greater likelihood of obtaining
a cooling sensation from either palm kernel stearine or fully hydrogenated palm
kernel stearine than from hydrogenated palm kernel oil.
Hydrogenated palm kernel oil can, depending on its melting point, also contain
a significant amount of solid fat even at 40 °C. Any fat remaining in the solid form
above 37 °C (mouth temperature) will appear to be waxy. This sometimes means
that a balance has to be attained between good heat resistance and minimal
waxiness.
Although in Table 5.5 it would appear that the non-lauric CBR would show
minimal waxiness, these types of compound coating fat, particularly the traditional
type produced by hydrogenation and fractionation, can show post-hardening on
storage. Post-hardening is generally a result of a further, slow crystallisation after
the product has been produced and packed. Many coatings exhibit this, even
chocolate. Post-hardening in chocolate generally results in an increase in the solid
fat content at around ambient temperatures, thus improving the hardness of the
chocolate when it is first bitten into. Post-hardening in non-lauric CBRs, however,
can often result in an increase in solid fat content at 35 °C which is more likely to
give a waxier coating.
5.5.2 Effect on shelf life and risk of fat bloom
Supercoatings exhibit the same polymorphism as does cocoa butter and therefore
are subject to the same risks of fat bloom. The mechanism of fat bloom formation
on chocolate is discussed in much greater detail in Chapter 10. All that will be said
here is that fat bloom on supercoatings results from a change from a βV to a βVI
polymorphic form. Such a change will be accelerated at higher storage temperatures or by migration of liquid oils from a centre into the supercoating.
Non-lauric CBRs are generally fairly resistant to fat bloom unless the level of
cocoa butter and milk fat is so high that the right-hand phase boundary in Fig. 5.2
is crossed. Then bloom will occur. Other than this, non-lauric CBRs produce a
glossy coating.
In many ways the same thing can be said of lauric CBRs. Well-produced lauric
CBR coatings can be highly glossy but if the cocoa butter content is too high then
bloom will be produced. Even a cocoa butter content of 10% is enough to produce
fat bloom on storage (Talbot et al., 2005) irrespective of storage temperature.
Interestingly though, if the product is stored at 15–20 °C, the bloom is rich in
triglycerides from cocoa butter, but if it is stored at higher temperatures (20–25 °C)
then the bloom is enriched in lauric fat, suggesting a change in mechanism at about
20 °C.
It is perhaps also worth saying a word or two about sugar bloom. This differs
from fat bloom in that it is a recrystallisation of sugar on the surface of the coating.
It is particularly a problem if moisture condensation on the surface of the product
Compound coatings
93
occurs. Sugar in the coating can dissolve in this moisture and come to the surface
of the bar as a sugar solution. When the moisture then evaporates the sugar remains
as crystals on the surface of the product. Even moisture from fingers touching the
bar can result in sugar bloom.
5.6
Effect of fat choice on manufacturing process
The main difference between the different types of coating fat in the context of
processing is whether or not they need to be tempered. Supercoatings, because of
their stability in the β polymorphic form, do need tempering, However, coating
compositions based on non-lauric CBRs or lauric CBSs that are in the right-hand
stable zone in Figs 5.2 and 5.3 are β'-stable. These types of fats crystallise directly
into this crystal form without anything more than a slight precrystallisation. This
means that they do not need to be tempered. This makes them much easier for small
to medium sized bakers and confectioners to use.
5.6.1 Coating production
The methods of coating production are essentially the same for compound coatings
as for chocolate itself. In other words, there is a mixing stage in which all the dry
components (cocoa powder, cocoa mass, milk powders, sugar) are mixed together
with a part of the fat to bring the fat content to about 23%. This mix is then passed
through a multi-roll refiner to reduce the particle size down to less than 25 µm. The
flaked material from the refiner is then conched to both remove moisture and also
‘round off’ the cocoa flavours.
There are two basic types of conching methods, ‘dry’ conching in which the fat
content remains at about 23% for most of the process before the rest of the fat is added
towards the end and ‘wet’ conching in which all the fat is added at the start of conching. Conching usually takes between 6 and 24 hours depending on the formulation
and quality of product desired and is carried out at 50–60 °C for milk and white
coatings and 55–65 °C for dark coatings. As already mentioned, it may not be strictly
necessary to conch a white coating other than to remove any excess moisture that may
be present. The emulsifier, usually lecithin, is added towards the end of conching.
Refining and conching can be carried out as two separate processes on different
pieces of equipment or they can be combined by processing the coating mix in
equipment that both grinds the particle size down and mixes the coating for a
number of hours at a conching temperature. Examples of these are ball mills in
which the particle size is reduced by stirring the coating mix in the presence of
metallic or ceramic balls and combined refiner-conches which consist of a ridged
drum within which rotates another drum with slats sprung against the walls of the
outer drum to grind the particles down.
5.6.2 Tempering
Supercoatings are tempered in much the same way as chocolate is tempered. The
94
Enrobed and filled chocolate, confectionery and bakery products
process of tempering is described in greater detail in Chapter 16. Depending on the
nature of the supercoating fat and the level of milk fat in the supercoating, the
actual tempering temperatures may need to change from those used with chocolate
itself. For example, if the supercoating is rich in palm fraction then the tempering
temperatures may need to be reduced. Conversely if a supercoating rich in cocoa
butter improvers is used to obtain enhanced heat resistance then the tempering
temperatures may need to be increased.
While coatings based on non-lauric CBRs and lauric CBSs do not need to be
tempered in the same way as chocolate and supercoatings do, they do benefit
from a degree of precrystallisation. The need for this, though, is greater when
thick bars are being moulded rather than when an enrobed coating is being
applied.
5.6.3 Enrobing
Enrobing of supercoatings is, again, similar to enrobing of chocolate with the
temperature of the coating being essentially the exit temperature from the tempering unit. Non-lauric CBR coatings are usually enrobed at 38–43 °C while lauric
CBR coatings are enrobed at the slightly higher temperatures of 40–45 °C. These
temperatures may need to be reduced if temperature-sensitive centres are being
enrobed but care needs to be taken not to take the temperatures so low that
crystallisation begins to take place in the coating, as this will cause an increase in
viscosity and the risk of the coating being too thick.
5.6.4 Cooling
Because of their similar polymorphism, supercoatings are cooled in a similar
way to chocolate. This means entry into a cooling tunnel at about 15 °C, cooling
to 10–12 °C in the centre of the tunnel and then emerging with an exit temperature of about 15 °C. Too rapid a cooling or too fast a wind speed can result in
unstable crystals of cocoa butter or CBE being produced which will then result
in fat bloom.
Despite their similar polymorphism, lauric and non-lauric coatings crystallise
in different ways. Foubert et al. (2006) compared the crystallisation of non-lauric
CBR and lauric CBS fats isothermally at different temperatures by differential
scanning calorimetry (DSC). The increase in melting enthalpy with time when held
isothermally is shown in Fig. 5.5. It is clear from this that lauric CBS fats crystallise
much more quickly than do non-lauric CBR fats at the same temperature. This, to
some extent, has consequences in terms of cooling conditions for coatings based
on these two types of fat.
Lauric fats have traditionally been cooled very quickly, having a low temperature of entry into a cooling tunnel, typically 8–10 °C. The temperature can be
slightly lower still in the centre of the cooling tunnel, finally increasing at the exit
to about 15 °C. The wind speed with lauric coatings is usually considerably higher
than with supercoatings. Wind speed can be quite critical in terms of cooling
Compound coatings
95
140
Melting enthalpy (J g–1)
120
100
80
60
40
20
0
0
Fig. 5.5
10
20
30
Isothermal time (minutes)
40
Crystallisation of non-lauric cocoa butter replacer (—) and lauric cocoa butter
substitute fats (---) (by DSC) (redrawn from Foubert et al., 2006).
coatings. We are all familiar with the wind chill factor that we feel going out into
a strong wind. The same effect applies to coatings in a cooling tunnel. Cooling a
lauric coating at 10 °C with a wind speed of 6–7 m s–1 has the same effect as cooling
at 5 °C with a wind speed of 3m s–1. If there was no wind in the tunnel then it would
be necessary to cool at –35 °C to obtain the same cooling effect (Boom, unpublished).
Because non-lauric fats are slower to crystallise than lauric fats then it would be
expected that the cooling conditions to be applied should be at least as cold as those
for lauric fats. Indeed, some workers recommend a cooling tunnel entry temperature of 6–8 °C followed by a gradual increase in temperature in the second part of
the tunnel. The author’s experience, however, is that a more moderate cooling
results in an excellent gloss on the coating, although it may then be necessary to
slow the throughput down to give the product enough time in the cooling tunnel to
crystallise. Figure 5.6 shows gloss scores on non-lauric CBR coatings crystallised
under various cooling tunnel temperatures and then stored at 15 °C, 20 °C and
25 °C for 3 months. The optimal tunnel temperatures for good gloss were entry and
exit temperatures of 12 °C with temperatures in the centre of the tunnel of 8–10 °C
(Talbot, 2006b).
It is particularly important to ensure that the exit temperature from the cooling
tunnel is above the ‘dew point’ otherwise there is a great risk of condensation on
the surface of the product. The dew point is related to the relative humidity in the
atmosphere and is the temperature at which condensation will occur. There are
general and specific problems associated with condensation on compound coatings. The general problems are (a) condensation can result in unsightly drying
marks on the surface, (b) if it is still present as water when the product is packed,
it can result in the formation and growth of moulds on the surface, and (c) it can
result in sugar bloom. The more specific problem is when condensation occurs on
96
Enrobed and filled chocolate, confectionery and bakery products
30
Gloss score
25
20
15 °C
15
20 °C
25 °C
10
5
0
15-12-15 15-10-15 15-10-12 12-10-12 12-8-12
10-8-12
Tunnel temperatures (°C)
Fig. 5.6 Effect of cooling conditions on gloss of non-lauric coatings (after 3 months).
lauric coatings there can be a risk of soapy off-flavour being produced. This is
discussed in more detail in Chapter 5, Section 5.6.6.
5.6.5 Packing and storage
Products enrobed with any of these compound coatings should be packed as soon
as possible after exiting the cooling tunnel but (a) not before the coating is fully
dry, otherwise smearing of the coating can result, especially in flow-wrapped
products and (b) ensuring that the dew point in the packing area is below the
product temperature, otherwise condensation can again be a problem with all the
associated issues described in the previous section.
Supercoatings and non-lauric CBR-coated products are best stored at 16–18 °C
to ensure a good bloom-free shelf life. Lauric CBS-coated products are usually
stored at a slightly higher temperature (20–22 °C). This is again to ensure a good
bloom-free shelf life but, in particular, to ensure the absence of a phenomenon
known as ‘ghost bloom’. Ghost bloom can be a problem if chocolate containing 3–
5% of either palm kernel oil or palm kernel stearine is stored at 10–15 °C
(Gunstone and Padley, 1997). It has, however, also been observed on lauric-rich
compound coatings and is essentially a phase separation in which low-melting
triglycerides recrystallise on the surface as bloom. When the product is warmed up
to ambient temperatures the bloom melts and disappears. Hence the term ‘ghost’
bloom.
5.6.6
Specific problems associated with lauric cocoa butter substitute
coatings
The problems of incompatibility between lauric fats and cocoa butter has already
been considered in some detail. While this has a considerable effect on the recipe
and composition of coatings containing lauric fats it can also have an effect on
Compound coatings
97
processing equipment that is used for both lauric coatings and non-lauric coatings,
especially chocolate coatings. This equipment could be mixing vessels, refiners,
conches, enrobers and all the associated pipework and pumps. If chocolate has
been processed in any of these units and this is then followed by a lauric coating (or
vice versa) there is a great risk of cross-contamination and a crossing of the phase
boundaries shown in Fig. 5.3.
It is important, therefore, that such equipment be thoroughly cleaned before
changing over from one type of coating to the other. In an ideal world this would
mean completely emptying, washing and thoroughly drying the equipment before
refilling with the next coating. In reality, this is often not feasible and, in any case,
the introduction of water into an essentially water-free environment produces its
own problems. A ‘washout’ of all the equipment, pipes and pumps with a
disposable oil phase is most often recommended. If possible, it is best to use the fat
phase of the coating to be used next, so if a lauric coating is to follow chocolate then
wash out with the lauric fat or, if a chocolate is to follow a lauric fat then wash out
with cocoa butter. Since this fat will eventually be discarded it can be quite
expensive, particularly in the case when cocoa butter is used as the flushing oil. In
some instances it may be possible to use a cheaper oil. For example, palm kernel
oil could be used in place of the more expensive lauric CBS fat when moving from
chocolate to a lauric coating. If the changeover is in the opposite direction
(chocolate being used after a lauric coating) it may be possible to use a CBE
component fat such as palm mid-fraction or even palm oil if the chocolate also
contains some vegetable fat (although not if the chocolate is free of vegetable fat).
A second problem associated with lauric coatings is that objectionable offflavours can be generated if hydrolysis of the lauric fat occurs. Hydrolysis is a
breakdown of the triglycerides into partial glycerides (diglycerides and
monoglycerides) and the release of free fatty acids. Three components are necessary for hydrolysis to occur: fat, water and a catalyst (usually a lipase enzyme).
Hydrolysis can therefore be prevented by ensuring the absence of either water or
lipase. Good specification of raw materials, particularly cocoa powders, milk
powders and nuts, can go much of the way to ensuring the absence of lipase. Good
manufacturing practice can help to ensure the absence of water since the main
source of water in these products is likely to come from condensation. If bars based
on lauric fats exit a cooling tunnel at a temperature below the dew point in that area
then condensation can occur. If this condensation then becomes trapped within
packaging and cannot escape, the risk of hydrolysis is always present. Such
hydrolysis can occur with any fat – cocoa butter, CBE, non-lauric CBR – so why
is it such a problem with lauric fats? The reason is that the free fatty acid produced,
lauric acid, has a very objectionable soapy taste even at low levels (less than 0.1%).
Free fatty acids generated as a result of the hydrolysis of non-lauric fats have a
much higher threshold before they are perceived by the consumer and, even then,
do not have this soapy taste.
A third problem that seems to be associated more with lauric coatings than other
compound coatings is ‘mottling’. This is more obvious on pastel and white
coatings and shows itself either as spots on the surface which are surrounded by a
98
Enrobed and filled chocolate, confectionery and bakery products
crystallisation of the coating fat or as whitish streaks within the surface layer of the
coating. It can be overcome in a number of ways (Talbot and ‘t Zand, 2007).
Precrystallisation of the coating to induce seed crystals to form helps in terms of
homogeneous crystallisation of the bulk coating. Alternatively, 1–3% of glycerol
monostearate can be added to the coating and the coating then used at 40–45 °C.
A third solution is to use a lauric coating fat containing a small amount of a highmelting fat which will then ‘seed’ the bulk coating, thereby minimising the
likelihood of mottling occurring.
5.7
Future trends
Many of the future trends in this area are going to be associated with nutrition and,
indeed, many of these trends have already begun. As has already been indicated,
hydrogenation and the presence of trans fatty acids has and continues to be an area
of major concern. New generations of non-lauric CBR fats are being developed. Initially, these were low-trans, but still hydrogenated products. More recently, though,
non-hydrogenated and therefore effectively trans-free products have been launched
(Slager et al., 2007). Undoubtedly, as our knowledge improves about how to
produce different fractions of oils, about the polymorphism of blends of these and the
implications of these blends for product quality and shelf life, then the quality of these
non-hydrogenated CBRs will also improve above and beyond where we are today.
However, a further area of concern with regard to nutrition is starting to come
to the fore – the amount of saturated fat which we consume as a proportion of total
dietary energy. By definition it is necessary to have solid fat present to give the
required structure to a confectionery coating. Also, by definition this solidity is
only going to be achieved if a reasonable amount of either trans or saturated fat is
present. Product development will, therefore, take place to try to reduce the level
of saturates in a coating while still maintaining the necessary solid fat content.
The lauric CBS fats contain the greatest amounts of saturated fat (>99% in a
fully hydrogenated palm kernel stearine). Both cocoa butter and the newer
varieties of non-lauric CBR contain considerably less but still significant levels of
saturated fatty acid (60–65%). To go to lower levels of saturates, yet still maintain
the required melting characteristics to make a coating, would mean moving to
more structured triglycerides containing longer chain saturated fatty acids such as
behenic acid with 22 carbon atoms in conjunction with a greater degree of
unsaturation in the triglyceride. For example, a fat has been developed (Tynek and
Ledochowska, 1995) which contains about 35% behenic acid and 50% oleic acid
that melts at 37.5 °C and which, on the face of it, could be suitable for a coating
application with only about one-third of its composition being saturated. The
disadvantages of this kind of development are that these fats do not occur in nature
and so would need to be synthesised, and that components such as behenic acid can
only be obtained in significant quantities by complete hydrogenation of erucic acid
(found in a variety of rapeseed oil whose cultivation has now been almost
discontinued because of nutritional concerns related to erucic acid).
Compound coatings
99
This brings us full circle to the problem of hydrogenation. In some countries
consumers have been led by the media always to make the link between the
presence of ‘hydrogenated vegetable fat’ on a label and the presence of trans fatty
acids in the product, even though this can be an erroneous link to make. Fully
hydrogenated fats do not contain trans fatty acids although they do have be
labelled as ‘hydrogenated’. This gives a problem to product developers because it
means that such fats, which are often highly functional at low levels, wrongly
attract the stigma of containing trans fatty acids. Greater consumer education is,
therefore, needed to counter these misconceptions.
5.8
Sources of further information and advice
The major suppliers of compound coating fats have published material giving
excellent advice on the use of these products. Some of this material is in the form
of booklets such as the Facts About Fats series from Loders Croklaan. Some of it
is provided in training courses to customers of these companies, such as the AAK
Oils and Fats Academy. Other excellent sources of information are the websites
(e.g. www.croklaan.com, www.aak.com, www.fujioil.co.jp) of these companies
where product information and reprints of articles can often be found.
Useful textbook sources are from Beckett (2008) and Talbot (2006a).
5.9
References
BECKETT ST (editor) (2009). Industrial Chocolate Manufacture and Use, 4th edition, Wiley-
Blackwell, Oxford, UK.
BOOM A, unpublished personal communication.
FOUBERT I, VEREECKEN J, SMITH KW AND DEWETTINCK K
(2006). ‘Relationship between
crystallisation behaviour, microstructure and macroscopic properties in trans containing
and trans free coating fats and coatings’, Journal of Agricultural and Food Chemistry,
54(19), 7256–62.
GORDON MH, PADLEY, FB AND TIMMS, RE (1979). ‘Factors influencing the use of vegetable
fats in chocolate’, Fette Seifen Anstrichmittel, 81(3), 116–21.
GUNSTONE FD AND PADLEY FB (1997). Lipid Technologies and Applications, Marcel Dekker,
New York, p. 416.
INTERNATIONAL COCOA ORGANIZATION (2008). http://www.icco.org/statistics/monthly.aspx.
LODERS CROKLAAN. ‘Cocoa Butter Alternatives for compound chocolate’, Facts About Fats
1, Customer Information, Loders Croklaan, Wormerveer, The Netherlands.
MENSINK RP, ZOCK PL, KESTER AD AND KATAN MB (2003). ‘Effects of dietary fatty acids and
carbohydrates on the ratio of total to HDL cholesterol and on serum lipids and
apolipoproteins: a meta-analysis of 60 controlled trials’, American Journal Clinical
Nutrition, 77, 1146–55.
SLAGER H, FAVRE L AND TALBOT G (2007). ‘The ultimate confectionery coating’, Food
Marketing and Technology, December, 12–14.
TALBOT G (2006a). Applications of Fats in Confectionery, Kennedy’s Publications, London.
TALBOT G (2006b). ‘The importance of correct cooling’. Lecture given at ZDS Chocolate
Technology, Cologne, Germany, December 2006. CD-ROM available from ZDS
(Zentralfachschule der Deutschen Süßwarenwirtschaft – German Confectionery School).
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Enrobed and filled chocolate, confectionery and bakery products
TALBOT G AND ’T ZAND I (2007). ‘Is mottling a problem?’ Kennedy’s Confection, January,
54.
TALBOT G, SMITH KW AND CAIN FW (2005). ‘Fat bloom on lauric coatings: composition’, The
Manufacturing Confectioner, 85 (1), 65–8.
(1995). ‘Structured triacylglycerols containing behenic
acid: preparation and properties’, Journal Food Lipids, 12, 77–89.
WONG SOON (1991). Speciality Fats versus Cocoa Butter, Wong Soon, Selangor, Malaysia.
TYNEK M AND LEDOCHOWSKA E
6
Fat-based centres and fillings
J. Birkett, AarhusKarlshamn Denmark A/S, Denmark
Abstract: This chapter discusses the effect of ingredients on the quality, sensory
attributes and stability of fat-based fillings and spreads. Recipes for truffles, nougats and
spreads are given. Various manufacturing processes such as aeration and cold pressing
are discussed. Stability and shelf-life issues such as fat migration, fat bloom and oil
separation are included.
Key words: fat-based fillings, fat-based spreads, nougats, truffles.
6.1
Introduction
Pralines, truffles, nougats – these are the descriptions frequently given to fat-based
fillings and centres. These fillings are used with chocolate, biscuits, wafers or nuts
to provide an enormous variety of products. These products can be made suitable
for all markets, from the premium market through to the low cost, high volume
market.
This chapter will describe the function that the various ingredients have on the
quality and sensory attributes of the filling. The various opportunities that different
processes offer the product developer will be discussed. Reference to the many
nutritional and environmental issues that concern most consumers will be included
where appropriate. It is generally thought that both health and indulgence will
drive the confectionery market. There is no reason why these two apparently
contradictory needs cannot be achieved in fat-based centres.
Legislation is seldom mentioned in this chapter because it varies from country
to country and is continually being changed. The reader is advised to check on the
relevant legislation for the country concerned.
102
6.2
Enrobed and filled chocolate, confectionery and bakery products
Effects of ingredients on quality
Variety is a part of our lives and recent legislation and nutritional concerns have
given product developers and ingredient suppliers an enormous incentive to create
new products. No product can meet all the possible expectations, so product
developers have to decide which attributes are important. The number of new
ingredients available has increased enormously and it is becoming more difficult
to know what is available so it is wise to seek the assistance of the ingredient
suppliers to ensure the most appropriate product is developed.
The final product will probably be a combination of such components as
chocolate, filling, nuts, wafers and it is critical that they complement each other in
terms of texture and other sensory attributes. Consideration must be given to their
interactions which might adversely affect their shelf life. If the new product is to be
made on an existing production line this can immediately restrict the type of
ingredients that can be considered.
Many governments are trying to encourage their populace to combat obesity
mainly through health campaigns and labelling legislation. Their intention to try to
reduce the consumption of sugar, fat, saturated fat, trans fatty acids and salt gives
the product developer many new challenges and opportunities.
6.2.1 Fats
The fat content has an enormous effect upon the sensory and rheological properties
of the fat-based filling. Generally speaking the fat content is about 30% of the
filling but it can be up to about 60%. Since fat is the continuous phase in a fat-based
filling, the viscosity of the filling decreases as the fat content increases. Rheological
properties are discussed in Chapter 13.
The type of fat that is used affects the sensory properties of the filling, its
compatibility with the other components of the product and the shelf life of the
product. Arishima and McBrayer (2002) suggest that filling fats for use with
biscuits and wafers should have a slower melt in the mouth than filling fats used
with chocolate. The nutritional and processing requirements will affect what type
of fat can be considered. Table 6.1 gives an example of the types of questions that
need to be considered before a filling fat can be chosen. There are a number of ways
of categorising the different types of filling fats. For convenience, three types have
been chosen, (i) polymorphic filling fats which are always non-lauric, (ii) nonpolymorphic, non-lauric filling fats and (iii) non-polymorphic, lauric filling fats.
Polymorphic filling fats
Cocoa butter is frequently used in fillings, either added as such or as a constituent
of cocoa liquor or cocoa powder. Cocoa butter, cocoa butter equivalents or fats
based upon palm fractions are compatible with each other and all require tempering or certainly precrystallisation. This speeds up their rate of crystallisation and
prevents recrystallisation which can cause a grainy unpleasant texture (see Chapters 12 and 14). These fat systems give a very pleasant melt down and under certain
conditions give rise to a cooling sensation (see Section 6.3 of this chapter).
Fat-based centres and fillings
Table 6.1
103
Example questions that need to be answered before choosing a filling fat
Final product requirements
1 ) Are other fats present, cocoa butter, milk fat, nut oils?
2 ) Is the product enrobed or moulded in milk or plain chocolate or compound coating?
What is the size and thickness?
3 ) Might fat bloom be an issue?
4 ) Are there any fat migration issues?
5 ) What will the packaging format be?
6 ) What is the shelf life of the product?
7 ) Are there any moisture migration issues, wafer or biscuit components?
Nutritional requirements
1 ) Is hydrogenation permitted ?
2 ) Is trans fat permitted?
3 ) Is the level of saturates a concern?
4 ) Is genetic modification or identity preservation an issue?
5 ) Any additive issues, for example lecithin?
6 ) Are there allergy issues, for example soyabean or peanut?
Process constraints
1 ) Is tempering or precrystallisation equipment available?
2 ) Is there plenty of cooling capacity?
3 ) Will rework be incorporated? How will the rework be recovered?
4 ) If aeration is required, what equipment is available?
5 ) Will the product be made on an existing plant?
6 ) If so, will it share with another product?
7 ) Supply chain – what quantities, what packaging format?
Filling fat
1 ) How hard or soft?
2 ) Is a cooling effect required?
3 ) Is aeration required, what density?
4 ) Is an existing fat suitable?
Their melting profiles, (solid fat content against temperature) are steep as
shown in Fig. 6.1 which compares West African cocoa butter with a typical hard
and soft polymorphic filling fat. Fillings made with these fats are ideally suited for
covering with chocolate or supercoatings composed of cocoa butter equivalents
(see Chapter 5).
Non-polymorphic, non-lauric filling fats
Fats based upon hydrogenated rapeseed, soyabean oil and palm fractions have
been used successfully as filling fats for many years. Their advantages included
excellent oxidative stability and speed of solidification, crystallising directly into
the β' form. Their major disadvantage was that they had a high trans content, about
50% in some cases.
Recently, low trans and non-hydrogenated non-polymorphic, non-lauric filling
fats have been developed. Polymorphism is attributed to high concentrations of
symmetrical triglycerides and low concentrations of asymmetrical monounsaturated
triglycerides. Interesterification of symmetrical triglyceride feedstock increases
the concentration of asymmetrical monounsaturated triglycerides and renders the
fat non-polymorphic.
104
Enrobed and filled chocolate, confectionery and bakery products
90
80
Solid fat content (%)
70
60
50
40
30
20
10
0
20
25
30
35
40
Temperature (°C )
Fig. 6.1 Typical melting profiles for West African cocoa butter and hard and soft
polymorphic fats (, cocoa butter; ü, hard polymorphic fat; ¸, soft polymorphic fat).
A new range of aerating filling fats that falls within this category has recently
been developed. These filling fats can easily be aerated to a density of 0.6 g cm–3
in a simple whipping operation. With pressurised mixing systems, lower densities
can be achieved. These aerating properties are a result of the fat’s specific
solidification properties.
Lower saturated fats are now available. The hardness of a fat is related to its
level of unsaturation and the length of the carbon chain in the fatty acid, the lower
the unsaturation and the longer the chain length, the harder the fat. Until recently
the main way to reduce saturates was to replace lauric with non-lauric filling fats
thereby increasing the length of the carbon chain of the fatty acid. The new range
of lower saturated fats permits a further reduction without compromising hardness
(see Fig. 6.2). These fats are non-lauric and do not require precrystallisation
because they solidify in the stable β form. Fillings made with these fats are ideally
suited for covering with chocolate or supercoatings composed of cocoa butter
equivalents.
Non-polymorphic, lauric filling fats
These fats are based upon coconut and palm kernel oils. Hydrogenated palm kernel
oil was an extremely popular filling fat which has an excellent oxidative stability
Fat-based centres and fillings
105
60
Saturated fatty acids ( % )
50
40
30
20
10
0
100
180
Hardness ( g )
Fig. 6.2 Correlation between hardness and saturated fatty acids measured at 20 °C
(, unhydrogenated non-lauric filling fat; ü, low saturated filling fat).
and a fast speed of solidification. With the general concern about trans fats and
hydrogenation, blends based upon palm kernel stearines are often being used
instead of hydrogenated palm kernel oil. All lauric fats have eutectic properties
with non-lauric fats including cocoa butter. This effect must be considered,
especially if a consistent product is essential. The principle of eutectics is discussed
in Chapter 10.
The use of filling fats composed of interesterified blends of palm fractions and
palm kernel oil fractions has increased significantly. These part lauric blends are
non-hydrogenated, can have a pleasant meltdown, offer fat-bloom protection and
have a reasonably fast speed of solidification. These part lauric blends can offer a
wide range of hardnesses (Fig. 6.3). Both lauric and part lauric filling fats can have
a significant effect upon the softening of the outer chocolate (see Section 6.5.1).
Lipolysis (also referred to as lipolytic or hydrolytic rancidity) is always to be
considered when lauric fats are used, especially in combination with milk powders
or nuts which can contain lipases. Special care must be taken if recovered rework
is incorporated back into the filling. Soapy flavours, the consequence of lipolysis,
can easily be prevented provided these risks are correctly controlled.
Fillings made with these fats are ideally suited for covering with lauric coatings.
If they are covered with chocolate or supercoatings composed of cocoa butter
equivalents the migration effect will be more noticeable owing to eutectic effects.
106
Enrobed and filled chocolate, confectionery and bakery products
100
90
Solid fat content (%)
80
70
60
50
40
30
20
10
0
20
25
30
35
40
Temperature (°C)
Fig. 6.3 Part lauric blends can offer a wide range of hardnesses
(, hard; ü, medium; ¸, soft).
There are, however, many delicious products on the market composed of lauric
fillings enrobed in chocolate but a significant softening of the chocolate is
frequently noticed.
6.2.2 Fat replacers
The pleasant sensory attributes of confectionery fat fillings generally improves as the
quantity of fat increases. There has been a lot of research on fat replacers over the last
20 years. The replacement of some or all of the fat could improve the nutritional
profile of the product, be it a reduction of the total fat or its calorific value, an
objective that many governments have to fight obesity. It is also recognised that
dietary protein increases satiety more than dietary fat or carbohydrate.
Fat replacers are continually being evaluated and approved by various legislative bodies, usually for specific applications. The use of fat replacers in confectionery
fillings, especially those considered to be high quality premium products, is
negligible but they certainly offer a possible opportunity for the future. Fat
replacers can be classified into two categories, those based upon the glycerol
molecule, and those that are not.
Fat replacers based on the glycerol molecule
Examples of fat-based replacers include Caprenin, Captrin and Salatrim. All these
Fat-based centres and fillings
107
replacers have a calorific value of about 5 kcal g–1 rather than 9 kcal g–1 for standard
triglycerides. This reduction has been achieved by control over the fatty acids that
are present. Timms (2003, p 250) discusses this category of fat replacers in more
detail.
Fat replacers not based on the glycerol molecule
Sucrose polyesters that can be used as fat replacers are based on the sucrose
molecule esterified with six to eight long chain fatty acids. These have been
extensively studied and are considered to be non-caloric. Alkyl glycoside fatty
acid esters, starch derived, fibre-based, hydrocolloid gums and microparticulated
gums are all fat replacers that are in this category. Gunstone (2006) gives a good
overall appreciation of reduced and zero calorie lipids for foods.
6.2.3 Sugars
Sugar is generally the main ingredient of fat-based fillings and confectionery
products. Highly refined white sugar is 99.9% sucrose, a non-reducing disaccharide. It is manufactured from either sugar cane or sugar beet which are different
types of plant yet they give rise to white sugar which is virtually indistinguishable.
Besides white sugar, there are various other grades of sugar, including brown
sugar, golden syrup, treacle and molasses. These are generally used to introduce
either colour or flavour into the filling. Malt extracts are often used as a sweetening
ingredient which imparts its characteristic flavour.
Various alternatives to sucrose are now available to meet the needs of the
industry. These overcome some of the disadvantages of sucrose, namely it being
cariogenic, unsuitable for diabetics and it being a sugar with a calorific value of
4 kcal g–1. The monosaccharides, dextrose and fructose, are readily available.
Dextrose has the same disadvantages as sucrose although it is only about 60% as
sweet as sucrose. Fructose is slightly sweeter than sucrose and is suitable for
diabetics but is hygroscopic. Both these saccharides have a calorific value of
4 kcal g–1. Replacing sugar enables a variety of nutritional claims to be made such
Table 6.2
Permitted nutritional claims for replacing sugar
Nutritional claim
Definition
Sugar-free
With no added sugar
Less than or equal to 0.5 g sugarsa per 100 g or 100 ml of product
The product does not contain any added mono or disaccharides or
any other food used for its sweetening propertiesb
Less than or equal to 5 g sugarsa per 100 g or 100 ml of product
Reduction in sugar content of at least 30%a compared to a similar
product
Reduction in energy of at least 30% compared to a similar
product
Low sugars
Reduced sugars
Energy reduced
a
Directive 90/496/EEC defines sugars as all monosaccharides and disaccharides present in food but
excludes polyols. bAccording to Directive 94/35/EC.
108
Enrobed and filled chocolate, confectionery and bakery products
Table 6.3
Sugars and sugar replacers
Type
Tooth friendly
Suitable for
diabetics
Sucrose
Trehalose
Lactose
Isomaltulose
Tagatose
Fructose
Dextrose
Sorbitol
Mannitol
Xylitol
disaccharides
disaccharides
disaccharides
disaccharides
monosaccharide
monosaccharide
monosaccharide
monosaccharide alcohol
monosaccharide alcohol
monosaccharide alcohol
No
No
No
Yes
Yes
No
No
Yes
Yes
Yes
No
No
No
Yes
Yes
Yes
No
Yes
Yes
Yes
Erythritol
monosaccharide alcohol
Yes
Yes
Maltitol
Lactitol
Isomalt
Polydextrose
Inulin
disaccharide alcohol
disaccharide alcohol
disaccharide alcohol
polysaccharide
polysaccharide
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Comments
A strong cooling
sensation
A strong cooling
sensation
Often classified
as dietary fibre
as ‘low sugar’ and ‘reduced sugar’. As an example the various descriptions
permitted by European Regulation (EC) No 1924/2006 of the European Parliament and of the Council of 20 December 2006 on nutrition and health claims made
on foods are shown in Table 6.2.
There are informative chapters on sugars in both Minifie (1989) and Beckett
(2009).
6.2.4 Sugar replacers
Sugar replacers currently fall into two general categories, soluble fibres and
polyols. There are now available a variety of polyols, all with a calorific value of
2.4 kcal g–1 (European legislation). Examples of monosaccharide polyols are
sorbitol, mannitol, xylitol and erythritol. Maltitol, lactitol and isomalt are disaccharide polyols. Some, such as maltitol and sorbitol, are available in liquid form. Some
of their properties are shown in Table 6.3. Not all the sugar replacers listed are
permitted throughout the world for all applications. By law manufacturers have to
label products containing sorbitol and other polyols with the statement ‘Excessive
consumption may produce laxative effects’.
The sweetening power of these sugar replacers has been compared with sucrose
in an aqueous phase but this comparison can be misleading for fat-based fillings.
When they are used in fat-based fillings, especially when used in a combination
with other polyols, it is important to make up the filling to assess its complete
sensory properties. Non-nutritive sweeteners such as saccaharin, cyclamates,
acesulfame K, sucralose and aspartame are often used with the sugar replacers to
Fat-based centres and fillings
109
correct the lower sweetening effects often associated with many of the polyols. The
combination of lactitol, polydextrose and aspartame has been shown to give a good
sensory effect. A comprehensive review of bulk and intense sweeteners is given in
Wilson (2007).
6.2.5 Chocolate, cocoa liquor and cocoa powder
Chocolate is still a very popular flavour and most fat-based filling products are
enrobed or moulded in chocolate. The chocolate flavour can be incorporated into
the filling as chocolate, cocoa liquor or cocoa powder. All of these components
contain various amounts of cocoa butter, ranging from more than 50% in cocoa
liquor to 11% in cocoa powder. This cocoa butter influences the sensory and
physical properties of the filling. If necessary cocoa powders are available with
low cocoa butter contents, (less than 1% cocoa butter). For high premium fat-based
fillings, the flavour of the cocoa will be particularly important and so control of the
cocoa source and processing is essential. Cocoa and cocoa products are considered
in Chapter 2 and also in Beckett (2009). Milk crumb can be used as both a source
of cocoa and milk for those markets which appreciate milk crumb’s distinctive
flavour profile. Milk crumb was discussed in Chapters 2 and 3.
6.2.6 Milk powders and milk powder replacers
Most fat-based fillings contain some milk component, often a milk powder, in
order to affect the flavour and texture positively. A simple fat and sugar mix is not
generally considered to be acceptable. Milk is a complex natural product. The fat
consists of a wide variety of fatty acids (Table 6.4). Milk protein can be classified
Table 6.4
2007)
Fatty acid
C4:0
C6:0
C8:0
C10:0
C12:0
C14:0
C14:1
C16:0
C16:1
C17:0
C18:0
C18:1
C18:2
C18:3
C20:1
Average fatty acid composition of milk fat (AAK,
% by weight
3.5
2.0
1.0
2.5
3.0
11.0
1.0
27.0
2.0
0.5
12.0
28.5
3.0
0.5
0.5
110
Enrobed and filled chocolate, confectionery and bakery products
Table 6.5
Data for some typical commercially available milk powders
Whole milk Skimmed milk Buttermilk
Cream
Demineralised
powder (%)
powder (%)
powder (%) powder (%) whey powder (%)
Fat
Moisture
Minerals
Protein
Lactose
27.0
3.0
5.8
26.5
38.0
1.0
3.5
8.0
37.0
51.0
10.0
3.5
7.4
34.0
47.0
36.0
2.3
6.0
22.5
32.5
1.0
2.5
3.5
14.5
78.0
into casein and whey which can be further subdivided into specific proteins. Milk
sugar or lactose is a disaccharide with reducing properties. The dairy industry is
now able to separate milk into many components and modify them to meet specific
requirements and thereby reduce variability.
The properties of the milk powders most likely to be used in fat-based fillings
are shown in Table 6.5. Skimmed milk powders are available that have had a
variety of heat treatments before spray drying. This is expressed as the whey
protein nitrogen index. It is not thought that the different heat treatments will have
any effect upon the physical properties of the filling other than flavour. Whey
powders are generally used instead of skimmed milk powder to reduce ingredient
costs. Care must be taken to ensure that the type used does not adversely affect the
sensory attributes of the filling. For this reason, demineralised whey powders are
generally used.
The total milk fat, available milk fat and type of milk powder affects the flavour
and physical properties of the filling. A mix of skimmed milk powder and milk fat
can have the same milk fat content as whole milk powder but the mix will have
more free fat than the whole milk powder. This free fat will give a less viscous
filling and increase the rate of fat migration.
6.2.7 Nuts
Nuts can offer many advantages to confectionery, such as flavour, texture and
nutritional attributes, since they contain essential fatty acids and trace elements.
The type of nut needed will depend mainly upon the flavour required. Almonds,
brazils, hazelnuts and peanuts are particularly popular but many others such as
walnuts, cashews, pecans, macadamias and pistachios are available. All nuts
contain about 50–65% oil, all with good nutritional properties (Table 6.6). Nuts go
mouldy if they are not stored correctly, producing mycotoxins and giving rise to
very distinctive unpleasant flavours.
If nut paste is used then the nut oil is more available to contribute to the
properties of the filling than if whole nuts are used. Nut oils reduce the hardness of
the filling fat significantly (Fig. 6.4) and increase the speed of fat migration from
the filling into the outer component which is, more often than not, chocolate (see
Section 6.5.2). Nut oils have poor oxidative stabilities so their use will adversely
affect the shelf life of the product. The many aspects of the use of nuts in
confectionery are discussed by Stuart (2007).
Fat-based centres and fillings
Table 6.6
111
Typical fatty acid contents of nut oils
Almonds
Brazils
Cashews
Hazelnuts
Macadamia
Peanuts
Pecans
Pistachio
Walnuts
Saturated
(g/100 g)
Mono-unsaturated
(g/100 g)
Polyunsaturated
(g/100 g)
8
24
20
8
12
20
8
14
9
65
32
61
75
82
44
67
50
17
23
41
18
13
8
31
23
32
70
90
80
Solid fat content (%)
70
60
50
40
30
20
10
0
10
20
30
35
40
Temperature (°C)
Fig. 6.4
Effect of nut oil on the solid fat content of a filling fat (, filling fat; ü, 50/50
filling fat/nut oil).
6.2.8 Colours
Since fat-based fillings are generally covered with another component, the colour
of the filling is not as important as for other confectionery products. Many
consumers are now concerned about the safety of artificial colours so there is a
move towards using natural alternatives. A Southampton study, published in 2007,
showed that six artificial colours (Quinoline yellow (E104), Sunset yellow (E110),
112
Enrobed and filled chocolate, confectionery and bakery products
Tartrazine (E102), Carmoisine (E122), Ponceau 4R (E124), Allura red (E129))
when eaten with the preservative sodium benzoate (E 211) could be linked to an
adverse effect on children’s behaviour (McCann et al., 2007).
Replacing artificial colours with more acceptable alternatives is not generally
simple; a thorough understanding of the process is required. Emerton (2008)
reviews synthetic, nature-identical and natural colours.
6.2.9 Flavours
Spices in the form of oils and extracts are becoming increasingly popular in a
variety of confectionery products and fat-based fillings are an ideal medium. Many
spices have a significant effect, even at concentrations as low as 1%, upon the
sensory properties of the filling such as fragrance and taste and many positively
affect our metabolism and digestion. Examples include chilli, ginger, coriander,
cinnamon, nutmeg and pepper. These often have the added advantage of introducing antioxidants into the product (see Section 6.5).
Vanilla extract is a spice that has been traditionally used in fat-based fillings.
Vanillin, one of the numerous compounds (more than 100) of vanilla extract can be
made synthetically from eugenol and ligninsulfon acid. Vanillin and ethyl vanillin
are often used in fillings at concentrations up to 0.05%.
Essential oils are complex mixtures whose sensory properties depend upon
their origin. Examples include peppermint, spearmint and orange oils. Their
inclusion in fat-based fillings can be both positive and significant.
6.2.10 Emulsifiers
Lecithin is the most frequently used emulsifier in fat-based fillings, giving the
filling an acceptable viscosity with less fat. Lecithin can be sourced from soya, rape
and sunflower to meet specific allergy requirements. Fillings based upon complex
emulsions are being used to meet some of the nutritional objectives and these
products need specific emulsifiers. This development, however, is outside the
scope of this chapter.
6.3
Recipes
A cool-melting effect is often required, a sensation attributed to a rapid loss of
heat in the mouth owing to the latent heat requirements of the ingredients. This
effect can be achieved by using a high fat content and a careful choice of
ingredients. The fat content should be as high as possible, typically 40–50%.
The fats used should be fully molten at 28 °C; the harder the fat at 20 °C, the
greater the cooling effect. Thus some unhydrogenated polymorphic fats and
lauric fats, particularly coconut-based fats are ideally suited for this purpose. As
previously mentioned, sugar alcohols such as xylitol and erythritol can be used
to enhance this sensation.
Fat-based centres and fillings
Table 6.7
113
Recipes for a low and a high content of hazelnut truffle
Low hazelnut (%)
Milk chocolate
Vegetable fat
Hazelnut paste
Full cream milk powder
Sugar
Total
Total fat content
Fat composition
Vegetable fat
Hazelnut oil
Cocoa butter
Milk fat
Total
High hazelnut (%)
42.0
26.0
6.0
10.0
16.0
100.0
46.5
42.0
26.0
16.0
–
16.0
100.0
50.5
55.9
8.5
25.3
10.3
100.0
51.5
20.9
23.3
4.3
100.0
6.3.1 Truffles
A fat-based truffle is a mix of chocolate, milk or dark, with milk fat and or
vegetable fat. The recipes for two truffles, one with a low and one with a high
content of hazelnut paste are given in Table 6.7. Polymorphic filling fats give a
very pleasant product when used in these recipes. A harder fat would be more
suitable with the higher hazelnut paste content.
6.3.2 Nougats
Nougats consist of nuts, nut pieces or nut pastes. There are examples of four
different nougat recipes in Table 6.8 with various hazelnut contents and total fat
Table 6.8
Recipes for some simple nougats
Low hazelnut High hazelnut Low hazelnut High hazelnut
(low fat) (%) (low fat) (%) (high fat) (%) (high fat) (%)
Cocoa powder ( 10–12% )
Vegetable fat
Hazelnut paste
Skimmed milk powder
Full cream milk powder
Sugar
Total
Lecithin
Vanillin
Total fat content
Fat composition
Vegetable fat
Hazelnut oil
Cocoa butter
Milk fat
Total
8.0
26.0
12.0
3.0
8.0
43.0
100.0
0.4
0.05
36.9
4.0
20.0
22.0
–
10.0
44.0
100.0
0.4
0.05
37.5
8.0
32.0
12.0
3.0
8.0
37.0
100.0
0.4
0.05
42.9
4.0
26.0
22.0
–
10.0
38.0
100.0
0.4
0.05
43.5
70.5
21.5
2.4
5.6
100.0
53.2
38.7
1.2
6.9
100.0
74.6
18.5
2.1
4.8
100.0
59.6
33.4
1.0
6.0
100.0
114
Enrobed and filled chocolate, confectionery and bakery products
contents. Detailed recipes for a hazelnut content praline and for a low saturates
confection are included in Tables 6.9 and 6.10, respectively.
Table 6.9
Detailed recipe for a hazelnut praline
(%)
Cocoa powder
Vegetable fat
Hazelnut paste
Skimmed milk powder
Full cream milk powder
Sugar
Total
Lecithin
Vanillin
Total fat content
Fat composition
Vegetable fat
Hazelnut oil
Cocoa butter
Milk fat
Total
8.0
32.0
12.0
3.0
8.0
37.0
100.0
0.3
0.02
42.0
75.0
18.0
2.0
5.0
100.0
The vegetable fat suggested is a polymorphic filling fat with 54% saturates, 38%
mono-unsaturates, 8% polyunsaturates. N20 °C = 55%, N30 °C = 2%, as measured
using IUPAC method 2.150(b) with the modification that the fat is stabilised for 24
hours at 20 °C.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Clean and preheat the mould to 28 °C.
Make the chocolate shells, using tempered milk chocolate.
It is important that the vegetable fat is completely melted at 60 °C before use.
Mix the ingredients (apart from lecithin) at a temperature between 35 and
40 °C.
Refine and conche in the normal way at 60 °C.
Reduce the temperature to 50 °C and add the lecithin and mix well.
It is necessary to temper the filling before use, cooling down the filling to
approximately 21.5–22 °C, whereupon it is heated to approximately 25 °C.
Fill pre-made empty chocolate shells almost to the rim and crystallise at 12 °C
for 20 minutes.
After the crystallisation, back-off the shells with tempered milk chocolate.
De-mould and decorate with plain tempered chocolate.
The pralines benefit from being stored at a temperature of 18 °C for at least 48
hours in order to get a product with good stability and eating qualities.
In order to keep the best properties in the pralines during its whole shelf life,
store them in a dry and cool place at 15–18 °C, <65% humidity and in the
dark.
Fat-based centres and fillings
115
Table 6.10 Detailed recipe for a low saturates confection
Dextrose (%)
Vegetable fat (%)
Pistachio paste (%)
Skimmed milk powder (%)
Full cream milk powder (%)
Sugar (%)
Total (%)
Lecithin (%)
Vanillin (%)
Total fat content (%)
Fat composition
Vegetable fat (%)
Pistachio oil (%)
Milk fat (%)
Total (%)
5.0
35.0
10.0
5.0
10.0
35.0
100.0
0.3
0.02
42.0
82.0
12.0
6.0
100.0
The vegetable fat suggested is a low saturates filling fat with 41% saturates, 26%
mono-unsaturates, 33% polyunsaturates. N20 °C = 28%, N30 °C = 10%, as measured
using IUPAC method 2.150(a), the fat being held for 60 minutes at 0 °C.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Clean and preheat the mould to 28 °C.
Pipe an inside line in the mould forms using tempered plain chocolate.
Make the chocolate shells using tempered milk chocolate.
It is important that the low saturates vegetable fat is completely melted at 60 °C
before use.
Mix the ingredients (apart from the lecithin) at a temperature between 35–
40 °C,
Refine and conche in the normal way at 60 °C.
Reduce the temperature to 50 °C and add the lecithin and mix well.
It is not necessary to temper the filling before use.
Cool down the filling to approximately 32–33 °C.
Fill pre-made empty chocolate shells almost to the rim and crystallise at 12 °C
for 25 minutes.
After the crystallisation, back-off the shells with tempered milk chocolate.
The pralines benefit from being stabilised at approximately 18 °C for at least
48 hours in order to get a product with good stability and eating qualities.
6.3.3 Spreads
Spreads generally contain chocolate and/or nuts to give flavour and richness.
Traditionally, partially hydrogenated oils with a high trans content were used to
give good oxidative stability and the required consistency. Low trans or nonhydrogenated alternatives are frequently being used together with a structuring fat
to prevent oil separation, as mentioned in Section 6.5.3. Table 6.11 gives some
typical recipes for chocolate and nut spreads.
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Enrobed and filled chocolate, confectionery and bakery products
Table 6.11 Recipes for some simple spreads
Cocoa powder (10–12%)
Vegetable fat
Hazelnut paste
Skimmed milk powder
Full cream milk powder
Sugar
Total
Lecithin
Vanillin
Fat composition
Vegetable fat
Hazelnut oil
Cocoa butter
Milk fat
Total
6.4
Hazelnut (%)
Dark (%)
Milk (%)
White (%)
7.5
22.0
13.0
9.0
–
48.5
100.0
0.4
0.05
10.0
30.0
–
10.0
–
50.0
100.0
0.4
0.05
5.0
28.0
–
7.0
10.0
50.0
100.0
0.4
0.05
–
29.0
–
11.0
15.0
45.0
100.0
0.4
0.05
70.0
27.4
2.6
–
100.0
96.5
–
3.5
–
100.0
89.9
–
1.8
8.3
100.0
88.1
–
–
11.9
100.0
Manufacturing processes
6.4.1 Reduction of particle size
The optimum particle size for a filling is dictated by its application. If the filling is
a high indulgent truffle enrobed in a highly refined chocolate then the particle size
should be similar to that of the chocolate, typically 15–25 µm (measured by a
micrometer). If the filling is to be in a product containing wafer, biscuit or nut
pieces then a coarser filling will be more appropriate, typically 100–120 µm.
The ingredients may be reduced to the correct particle size and then mixed or the
ingredients are mixed and then the filling is ground to the required particle size.
The latter is the more common method and this procedure will usually give a better
flavour. Rework is often incorporated back into a filling and often this might
contain wafers or biscuits which will usually need to be broken down.
There are many systems available for reducing particle size. The optimum
equipment will depend upon the raw materials, the required particle size and
distribution, as well as energy and maintenance requirements and ease of cleaning.
Since the particle size of the filling affects the overall perception of the final
product, it is important that this attribute is optimised.
6.4.2 Aeration
The aeration of fillings helps increase the size of the product and can therefore
appear to provide lower calorie alternatives. The amount of aeration has a
significant effect upon the sensory attributes. If a high fat filling is aerated to a low
density such as 0.25 g cm–3 it can appear quite dry and crumbly. The increased
Fat-based centres and fillings
117
1000
900
800
Density (g/litre)
700
600
500
400
300
200
100
0
30
32.5
35
37.5
40
Fat content ( % )
Fig. 6.5 Influence of fat content on the density after aeration. Density determined on a
fat/sugar/skimmed milk powder filling made at 40 °C after whipping in an open bowl
held at 15 °C for 6 minutes (, low trans aerating fat; ü, high trans non-lauric fat).
surface area can also adversely affect the shelf life of the product. So it is important
to optimise the level of aeration.
Aeration can be achieved simply by whipping, provided a suitable vegetable fat
is used. A density of 0.6 g cm–3 can be achieved in this manner. Figure 6.5 shows
the effect of fat content. A less dense filling can be achieved as the total fat content
increases. It can be seen from the graph that an aerating fat gives a significantly less
dense filling than a standard fat at the same fat content of 40%.
Aeration can also be achieved by vacuum but the more common procedure is by
introducing a gas under pressure. The gas that is used affects both the size and
shape of the aeration as well as the shelf life and sometimes the flavour. Carbon
dioxide and nitrous oxide produce larger irregular shaped bubbles whilst nitrogen
and argon give smaller spherical bubbles. Whichever type of process is used, fat
crystals have to be present to retain the gas. Thus the crystallisation process has to
start and the correct level of cooling is essential to remove the heat of solidification
to ensure the viscosity of the filling is optimised for gas retention.
6.4.3 Precrystallisation
As mentioned earlier, polymorphic filling fats need to be precrystallised to ensure
that they solidify quickly in the most stable form. This ensures that the filling does
118
Enrobed and filled chocolate, confectionery and bakery products
not undergo transformation during storage resulting in the formation of larger fat
crystals which often produce a gritty texture. Precrystallisation also helps to reduce
fat migration and fat bloom. Precrystallisation is the same as tempering, except that
the final warming-up stage is omitted. Tempering is discussed further in Chapters
15 and 16.
6.4.4 Seed precrystallisation
A recent new development enables polymorphic fats to be crystallised into a stable
form by introducing seeding material in the βVI form. Seed precrystallisation has
been used mainly for chocolate but it also has advantages for fillings. A product
with a denser texture and greater fat bloom stability is achieved for nut oil, cocoa
butter fillings giving rise to a smoother product with an improved shelf life. Further
details are given in Zeng (2002).
6.4.5 Shell moulding
Shell moulding is the traditional method for producing a chocolate shell in which
the mould is completely filled with chocolate and inverted to remove excess
chocolate. There are basically three alternative procedures.
Wet shell moulding where the centre is deposited before the shell has been
subjected to any cooling. This is suitable for centres which have irregular shapes.
Cool shell moulding involves cooling the shell after re-inverting but before centre
deposition whilst with inverted cool shell moulding the shell is cooled before reinverting. This ensures a more even thickness of chocolate. The most appropriate
method depends upon the shape and nature of the components in the filling and in
the chocolate. The possible process variations enable a wide range of products to
be made. One disadvantage of shell moulding is the energy that is wasted in
reprocessing the recovered tempered chocolate, a disadvantage that is overcome in
one shot depositing and cold pressing.
6.4.6 One-shot depositors
One-shot depositing is not as versatile as shell moulding but is generally cheaper
to install and occupies less space. It is ideal for producing deep symmetrical
products. The principle is that the chocolate and filling are in two adjacent
hoppers. The chocolate is deposited into the mould, quickly followed by the
filling which stops depositing just before the completion of chocolate. Basically
the filling is enveloped into the chocolate ensuring a complete unit with no
interfaces, reducing the risk of the filling leaking out. The principle is most
suitable for products where the filling and chocolate have similar attributes. The
viscosities of the filling and chocolate are critical, the ideal situation is for the
filling and chocolate to have the same viscosity and temperature. The rheological
issues are discussed in Chapter 13. The depositing temperature is also important.
If it is too high, the temper of the chocolate is adversely affected, if it is too low,
Fat-based centres and fillings
119
the viscosity of the filling can become too high. The type and content of fat used
in the filling is therefore critical.
Triple shot depositors are now available. Three components can be simultaneously deposited to produce a single product. This gives the opportunity to create a
barrier layer between the chocolate and the filling enabling moisture migration,
alcohol migration or fat bloom to be significantly reduced.
6.4.7 Cold pressing
The principle in cold pressing is for a very cold plunger (–5 °C to –20 °C) to be
inserted into a mould containing a precise quantity of tempered chocolate so that
the chocolate fills the gap between the mould and the plunger forming a chocolate
shell with precise dimensions. The entire equipment has to be within a dehumidifying system to prevent ice forming on the plunger. The uniform shell is now ready
for deposition of the filling. The advantage of this method is that very uniform
shells are produced to a predetermined thickness which helps to control fat
migration and the leakage of the filling. The production of chocolate shells and
deposition of fillings is discussed further in Chapters 19 and 20, respectively.
6.5
Stability and shelf-life issues
Chocolate covered fat-based fillings generally undergo changes during storage, so
that having an accelerated keeping test is useful during the development stages.
Shelf life prediction is discussed in Chapter 12. Subramaniam (2005) suggests that
storage at 24 °C and 70% relative humidity gives information on the likelihood of
fat bloom and fat migration for hazelnut pralines covered in milk chocolate. The
stability and the shelf life of confectionery are discussed by Kilcast and
Subramaniam (2000).
Reducing the trans content and saturated fatty acid content of filling fats and
increasing the surface area by aeration all potentially reduce the oxidative stability
and hence the shelf life of the product. The appropriate stability for the product can
be achieved by ensuring the fat is kept under optimum conditions, (temperature,
time, removal of trace metals), as well as by the use of antioxidants either from the
other ingredients, such as cocoa powder, or by addition to the filling fat. The
correct type of packaging for the product makes a significant positive contribution
to the product’s shelf life.
6.5.1 Fat migration
In fat-based fillings covered in milk or plain chocolate, fat migration will occur; it
is simply a question of how quickly and what the consequences will be. Usually the
filling will be softer than the outer chocolate so fat migration will cause softening
of the chocolate and hardening of the filling. The incorporation of this new fat into
the chocolate increases the chances of the development of fat bloom.
120
Enrobed and filled chocolate, confectionery and bakery products
In general, the higher the liquid oil content of the filling, the faster the migration.
The types of fat in the filling are therefore critical; free nut oils will migrate quickly,
a palm mid fraction or cocoa butter will be slower. Since the liquid oil content
increases with temperature, keeping the temperature as low as possible during
storage and transportation will be beneficial. The migration effect can be reduced
by increasing the thickness of chocolate and reducing the particle size of the filling.
Fat migration can also be reduced by adding fats which can create some structure.
These fats crystallise at high temperatures producing small crystals which form a
matrix for the other filling fats. Fat migration is discussed further in Chapter 10 and
in Timms (2003, chapter 7).
6.5.1 Fat bloom
Fat bloom on chocolate covered fat-based fillings can also be caused by fat
migration. Smith et al. (2007) discuss the effect of nut oils on the transformation
of cocoa butter in a model system suggesting that concentrations as low as 1% nut
oil can cause fat bloom. Optimisation of the processing to ensure the formation of
the most stable crystal structures in both the filling and chocolate is essential.
The use of certain fats can help. These generally fall into two categories. The
first are those containing high concentrations of StOSt, often referred to as cocoa
butter improvers, or BOB fats (St = stearic acid, O = oleic acid, B = behenic acid).
The second type are bloom-inhibiting fats which are based upon triglycerides
containing both long and medium chain saturated fatty acids such as lauric,
palmitic and stearic fatty acids.
6.5.2 Oil separation
This is an extreme case of fat migration and is significant in fat-based spreads such
as those containing cocoa and/or nut components. Generally these spreads are
intended to be soft, spreadable over a wide range of temperatures from room to
refrigerator temperatures and have good shelf-life properties. The oil should not
separate out to form a distinct layer above the spread. This can be prevented by
adding structural fats as mentioned in Section 6.5.1 above.
6.5.3 Rework incorporation
Even well-managed processes generate rework which is often produced at different stages of the process. The ideal situation is to incorporate it back into its own
product rather than into another. The storage of the rework should be carefully
controlled; it should be considered as an ingredient. The variation in quality of the
rework will probably be greater than for the other ingredients and this should be
taken into account. It is particularly important to be aware of its fat composition to
ensure that incorporation back into the product does not cause unexpected eutectics
and/or a significant reduction in shelf life. This is particularly important for rework
generated during a product changeover or where nut oils or lauric fats are present.
Fat-based centres and fillings
6.6
121
Future trends
Satiety is being studied extensively with the aim of controlling our appetite by
adding components such as galactolipids which are naturally found in oats and
green leaves. Other products are being marketed such as those obtained from pine
nut oil. Fat-based fillings may be the ideal way to introduce many of these
products.
Fats with lower saturates, such as those based on diglycerides (DAG-oils) are
already available but this development is still in its infancy. They are already used
in cooking oils and are now being examined for use in confectionery.
It is an enormous challenge to produce hard unhydrogenated confectionery fats
that are lower in saturates than those that are used now. New crops such as
Allanblackia, an upper Guinean rainforest species with a high stearic acid content
(above 50%) are being grown in Ghana and will give significant opportunities.
Other new crops or new varieties of existing crops will become commercially
available.
Proposed labelling legislation might change the emphasis from hydrogenation
to trans content. Fully hydrogenating rapeseed oil and soyabean oil will give
access to stearic acid to help produce lower saturated fats with less than 1% trans.
Fat-based fillings could also be suitable media for incorporating omega-3 long
chain polyunsaturated fatty acids fats. The challenge would be to create an
acceptable stability. Sugar-free confectionery also continues to gain in popularity.
6.7
Sources of further information and advice
Information is available in several textbooks mentioned in the list of references
(Shahidi, 2005; Talbot, 2006). In addition, Whitefield (2005) gives a comprehensive account of shell moulding, one shot depositing and cold pressing.
The suppliers of ingredients, confectionery equipment and packaging often
have informative web sites. These can be found in the Buyer’s Guides which are
produced annually by such publications as Confectionery Production.
6.8
References
(2007). Handbook – Vegetable Oils and Fats, 2nd edition, Section 8.4, AarhusKarlshamn, Sweden.
ARISHIMA T AND MCBRAYER T (2002). ‘Applications of speciality fats and oils’, The
Manufacturing Confectioner, 82(6), 65–76.
BECKETT ST (2009). Industrial Chocolate, Manufacture and Use, 4th edition, Blackwell
Science, Oxford.
EMERTON V (2008). Food Colours, Ingredients Handbook, 2nd edition, Leatherhead Food
International, Leatherhead.
GUNSTONE FD (2006). Modifying Lipids for Use in Food, Woodhead Publishing, Cambridge,
Chapter 18.
KILCAST D AND SUBRAMANIAM P (2000). ‘The stability and shelf-life of food’ CRC,
Woodhead Publishing Limited, Cambridge.
AAK
122
Enrobed and filled chocolate, confectionery and bakery products
MCCANN D, BARRETT A, COOPER A, CRUMPLER D, DALEN L, GRIMSHAW K, KITCHIN E, LOK
K, PORTEUS L, PRINCE E, SONUGA-BARKE E, O WARNER J AND STEVENSON J (2007). ‘Food
additives and hyperactive behaviour in 3-year old and 8/9-year-old children in the
community: a randomised, double-blinded, placebo-controlled trial’, The Lancet,
370(9598), 1560–7.
MINIFIE BW (1989). Chocolate, Cocoa and Confectionery, 3rd edition, Van Nostrand
Reinhold, New York.
SHAHIDI F (2005). Bailey’s Industrial Oil and Fat Products, 6th edition, John Wiley & Sons,
Hoboken, New Jersey.
SMITH KW, CAIN FW AND TALBOT G (2007), ‘Effect of nut oil migration on polymorphic
transformation in a model system’, Food Chemistry, 102, 656–63.
STUART DA (2007). ‘Nuts – from rags to riches in a decade’. The Manufacturing Confectioner, 87(5), 35–44.
SUBRAMANIAM P (2005). Accelerated Shelf-life Testing Conditions for Milk Chocolatecoated Hazelnut Pralines, Research Report 882. Leatherhead Food International,
Leatherhead.
TALBOT G (2006). Application of Fats in Confectionery, Kennedy’s Publications, London,
139–51.
TIMMS RE (2003). Confectionery Fats Handbook, Volume 14, The Oily Press Lipid Library,
Bridgwater.
WHITEFIELD R (2005). Making Chocolates in the Factory, Kennedy’s Publications, London.
WILSON R (2007) Ingredients Handbook, Sweeteners, 3rd edition, Leatherhead Food
International, Leatherhead.
ZENG Y, BRAUN P AND WINDHAB EJ (2002). ‘Tempering’, The Manufacturing Confectioner,
82(4), 71–80.
7
Caramels, fondants and jellies as centres
and fillings
W. P. (Bill) Edwards, Bardfield Consultants, UK
Abstract: The chapter covers the sugar confectionery products that are commonly used
as centres or fillings in chocolate confectionery, viz. fondant, jellies, caramels and
toffees. The need for the product to be stable and the means to achieve this are covered.
The areas of water activity, fat stability and crystallisation are covered. The ingredients
commonly used in these products such as sugar, glucose syrup, invert sugar, molasses,
golden syrup, sweetened condensed milk, milk powder, whey, whey syrup, butter, other
fats, emulsifiers, flavours, colours as well as gums and gelling agents are covered. The
means of processing and shaping the centres and fillings is covered. Other issues covered
are organic and sugar free products
Key words: caramels, fondants, gelling, jellies, toffees, Turkish Delight.
7.1
Introduction
Caramels, fondants and jellies are popular as centres and fillings in chocolate
products. A successful product has to deliver the taste and texture that the
consumer wants. The confectioner must decide whether the product has a strong
flavour from the chocolate, possibly overpowering the centre, or a strong centre
flavour and a weaker flavour from the coating. There are examples of both classes
of product. If there is a trend in these things the current trend is, if anything, towards
a stronger chocolate flavour. Of course, the sort of flavour balance that is
successful in a chocolate assortment might not be suitable for a count line.
The centre or filling has to be sufficiently stable not to deteriorate during the
shelf life of the product. The shelf life of a luxury chocolate assortment needs to be
124
Enrobed and filled chocolate, confectionery and bakery products
longer than that required for a rapid turn over count line. The stability of the centre
or filling has to include:
• stability to degradation from yeasts or bacteria,
• lipolysis, either enzymatic or oxidative,
• crystallisation where it is not desirable or redissolving of crystals where it is
(gelled centres should remain gelled and not undergo syneresis),
• a flavour level that remains sufficient at least until the flavour of the chocolate
fades.
In addition to the above, the issue of the available plant has to be considered. In an
ideal world a confectioner would be able to specify the equipment to be used in
making a given product. In practice, products often have to be made on the available
plant. In the case of a new product, the financial risks are great enough without adding
the risk of installing new plant. Another area of considerable importance is the
balance between cost and quality. While sugar-based fillings and centres are usually
cheaper than chocolate the proportion of the centre or filling is often higher.
While these products are normally made from sugar, glucose syrup, invert sugar
and similar materials, it is possible to make sugar free versions. Such products are
aimed at the healthy food market and possibly the diabetic market. British medical
opinion is currently moving against special products for diabetics. It remains to be
seen what the future holds for these products.
7.2
Stability
A centre or filling needs to be stable but the question is how stable? Obviously
there is no benefit in the inside of the product having a longer shelf life than the
chocolate. While chocolate remains fit to eat for a long time, a best before date of
nine to twelve months is usually assumed. This gives the maximum length of time
that a filling or centre needs to last as 12 months. Shorter times are acceptable in
high turn over count lines and high value artisanal products.
7.2.1 Biological stability
Biological stability is stability against degradation by live organisms such as
yeasts, other moulds or bacteria. In food products this can be obtained either by
ensuring the product is sterile or by arranging that the water activity is so low that
the organism in question can not multiply (Edwards, 2000).
The water activity is a useful thermodynamic concept which reflects the fact
that the water in different systems can be more free or less free to support chemical
or biological activity irrespective of the concentration. This effect occurs because
the water interacts more or less strongly with the other components of the system.
At one time it was more common to consider this issue in terms of the equilibrium
relative humidity (ERH). The ERH, of course, is determined by the water activity
but was easier to measure than the water activity which could not be measured
Caramels, fondants and jellies as centres and fillings
125
directly. Now instruments are available which measure the water activity directly.
The ERH remains important providing information on the relative humidity at
which the product can safely be stored. The sterile product route is normally used
in tinned foods. It is not used in confectionery because it is easier to make
confectionery with a low water activity.
7.2.2 Fat stability
Fats undergo two different sorts of deterioration which are characterised as
oxidative and lipolytic rancidity. In lipolytic rancidity the triacylglycerols, also
known as triglycerides, are broken up into free fatty acids, partial glycerides and
glycerol. While this reaction can be obtained by chemical means, in confectionery
products the problem is usually caused by the presence of lipolytic enzymes. These
enzymes are normally present as a residue from the activities of moulds or bacteria
on the raw material at an earlier stage of the process. The problem is that although
the moulds or bacteria have themselves been inactivated by heat treatment, the
enzymes remain active. One way of reducing this problem is to specify ingredients
carefully, for example specifying highly heat-treated milk powder.
The problems caused by lipolytic activity vary depending on the fat present.
Some free fatty acids are more acceptable in products that others. Butyric acid,
which is found in milk fat, is a case in point. At low levels, free butyric acid gives
a pleasant buttery flavour which is usually preferred over products with a lower
level of free butyric acid. As the level rises, the perceived taste shifts to ‘cow like’,
‘cheesy’ followed by ‘Parmesan cheese’. Cheese flavours are not normally liked in
confectionery products. It should be stressed that the response of individuals to
flavour varies markedly. Levels of free butyric acid that are acceptable to some are
unacceptable to others.
Another fatty acid that causes problems is lauric acid. Lauric acid is found in
coconut and in toffee fats based on coconut or palm kernel oils. If a lipase acts on
a lauric-containing triacylglycerol then free lauric acid will appear giving the
product a soapy taste. Once again the sensitivity to this ingredient varies considerably between individuals. Special caution needs to be exercised over this point
when considering products containing coconut. Some manufacturers restrict their
coconut centres to plain chocolate since plain chocolate does not contain lipase.
7.2.3 Crystallisation
Sugar confectionery can be neatly divided into those products that are intended to
crystallise and those that are not. Figure 7.1 shows the different sugar to glucose
syrup ratios for a number of different products. In products that are intended to
crystallise there is a high ratio of sugar to glucose while in those products where
crystallisation is undesirable there is a much lower ratio. Where crystallisation has
occured, the solid and the liquid phase will have different compositions. The
factors that control the tendency to crystallise are the sucrose to glucose syrup
solids ratio, the total solids and the temperature.
126
Enrobed and filled chocolate, confectionery and bakery products
Boilings
Ungrained
Edinburgh rock (graining)
Nougat
95
Toffees
Fudge
Gums and
pastilles
Fondant
pastes
Soluble solids (%)
90
Grained
Jellies and mallows
80
Saturated solution
Syrup solids too low
70
1S:3G 1S:2G 1S:1G 2S:1G 3S:1G 4S:1G 5S:1G
Ratio of sugar to glucose syrup solids
Fig. 7.1
Different sugar to glucose syrup ratios for a number of different products.
The horizontal line between 70 and 80% soluble solids represents the stability,
that is, the solids should be above this line to avoid biodeterioration. Products that
are intended not to grain, for example high boilings are made with sucrose to
glucose ratios at the left of the diagram. Products like fudge and fondant paste are
on the right of the diagram. Toffees, gums and pastilles occupy the middle of the
diagram as non-crystallising products. Nougat is an unusual product, as some
varieties do not grain while other varieties do grain. Clearly the non-graining
nougats are to the left of the diagram while the graining varieties are to the right.
7.2.4 Gelling
Gelling agents are normally stable once set. One notable exception is proteinbased gels such as gelatine. If a proteolytic, that is a protein breaking enzyme, is
present then the gel will break up. Fortunately proteases that can work at the water
Caramels, fondants and jellies as centres and fillings
127
activities that are present in these systems do not normally occur in these systems.
The only common food material that contains a protease is raw pineapple which
contains bromelain. If a table jelly is made up with raw pineapple then the
bromelain will destroy the gelatine gel. However, raw pineapple would not be
stable enough to be used in fillings or centres and the water activity is too low for
most enzymes to work. Proteases where they do occur, for example in some whey
products, are undesirable not only because of any action on protein gels but
because the effect of proteolyosis leaves small peptides which can leave unpleasant bitter flavours.
Gelatine gels are thermoreversible, so if the product is heated the gel will melt. In
chocolate-covered gels the heat necessary to melt the gel would melt the chocolate
first. The thermoreversibility of gelatine gels makes it easy to recover rework.
7.3
Ingredients
7.3.1 Sugars
While in common parlance sugar is sucrose, strictly speaking sugars are a class of
chemical compounds. The commonest sugar in food is sucrose. Sucrose has a
number of unusual properties. It is not a reducing sugar, unlike the other sugars
used in confectionery, so it does not undergo the Maillard reaction (Edwards,
2000). The Maillard reaction is the browning reaction between reducing sugars
and proteins. It is responsible for all the browning reactions in foods except those
that occur by enzymic means. Thus the browning of a freshly cut apple is not a
Maillard reaction since it is enzymic in origin. The problem in sugar confectionery
is to ensure that the Maillard reaction occurs, for example in toffees, and to prevent
it where it is not required, for example in fondants.
One important property of sucrose is that it makes a 66% saturated solution at
room temperature. This solution is not sufficiently concentrated to have a low
enough water activity to be stable against moulds and bacteria. The effect of this is
that some other sugar or sugars have to be added to increase the concentration. In
practice this is achieved either by adding glucose syrup or invert sugar. Rarely does
the recipe rely on invert sugar produced in situ by heating sucrose in the presence
of acid. This is a very old fashioned procedure. The balance of sugars in a product
is chosen either to preclude crystallisation or to induce it, depending on the nature
of the product. Other factors are the need to encourage or discourage the Maillard
reaction and, of course, cost.
In the United Kingdom, glucose syrup solids are cheaper than either sugar or
invert sugar. The EU Common Agricultural Policy in Europe has typically
increased the price of sugar above world prices increasing this difference. As
invert sugar is made from sucrose, its price is tied to that of sucrose unless it is
produced from recovered sugar waste. One tonne of such waste costs approximately £400 in sewerage charges, so any invert sugar from this source has a
notional negative cost. As improved methods of recovery which can recover
128
Enrobed and filled chocolate, confectionery and bakery products
sucrose in a reusable form have become available, the production of invert from
this source is declining.
Sucrose
Sucrose is the ordinary white or brown sugar commonly encountered. Both sugar
cane and sugar beet can be used to produce sucrose. The only difference in white
sugar from these two sources is that the minor impurities are slightly different.
While small quantities of raw cane sugar are produced that are less than
completely refined, beet sugar has undesirable tastes. In the past, brown sugars
have been produced by partially refining cane sugar, but in the United Kingdom,
brown sugars are now produced by adding molasses to white sugar. In some cases
white beet sugar has cane molasses added to produce a brown sugar.
In confectionery, small quantities of product are made from raw sugar where a
‘health food’ or ‘all natural’ claim is made. The other area where sugar other than
white is used is in toffees and fudges where special brown sugars have traditionally
been used to give additional colour and flavour.
Invert sugar
Invert sugar is the mixture of fructose and dextrose produced by breaking sucrose
into its two constituent monosaccharides. This process is referred to as inversion
since the effect is to invert the plane of rotation of polarised light. Indeed this
change has been used to follow the progress of the reaction. Inversion can be
achieved by heating a sucrose syrup with either acid or alkali or by using the
enzyme invertase. A small amount of inversion occurs whenever a sucrose syrup
is boiled.
Unlike sucrose, invert sugar is sufficiently soluble that syrups that are stable
against microbial or yeast activity can be made. Invert sugar is only encountered as
a syrup. Invert sugar was the original doctor sugar used to make the water activity of
sugar confectionery sufficiently low to be stable against biological deterioration. Its
other role is that it facilitates the Maillard reaction, which is an advantage in toffees
and similar products. This is because both of its components are reducing sugars.
Glucose syrup has replaced invert sugar in many applications as it is normally
cheaper and is more effective at inhibiting crystallisation. As the price of invert
sugar is linked to that of sucrose, invert has become more expensive as the price of
sugar has risen. There are only two exceptions to this rule, one partial, the other
total. Where invert is produced from recovered sucrose the price of disposing of
the sucrose as waste may be the dominant factor rather than the price of the sucrose
it was made from.The other possibility is where the variety of glucose syrup known
in Europe as isoglucose and in the United States as high fructose corn syrup
(HFCS) (that is 50% fructose) is substituted for invert sugar. As this ingredient is
made from starch, its price is not tied to the price of sugar. Details of this material
are covered under glucose syrup.
Glucose syrup
Glucose syrup is a mixture of saccharides that are produced by hydrolysing starch.
Caramels, fondants and jellies as centres and fillings
129
In the United States, glucose syrup is known as corn syrup. Neither name is entirely
accurate since the major ingredient is normally maltose and the product can be
made from any starch. In Europe it is commercially made from wheat as well as
maize starch.
Molasses
Molasses are the residue left after the crystallisation of sucrose. It is relatively little
used in confectionery apart from in the manufacture of liquorice, which is its
largest use, and in making treacle toffee. In this product the treacle adds colour and
flavour. The definition of treacle in some dictionaries is sufficiently wide to
include golden syrup, however in this work treacle means a black syrup made by
diluting molasses. Golden syrup is a golden coloured syrup produced by partially
inverting a cane sugar syrup, which could be regarded as the equivalent of invert
sugar lightly contaminated with molasses. Golden syrup is occasionally used in
confectionery for flavour and colour
7.3.2
Dairy ingredients
Sweetened condensed milk
Sweetened condensed milk, despite its price and the difficulties in handling,
remains the preferred source of milk solids for toffee manufacture. No other source
of milk solids gives as good a finished product. Depending on the recipe either full
cream or skimmed condensed milk can be used. In some parts of the world
condensed milk is manufactured from milk powder.
Milk powder
Milk powder is the cheapest source of milk solids for manufacturers. Both full
cream and skimmed milk powder are used. Skimmed milk powder has two
advantages in that not only does it allow the use of vegetable fat instead of milk fat
but it also keeps better. A long shelf life is important in places where manufacturing
milk is only available in the summer or where milk is not produced.
Almost all milk powder is now spray dried rather than roller dried. The spray
drying process usually applies less heat than the old roller drying process. Low heat
treatment makes the powder easier to reconstitute and improves the biological
availability of the protein. Unfortunately low heat treatment and bulk cold storage
of liquid milk leads to products containing heat-resistant lipases. Organisms that
can live in milk at low temperature produce these lipases.
Whey
Whey is the liquid by-product of cheese manufacture. The soluble solids of whey
are too low to give a stable product. Whey can be spray dried to produce whey
powder but cannot be concentrated to produce a stable sticky syrup. The composition of whey varies, both because the composition of milk varies, as well as
because of the variations produced by different cheese-making processes.
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Enrobed and filled chocolate, confectionery and bakery products
The majority of the solids in whey consist of lactose, a disaccharide-reducing
sugar. There are a number of problems with lactose. First, its solubility is relatively
low, which restricts its use. Second, products containing high proportions of
lactose tend to have a metallic taste. The level of lactose at which this taste is
perceived varies between individuals. There is also the problem of lactose intolerance. Humans are normally born with the enzyme lactase which splits lactose into
dextrose and galactose. However if people cease to consume dairy products after
weaning, the enzyme will disappear. If they then consume lactose, the lactose will
pass intact into the intestines producing either flatulence or diarrhoea. Lactose
intolerance is not, of course, a problem restricted to whey powder. It is a problem
with any product containing skimmed milk solids. Lactose intolerance is common
among Asians and, indeed, it is possible that the majority of the world’s population
is lactose intolerant.
The other major constituent of whey solids is protein. While these proteins have
useful emulsifying properties, in systems like toffees, they are of high nutritional
value. Whey protein concentrates are produced for use in nutritional supplements
and are often used in high protein bars aimed at body builders and athletes. In these
products the whey concentrate is a high added value ingredient rather than a
substitute for skimmed milk solids.
The high prices for skimmed milk prompted by the EU Common Agricultural
Policy have made whey a more attractive ingredient than it would otherwise have
been. In spite of this, there is interest in using whey in countries outside the EU. The
problems of using the lactose in whey have been approached by enzymically
splitting the lactose to dextrose and galactose. Two different approaches have been
tried, either producing a purified syrup of the sugars or producing a concentrate of
the sugars and the protein.
Whey products can cause problems because whey as produced can contain
cheesy flavours, lipases and proteolytic enzymes. While cheese flavours do not
go with fruit-flavoured products, cheesy flavours can be beneficial in toffees
since under the processing conditions used they can evolve into buttery flavours. Another problem that can be caused by using too much whey protein is
cold flow. If a toffee is formulated with insufficient casein, although the toffee
is physically hard, it can cold flow on storage. Cold flow is a strange phenomenon which occurs when a physically hard cold product, for example a hard
toffee, flows on standing. The flow normally takes place over a number of days.
One effect of replacing skimmed milk solids with whey solids is to reduce the
proportion of casein in the protein part of the product because whey contains no
casein.
Milk powder replacers
Some dairy companies have produced powders that are intended to replace milk
powder in toffee without risking cold flow. These products can be regarded as
being produced by breaking milk into different fractions to add value. The
advantage of these products to the end user is that they produce a cost saving while
still guaranteeing satisfactory performance in the finished product.
Caramels, fondants and jellies as centres and fillings
131
Butter fat
Butter fat was the original fat used in products like toffee and fudge. It is prized for
its flavour and natural origins. In some markets the claim ‘made with pure butter’
is a marketing advantage. As butter fat was the original fat that was used, other
products were developed around its properties. Butter fat normally enters the
product either as full cream milk solids, butter or possibly butter oil. Chemically,
butter fat contains a very wide range of triglycerides and would be chemically
difficult to match.
Fats other than butter fat
As butter fat is normally the most expensive ingredient in a toffee, it has long been
the practice to replace some or all of the butter fat with a vegetable fat, with or
without the addition of a butter flavour. Historically, a product like hydrogenated
palm kernel oil might be used. This has been succeeded by specially produced
toffee fats which are produced by fractionation from vegetable fats. These products are sold on a specification of physical properties and may also include a
specification based on fatty acids which puts maximum levels on, say, lauric acid
and trans fatty acids.
7.3.3 Emulsifiers
Emulsifiers are a class of substances that help to form or stabilise an emulsion.
Some natural products, particularly gums and proteins, act as emulsifiers. Natural
products often escape being defined legally as emulsifiers even though they
undoubtedly are emulsifiers in practice.
Substances capable of acting as an emulsifier tend to have one part of the
molecule which is best suited to oily surroundings, that is it is said to be lipophilic,
while the other end of the molecule is best in an aqueous environment, that is it is
hydrophilic. The two opposite terms, hydrophobic, meaning water hating and
lipophobic, meaning fat hating, are also in use. Emulsifiers are classified by a
system of hydrophile lipophile balance (HLB) numbers which refers to the ratio of
hydrophilic to lipophilic groups present. Molecules with both hydrophilic and
lipophilic groups are referred to as amphiphilic. Emulsifiers, whether natural or
synthetic in origin, tend to be amphiphilic. An amphiphilic molecule is likely to be
in its lowest energy state in the interface between an oil and a water phase.
Real food systems tend to have a complex mixture of ingredients. The sugar
confectionery system that most commonly relies on emulsifiers is toffee. A typical
toffee will have a continuous phase of a high solids sugar syrup with milk proteins
present. The disperse phase could be all milk fat or a mixture of vegetable fat and
milk fat or purely vegetable fat. The interface between the two phases is likely to
be formed from some of the milk protein and any added emulsifier. Emulsions are
normally classified as either oil-in-water or water-in-oil. The kind of systems
described in this chapter can be regarded as oil dispersed in a sugar syrup.
Emulsifiers are used in these products to achieve two different ends, as an aid
to emulsification and to modify texture. A typical application of an emulsifier
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Enrobed and filled chocolate, confectionery and bakery products
would be in a toffee where the skimmed milk content can be reduced and an
emulsifier added to help disperse the fat. Without the emulsifier, the fat would not
disperse properly. The ability of emulsifiers to modify textures comes largely
because an emulsifier can modify the size of the droplets in a dispersion. Small
droplets can have a different mouthfeel from large droplets in the product.
Emulsifier manufacturers tend to claim that emulsifiers aid fat dispersion and
reduce stickiness. While the first claim is usually true, the second claim sometimes
is not. In a toffee, a layer of fat often forms on the surface. This layer actually aids
the handling of the toffee, for example because it does not stick to cutters and other
metal items. A very efficient emulsification of the fat removes this surface layer,
making the product stickier.
The performance of an emulsifier can be affected by the purity of the emulsifier
and the way that it is incorporated into the product. Distilled monoglycerides, as an
example, perform differently from less pure monoglycerides. Adding an emulsifier
to the fat and then mixing it in can produce different effects from adding the same
emulsifier to the sugar syrup or simply mixing all the ingredients together at the same
time. Different brands of the same emulsifer also sometimes perform differently.
Some emulsifiers, for example lecithin, are purely natural products while others
are manufactured (usually from natural materials). Typical materials for manufactured emulsifiers are vegetable oils (e.g. soya bean oil or palm oil), or animal fats,
(e.g. lard or tallow and glycerol). Where required, some manufacturers can supply
products with kosher or halal certificates. Other raw materials are organic acids
such as fatty acids, citric acid, acetic acid, tartaric acid, in addition to sorbitol and
propylene glycol.
Emulsifiers are also subject to food labelling and other legislation. It is entirely
reasonable that only those substances that are safe for food use are permitted.
However, permitted emulsifiers can vary a great deal between countries. The EU
is working towards rationalisation in this area. The use of emulsifiers is normally
regulated on a permitted list basis. It is essential that users check the legal position
in all proposed markets before specifying emulsifiers.
Examples of emulsifiers
Mono- and diglycerides (E471): These products are made by heating a triglyceride with glycerol, a process known as interesterification. A possible relevant use
would be making a caramel softer and less sticky.
Distilled monoglycerides (E 471): These are high purity monoglycerides prepared by molecular distillation from a mixture of mono- and diglycerides. The
application most relevant to this work is in toffees and caramels where they
improve fat dispersion. Claims are also made about reduced stickiness. Texture
modifications occur because the size of the oil droplets alters the rheology.
Lecithin E322: First discovered in the 19th century, this is a naturally occurring
emulsifier. It is even believed by some to be a health food on its own. It is a polar
lipid, that is it is insoluble in acetone. Lecithin is one of a group of lipids known as
phospholipids. These are materials that are found naturally in membranes in
animals and in plants.
Caramels, fondants and jellies as centres and fillings
2
4
6
8
10
12
133
14
16
Sucrose esters
Sorbitan esters
Glycerol esters
Propylene glycol
esters
Fig. 7.2
HLB range covered by sucrose esters compared with the HLB range obtainable with sorbitan esters, glycerol esters and propylene glycol esters.
The definition that is used for food grade lecithin is ‘a mixture of polar and
neutral lipids with a polar lipid content of at least 60%’. Note that this is different
from the scientific usage where lecithin is used as a trivial name for phosphatidylcholine. The main commercial source of lecithin is the soya bean. Lecithins
are also produced from sunflower, rapeseed, maize and, in small quantities,
peanuts. Lecithin can be produced from egg yolk but this is not commercially
competitive. In the future it might be possible to produce lecithins from microorganisms.
Sucrose Esters E473: These emulsifiers are prepared from sucrose and edible
fatty acids. The primary hydroxyl groups of the sucrose are esterified by the fatty
acid. It is possible to react fatty acids with one, two or three primary hydroxyl
groups to yield mono, di- or tri-esters.
One advantage of sucrose esters is that they can be made with a wider range of
HLB values than other emulsifiers. In Fig. 7.2 the HLB range covered by sucrose
esters is compared with the HLB range obtainable with sorbitan esters, glycerol
esters and propylene glycol esters. These materials are all families of emulsifier
that are, chemically, esters. As an emulsifier needs to be amphiphilic, esters are a
popular structure for synthetic emulsifiers. Available grades of sucrose esters
cover the range of HLB from 2 to 15. This wide range of HLB values is obtained
by varying the monoester content from 10 to 70%. Thus a high HLB emulsifier
would be suitable for use in an oil-in-water emulsion while a low HLB emulsion
would be used in a water-in-oil emulsion.
The practical effect of this very wide HLB range is that sucrose esters can be
used in a very wide range of confectionery products. It should be remembered that
it is not necessarily the same sucrose ester that is used in all products. Another
property of sucrose esters is that they are stable up to 180 °C. Claims are made that
sucrose esters improve the handling, texture and whiteness of fondants.
It might be thought that sucrose esters that are made from two food ingredients
would have an easy passage in food legislation. This has not been the case. The
early production method for sucrose esters involved the use of the solvent
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Enrobed and filled chocolate, confectionery and bakery products
dimethylformamide (DMF). There were worries about the effect of DMF residues
in the product. These problems have now been dealt with by tight specifications on
residual DMF. Some sucrose ester production does not now involve DMF. The EU
has included sucrose esters in Directive 78/663 covering the emulsifiers permitted
in all states of the EU. The number E473 has been assigned to all sucrose esters.
The Scientific Committee for Food has assigned an ADI (acceptable daily intake)
of 20 mg kg–1 of body weight.
7.3.4 Flavours
Flavours are used in these products for one of two reasons, either to enhance the
product or because the product could not be made without an added flavour. Butter
and toffee flavours are added to toffees to enhance the product. The butter flavour
could make up for the toffee containing vegetable fat rather than butter. A toffee
flavour is often used because toffees made on modern continuous plants tend to
develop less flavour during cooking than the same recipe cooked in an open toffee
pan. Products such as fruit flavoured products, mint flavoured products and
Turkish Delight depend on an added flavour. Some consumers tend to regard all
added flavours with suspicion but are usually willing to accept natural flavours.
The smallest range of flavours available is organic flavours. At the time of
writing only orange, lemon and mint are available. A much wider range of natural
flavours is available including most citrus fruit, strawberry, mint and rose water
(for Turkish Delight). These flavours perform well but are more expensive than
synthetic flavours. The range of synthetic flavours available is obviously wider
than the range of natural flavours, although there are some flavours which are
never a very succesful representation of the original product.
7.3.5 Colours
Colours are added to these products for two reasons; either to improve the original
appearance of the product or to give the consumer an added hint of the flavour.
Tests tend to show that most consumers if given a yellow coloured sweet with a
strawberry flavour and a lemon flavoured sweet coloured red will detect the wrong
flavours. Some consumers object to added colours and avoid products with added
colours. It is up to the confectioner to decide whether to use them.
Synthetic colours
Synthetic colours are much more stable and economical than natural colours. The
range of synthetic colours available is much greater than that of natural colours and
the purity of the colour is also greater. In technical terms synthetic colours are the
automatic choice.
The disadvantage of synthetic colours is in marketing terms. Some consumers
avoid synthetic colours whenever possible, presumably on health grounds. When
synthetic colours were first added to foods, the colours used were textile dyes.
Some of those colours subsequently have turned out to be carcinogenic and have
Caramels, fondants and jellies as centres and fillings
Table 7.1
135
List of synthetic colours
Shade
Name
EU E No.
USA FD&C No
Chemistry
Red
Red
Red
Red
Red
Red
Orange
or yellow
Orange
or yellow
Orange
or yellow
Orange
or yellow
Green
Allura red AC
Ponceau 4R
Carmoisine
Amaranth
Erythrosine BS
Red 2G
Tartrazine
E129
E124
E122
E123
E127
E128
E102
Red 40
Not permitted
Not permitted
Not permitted
Red 3
Not permitted
Yellow 5
Monoazo
Monoazo
Monoazo
Monoazo
Xanthene
Monoazo
Pyrazolone
Yellow 2G
E107
Not permitted
Monoazo
Sunset yellow FCF
E110
Yellow 6
Monoazo
Quinoline yellow
E104
Not permitted
Quinoline
E142
Not permitted
Triarylmethane
Green
Blue
Blue
Blue
Brown
Green S (Brilliant
green BS)
Fast green FCF
Indigo Carmine
Patent Blue V
Brilliant Blue FCF
Brown FK
–
E132
E131
E133
E154
Green 3
Blue 2
Not permitted
Blue 1
Not permitted
Brown
Brown
Black
Chocolate brown FB
Chocolate brown HT
Black PN
E155
E151
Not permitted
Not permitted
Not permitted
Triarylmethane
Indigoid
Triarylmethane
Triarylmethane
a
Mixture of a
monoazo and
diazo
Monoazo
Diazo
Diazo
a
Brown FK is a mixture of a monoazo and a diazo compound.
been banned. Those colours currently in use have been most rigorously tested for
safety.
One other problem with synthetic colours is that although they are permitted
everywhere, the actual list of permitted colours varies between countries. It might be
thought that a universal list of accepted colours could be agreed but unfortunately
this has not happened at the time of writing. Table 7.1 gives a list of synthetic colours
Natural colours
Natural colours have a considerable marketing plus together with the possibility
that the colour will be universally acceptable. The disadvantages are greater cost,
lower stability and a much reduced availability of shades. The colour purity of
natural colours tends to be lower than that for synthetic colours. Table 7.2 gives a
list of natural colours.
7.3.6 Gums and gelling agents
Table 7.3 gives a list of gum and gelling agents. The gums are included because
they are sometimes used in combination with gelling agents.
Table 7.2
Natural colours in the chemistry of sugar and confectionery
Shade
Name
EU E No.
Pigment
Source
Red
Red
Red
Yellow to red
Yellow to red
Yellow to red
Yellow to red
Yellow to red
Yellow to red
Yellow to red
Yellow
Yellow
Yellow
Green
Green
Brown
Black
Anthocyanins
Betanin, vulgaxanthin
Cochineal
β-Carotene
Annatto
Lutein
Crocin
Paprika
β-Apo-8' carotenal
Canthaxanthin
Turmeric
Riboflavin (vitamin B2)
Riboflavin 5'-phosphate
Chlorophyll
Copper chlorophyll
Caramel
Carbon black
E163
E162
E120
E160a
E160b
E161b
Anthocyanins
Betanin, vulgaxanthin
Carmine and carminic acid
Carotene
Bixin, norbixin
Carotenoid
Carotenoid
Capsanthin and capsorubin
β-Apo-8' carotenal
Canthaxanthin
Curcumin
Riboflavin
Riboflavin 5'-phosphate
Chlorophyll and chlorophyllins
Copper chlorophyllin
Melanoidins
Carbon
Grape skins, red cabbage
Beetroot (Beta vulgaris)
Cochineal beetle
Carrots, alfalfa
Bixa orellana seeds
Tagetes or Aztec marigolds
Saffron crocus Gardenia jasminoides fruit
Sweet red pepper (Capsicum annum)
Normally nature identical
Normally nature identical
turmeric root (Curcuma longa)
Milk, yeast, normally nature identical
Normally nature identical
Green leaves, alfalfa, grass
Derived from chlorophyll
Carbohydrates heated possibly with ammonia
Carbonised vegetable matter
E160c
E160e
E161g
E100
E101
E101a
E140
E141
E150
E153
Table 7.3
Properties, chemistry and sources of gum and gelling agents
Agent
Properties
Chemistry
Source
Gelatine
Starch
High amylopectin starch
Gum acacia
Agar agar
Alginate
Carrageenan
Gellan gum
Thermoreversible gelling agent
Irreversible gelling agent
Non-gelling starch
Gum
Thermoreversible gelling agent
Irreversible gelling agent
Thermoreversible gelling agent
Thermoreversible or irreversible gelling
agent
Thickener exhibits synergy with some
gelling agents
Irreversible gelling agent
Thermoreversible gelling agent
Gum or mucilage
Thickener exhibits synergy with some
gelling agents
Thickener exhibits synergy with locust
bean gum
Whipping agent and irreversible gelling agent
Whipping agent
Protein
Carbohydrate
Carbohydrate
Polysaccharide
Polysaccharide
Polysaccharide
Sulphated polysaccharide
Polysaccharide
Bovine or porcine hides or bones
Maize or wheat or potatoes
Waxy maize
Trees of the species Acacia senegal
Red seaweeds
Brown seaweed
Red seaweeds
Pseudomonas elodea
Galactomannan
Seeds of Cyamopsis tetragonolobus
Polygalacturonic acid
Demethoxylated pectin
Polysaccharide
Galactomannan
Citrus peel or cider apple pomace
Citrus peel or cider apple pomace
Astralagus shrub
Endosperm of locust beans from
Ceratonia siliqua
Aerobic fermentation of Xanthomonas
campestris
Egg white
Soy beans
Guar gum
Pectin high methoxyl
Pectin low methoxyl
Gum tragacanth
Locust bean or carob gum
Xanthan gum
Egg albumen
Enzyme modified soy protein
Polysaccharide
Protein
Protein
138
Enrobed and filled chocolate, confectionery and bakery products
One of the most important issues with gelling agents is what causes them to gel.
Gelatine forms thermoreversible gels so a gelatine product will gel on cooling. If
a gelatine product cannot be deposited at final solids, it will have to be deposited
at the highest practicable solids and the centres will then have to be stoved to the
final solids (see Section 7.4.3 Depositing into starch). One advantage of
thermoreversibility is that rework can be recovered and the expensive gelling agent
can be recycled. This is not the case for example for high methoxyl pectins which
set irreversibly and rework can only be introduced if finely comminuted and at a
maximum of 5%.
Both high and low methoxyl pectins will only gel under certain conditions
which allow their gelation to be controlled. High methoxyl pectin will only gel at
acid pH so an appropriate buffer is added immediately before depositing. Only
slow set types of high methoxyl pectin are suitable for depositing to avoid the
product setting in the depositor. Low methoxyl pectin sets on the addition of
calcium ions. Care needs to be taken when this material is used in factories with
very hard water supplies.
7.4
Processing
The preparation of most of the centres and fillings described in this chapter
involves the use of the traditional methods used in sugar chemistry. The first
step with many of these products is to dissolve the dry ingredients. Sugar can
normally be dissolved in water or water and glucose syrup. Some modern
machines have the facility to run a boiling pan under pressure to allow ingredients to be dissolved at temperatures above normal boiling point and hence more
quickly (Fig. 7.3). Some gums and gelling agents have to be pre-soaked bcause
they will not dissolve directly in water. Pectins can be dissolved directly if a
high shear mixer is available but otherwise have to be pre-soaked. Some gums,
which in the past had to be pre-soaked, are now available in a spray dried form
which can be dispersed directly.
The traditional way of boiling sugar confectionery is to use a steam heated
open pan. Some toffees and caramels are still made by this method. The next
evolution in cooking sugar confectionery is to use a steam heated vacuum pan.
In these machines, after boiling the material to final solids, a vacuum is applied
(Fig. 7.4). This causes the liquid to boil under reduced pressure which allows
water to boil off as well as cooling the liquid by the latent heat of evaporation.
This rapid cooling has the effect of speeding up the process.
Large-scale manufacturers tend to use continuous plants for cooking and
evaporation. These plants consist of mixers, either batch or continuous, that feed
material into a heat exchanger where cooking occurs. If evaporation is required,
the heat exchanger will discharge into a vacuum chamber. After all forms of
cooking, the product is likely to be cooled and any colours and flavours will be
added. The product will then be shaped as required.
Caramels, fondants and jellies as centres and fillings
Fig. 7.3
Confectioners’ boiling pan.
Fig. 7.4 Vacuum plant high boilings.
139
140
Enrobed and filled chocolate, confectionery and bakery products
Fig. 7.5
Drop roller: this is a small hand one but large electrically driven ones exist.
7.4.1 Rheology
Rheology affects centres and fillings in two quite different ways; the rheology of
the finished product will control the texture as perceived by the consumer while the
rheology of the material will control how it can be shaped. While rheology is a
complex science on its own (and is dealt with in more detail elsewhere in this
book), this section will deal with it in simple terms. Fluids can be classified as
Newtonian, for example like water, or non-Newtonian. When a material is being
deposited, the two important questions are will it run out of the depositor under
gravity and will it deposit cleanly without leaving a tail? Whenever a drop of liquid
is formed a tail forms and breaks off forming a smaller drop. In the case of water
this happens so quickly that it can only be seen with a high speed camera. Some of
the thicker materials of interest in sugar confectionery form a tail much more
slowly but still deposit cleanly. The difficult materials are those where the tail does
not break cleanly.
7.4.2 Shaping
A filling will be deposited into chocolate, which is how the product is shaped.
Centres will be shaped before enrobing using those methods used in sugar
confectionery. Most of these methods involve depositing the material into a mould.
High boiled products can be deposited into metal moulds, starch moulds or they
can be shaped with a drop roller (Fig. 7.5). A drop roller has counter-rotating
rollers with depressions in them in the shape of half a centre. When the product
passes between the rollers, the depressions are filled and the rotating rollers come
together at the edge of the sweet nipping it so that the sweet breaks away from the
web of centres formed.
Caramels, fondants and jellies as centres and fillings
141
7.4.3 Depositing
Both centres and fillings are deposited at some point. In the manufacture of centres
the commonest depositing systems are into either starch or starchless moulds
which are discussed below. There are separate issues with filling into chocolate
which are discussed separately.
Depositing into starch
Most centres are shaped by depositing either into starch or rubber moulds (sometimes referred to a starchless moulding). Starch moulding is the older technology,
while starchless moulding is the newer one. In starch moulding, trays are filled
with starch that has had a small quantity of oil added. Mineral oil was used but has
now been replaced with a long-life vegetable oil. Originally the trays were wooden
but are now often fibreglass. Depressions are made in the starch with a mould
board which has stampers shaped as a buck mould for the centre shape. Thus the
size and shape of the depressions can be easily changed by changing the mould
board. This makes it easy for one machine to be used to deposit a range of shapes
such as might be required in a chocolate assortment.
In use the stamped starch mould passes under the depositing head and the
depressions are filled with product. If the product needs to be dried by stoving, the
trays are moved to a stove, a chamber where heated air is blown across them to dry
the product to the final solids. When the product has cooled, the trays are inverted
and the centres can be sieved out of the starch. The centres are then cleaned and fed
to the enrober as required. If the centres are not being stoved, the trays are allowed
to cool as necessary and then inverted as above. The starch is recovered, dried and
used to refill trays.
Starchless moulding
In a starchless moulding plant, the moulds pass under the depositor to be filled and
are then cooled as necessary and the centres are demoulded. In this system there is
no starch to be recovered, dried and reused. The first cost of the rubber moulds is
much greater than that for starch moulds and the moulds will need periodic
replacement. Different product shapes and weight will require different moulds.
Starchless moulding is less suitable for stoving than starch moulding since in a
starch mould the product can dry from all sides because water can be lost to and
evaporated from the starch, while in a rubber mould evaporation can only take
place from the exposed surface.
The manufacturers of starch moulding machines have updated their machines
to reduce the amount of labour needed and to stay competitive with starchless
moulding. Early starch moulding machines needed the trays to be stacked manually while modern machines stack their own trays. It appears that starch and
starchless moulding will continue to coexist. Starch moulding is best suited to a
stoving operation and where flexibility is important. Starchless moulding is best
suited where stoving and flexibility are not needed.
Depositing into chocolate
Any filling that is being deposited into chocolate has to fit in a number of
142
Enrobed and filled chocolate, confectionery and bakery products
constraints. The filling has to have a high enough total solids to be stable and yet
a low enough viscosity to deposit. The two easiest ways to make a product less
viscous are to increase the temperature and to reduce the total solids. If the product
is being filled into chocolate, the maximum temperature of deposit is restricted by
the requirement that the chocolate should not melt.
7.5
Products
The materials used as centres or fillings are all versions of sugar confectionery
products but some have to be modified to fit the process. The classes of products
and some examples are discussed below.
7.5.1 High boiled products
There not many high boiled products that are used as centres of enrobed products;
the most common is butterscotch.
Butterscotch
Butterscotch can be regarded as a high boiled sugar product with some butter
added. UK law is logical in insisting that butterscotch should contain some butter.
Butterscotch can be deposited either in to metal moulds or starch. The centres can
then be demoulded, cleaned and enrobed.
7.5.2 Caramels and toffees
In this work, the terms caramels and toffees are used interchangeably as is normal
in the United Kingdom. In some jurisdictions caramels have a higher milk solids
content than toffees. In these products there is a divide between the softest and the
hardest products. Hard and chewy toffees are most suitable as centres since they
can easily be deposited into starch or rubber moulds and then enrobed, while they
are difficult to fill into chocolate in case the chocolate melts. Soft caramels
conversely are most suitable as fillings since they can be filled into chocolate but
would be difficult to shape and enrobe. Recipe 1 is a caramel recipe. Figure 7.6
shows some toffees.
Caramel recipe 1
Ingredients (in parts by weight)
•
•
•
•
•
•
•
Confectioners glucose (42DE):
Full cream sweetened condensed milk:
Brown sugar:
Toffee fat:
Butter oil:
Salt:
Vanilla flavouring:
170
140
115
45
30
3
0.9
Caramels, fondants and jellies as centres and fillings
Fig. 7.6
143
Some toffees.
Method
• Add the sugar, glucose, salt and condensed milk to a boiling pan, stir and heat
to 45 °C.
• Add the fats.
• Mix thoroughly.
• Boil to 124 °C.
• Cool slightly and mix in the flavouring.
• Cool the batch prior to shaping.
7.5.3 Grained products
The problems with grained products are that they have to be agitated to induce
crystallisation and that when crystallised they undergo Ostwald ripening. Ostwald
ripening is a process in which the smallest crystals redissolve to be replaced by
larger ones. The practical effect of this is that the texture tends to change with time.
Fondants
Fondants are normally made by dissolving sugar in water and glucose syrup then
boiling the resulting syrup to concentrate it. The syrup is then beaten with cooling
which induces crystallisation. The fondant is normally left to mature for a day. The
crystallised fondant can then be deposited either into a starch or starchless
144
Enrobed and filled chocolate, confectionery and bakery products
moulding system and enrobed or it can be used as a filling. The enzyme invertase
is sometimes added to fondants. This has the effect of causing the fondant to soften
with time as the sucrose is converted to invert sugar. This also has the effect of
reducing the water activity and preventing drying out. Recipe 2 is a fondant recipe.
Fondant recipe 2
Ingredients (in parts by weight)
• Sucrose:
• Water to disolve:
• Confectioners glucose (42DE):
100
50
25
Method
•
•
•
•
•
Dissolve the sugar in the water.
Add the glucose.
Boil to 120 °C.
Cool to 38–43 °C and then beat.
The finished fondant should be matured for a day before use.
Fudges
A fudge can be regarded as a toffee with crystallised sugar added. There is no
definition of a fudge. It is possible to make a fudge by either adding fondant to a
toffee or adding milled sugar to a toffee. Alternatively a caramel formulated with
an excess of sugar can be beaten on cooling. Some would argue that this product
is a grained caramel but it will pass as a fudge.
Fudges can either be deposited into starch or rubber moulds to produce a centre
that can be enrobed or a suitably modified fudge can be used as a filling. Fudges,
like other grained products, mature on storage. Recipe 3 is a fudge recipe. Figure
7.7 shows fudge pieces.
Fudge recipe 3
Ingredients (parts by weight)
•
•
•
•
•
Sucrose:
Full cream sweetened condensed milk:
Glucose syrup (42DE):
Butter:
Water:
Method
•
•
•
•
•
Place ingredients in pan and mix until smooth.
Cook to 115 °C.
Allow to cool to 93 °C.
Add 20 parts of fondant (see fondant recipe).
Stir and add salt and flavour as required.
30
22
18
2
5
Caramels, fondants and jellies as centres and fillings
Fig. 7.7
145
Fudge pieces.
Nougat
There are a range of products sold as nougat. The original product was Nougat de
Montelimar. This was made with eggs, sugar, honey and had almonds, cherries and
angelica added. Some confectioners would argue that montelimar is a separate
product. The common dark montelimars are made by adding cocoa powder usually
to a less aerated confection.
Nougat can be made either in batches or continuously. The best nougat is made
in batches. Various whipping agents can be used such as egg albumen, gelatine,
milk protein and enzyme modified soya protein. Starch or gum arabic can be used
in addition. The composition can be adjusted to give the desired texture.
In continuous processing the whipping agents are beaten into a hot mixed sugar
syrup. The product is then extruded, cooled and cut to shape. In the batch process
a mixture of sugar and glucose syrup is boiled to 8% moisture content typically
using a vacuum pan. The syrup is transferred to a whipping machine and the
whipping or gelling agent or agents are added. The traditional material is egg
albumen. The product is whipped, with the egg albumen being set by the heat. The
fat, nuts, fruit and possibly a small amount of milled sugar are then added. The
product is then poured into trays lined with rice paper. The trays are left overnight
for some sugar to crystallise. The product can then be cut into shape and enrobed
in chocolate. Recipe 4 is a nougat recipe (see Fig. 7.8).
146
Enrobed and filled chocolate, confectionery and bakery products
Fig. 7.8
Chocolate enrobed bar containing a nougat with expanded cereal pieces.
Nougat recipe 4
Ingredients: part 1 (parts by weight)
• Water:
• Glucose syrup (42DE):
0.75
2.5
Method 1
• Pre-soak the albumen in the water.
• Add the glucose syrup.
• Whip to a stiff foam.
Ingredients: part 2 (parts by weight)
•
•
•
•
•
Spray dried egg albumen:
Sugar:
Glucose syrup (42DE):
Water:
Toffee fat:
0.37
12.5
10
4
0.25
Method 2
•
•
•
•
•
•
•
Boil to 132 °C.
Mix part 2 slowly into part 1 until the volume increases.
Mix the toffee fat in very slowly.
Add any flavour.
Pour onto a cold slab.
Leave to stand overnight.
Cut pieces to size.
Caramels, fondants and jellies as centres and fillings
7.6
147
Gelled products
There are a number of gelled centres or fillings that are used. Fruit flavoured jellies
are common. Mint flavoured jellies are rare but are sometimes seen. There is a whole
class of products sold as Turkish Delight almost none of which would be recognised
as the traditional product from the Middle East. Custom and practice seems to be that
a gel made from almost any gelling agent with a flavour either of or resembling rose
water and a pink colour can be sold as Turkish Delight. Turkish Delight has been
made from gelatine, starch, pectin and agar. Mixtures of gelatine and other gelling
agents have been used to reduce costs while maintaining the preferred texture of
gelatine. Recipe 5 is an agar jelly recipe, recipe 6 is a gelatine jelly recipe, recipe 7 is
a pectin fruit jelly recipe, while recipe 8 is a Turkish Delight recipe.
Agar jelly recipe 5
Ingredients: part 1 (parts by weight)
• Agar agar:
• Water:
• Sodium citrate:
2
70
0.7
Method 1
•
•
•
•
Pre-soak the agar in the water for 3–12 hours.
Heat the water and agar until the agar dissolves.
Add the sodium citrate.
Strain through a fine sieve.
Ingredients: part 2 (parts by weight)
• Sugar:
• Glucose syrup:
• Colour flavour and acid:
60
40
to taste
Method 2
•
•
•
•
•
•
Add the sugar and glucose syrup to part 1.
Boil to 107 °C.
Cool to at least 76 °C and add the acid.
Add colour and flavour.
Deposit into starch moulds.
Hold for 12–24 hours then demould.
Gelatin Jelly recipe 6
Ingredients (parts by weight)
•
•
•
•
•
180 bloom gelatine:
Hot water:
Glucose syrup (42DE):
Sugar:
Water:
25
50
80
80
40
148
Enrobed and filled chocolate, confectionery and bakery products
Method
•
•
•
•
•
•
•
Dissolve the gelatine in the hot water overnight.
Dissolve the sugar in the water and add the glucose syrup.
Boil to 116 °C.
Cool to 70 °C and mix in the gelatine solution.
Add any colour and acid.
Mix in the flavour.
Deposit.
Pectin fruit jelly recipe 7
Ingredients (parts by weight)
•
•
•
•
•
•
•
Slow set high methoxyl pectin:
Citric acid monohydrate:
Potassium citrate:
Sugar:
Glucose syrup (42DE):
Water:
Colour and flavour:
0.82
0.28
0.25
51
29
40
as required
Method
•
•
•
•
•
•
Dissolve the potassium citrate and one third of the citric acid in the water.
Heat to 70 °C.
Mix the dry pectin with three times its weight of sugar and stir into the water.
Boil the mixture for 1 minute to make sure all the pectin has dissolved.
Add the rest of the sugar and the glucose syrup and boil to 108 °C.
Dissolve the remainder of the citric acid in an equal weight of water an mix well
into the mixture.
• Add flavour and colour.
• The product must be deposited in the next 20 minutes.
Turkish Delight recipe 8
Ingredients: part 1 (parts by weight)
•
•
•
•
•
Low methoxyl pectin:
Sugar:
Glucose syrup (42DE):
Water:
Colour and flavour:
2
42.5
45
40
as required
Method 1
• Dry mix the pectin with 4 parts of the sugar.
• Heat the water to 70 °C and stir in the sugar and pectin mixture.
• Boil the mixture for 1 minute.
Caramels, fondants and jellies as centres and fillings
Fig. 7.9
149
Enrobed Turkish Delight: this one is based on starch and pectin.
Ingredients: part 2 (parts by weight)
• Acid thinned boiling starch:
• Water:
3.5
18
Method 2
•
•
•
•
•
•
7.7
Make a slurry of the above.
Slowly add the slurry to the first part while it is boiling.
Add the glucose syrup and the rest of the sugar.
Boil to 107 °C.
Add the colour and flavour.
Deposit.
The future
It is always difficult to predict future developments. In terms of equipment, the
major trends have been the use of microelectronics to control machinery and
mechanical handling to reduce manual labour.
At present the confectionery industry is being attacked on nutritional grounds.
There seem to be various responses in the industry. One approach is to produce
luxury products which are sold as an indulgence. The problem with this is that it is
likely to lead to low sales volumes which might reduce in an economic downturn.
One way of countering the attacks is to produce organic products. Other approaches
are to produce sugar free or low calorie products.
7.7.1 Organic products
Organic products require organic ingredients and compliance with the necessary
150
Enrobed and filled chocolate, confectionery and bakery products
paperwork. Some materials are not available in an organic form while all are more
expensive than conventional ingredients. The relativities between organic ingredients are also different, for example organic glucose syrup is more expensive than
organic sugar. At present the possibilities for organic foods are limited by the
available tonnages of organic raw materials.
7.7.2 Sugar free products
Sugar free products are an opportunity but one that has its problems. The easiest
problem to solve is sweetness, as the range of intense sweeteners that are now
permitted almost everywhere, makes achieving a clean sweet taste fairly easy. The
difficulties usually occur in choosing the right combinations of bulk sweetener.
There is another problem with most bulk sweeteners in that they have a laxative
threshold, that is excess consumption will cause a gastrointestinal disturbance. The
amount that can be consumed varies between individuals and between substances.
There is also some evidence that the effect for a given individual varies, depending
on whether their stomach was full or empty before the product was consumed.
Erythritol has a much higher laxative threshold than other polyols. This occurs
because at most levels of erythritol consumption the erythritol is excreted via the
kidneys. Erythritol is usually assigned a calorie value of 0.2 kcal g–1 while in Japan
the value of zero has been approved. The major problem with erythritol is that
although it has been permitted in the United States and some other countries for
some time, approval for use throughout the EU is being obtained at the time of
writing. It always pays to check the legal position of sugar free products in the
relevant countries before launching the product.
7.7.3 Low calorie products
As with sugar free products, it pays to check the rules and regulations regarding
claims that are permitted. The problem with reducing the energy content of any
product containing chocolate is that the amount of energy reduction that can be
achieved is limited by the energy content of the fat in the chocolate. Fats contain
9 kcal g–1, while protein and carbohydrate contain 4 kcal g–1. In the EU, polyols
contain 2.4 kcal g–1 except erythritol which will probably be accepted as containing 0.2 kCal.g–1. The other useful ingrdient in this context is polydextrose
which is accepted as containing 1 kCal.g–1. In view of these figures in can be
seen that any conventional confectionery product which has to maintain a high
total solids for stability can only have its energy content reduced by a certain
amount.
7.8
Conclusions
Fondants, toffees and jellies are useful components as centres and fillings. They
can be developed to produce a whole range of different products.
Caramels, fondants and jellies as centres and fillings
7.9
151
References
EDWARDS W. P.
(2000) The Science of Sugar Confectionery, Royal Society of Chemistry,
Cambridge.
7.9.1
Further reading
JACKSON E. B.
(1995) Sugar Confectionery Manufacture, 2nd edition, Chapman & Hall,
London.
EDWARDS W. P.
(2000) The Science of Sugar Confectionery, Royal Society of Chemistry,
Cambridge.
LEES R. AND JACKSON E. B. (1973) Sugar Confectionery and Chocolate Manufacture,
Blackie Academic & Professional, Glasgow.
8
Biscuits and bakery products
Mike Brown, Burtons Foods Ltd, UK
Abstract: The aim of this chapter is to explain why chocolate is used to cover biscuits
and cakes, to explore the fundamental differences between the chocolate formulation
used and that used with sugar confectionery and tablet chocolate and briefly to examine
the enrobing process used with baked products using this formulation of chocolate which
has its own complications that may lead to quality issues.
Key words: chocolate formulation, cooling, cracking, emulsifiers, enrobing, hardness,
moisture migration.
8.1
Introduction
When looking at chocolate-coated biscuits and cakes it is important to take into
account the reason why the product is being covered in chocolate. Some people
would say that everything tastes better when it is covered in chocolate but the
reasons for covering the product may be a little more than simply a matter of
flavour.
Covering a biscuit or cake in chocolate introduces a moisture barrier between
the product and the atmosphere. Cakes have a tendency to lose water into the
atmosphere and dry out becoming hard and stale, whereas biscuits tend to do the
opposite and absorb moisture from the atmosphere becoming soft and stale.
Chocolate, being a fat-based product, tends to inhibit this moisture transfer thus
extending the shelf life of the product. Furthermore, when biscuits or cakes are
eaten they tend to require some considerable amount of saliva to lubricate the
product within the mouth. The addition of chocolate aids in this lubrication.
However, it has to be stressed that it is important to get the right chocolate, one that
complements the flavour of the biscuit or cake. Mistakes have often been made by
Biscuits and bakery products
153
manufacturers of well-known and loved brands of chocolate who have put their
branded chocolate on every product in the food sector. It does not always work.
The sweetness of the cake, the bitterness of the digestive biscuit, the amount of the
chocolate on the product, all contribute to the overall ‘eat’ and flavour of the
product.
When enrobing biscuits and cakes, it has to be acknowledged that this process
introduces the chocolate into its most hostile environment. To one side of the
enrober there is an oven which is set at 150 °C or more to bake the biscuit or cake.
At the other side of the enrober there is the chocolate cooling tunnel which often
has an entry temperature of 18 °C or less. In between there is the enrober which is
attempting to keep the temperature of the chocolate (and its local environment)
between 26 and 30 °C. If the atmosphere is too cool, the chocolate becomes solid
and if it is too warm, the chocolate becomes detempered. Along with the main
enrober there are also the various methods of decorating the cake or biscuit so as
to make them appear different from other products of the same type.
8.2
Chocolate formulation
When formulating a chocolate that is to be used for enrobing a biscuit or cake, it is
vital that the percentage coverage and the dimensions of the finished product are
known. For example, a fully coated long thin biscuit which is to have 50%
chocolate on it requires a chocolate with a higher viscosity than a similar biscuit
that has only 35% chocolate. This change in chocolate viscosity can be achieved by
altering the fat content of the chocolate or by chemical means, that is by the use of
emulsifiers such as lecithin.
The main problem encountered with a coating chocolate is the cost of the fat
used to ‘thin’ down the chocolate. The majority of fat within the fat phase of a
coating chocolate is cocoa butter but in recent years the acceptability of cocoa
butter equivalents (CBEs) has been extended to the whole of the European Union
(EU).
CBEs have three major advantages over cocoa butter:
1. They are manufactured to a specification and thus they are relatively consistent in terms of their fatty acid profiles and physical characteristics.
2. They can be manufactured to give a variety of effects to the chocolate. For
example, they can make the chocolate softer or make it solidify at a slightly
higher temperature, thus helping in conditions where ambient temperatures
are high.
3. Cost – CBEs tend to be more cost effective (i.e. cheaper) than other fats found
in chocolate.
The formulation of a chocolate that is to be used on a biscuit or cake is fundamentally different from the formulation used when the chocolate is in tablet form. This
is because the chocolate used on an enrobed product has a different flavour or
series of flavours and textures both competing with and complementing it.
154
Enrobed and filled chocolate, confectionery and bakery products
Tablet chocolate needs to be ‘hard’ and have a ‘snap’ so that it can be broken
into pieces when eaten, whereas a biscuit or cake may be eaten ‘as a whole’ and
the teeth used to break the biscuit into bite-sized pieces. This means that the
chocolate on an enrobed, baked product may be ‘softer’ than that used in a
tablet. An additional factor is that, in the case of a large cake, the cake itself may
need to be cut. If the chocolate is too ‘hard’ it will tend to shatter and break
away from the cake mass when cut thus leaving the cake with a reduced covering of chocolate.
By altering and manipulating the fat phase of the chocolate it is possible to alter
the hardness of the chocolate. Typically the fat phase of chocolate consists of three
main fat types:
• cocoa butter
• CBEs
• milk fat
By changing the ratio of cocoa butter to milk fat it is possible to change the
hardness of the chocolate. The more milk fat used in the chocolate the softer it will
be, and vice versa. This is because of the incompatibility that exists between cocoa
butter and milk fat when they are mixed together. Indeed, as a rule of thumb if a fat
phase of a chocolate contains over 25% milk fat, the chocolate will be untemperable.
Because CBEs have a range of formulations that can make them harder or softer
than cocoa butter, they are able to have either a softening or a hardening effect on
the final chocolate, depending on their nature and physical characteristics.
It is important to ensure that the chocolate is not too soft, otherwise it tends to
become a sticky glutinous mass rather than the crisp texture that is expected. This
sticky cloying mass has a tendency to stick within the palate and so exaggerate the
dry feeling of the cake. It also tends to get to the stage where the chocolate does not
melt rapidly enough, as the fat becomes ‘bound’ to the cake mass causing a slow
flavour release and a false ‘waxy’ feel to the chocolate which is similar to that
sometimes found with a chocolate flavoured compound.
CBEs are sometimes formulated so that when they are part of the fat phase of
an enrobing chocolate they enable the processing of the biscuit or cake to be
carried out at higher ambient temperatures (such as might be found, for example,
in warm climates). The problem with higher ambient temperatures arises when it
comes to wrapping and packing the product, particularly with the use of high
speed wrapping machines that utilise various conveyer belts at differential
speeds. If the chocolate is not sufficiently crystallised, the scraping of these
belts on the chocolate-covered base of the biscuits can cause the belts to be
smeared with chocolate. The smeared chocolate builds up to a point where
the plant has to stop so that the belt can be cleaned. By using a tailored CBE
to increase the temperature at which the chocolate begins to melt, it is possible
to reduce the smearing of the belt so that the downtime caused by cleaning
these belts can be reduced, thus improving the efficiency of the manufacturing
plant.
Biscuits and bakery products
8.3
155
Emulsifiers in chocolate
The term ‘emulsifier’ when used in chocolate formulation is somewhat of a
misnomer as the function of an emulsifier is to stabilise an oil-in-water or water-inoil emulsion. Chocolate has very low water content and thus there is little to
‘emulsify’. In practical terms emulsifiers used in chocolate are there as fat
extenders in that they enable the fat to coat the solid particles more effectively than
fat can do on its own, thus reducing the quantity of fat required to achieve the
desired viscosity. The rheology of chocolate is discussed in detail in Chapter 13.
Various emulsifiers are permitted for use in chocolate. The main one commonly
used is lecithin (E322), normally derived from soya. However with the advent of
genetic modification of soya and consumer resistance to genetic modification,
other sources of lecithin, such as sunflower and colza (rapeseed) lecithin, have
been more readily available on the market.
One emulsifier that is gaining popularity in enrobing chocolate is polyglycerol
polyricinoleate (PGPR). This emulsifier has the advantage that it reduces the yield
value of a chocolate, that is the force that is required to make the chocolate flow.
This reduction in the yield value makes it possible to reduce the thickness of the
chocolate coating on the product thus making savings in the amount of chocolate
on the product as well as reducing the amount of expensive fat within the chocolate
formulation. The reduction in the yield value of the chocolate also has the
advantage that air bubbles trapped with the chocolate are more easily removed as
there is less resistance to them coming to the surface of the chocolate.
The advantage of PGPR can also prove to be a disadvantage because once the
chocolate begins flowing off the product it continues to flow until it is set. This can
lead to products with ‘feet’ or ‘flanges’ on their base or bald spots on the upper
surface of the product where the chocolate has either failed to adhere to the product
being enrobed or where the air blowing units within the enrober have been
incorrectly set so that the chocolate is literally blown completely off the product.
The ‘feet’ or ‘flanges’ may cause problems when the product is to be wrapped
because they make the product too big for its wrapper.
The problem caused by bald spots is that the moisture barrier provided by the
chocolate is incomplete so the moisture protection awarded to the biscuit or cake
is vastly reduced leading to a reduced shelf life for the product.
8.4 Moisture barriers for caramel- and jam-containing
biscuits
Sometimes the biscuit being enrobed has another ingredient that introduces a
moisture imbalance between the biscuit and the chocolate. Often this is a caramelbased or jam-based layer that is put onto the top of the biscuit. With this type of
product the biscuit–caramel or biscuit–jam interface requires the presence of some
type of moisture barrier to prevent the biscuit going soggy and the caramel
becoming brittle and hard. Various studies have taken place to determine the best
156
Enrobed and filled chocolate, confectionery and bakery products
type of barrier to use. Other than the cost implications of using chocolate as a
barrier it is questionable whether this is the most effective barrier material or
whether a pure fat would be a better material. On the other hand, the use of a pure
fat can cause its own problems because the fat must be compatible with chocolate
or else it will tend to migrate through the chocolate giving rise to fat bloom. If a
barrier coating (either chocolate, fat or a flavoured compound) is to be used, the
barrier and the caramel need to be applied and cooled sufficiently to prevent the
chocolate becoming detempered during the subsequent enrobing process. With a
caramel this may be achieved by the use of a cold formed caramel which is liquid
at room temperature. The phenomenon of moisture migration is discussed in detail
in Chapter 11.
8.5
Non-hydrogenated coatings
An alternative to chocolate in enrobing biscuits and cakes is to use a compound
coating (see Chapter 5), although, to a large extent their use has diminished for a
number of reasons. First, those based on hardened palm kernel oil (HPKO) were
seen by the consumer as being cheap and inferior to chocolate. This is in spite of
their popularity with manufacturers because not only are they cheap but they are
also easy to use as they do not require tempering or cooling in a controlled manner.
Their disadvantage is that they are incompatible with cocoa butter so any chocolate
flavour is either derived from an artificial flavour or from cocoa powder. HPKObased coatings also have a relatively short shelf life (somewhere in the region of
three months) owing to the stability of the lauric fat. Compound coatings based on
hydrogenated and fractionated non-lauric oils were also used. These had the great
advantage of not shattering when they are cut when they were used on cakes.
In recent years, considerable information has been published on the adverse
health properties of trans fatty acids (TFA) which are produced during the
hydrogenation of unsaturated fats. This has led to legislation changes in some
countries and guidelines in others regarding the acceptability of hardened fats
within the food industry. This has led the oils and fats industry to become more
inventive in developing alternatives to these hydrogenated compound fats.
One type of fat that has become more widely used is the group known as
‘supercoatings’. These fats have a greater tolerance of cocoa butter (and vice
versa) and so may be used with cocoa mass to give a flavour closer to chocolate
than one based on HPKO. They usually require tempering and similar cooling
conditions to standard chocolate. However the shelf life of such products is similar
to chocolate and they have the added advantage to the user that equipment used to
enrobe is readily interchangeable with standard chocolate products. Thus a more
cost effective ‘chocolate’ biscuit or cake may be manufactured on the same plant
as a standard chocolate biscuit or cake. The ultimate super coating is one where the
main fat used is a CBE. These coatings are totally compatible with chocolate but
enable the biscuit and cake manufacturer to take advantage of the cost difference
between the CBE price and that of cocoa butter.
Biscuits and bakery products
157
New, non-hydrogenated alternatives to the hardened non-lauric compound fats
are also now appearing on the market and these retain the advantage of malleability, enabling cake coatings to be cut without shattering. Where a manufacturer still
wishes to use a lauric (palm kernel oil-based) system, fractionated palm kernel oil
(PKS) can be used in place of HPKO. This also gives an enhanced shelf life
compared with HPKO, although the lack of compatibility with cocoa butter is still
present.
It must be remembered, of course, that chocolate, milk chocolate and white
chocolate are all reserved descriptions and may only be used where the product
conforms to the appropriate legislation. When compound coatings are used,
descriptions such as ‘chocolate-flavoured coating’ must be used. As always,
though, the legislation in the country where these products are sold must be
checked first.
8.6
Processing
8.6.1 Full coated products
To coat a product fully in chocolate, it is necessary to have both a method of coating
the base of the biscuit or cake and a continuous curtain of chocolate to coat the
remainder (top and sides) of the biscuit or cake. These form the major parts of any
enrober unit. To help in the weight control ‘licking rollers’, shakers and fans are
used. These different components in an enrober and their operation are described
in more detail in Chapter 17.
The licking rollers are used to skim excess chocolate off the base of the biscuit
or cake and to redistribute the remaining chocolate to give a complete and
continuous coverage of chocolate on the base of the product. The shakers are used
in conjunction with the fans to remove excess chocolate from the top of the product
and move it down the sides. They are basically a means of vibrating the wire belt
to overcome the yield value of the chocolate and cause it to move more freely over
the product. The fans are nozzles of air (taken from outside the enrober hood)
which blow the air over the chocolate-coated product, literally blowing excess
chocolate off the products. The direction of the fans can be altered so that they can
point against the direction the product is travelling, thus blowing chocolate
towards the back of the biscuit or cake. Alternatively, they can point in the
direction of travel, thus blowing chocolate toward the leading face of the biscuit or
cake.
Shakers can be used both before the fan and after the fan, allowing a range of
effects to be achieved. When the shaker is used ahead of the fans, the surface of the
chocolate on the biscuit or cake will have a rippled effect. This is useful because it
will hide defects such as scuffing, as well as looking attractive. However if a shaker
is used following the fan the chocolate will have a smooth finish as the shakers will
remove any irregularities caused by the fans. Both shakers and fans should be
variable so as to increase or decrease the amount of chocolate being removed.
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Enrobed and filled chocolate, confectionery and bakery products
Ideally, both the amplitude and the frequency of the shaker should be adjustable in
order to achieve the desired chocolate weight.
8.6.2 Half coated products
Half coating biscuits offers an opportunity to have two distinct patterns on the
biscuit. Generally most half coated biscuits are manufactured using a turn over
device. The enrober is modified (either permanently or temporarily) so that it does
not produce a curtain of chocolate thus leaving only the bottoming pan full of
chocolate. The biscuit travels through the enrober and picks up the desired amount
of chocolate on the base (this is achieved by use of the shakers and the licking
rollers). As the biscuit leaves the enrober, the turn over device (see Fig. 17.9 in
Chapter 17) inverts the biscuit and drops it onto the cooling conveyer. This gives
a very distinctive pattern on the chocolate.
One problem with a turn over device is that the desired ‘stack height’ of the
biscuit may be exceeded. This is defined as the height of a given number of biscuits
placed on top of each other. The stack height is critical when wrapping the biscuits
because if the stack height is too great the biscuits will not fit into their wrapper.
Conversely if it is too low either too many biscuits will be wrapped or there is a risk
of customer complaints because of an under-filled packet. With half-covered
biscuits the stack height is affected by both the baked height of the biscuit plus the
height of the chocolate (including the peaks of chocolate obtained using the turn
over device). One way to control the height of the peaks of chocolate is to alter the
height of the drop from the turn over device to the cooler conveyer. Increasing the
height that the biscuit drops reduces the height of the peak and reducing the height
of the drop will tend to increase the definition of the peaks.
The other commonly used method of half coating biscuits is termed ‘flat
plaque’. This is where the biscuit is passed through the enrober and then the
chocolate coated surface placed onto the cooling conveyer. Using this method the
chocolate will pick up the pattern that is on the cooling conveyer plaque. This
decoration can include a wavy line pattern, the name of the manufacturer or brand
of biscuit or it can have no pattern at all, that is a flat plaque.
8.6.3 Biscuit and cake crumb-causing problems
When biscuits and cakes are manufactured, they are baked and during the baking
process the outer surface of the biscuit or cake may become hard and brittle with
small pieces being easily broken off during the enrobing process. These small
pieces of ‘crumb’ (as they are known) cause problems by blocking pipe work
within the tempering column. Although they may not block the tempering column
totally they do reduce the flow of chocolate and thus the throughput of the
temperer. To reduce this possibility, chocolate returned from the enrober should be
passed through an open vibrating sieve which may be located on top of the
chocolate storage tank. The mesh size of the sieve should be in the region of 0.5
mm. However this sieve will not protect the detempering column from being
Biscuits and bakery products
159
blocked by the crumb, as the sieve would need to be positioned before the
detempering column. The chocolate passing through this sieve would still be
tempered and the chocolate, owing to the temperature it is being kept at, would tend
solidify on the wires of the sieve causing the sieve to ‘blind’ and eventually block
completely.
Another common problem with biscuit and cake crumb is that they circulate
within the enrober and eventually cause localised holes in the enrober curtain thus
leading to partially covered biscuits. These are a major cause of complaints from
customers.
8.6.4 Cooling the coating
The method of cooling of a coating used on biscuits and cakes is arguably no
different from that used with other enrobed products. The cooling regime depends
on the nature of the coating and its composition.
As noted previously, most biscuit and cake chocolates are deliberately made
softer than a standard confectionery chocolate to help with the lubrication of the
product within the mouth. The softer the chocolate, though, the longer the cooling
time required to set the chocolate before the product may be packed. It is also
important when using chocolate that the cooling tunnel temperatures should be set
such that the chocolate is not shock cooled as it enters the chocolate cooling tunnel
because this can lead to unstable cocoa butter crystals being formed resulting in a dull
appearance. Also the final cooling zone of the cooling tunnel should be set so that
when the product exits the cooling tunnel, the surface temperature of the chocolate
is above the dew point of the ambient air that it is entering. Failure to do this results
in condensation on the surface of the product which can result in the appearance of
small sugar crystals on the surface of the chocolate (known as sugar bloom).
If a supercoating is being used, the same cooling requirements as for chocolate
should be used. This is because of the potential presence of cocoa butter or other
polymorphic fat crystals within the fat phase. A typical setting for a cooling tunnel
for chocolate and supercoatings is (in a four zone cooling tunnel) 18 °C, 15 °C,
12 °C and 18 °C (the last zone being governed by the dew point of the ambient air
in the factory). A good cooling time is between 10 and 20 minutes. While these
conditions are preferred, in reality, chocolate cooling times within biscuit and cake
factories tend to be less than 10 minutes. If a lauric compound is being used the
cooling can be as harsh and as short as desired. This is because lauric fats (such as
HPKO) are not polymorphic, so there is no need to allow time for the correct crystal
form to be produced.
8.7
Quality issues
8.7.1 Legislative quality issues
The main issue here is when the product sold to the consumer is below the declared
weight on the packaging (allowing for the average weight legislation currently in
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Enrobed and filled chocolate, confectionery and bakery products
force in the relevant country). If the product is below the declared weight it may be
perceived by the local enforcement body that the customer is being cheated by the
manufacturer and they may prosecute the manufacturer which may lead to a fine
or, even more seriously, to damaging publicity.
8.7.2 Quality issues that cause consumer dissatisfaction
Most of these have already been discussed in this chapter. Poor coverage of the
coating not only leads to a perception that the product is of ‘poor quality’ but also
to a staling of the product because the moisture barrier between the biscuit or cake
and the outside atmosphere is broken allowing the passage of moisture between the
two. A customer dissatisfaction quality issue has the potential to harm the business
doubly. First, most businesses need repeat purchases so if a customer is dissatisfied
they may not buy the product again. Secondly they may complain in which case the
business will have to investigate the complaint and send some financial recompense to the customer in order to attempt to compensate the customer for their
dissatisfaction.
In most biscuit and cake manufacturing, enrobing of the product is the final
stage of processing and because of this any weight or volume deficiencies within
the previous processes will be compensated for in the enrober. However as
chocolate has traditionally been the most expensive bulk ingredient used, using the
enrober to rectify deficiencies of previous weight control is economically unwise.
8.7.3 Bloom, thermal cracking and moisture migration
Because we are dealing with products that have been through a heat process (i.e.
baking), before it is enrobed care must be taken to cool the biscuit or cake to the
correct temperature before it enters the enrober. Care must also be taken to ensure
that the core of the biscuit or cake is also cooled. Often biscuits and cakes are
deemed to be cooled to the correct temperature but it is, in fact, only the surface of
the biscuit and cake which is cooled. Then, when the product is enrobed, the heat
energy within the biscuit or cake dissipates to the surface and detempers the
chocolate. This is often not noticed immediately and fat bloom can result.
However if the biscuit or cake is cooled too much before it enters the chocolate
enrober and contacts the chocolate curtain, a microscopic layer of chocolate can
immediately set on the biscuit. Because this microscopic layer of chocolate has set
too quickly, the correct cocoa butter crystals have not had time to form. This leaves
unstable cocoa butter crystals which can migrate to the surface of the product
leading to a dull appearance of the chocolate.
Ideally when a biscuit or cake enters a chocolate enrober, it should neither give
heat to the chocolate nor take heat from the chocolate. In reality this means that the
core temperature of the biscuit or cake should be in the range of 25–30 °C. Biscuits,
cakes and chocolate have different rates of thermal expansion and contraction.
This is most noticeable when an enrobed biscuit or cake is stored at too cool a
temperature and is then bought back to ambient temperature. Generally biscuits
Biscuits and bakery products
161
and cakes thermally expand and contract less than chocolate. This imbalance in the
thermal expansion and contraction leads to the need to store fully coated biscuits
and cakes at temperatures no lower than 10 °C and no higher than 25 °C to reduce
the risk of the chocolate coating becoming cracked and thus losing its moisture
barrier properties.
When a moisture rich product (e.g. caramel) is used in conjunction with a
biscuit or cake it is possible for the moisture to migrate from the high moisture
component (caramel) to the low moisture biscuit and cake. This moisture migration has two effects. First, the high moisture product will lose its characteristic
texture (i.e. it will go hard and fudge-like in the case of caramel) and, second, the
moisture will cause the biscuit and cake to become stale and, more importantly,
cause it to expand thus cracking the chocolate coating. As has been noted before,
once a chocolate coating has cracked it loses its moisture barrier properties thus
leading to greater staling and expansion of the base product.
8.8
Fillings for bakery products
This chapter has dealt with the covering, either total or partial, of biscuits and cakes
with chocolate or chocolate flavoured coatings. There has been a trend, however,
to fill biscuits or cakes with a chocolate flavour filling. This has mainly been due
to the growth of ‘mall grazing’, that is eating fast or finger food while in an
enclosed shopping area. Traditional chocolate coatings have been too hard to use
within a bakery product and so this has led to the development of a filling that has
the flavour of chocolate but remains liquid at room temperature, leading to a
product that has a runny centre.
As stated before, traditional coatings and chocolate are based on fats that are
solid at room temperature and so are too hard for use in this type of centre. The
reason that these products are solid is because of the type of fat used within the
product. By changing the fat formulation it is possible to make a ‘runny chocolate’
at room temperature. The choice of the fat is, therefore, quite critical to the
formulation.
If a product is to be made to mimic the flavour profile of milk chocolate, it is
desirable to have some cocoa mass used with in the formulation. Since cocoa mass
contains a high proportion of cocoa butter, the fat used for the filling must be
compatible with cocoa butter otherwise the cocoa butter will solidify into small fat
globules within the filling leading to a course gritty texture. For this reason ‘soft
fats’ such as peanut and sunflower oil have been used in the formulation of filling
fats.
Where the main chocolate flavour is to be derived from cocoa powder, the type
of fat used in the formulation is not so critical as there is very little cocoa butter
within the formulation. However, a fat that has a ‘clean’ taste with good stability
is required in order to give an acceptable product.
One major problem with these types of fillings is that the equipment used to
inject the filling is often the same as that used to inject water-based fillings such as
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Enrobed and filled chocolate, confectionery and bakery products
jams. Chocolate and water do not mix and any attempt to make them mix produces
a thick product that is almost impossible to pump. Even small amounts of water
(less than 1% added as free water) will thicken the chocolate to a point where it is
unusable. If the equipment that is used to inject the chocolate flavour filling is
cleaned with water it must be dried totally before the chocolate flavour filling is
used, otherwise any water left in the equipment will cause the filling to become a
thick, mud-like mass that will be unusable and cause damage to the equipment.
8.9
Future trends in chocolate enrobing
Consumers in the western developed world are constantly being told that their diet
is too rich in fatty foods and that this is leading to a large proportion of the
population being overweight and obese. The challenge for the chocolate industry
is to manufacture a chocolate that has less fat within its formulation. It is possible
to produce a milk chocolate that conforms to the legal requirement in that it has a
minimum of 25% fat (made up of milk fat and cocoa butter). However, in order to
use this chocolate to enrobe, it must flow very easily. The general rule is that the
easier the chocolate flow, the greater is its fat content. This means that an enrobing
chocolate has a higher fat content than a chocolate that is going to be used for a
moulded product. The use of acceptable fat extenders may be a way forward but the
consumer’s resistance to additives must first be overcome before this will be
acceptable in the marketplace.
8.10 Sources of further information and advice
AARHUSKARLSHAMN (AAK) (2007). Handbook of Vegetable Oils and Fats, AAK, Karlshamns,
Sweden.
(THE BISCUIT, CAKE CHOCOLATE AND CONFECTIONERY ALLIANCE) (no date).
Chocolate Enrobing and Moulding, CABATEC Training Module C10. BCCC Sector of
Food and Drink Federation, London.
BECKETT ST (2009). Industrial Chocolate Manufacture and Use, 4th edition, Blackwell
Science, Oxford.
LODERS CROKLAAN. Speciality Fat Technology, Loders Croklaan BV, Wormerveer, The
Netherlands.
MANLEY D (1998). Secondary Processing in Biscuit Manufacture, Woodhead Publishing,
Cambridge.
MINIFIE BW (1999). Chocolate, Cocoa & Confectionery: Science and Technology, Springer,
Aspen, Gaithersburg, MD.
BCCCA
9
Chocolate and couvertures: applications
in ice cream
D. J. Cebula and A. Hoddle, Unilever R&D, UK
Abstract: We describe the combination of ice cream and chocolate as a complement of
contrasts in physical and sensory properties and show how these are addressed in the
manufacturing process of chocolate-coated ice cream products. Each material has
distinctive features of texture, melting characteristics and flavour and, to the manufacturer, the combination presents significant technical challenges to making good products.
We introduce the various different formats (sticks and cones etc.) and describe different
formulations, comparing and contrasting chocolate and couverture. The evolution of
manufacturing is discussed and how new technologies provide a source of product
innovation. Lastly we consider the consumer drivers for products to be more nutritionally
sound.
Key words: application process, chocolate-coated ice cream, chocolate coatings,
chocolate-filled ice cream, couverture coatings, enrobing, ice cream, spraying.
9.1
Introduction
For the consumer, the combination of ice cream and chocolate is highly desirable
and derives from the complement of contrasts in the physical and sensory properties of the two materials. Both ice cream and chocolate are essentially sweet and
both have ‘body’ and smooth mouthfeel and, in those respects, are similar. Both
materials are constructed from lists of ingredients, require significant processing,
and result in a structure that confers unique sensorial properties. However, each
material has very distinctive features and there are outstanding differences in their
texture, their melting characteristics and their flavour. Ice cream is soft, creamy
and cooling to eat. Chocolate is firm, often brittle, smooth and warm in the mouth.
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Enrobed and filled chocolate, confectionery and bakery products
Nevertheless the differences conspire and result in irresistible products. In this
chapter we will examine the origins and nature of the differences in texture and
melting behaviour and we will address the challenges consequently faced by the
manufacturer in assembling products, often with highly complicated structures.
For the classical formats (such as sticks and cones etc.) we will describe details of
the different formulations and the demands placed on the manufacturing processes. Lastly we will reflect on how manufacturing is evolving and indicate the
emergence of new technologies that are providing a source of product innovation.
We will also consider the drivers from the consumer side with particular reference
to the requirement for products that are both perceived to be and actually are more
nutritionally sound.
9.2
Features of ice cream and chocolate
It would seem that the first (industrial) use of the combination of ice cream and
chocolate was in the 1920s. Several citations are possible such as choc ices on the
price card from Lyons Maid (2008), Eskimo Pie’s (2008) block of vanilla ice
cream covered in chocolate and also the tale (Shilling, 2006) of how Good Humor
launched stick products:
‘It was 1920. Harry Burt had just created the Jolly Boy Sucker, a lollypop
on a stick. Later, while working in his ice cream parlor, Burt developed a
smooth chocolate coating that was compatible with ice cream. Unfortunately, the new combination was too messy to eat. Burt’s young son,
Harry Jr, suggested that his dad take some of the wooden sticks used for
the Jolly Boy Suckers and freeze them into the ice cream. The first ice
cream on a stick was born from the resourceful tip by a son to his dad’.
Today, significant use is made of chocolate (and related cocoa-based products) in
ice cream on the scale of thousands of tonnes per year.
The two basic components, ice cream and chocolate, are both composed of
ingredients from which complex structures are created. In the case of ice cream,
four phases are present (in varying proportions): ice, air, fat (as droplets) and
‘matrix’ which comprises the unfrozen concentrated aqueous solution of sugar,
milk solids and so on. Chocolate too is multi-phase comprising a dispersion of
sugar crystals, cocoa and milk solids in a continuous phase of fat (cocoa butter,
milk fat etc.) which itself is largely solid.
9.2.1 Ice cream
Ice cream is a material that truly operates on a range of spatial scales (see Fig. 9.1).
On a macro scale the sensory properties of the texture are perceived; these are
determined by the microscopic details of the structure which, in turn, are determined by complex molecular interactions. The main aim is to generate the correct
microstructure in the ice cream to achieve the desired organoleptic characteristics
Chocolate and couvertures: applications in ice cream
Air bubbles
(50% of volume)
165
Fat
droplets
Ice crystals
Matrix
Water
Sugars
Fat
Milk protein
Stabilisers
Emulsifiers
Flavours
Fig. 9.1
0.1 mm
Typical ice cream microstructure by scanning electron microscope.
so that the product can breakdown and melt away in the mouth thus delivering the
consumers’ preferences for taste. However, the structure needs to be sufficiently
robust to withstand transportation and storage, so that quite a balancing act must be
performed to reconcile these simultaneous and often conflicting requirements.
Therefore, in achieving the optimum microstructure, there are tradeoffs between
the formulation (levels and types of ingredients and actives such as process aids
and stabilisers) and the processing regimes (heat transfer rate, temperature of
freezing etc.). A general description of the science of ice cream is given by Clarke
(2004). Increasingly, as consumers demand healthier products, nutritional aspects
of formulation become significantly more important and whereas, for example,
reduction of both saturated fat or sugar are desirable, they may not be immediately
possible since these are crucial components for both the process conditions and the
microstructure per se.
A typical microstructure is one that consists of ice crystals and air bubbles in the
size range 20 µm to about 100 µm, and fat droplets in the size range from 1 µm to
0.1 mm. These fine entities are embedded throughout a viscous solution of sugars,
polysaccharides and milk proteins known as the ‘matrix’. At another order of
magnitude lower in scale, it is possible to identify the location of the fat. Fat
droplets of size <1 µm can be seen which exist as clusters located on the surface of
the air cells as well as distributed throughout the matrix. Not visible in the figures
here, milk protein is also partially located on the air interface and together fat and
protein both help to stabilise the air. Fat has an incredibly important role in the
microstructure which relates directly to the sensory properties like mouthfeel,
creaminess and flavour delivery but it is also critical to the stability of products
such as meltdown. It can be appreciated that reducing the fat by 50% or more, to
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Enrobed and filled chocolate, confectionery and bakery products
enable healthier products, may not only compromise the sensory quality but may
put the stability, specifically of the air phase, at considerable risk.
As mentioned previously ice cream is thermodynamically unstable and even
under ideal storage conditions the structure, specifically the ice and the air phases,
will coarsen over time resulting in loss of quality and loss of stability. This situation
is exacerbated by upward temperature fluctuations and by pressure changes which
affect the air phase. In addition, stability becomes a real problem when distributing
products across different altitudes when the ice cream expands in response to a
lower pressures then shrinks to lower volume as normal pressure is restored. Low
fat or reduced nutritional energy products are particularly susceptible to variations
in ambient conditions.
The structure is created by preparing the ‘mix’ of the ingredients forming an
emulsion of fat droplets. After homogenisation (at high pressure) the size of the
droplets is significantly reduced. Aeration (under pressure) and freezing occur in
a single step in a scraped surface heat exchanger. This produces air bubbles and ice
crystals dispersed throughout the continuous phase. The resulting architectured
structure is held in place largely through kinetics rather than thermodynamics, the
presence of interfaces and structural stability achieved by formation of crystals of
ice. Storage of the structure is effected at low temperature until consumption,
whereupon the structure rapidly breaks down by melting of the ice which gives a
distinct mouth cooling with definite creaminess provided by the fat droplets and
the very small air bubbles.
9.2.2 Chocolate
For chocolate, the principal phases are given by the ingredients namely cocoa
powder and milk solids as particles, and tiny crystals (ca. 25 µm) of sugar all
dispersed throughout a continuous phase of fat. The fat is present as a mixture of
liquid and solid depending on the composition of the fat and the temperature.
Figure 9.2 shows a scanning electron microscope image across the fractured
surface of chocolate which reveals, at least, the spatial scale of granularity of the
microstructure of a typical chocolate.
The microstructure is obtained by a series of processing steps from grinding the
beans, mixing with sugar and refining to reduce the particle size. Then extra fat is
added (cocoa butter and milk fat, in the case of milk chocolate) and milk solids and
natural emulsifiers (lecithin) to facilitate easy flow. The conching stage, at elevated
temperature, drives off unwanted volatiles and helps to develop the distinct
flavour. The chocolate is stored until use, that is crystallising the fat and solidifying
the chocolate (often with a tempering step to ensure the presence of specific
polymorphic forms of the fat). This is necessary to achieve equilibrium of the fat
and prevent recrystallisation, a process that leads to bloom formation spoiling the
product’s appearance. As a solid, chocolate is quite hard but readily melts in the
mouth. The exact melting temperature depends largely on the fat composition of
the chocolate (particularly the level of milk fat) and the degree to which tempering
has been effected (most ambient chocolate melts at around 30 °C whereas
Chocolate and couvertures: applications in ice cream
009970
Fig. 9.2
5 KV
10µm
× 2,000
167
19 mm
Typical chocolate microstructure by scanning electron microscope.
untempered chocolate, usually employed in combination with ice cream and
already much softer, melts at around 17 °C).
9.2.3 Chocolate and couvertures
Forsaking many of the exact details that can be found elsewhere (Marshall et al.,
2003), several types of chocolate formulation are employed in combination with
ice cream. For simplicity chocolate can be real chocolate (containing only cocoa
butter and dairy fat, no vegetable fat except in certain countries where this is
permitted) or couverture (or compounds) which includes products in which some
or all of the cocoa butter has been replaced by other vegetable fats, such as coconut
oil or fractions of palm, see Fig. 9.3 for typical compositions. Depending on the
application (moulding, enrobing or spraying etc) greater levels of fat are required
to facilitate that particular coating process. Since cocoa butter is a very expensive
ingredient, in application for ice cream, cocoa butter is often replaced by vegetable
fat. However, both chocolates and couvertures must possess specific properties to
suit the application in the ice cream sector.
Whereas the properties of chocolate can mainly be changed by altering the fat
content (cocoa butter, milk fat) the couverture properties can be varied over a very
wide range by using different fat levels and fat types (cocoa butter, milk fat,
vegetable fat). Therefore it is possible to get couvertures with specific advantages
in respect of processing, functional properties and oral response.
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 9.3
Variation of fat content and type for typical chocolates and couvertures.
9.2.4 Differences between ambient chocolate and chocolate for ice cream
Chocolate coatings for the ice cream sector have generally higher fat levels (40–
60%) than their ambient counterparts (28–35%). This is in order to obtain a more
fluid chocolate allowing it to flow across the whole product. Even in the short time
during which chocolate is applied, the higher fat level counteracts the fast rates of
setting on the cold surface of the ice cream. Higher fat levels tend to make the
chocolate more expensive than its ambient counterpart. The chocolate for the ice
cream sector generally contains higher milk fat levels to obtain a less brittle
structure. In many countries, the standard couvertures for the ice cream sector are
usually based on coconut oil at levels of 45–60%. Other vegetable fats could be
added to achieve variations in texture and melting characteristics. For example, to
make it softer, sunflower oil and soft fractions of palm oil are added but, to make
it harder, hardened palm oil is used. Premium couvertures contain cocoa mass and
therefore (some) cocoa butter.
In terms of sensory delivery, owing to the cooling effect of ice cream in the
mouth, chocolate in ice cream products should have a lower melting point than in
ambient chocolate (melting point: 21–23 °C vs. 32–34 °C). For this reason, the
normal tempering process that is applied to ambient chocolate ensuring crystallisation into one of the high polymorphic forms of cocoa butter, leading to good
mould release, surface sheen, and so on, is not required for ice cream-coated
products and would actually be counterproductive as the chocolate would taste
waxy.
Chocolate and couvertures: applications in ice cream
Table 9.1
169
Differences between chocolate and couverture as ice cream coatings
Properties
Chocolates
(based on cocoa butter)
Couvertures
(based on coconut oil,
for example)
Formulation
Narrow
Confined to palmitic, oleic and
stearic acids (chocolate legally
defined)
High
Requires optimisation by
emulsifier concentration
adjustment
Fast
Melts over a wider temperature
range (21 to –23 °C).
Higher degree of after cooling
required.
ca. 30 s
6 crystal forms.a
Melting range 18–23 °C when
fresh and rises to 23 °C after
long storage
Plastic to brittle
Wide
Many fatty acid types
The composition can be changed
to obtain special properties
Low
• Low pick-up weight
• Easier to spray than chocolate
Viscosity
Crystallisation rate
Drying times
Melting
Texture on storage
Fast
Melts over a narrow temperature
range (12 to –3 °C).
ca. 10 s
2 crystal forms (α and β')
α hardly survives and β' melts at
around 23 °C both as fresh and
after storage
Brittle (no change)
a
The traditional view is that cocoa butter has six crystal forms. More recent work has modified this view
(see Chapter 4.2). Tables 4.2 and 4.3 compare these two views.
9.2.5 Key properties of coatings in ice cream applications
Each application and final product demand different and specific attributes from its
coating. There can be a conflict between the fat properties required for a particular
couverture attribute (e.g. with respect to processing) and those required for another
attribute (e.g. in the final ice cream product). In these cases, an optimum balance
must be found. The advantages and disadvantages of each couverture or chocolate
must be weighed up before choosing which to use for a particular application. The
key considerations are listed in Table 9.1.
9.2.6 Challenges in processing ice cream and chocolate together
Their basic characteristics define that ice cream is cold and hydrophilic but
chocolate is warm and hydrophobic. The interplay of the characteristics lead to
challenges in processing.
Ice cream must be kept cold during application of hot liquid chocolate; it is deep
frozen to ensure that ice does not melt leading to the release of air bubbles. It thus
presents a rigid ‘former’ of specific shape around which the chocolate must flow
thinly and then set. In a coating process, for example, attention must be paid to the
dynamics of heat flow and viscosity change because these affect the rates of
170
Enrobed and filled chocolate, confectionery and bakery products
solidification, drying and melting of the materials. Balance is required between the
depth of ice cream temperature and the ‘pick-up’ of chocolate achieved; lower
temperature causes a faster crystallisation rate in the chocolate and a subsequent
increase in viscosity. That increase prevents efficient drainage and results in a thick
and uneven layer. Overall adhesion is a perennial problem but is achieved largely
by encasement of the ice cream piece and from the mechanical integrity of the
coating, rather than a specific bond between ice cream and chocolate.
For ice cream bars or mono-bite products that pass through a bath of liquid
chocolate, buoyancy becomes the source of a problem. The low density ice cream
simply floats in the chocolate and so incomplete coating is achieved. Mechanical
arrangements are required to keep ice cream portions submerged to achieve good
coating but not for long enough to allow any melting of the ice cream. As time goes
on, inevitably, ice cream is melted into the chocolate reservoirs. The release of
water has a dramatic affect on the viscosity of the chocolate causing it to thicken
to a paste. For the enrobing process, ingress of water can lead to serious alteration
of viscosity and loss of stability in the chocolate curtain.
When in combination with ice cream, chocolate is required to melt at about
17 °C for good sensory delivery in the final product. Flavour release for chocolate
is better at higher temperatures but the low temperature required to preserve ice
cream structure and delivery of its sensory offering is a limitation. Therefore the
chocolate must be cooled rapidly by the ice cream. Immediately on drying, the
chocolate has a rather plastic and leathery texture and it requires further storage at
low temperature to prevent higher order polymorphic transitions from occurring.
Even during processing this can present a range of problems related to the ease
with which products ‘slide’ efficiently into packaging sleeves. This stabilisation
process is very slow and it can take days in cold store to achieve formation of the
brittle crack features which are particularly associated with chocolate.
Ice cream products with an external moulded chocolate surface are also very
difficult to achieve. In general, successful moulding is largely determined by the
density increase (and hence volume reduction) attained in chocolate as the confectionery fat undergoes polymorphic transition. Efficient release from the mould is
crucial to the surface quality. A special tempering process arranges for crystallisation into one of the high melting point forms for ambient chocolate and achieves
melting around 28–30 °C. For ice cream products, however, special cryogenic
conditions are required to achieve the best mould release and these have been
codified by Cebula and Rayet (1997).
9.2.7 Examples of requirements for these properties in ice cream
Oral response is a very important parameter. The required properties depend on the
final ice cream product. For example:
• The flavour is very important in dipped stick products or in enrobed products
such as bars.
• In layered architectures, the texture contrast is of paramount importance between the ice cream and the ‘chocolate’.
Chocolate and couvertures: applications in ice cream
171
• In cone products the main purpose of couverture is to make sure that the cone
remains crisp on eating. Here the couverture is used as a waterproof layer
between the aqueous ice cream part and the dry wafer.
Chocolate or couverture in contact with ice cream or other products will change
its flavour. Since some of the chocolate flavour moves into the ice cream during
storage time, the sensory attributes of the product should not be tested until at least
one week after production.
9.3
Application processes, formats, requirements, defects
9.3.1 Dipping
Ice cream products carried on sticks can be easily dipped into chocolate to achieve
a good coating. There are a number of process options for manufacturing and
dipping stick products and two examples are shown in Figs 9.4 and 9.5. The two
routes involve different ice cream temperatures, ice cream densities (and therefore
thermal mass), timescales and complexity.
The first route, shown in Fig. 9.4, is for premium products where a good quality,
thick coating can be obtained. In this example, sticks are inserted into an ice cream
flow (typically –6 °C) as it is extruded through a shaped nozzle, then cut into thin
sections before dropping onto plates. The products are passed through a hardening
tunnel and the ice cream is cooled to approximately –25 °C. The sticks are gripped
by mechanical dipping racks and the plates are struck sharply to release the ice
creams. The ice creams are dipped for a very short time (<1 s) into chocolate
coating which is held at 40–45 °C. The ice creams then pass over a drip tray on the
way to wrapping. Wrapping is carried out when the coating surface is sufficiently
dry to prevent smearing on the wrapper (typically within 90 s). Packing is normally
done fairly quickly, before the coating is brittle, in order to prevent products being
damaged or cracked. The chocolate normally sets in an unstable polymorph, which
is fixed owing to the low temperature. The freshly dipped chocolate can remain
plastic or leathery for a number of days before full brittleness is achieved. The
liquid chocolate typically has a Casson viscosity of 0.3–0.6 Pa s and Casson yield
value of 1–3 Pa at 40 °C.
The second example is normally for standard grade products, typically coated
in couvertures which have much more suitable setting properties for this process.
Ice cream is extruded at much higher temperatures (typically –3 °C) and is filled
into metal pockets (moulds) on a turntable over cold brine. At this temperature the
ice cream is quite fluid and fills the pockets without trapping large air voids. The
ice cream is then further frozen from the outside towards the middle. For some
product types, some ice cream can be removed before complete setting and
replaced with a core to provide flavour or texture contrast. Just before freezing is
complete, sticks are inserted. After freezing is complete, the turntable passes over
a warm brine section and the ice cream in contact with the metal is melted
sufficiently to allow products to be removed from the pockets. Products are
172
Enrobed and filled chocolate, confectionery and bakery products
Ice cream extrusion
Stick insertion/
cutting
Conveyed on
plates
Hardening tunnel
Release from plates
Chocolate storage
tanks
Chocolate temperature
control unit
Transfer to dip rack
Feeder for nuts or
other inclusions
43–54 s
Conveyed to dip tank
Chocolate
recirculation
Dipping
0.6 s
Dip tray and blower
55 s
Wrapping
Outer case
Ideal: 15 min
Max: 30 min
Cold store
Fig. 9.4
Process flow chart for dipping extruded and cut ice cream stick products.
transferred to a dip tank and dipped for a short time (<1 s) in couverture which is
held at 35–40 °C (see Fig. 9.5). The reason for the cooler dip with this process is
that the ice cream is typically –17 °C at this stage and can be easily melted. The
products then pass over a drip tray on the way to wrapping. Wrapping is carried out
after the coating surface is sufficiently dry to prevent smearing on the wrapper
(typically within 60 s). Packing is done carefully, since the coating becomes fully
brittle within 2 min and products can be easily damaged or cracked. At this point
the ice cream has warmed to approximately –5 °C and the products are very
delicate. The couverture typically has a Casson viscosity of 0.1–0.2 Pa s and
Chocolate and couvertures: applications in ice cream
173
Frozen ice cream
Cold brine
Pockets of
rotating turntable
Freezing
6 min
Warm brine
Stick insertion
Warm up
Removal from pockets
10 s
30 s
Dip
tank
Baffle
plate
Chocolate
over flow
Sieve
0.9 s
Dipping
Chocolate
from
temperature
control unit
30 s
Drip tray
Weir
50 s
Wrapping
Outer case
Chocolate Chocolate
intake in return line
weir
15 min
Cold store
Fig. 9.5
Process flow chart for dipping moulded ice cream stick products.
Casson yield value of 0.1–0.3 Pa at 40 °C. This gives a much thinner coat than
chocolate but is therefore less likely to melt the ice cream and cause pinholes.
Depending on several factors the ice cream density chosen is typically between
0.5 and 0.7 g cm–3. This allows for ease of ice cream processing such as ability to
retain overrun during freezing, extraction from moulds and preservation of cutting
equipment, and achieving the desired texture contrast of the coating with the ice
cream core.
The factors affecting the pick-up weight and quality of coating include:
•
•
•
•
•
number of dips
temperature of the ice cream
temperature of the chocolate
length of time of submersion
viscosity and yield value of the chocolate
174
Enrobed and filled chocolate, confectionery and bakery products
• mechanical vibration or shuddering
• setting rate of the chocolate.
It is important that the coating should dry quickly (e.g. less than 90 s) so as not
to smear the wrapper. It is also important that the coating remains slightly plastic
for a reasonable time (e.g. 3–4 min) so that any mechanical impact during the
packaging does not cause cracks.
The main defects in dipped products are drips and pinholes. Drips can form at
the bottom of the product cuased by drainage of the coating whilst it is still drying.
Mechanical vibration or shuddering may shake off the drip as the product is moved
from the dipping tank to the wrapping station. The drip can also be forcibly
removed by a de-tailing wire set at the required height. Pinholes are caused either
by too high a coating temperature or by too high an ice cream temperature. Ice
cream is melted during the dipping and entrapped air (as overrun) which is released
from the molten ice cream then forces its way through the coating before it sets.
9.3.2 Enrobing
Bars and other ice cream products which do not contain sticks are most easily
coated by enrobing. The enrober design for coating ice cream products is similar
to that used for enrobing ambient confectionery products. For example, most ice
cream enrobers feature a bottoming section (flood), a means of providing curtains,
air blowers to remove excess coating and a detailer for removing any tails (see Fig.
9.6). Additional features may include a hill, overhang or series of separate belts to
lift products and prevent adhesion to the wire mesh belt. Another difference
between ice cream and ambient product enrobing is the belt speed. Ice cream
enrober belts are much faster and typically travel at 1–2 m s–1 and the residence
time of products on the belt is <10 s. This is to prevent adhesion of products (or
coating) to the wire mesh belt which leads to melting of the ice cream. This is
vitally important as the coating can begin to set within seconds of being applied to
cold ice cream. In the enrobing process, the formation of solid chocolate ‘tails’ or
‘feet’ can be a major problem along the base of, say, the ice cream bar.
Ice creams to be enrobed are typically extruded from shaped nozzles onto a flat
conveyor belt, before being cut to length and passed through a hardening tunnel.
When the ice cream has been cooled to approximately –25 °C it is passed through
single or multiple curtains of 40–45 °C chocolate or 35–40 °C couverture. Each
curtain can be created by filling a trough which then overflows or by pumping
coating through pipes at speed which spreads out after hitting angled deflector
plates. The deflector plate method can be more effective at coating products with
vertical sides. Curtains applied directly from above may deflect over the edges of
vertically sided products leaving gaps in the coating. Bottoming can be carried out
before, during or after top coating. The coating typically has a Casson viscosity of
0.2–0.8 Pa s and Casson yield value of 0.5–3 Pa at 40 °C. For enrobing, ice cream
usually has a density of around 0.7 g cm–3 when applying chocolate and 0.5 g cm–3
for couverture enrobing, according to the needs of texture contrast between the
Chocolate and couvertures: applications in ice cream
Fig. 9.6
175
Enrobing operation for ice cream bars.
coating and the core. As with dipping, couverture coatings are normally much
thinner than chocolate. Downstream processing and packing of enrobed products
is much gentler than dipped products since products are transported on belts rather
than carried on and released from stick-grippers. This means that impact damage
during wrapping or post wrapping is less likely.
The quality and quantity of pick-up is affected by:
•
•
•
•
•
•
•
•
•
•
number of curtains
bottoming depth and duration
temperature of the ice cream and overrun (determines thermal properties)
temperature of the chocolate
length of time under the curtain
viscosity and yield value of the chocolate
setting rate of the chocolate
air knife or other devices for removal of excess coating
detailing rods
transfer from enrober mesh belt to post enrobing belts (with height and speed
synchronisation).
In most cases it is desirable to have a low yield value to keep the pick-up weight
low, but a higher yield value and an air blower can be used to introduce a ripple
pattern on the top surface. It is important to match belt speeds and heights during
transfer from the enrober belt to avoid either the front or back end from being
ripped from the bottom of the product. It is preferable to have a product that has a
shape or orientation which is wider at the bottom than the top as it is difficult to coat
below overhangs.
9.3.3 Spraying
Couverture can be sprayed into or onto ice cream products with great control over
176
Enrobed and filled chocolate, confectionery and bakery products
Fig. 9.7
Fig. 9.8
Cone spraying with couverture.
Ice cream and chocolate spraying for layered products.
dosage and positioning. One such application is as a moisture barrier in cones.
Here the coverage of the wafer needs to be complete and even to prevent moisture
transfer from ice cream to wafer. It is essential that the coating is complete where
the rim of the wafer is in contact with the sleeve as this is where moisture normally
first enters the wafer. Temperature control for spraying is vital since the couverture
needs to atomise easily, yet not drain after application. A degree of firmness needs
to be achieved rapidly, before ice cream filling, to prevent the barrier being
scoured, reducing its thickness and therefore effectiveness (see Fig. 9.7).
The plug which can form at the bottom of the cone, caused by drainage, is not
effective at preventing moisture transfer and if needed (to satisfy appreciative
consumers!) can be added directly. Couvertures for spraying typically have a
Casson viscosity of 0.35–0.45 Pa s and a Casson yield value of 1.5–3 Pa at 40 °C.
Chocolate and couvertures: applications in ice cream
177
Spraying is normally done at 40–45 °C. Various spray equipment is available, the
most important parameters being spray height and width to give appropriate
coverage.
Couverture can also be sprayed into layered fluted products to give a multiplicity of thin brittle layers (see Fig. 9.8). These products have immense texture
contrast, giving the consumer a clearly audible cracking experience when cutting
through the product. The application of thin layers means the couverture sets
quickly, avoiding the risk of being squeezed out of the product after the addition of
the next layer of ice cream. In this application, couverture and air flow rates, spray
height and spray width are important to control distribution and thickness of
sprayed layers. Alternatively it is possible to dribble couverture to form layers
using air-knives to spread the coating evenly and thinly before addition of the next
ice cream layer. In this case a higher viscosity couverture (or chocolate) can be
used, which would not atomise sufficiently during spraying.
9.3.4 Co-extrusion
A further alternative to place chocolate within a product is the method of coextrusion. Here, chocolate is rapidly cooled, using a scraped surface heat exchanger
and, whilst still in a plastic state, is extruded alongside ice cream. An example of
this is shown in Fig. 9.9, where a plastic sheet of chocolate is formed and it follows
the flow contour of an ice cream wave as the wave is formed. The relative
viscoelastic properties of the two materials are critical to the stability of the process
and, in particular, to the solidification kinetics of the chocolate and the melting
characteristics of the ice cream. Another format example is where cylinders of ice
cream are simultaneously formed and coated with chocolate, where the chocolate
is extruded through an annular nozzle around a stream of ice cream. For this
application chocolate is held at 45 °C before rapid cooling to 25 °C immediately
prior to application. Recirculation is vital, to ensure that chocolate is not held
without shear at the point of extrusion long enough for complete solidification to
occur. In this application, the chocolate is crystallised into an unstable low melting
polymorph. This is different to the high pressure cold extrusion of tempered
chocolate (Beckett et al., 1994) used to form shaped chocolate direct from the solid
state.
9.3.5 Chocolate aeration
Chocolate in ice cream can be perceived as very hard, especially where used as a
large proportion of a product. This is due to the combination of high solid content
and low consumption temperature. There are a number of routes to reducing this
hardness, one of which is consuming the product at warmer temperatures, however
this is largely impractical as the ice cream will become extremely soft. Another
route is the use of high butterfat levels or use of couvertures where the solid fat
content is reduced. An alternative method is the addition of large amounts of water,
such that an aqueous phase of sugar solution is formed, reducing the solid phase
178
Enrobed and filled chocolate, confectionery and bakery products
Fig. 9.9
Co-extruded ice cream and chocolate product.
volume. A further method of reducing the solid phase volume is incorporation of
air, a simple expression being the use of ‘flake’. The use of ‘flake’, even in a
relatively warm (typically –5 °C) freshly extruded whippy ice cream is much more
acceptable than a solid lump of chocolate of the same dimensions. Chocolate can
also have gas incorporated in the form of bubbles to reduce the overall solid phase
level. There are two ways of incorporating gas, one of which is whipping gas, for
example air, into the chocolate before application into a product. More recently it
was discovered that certain gases, for example carbon dioxide, could be dissolved
in the fat phase of the chocolate under excess pressure and that this gas would come
out of solution as the chocolate is returned to atmospheric pressure. Use of this
discovery was applied in a product called ‘Sky’, where aerated chocolate was
extruded into the core of a spirally extruded outer cylinder of ice cream (see Fig.
9.10). The CO2 was dissolved into the chocolate at 40 °C under 4 bar pressure
during shear. It was cooled to approximately 30 °C whilst being pumped to the
point of extrusion before exiting the pipe work at atmospheric pressure. At this
point the chocolate is rapidly cooled by the ice cream and an aerated structure
becomes fixed. The gas volume of the chocolate core of Sky was typically 50% and
this enabled a large volume core with the right degree of texture contrast where a
pure chocolate core would have been excessively hard.
9.4
Inclusions in ice cream
Chocolate can be used within products as inclusions, where they provide flavour,
texture contrast and visual contrast with ice cream. In these applications the
chocolate is normally prehardened, usually tempered, unlike chocolate toppings,
coatings or the plug within a cone, where the chocolate is rapidly cooled into a low
melting polymorph. For this reason inclusions are usually quite small or thin, to
avoid perception of excessive hardness. Examples of inclusions are chunks, chips,
drops and curls. For a more visual treat, some manufacturers use premoulded
inclusions, for example fish, animals and other entertaining shapes. Where the
Chocolate and couvertures: applications in ice cream
Fig. 9.10
179
Aerated chocolate stabilised (frozen in) by encasement in ice cream.
inclusions are made with tempered chocolate, or stable couvertures, they can be
stored, under suitable conditions (in a cool, dry place free from sources of taints)
for months before use. They can be fed into a stream of ice cream between the
scraped surface heat exchanger and product container (usually pot or tub). A fruit
feeder can be used to disperse the inclusions evenly and minimise damage to the
inclusions during incorporation. The ice cream needs to be reasonably firm to
prevent inclusions from settling at the bottom of the container after filling. With
certain inclusions, however, the ice cream needs to be reasonably soft to avoid
damage to the inclusions, for example curls or thin flakes where the thickness can
be less than 1 mm. It is extremely fortunate that although these shapes are
particularly vulnerable to damage, they also resist settling! It is important to
minimise downstream shear after feeding delicate inclusions in order to prevent
disintegration. This usually means wide, preferably flexible, pipe work and an
avoidance of sharp bends and valves.
Inclusions normally preclude ‘extrude and cut’ products for two reasons. First,
wire cutters employed for cutting ice cream between –5 °C and –12 °C could be
snapped when encountering hard particles which are firmly embedded in the ice
cream. Second the cutter could drag particles across or out of the surface where
they are not firmly embedded, leaving an uneven surface. For hand-held products,
an alternative method for manufacture is the use of cold rollers, where inclusions
are incorporated into the ice cream stream shortly before moulding between very
cold rotating rollers with shaped depressions. Products made in this manner can
have a much higher volume of inclusions since they are not cut. Also, since the
mould surface is solid, the product surface is rendered smooth and easily released
by the very cold surface of the mould giving excellent surface definition. Unlike
the example given earlier of lolly manufacture, where sticks are inserted into ice
180
Enrobed and filled chocolate, confectionery and bakery products
Fig. 9.11
Cold stamping on the surface of chocolate.
cream, inclusions prevent this owing to resistance during stick insertion, with the
inherent risk of stick breakage within the products. Use of cold rollers allows stick
insertion at the nip point when the product halves are compressed together.
9.5
Future trends
To date, the preponderance of chocolate use in ice cream is for coatings on stick
and bar products applied by dipping or enrobing and inclusion of pieces into the
bulk. However, as with all product types that are susceptible to innovation, this
situation is evolving. This evolution is driven by several factors. First, the needs of
consumers is at the heart of growth in a business and the clear demand in the
emerged markets (of Europe and North America) is for increases in sophistication,
quality, novelty and convenience. Increasingly the concern to have nutritious food
(including that in the ice cream and confectionery sector) is a major factor
contributing to trends. Progressively there is a greater overlap between chocolate
confectionery containing ice cream with ambient confectionery and this too
stimulates the initiatives in cross-over products.
Ice cream and chocolate, both being technically based, in that they require
elaborate manufacturing processes, will make progress towards satisfying consumer demand and trend through the evolution and purposeful development of
technology. There are new initiatives in transferring ambient chocolate manufacturing technology to chocolate-coated ice cream in terms of shaping and making
small format products (such as mono- and duo-bites) and this will continue apace.
A major hurdle has been the development of high stroke rate machinery utilised in
Chocolate and couvertures: applications in ice cream
Fig. 9.12
181
Examples of mono- and duo-bite chocolate-coated ice cream cold
moulded products.
a very low temperature environment. Advances in the manipulation of chocolate
into a solid form, yet still as an unstable polymorph, have really allowed this. Cold
moulding of chocolate is now possible, using cryogenically cooled tools to
decorate surfaces by ‘branding’ (Dyks et al., 2007), see Fig. 9.11. Methods in cold
extrusion of chocolate which may emerge on an industrial scale in the coming
years are also available. In this way chocolate-coated ice cream products will
emulate their ambient confectionery counterparts. Examples of these are now
starting to appear on the market (see Fig. 9.12).
To supply the consumer need for more healthy options, further manipulation of
chocolate (particularly the fat phase) and emphasis on its purported health benefits
will appear. Greater interest is being placed on the functional actives, such as
polyphenols for heart health, in chocolate. Nevertheless the conundrum of how to
deliver such important actives on which to base health benefits in conjunction with
the natural features of sugar and saturated fat of chocolate will remain a challenge.
Arguably it might fuel an increase in consumer acceptance of vegetable-based
‘chocolate’ in which fats and oils offering more unsaturated components are
substituted for modern nutritional benefits.
9.6 Sources of further information and advice
• Beckett, S (2000), The Science of Chocolate, The Royal Society of Chemistry,
Cambridge, UK.
• NIIR Board of Engineers (2005), The Complete Technology Book on Cocoa,
Chocolates, Ice Cream and Other Milk Products, National Institute of Industrial research, Delhi, India.
182
Enrobed and filled chocolate, confectionery and bakery products
• Pennsylvania Manufacturing Confectioners Association (PMCA), various an•
•
•
•
nual conference proceedings. PMCA, 2980 Linden Street, Suite E3, Bethlehem,
PA 18017, USA. http://www.pmca.com.
Trade Journal: Manufacturing Confectioner.
‘Inter Eis’ and ‘Choco-Technique’, Proceedings of the Annual Conferences of
the Zentral Fachschule der Deutschen Susswarenwirtschaft (ZDS). ZDS, DeLeuw-Straße 3–9, 42653 Solingen, Germany. http://www.zds-solingen.de/
home.html.
Publications from major chocolate manufacturers, such as Barry-Callebaut.
Books such as:
• Licks Sticks and Bricks, A World History of Ice Cream (1999). Reinders P
(ed.). Unilever, Rotterdam.
• The Science of Ice Cream (2004). Clarke C (ed.), The Royal Society of
Chemistry, Cambridge, UK.
9.7
References
BECKETT, S T, CRAIG, M A, GURNEY, R J, INGLEBY, B S, MACKLEY, M R AND PARSONS, R T
(1994), ‘The cold extrusion of chocolate’, Trans I Chem E, 72(C), 47–5.
(1997), Frozen Confectionery, EP662787 B1, European Patent
Office.
CLARKE, C (2004), The Science of Ice Cream, The Royal Society of Chemistry, Cambridge,
UK.
DYKS, S, HAGEMAYER, T AND THIELKER, H (2007), Process and Apparatus for Stamping a
Pattern on to Coated Frozen Confection, EP 1 767 099, European Patent Office.
ESKIMO PIE (2008), http://americanhistory.si.edu/archives/d8553.htm (viewed on 24 January 2008).
LYONS MAID (2008), http://www.kzwp.com/lyons/group2.htm (viewed on 24 January
2008).
MARSHALL, R T, GOFF, H D AND HARTEL, R W (2003), Ice Cream, VI edition, Kluwer
Academic/Plenum, New York, pp 285.
REINDERS, P (1999), Licks Sticks and Bricks, A World History of Ice Cream, Unilever,
Rotterdam.
SHILLING, D (2006), ‘A Youngstown candy maker invented the Good Humor Bar’, The
Vindicator, May 8.
CEBULA, D J AND RAYET, J
Part II
Product design
10
Product design and shelf-life issues: oil
migration and fat bloom
G. Ziegler, Penn State University, USA
Abstract: The shelf life of chocolate-containing confections is often limited by changes
in the fat crystal network. Fat bloom results from the recrystallization of the solid fat
fraction and can be accelerated by the migration of foreign oils into the chocolate. This
chapter discusses the physical mechanisms underlying oil migration and fat bloom,
summarizes recent research into these phenomena and makes practical suggestions for
their mitigation. The discussion stresses the care that must be taken when interpreting
investigations of oil migration and bloom.
Key words: chocolate shelf life, fat bloom, fat migration, oil migration, softening of
chocolate.
10.1
Introduction
The quality of chocolate and other fat-based confections depends on the structure
of the continuous-phase, semi-crystalline fat network. This network can vary in its
solid-to-liquid fat ratio, crystalline polymorph and crystal size and shape, all of
which affect the product quality attributes, including appearance (gloss), texture
(snap) and flavor release. As manufactured, this network is only metastable and,
consequently, changes occur during storage and transportation that have an impact
upon product shelf life. The rate and extent of these changes is determined by
product formulation, processing and storage conditions.
The visual appearance of ‘bloom’ on the surface of chocolate is due to light
scattering, resulting from an increase in surface roughness, which in the case of fat
bloom originates with the growth of fat crystals exceeding a few micrometers in
size protruding from the surface. Although most readily observed as a surface
186
Enrobed and filled chocolate, confectionery and bakery products
defect, this recrystallization within the chocolate degrades product texture and
alters flavor release.
While fat bloom results from redistribution of triacylglycerols within a fatbased product, many undesirable changes limiting the shelf life of chocolate and
confectionery coatings are accelerated by the migration of foreign fats and oils
from the centers of filled confections. Most problematic are the migration of highly
liquid nut oils or incompatible fats. A significant amount of original research on the
related topics of fat bloom and oil migration in chocolate, some employing
advanced analytical techniques or proposing new mechanistic explanations, has
appeared in the last decade (see Sections 10.6 and 10.7). This chapter will attempt
to bring some coherence to these findings, as well as to suggest practical means for
extending product shelf life.
10.2
Mechanisms of oil migration and fat bloom
A clear understanding of the fundamentals will aid the confectionery technologist
in mitigating the deleterious effects of oil migration or fat bloom and extending the
shelf life of fat-based confectionery.
10.2.1 Oil migration
The migration of natural fats and oils occurs only in the liquid phase and hence the
phenomenon will be referred to as oil migration. Oil migration often determines
the shelf life of composite confectionery when chocolate or coatings are in direct
contact with oil-rich components like nuts, biscuits or cream fillings. While oil
migration may result in bloom, the shelf life is often limited by textural changes,
especially softening of the chocolate or coating which in the extreme causes the
product to smear onto the inside of packaging or the consumer’s hands.
Diffusion
Diffusion is the process by which matter migrates from one part of a system to
another as a result of random molecular motion. The phenomenon of diffusion is
independent of the mathematics that may be used to describe it; just because
experimental data do not fit simple expressions of Fick’s laws does not mean that
the underlying mechanism of oil migration is something other than diffusion. Even
simplified models can provide valuable insight into the oil migration problem. For
example, adopting a simplified solution to Fick’s law (equation 10.1),
m
A√Dt
—t = ——–
ms
V
[10.1]
where mt/ms is the ratio of oil migrated at time t over the total oil migrated at
saturation, A is the contact area, V the sample volume and D is the effective
diffusion coefficient, Ziegleder et al. (1996a,b) calculated values of D for triolein
Product design and shelf-life issues: oil migration and fat bloom
187
(OOO) through chocolate at temperatures between 10 and 26 °C and demonstrated
the dramatic dependence of oil migration on the liquid fat content (LFC) of the
chocolate. Temperature, through its effect on LFC, is consistently shown to be the
most important factor affecting oil migration. Storage of composite confectionery
below 20 °C generally limits oil migration, while temperatures in excess of 25 °C
are abusive.
In a like manner, anything that alters the solid fat content will influence oil
migration. Oil will migrate faster through milk chocolate, softened by the presence
of milk fat, than plain chocolate (Choi et al., 2007) (unless the dark chocolate has
added milk fat) and the addition of nut pastes to chocolate formulations would
likewise increase the oil migration rate. Incompatible fats that otherwise are solid
and would not migrate do so because the formation of eutectics results in an
increase in LFC.
The effective diffusivity Deff is a function of the molecular diffusivity, Do, times
the ratio of the liquid fat content (liquid phase volume fraction, φl) to the tortuosity,
τ (equation 10.2),
φ
[10.2]
Deff = D0 –l
τ
In theory, diffusion can be slowed by placing impervious obstacles in the
diffusion path, thereby increasing τ. If τ, that is the length of the diffusion path, can
be increased, then the rate of diffusion can be slowed. However, within the
limitations set by the chocolate formulation and processing, only small changes in
tortuosity are possible and the influence of the liquid phase volume fraction
dominates. This is why non-fat particle size or tempering has little, if any, effect on
the oil migration rate. For this to be an effective strategy for mitigating oil
migration, the impervious particles should be highly asymmetric (flat plates) and
oriented perpendicular to the direction of migration. The first would be very
deleterious to the flow properties, increasing the viscosity, and the second would
be difficult to accomplish in chocolate processing.
Diffusion best describes oil migration within a single component, for example
the chocolate, driven by chemical potential gradients (approximated by gradients
in triacylglycerol (TAG) concentration). On this basis, one might conclude that
diffusion is not operative in solid eating chocolate, since it has a homogeneous
composition. However, while the composition may appear to be homogeneous in
the bulk, localized gradients drive diffusion resulting in the redistribution of
TAGs, which then causes bloom. There will be more about this in Section 10.2.2
Liquid-mediated recrystallization.
Capillary flow
While the net migration of oil is reasonably approximated by equation 10.1 at short
times, simplified solutions to Fick’s laws of diffusion, especially those assuming
a constant diffusivity, do not accurately predict the spatial distribution of oil within
the chocolate (Choi et al., 2007). This apparent discrepancy has led to the
hypothesis that mechanisms other than diffusion are responsible for oil migration,
and among the alternatives to diffusion is ‘capillary action’ (Aguilera et al., 2004).
188
Enrobed and filled chocolate, confectionery and bakery products
Capillary action is the tendency of liquids to rise up capillary tubes owing to the
surface tension (Atkins and DePaula, 2006), perhaps the most common example
being the wicking of liquid into a sponge. The kinetics of capillary rise is
commonly described by the Lucas–Washburn equation (equation 10.3),
2
dh + ρgh
– γcosθ = –82µh ––
r
r
dt
[10.3]
where r is the capillary radius, γ is the surface tension, θ is the contact angle, µ is
the viscosity of the liquid, h is the distance the fluid is drawn into the capillary, t is
time, ρ is the liquid density and g is the acceleration due to gravity. For fluid to be
drawn into a capillary, the contact angle between the fluid and the solid capillary
wall must be less than 90 º.
For oil migration to be driven by capillary forces, the chocolate must be
composed of interconnected, vacant pores, which it generally is not. While the
work of Loisel et al. (1997) has been used as evidence of porosity in chocolate,
the pore volume they measured was a mere 1–4% of the total chocolate volume,
hardly enough to account for the large amount of oil that can migrate into a
chocolate coating. From gas permeability measurements, Loisel et al. (1997)
concluded that the pores were ‘probably closed and/or almost totally filled with
the fraction of cocoa butter that remains liquid at room temperature’, and that
‘empty spaces left by such partial filling with no connection to each other,
should thus be considered as empty cavities rather than pores’. Work conducted
on moisture migration through chocolate coatings confirms these findings
(Ghosh et al., 2004, 2005).
More recently Rousseau (2005) described the surface porosity of chocolate, but
provided no evidence that these pores extended throughout the bulk. Smith and
Dahlman (2005) concluded that ‘pits or pipes’ of 1–4 µm in diameter penetrated
deep into the chocolate and could conceivably ‘reach down into the filling,
providing convenient routes for migration of the filling oil’, but this was mere
speculation, since only surface porosity was observable and no other data supported these conclusions.
The flow of liquid into a capillary network (dh/dt in equation 10.3) is relatively
fast – of the order of seconds to hours – much faster than the timescale of oil
migration, which is usually days to months. For example, Carbonell et al. (2004)
measured the capillary flow of sunflower oil into a bed of chocolate crumb with a
mean porosity of 0.43 and observed the oil front to move 4 cm in 4 hours. Altimiras
et al. (2006) concluded that the timescale for capillary rise would be far too short
compared to the timescale for oil migration determined experimentally. From this
evidence alone, it seems unlikely that Laplace pressure (‘capillary action’) exerts
much influence over oil migration through chocolate.
Aguilera et al. (2004) point out that flow driven by Laplace pressure should not
be confused with flow through porous media under the influence of an external
pressure gradient. It has been suggested that bloom forms after liquid oil has been
‘pumped’ to the surface through cracks and pores. In oleaginous cosmetics (e.g.
lipstick), oil droplets are forced to the surface at higher temperatures owing to
Product design and shelf-life issues: oil migration and fat bloom
189
expansion of the liquid oil phase within the solid wax matrix in a process called
‘sweating’ (Matsuda et al., 2001). However, Matsuda et al. (2001) concluded that
sweating and bloom formation were separate and unrelated phenomena. Sonwai
and Rousseau (2006) found little evidence that pores were involved in bloom
formation in chocolate or cocoa butter, despite the suggestions of Smith and
Dahlman (2005). This is discussed in further detail in Section 10.2.2.
It is often assumed that given enough time, the composition of the fat phase in
the coating will be the same as that of the filling (Smith et al., 2007). However, a
net migration of oil from softer fats to harder fats is often observed during the
relevant time period. The net migration of oil from peanut butter to chocolate may
occur to such an extent that the peanut butter appears to ‘dry’ out (Walter and
Cornillon, 2002). In this case, capillary pressure may be operative, but in a way to
oppose further oil migration, as the pores within the filling are vacated. This
suggests the potential importance of filling structure as a means of mitigating oil
migration. Capillary action may be an important mechanism in coated biscuits,
with the porous nature of baked goods. But why should there be a net migration of
oils into fats?
Interphase migration
Diffusion and capillary action are means of explaining oil migration within the
chocolate coating, but not necessarily between the filling and the chocolate. The
concept of the distribution coefficient, K, is helpful in understanding migration
between two components or interphase mass transfer. K is usually defined as the
relative concentration of a compound in phase x and y, cx/cy, and conceptually may
be thought of as the relative attraction each phase has for the compound. For the net
migration of oil to proceed to an extent that the filling appears to dry out, there must
be something in the chocolate attracting the oil to it.
When crystalline sucrose is stored in an atmosphere exceeding about 85%
relative humidity, there will be a net migration of water from the environment to
the sucrose, resulting in dissolution of the sucrose. This phenomenon is called
deliquescence and occurs whenever a crystalline solid is stored at a relative
humidity that exceeds the water activity of its saturated solution. The water acts as
a solvent to dissolve the sucrose and is attracted to the sucrose because its chemical
potential in the solution state is lower than it is in the vapor state. In a similar
manner, oil acts as a solvent for the solid phase of cocoa butter, and is attracted to
the chocolate because its chemical potential is lower in the solution state than the
pure liquid state.
To illustrate this point, Ziegler and Szlachetka (2005) demonstrated that when
hazelnut oil was ‘presaturated’ with cocoa butter (about 20% cocoa butter in
hazelnut oil) there was no net migration of oil from a soaked filter paper to a
chocolate wafer, despite the fact that the mixture was entirely liquid, while with
pure hazelnut oil, the 3 g chocolate sample gained nearly 0.5 g (Fig. 10.1). In
several instances, investigators have observed a dip in the concentration of oil at
the filling–chocolate interface (Walter and Cornillon, 2002; Choi et al., 2007). In
these cases, it appears that the diffusion of oil into the chocolate away from the
190
Enrobed and filled chocolate, confectionery and bakery products
Cumulative weight gain (g)
0.25
0.2
0.15
0.1
0.05
0
3
5
7
9
11
13
15
Time½ (hr½)
Fig. 10.1 Net migration of hazelnut oil into a 3-g sample of chocolate (38 mm × 38 mm
× 1.4 mm). Circles, hazelnut oil alone; squares, liquid phase of cocoa butter; triangles,
80:20 hazelnut oil:cocoa butter blend. (Ziegler and Szlachetka, 2005).
interface is more rapid than the diffusion of oil through the filling to the interface
and hence the interface becomes depleted in oil.
Unfortunately, few studies have considered migration in the filling and the
chocolate as a whole. For commercial products, coatings and fillings should be
developed systematically, as it is likely that the best coating for one filling may not
be the best for another with respect to oil migration. This filling–coating match–
mismatch has consequences for experimental studies also, and is discussed more
in Section 10.3.
Oil migration per se is not the culprit, but the subsequent change it brings about
in product quality is. Softening occurs because the oil, as it migrates, dissolves
some of the solid fat of the coating and fat bloom may be accelerated if the
migrating oil tips the balance toward recrystallization.
10.2.2 Fat bloom
Fat bloom is simply the result of recrystallization of the metastable lipid phase.
When it occurs, crystals of sufficient size grow from the surface, resulting in a
visible lightening of the product. As with oil migration, effective control of bloom
requires knowledge of the forces driving its formation. In nature, any phenomenon
that occurs spontaneously must result in a reduction in the free energy (e.g. the
Gibb’s free energy, G). Bloom occurs because the free energy of the newly formed
crystals is lower than that of the original crystalline state.
Three mechanisms are often discussed relative to fat bloom: polymorphic
transformations, phase separation (crystal ‘perfection’) and oil migration. All three
will result in a reduction in free energy and may be operative in bloom formation
simultaneously. While solid state transformations from lower melting poly-
Product design and shelf-life issues: oil migration and fat bloom
191
Liquid
∆G 1
∆G 2
A
B
Fig. 10.2
Changes in Gibb’s free energy (∆G) associated with a transition from
solid A to solid B.
morphs to more stable ones may occur, they are unlikely to result in bloom unless
they are also accompanied by crystal growth, that is, a simple conversion from βV
to βVI (see section entitled Polymorphic transformation) without a significant
change in the crystal size will not result in the dramatic appearance of bloom on the
surface. Similarly, the simple ‘ripening’ of a single crystal to increase its ‘perfection’ by expelling less compatible triacylglycerols is not likely to result in bloom.
Crystal growth requires mass transfer (i.e. diffusion) and this occurs through the
liquid phase. Hence we can speak of liquid-mediated recrystallization.
Liquid-mediated recrystallization
State A is at a higher energy than B and since a transition from A→B results in a
negative change in free energy (–∆G), the transition should occur spontaneously.
In the case of fat recrystallization, state A could represent a lower melting
polymorph than B, a smaller crystal than B, or a ‘less perfect’ crystal than B.
However, the fat must first dissolve in the liquid oil, which may require some
energy (∆G1), for example, from a temperature fluctuation. Once it dissolves from
the surface of A, the fat must diffuse through the liquid to the surface of B and be
incorporated into the growing crystal. The release of energy as this occurs is
enough to drive further dissolution and the process continues or even accelerates
(Fig. 10.2).
It would be reasonable to assume that the greater the amount of liquid phase the
faster the transformation since, like oil migration, the effective diffusivity would
increase. However, other phenomena are also at work, including the initial
dissolution and the eventual recrystallization. Therefore, anything that influences
the dissolution (solubility) of A, the diffusion to B, or the subsequent
recrystallization of B will alter the rate of bloom formation. Since bloom is a
(re)crystallization phenomenon it exhibits an onset (induction) time, a growth rate
and a final extent. It is not always stated or obvious which of these parameters
investigators are reporting on when they say that an ingredient or set of conditions
‘inhibits bloom’. For example, while it is generally believed that milk fat inhibits
bloom, the effect appears to be on the rate and extent of bloom formation; the onset
192
Enrobed and filled chocolate, confectionery and bakery products
time may actually be shorter for formulations containing milk fat (Ziegleder, 2006;
Ali et al., 1998). This lack of specificity often causes apparent contradictions
between studies.
Matsuda et al. (2001) demonstrated, somewhat counterintuitively, that fat
bloom on lipstick lessened as the solubility of stearic acid, responsible for bloom
formation, increased in the oil phase. Referring again to Fig. 10.2, while an
increase in solubility can be seen as a decrease in ∆G1 and more ready dissolution
of A, it also results in a decrease in the magnitude of –∆G2, slowing recrystallization.
This may partly explain why milk fat, while softening chocolate, also slows bloom
formation.
Milk fat may also interfere with the recrystallization process on the surface of
B, just as glucose can interfere with the graining of sucrose. However, the effects
of other fats and oils are less well understood and more research is needed on the
intersolubility or phase behavior of triacylglycerols.
Incompatible fats and oil migration
Natural fats and oils are mixtures of numerous TAG species, the phase behavior of
which can be quite complex (Timms, 2002). To simplify matters, mixtures of two
natural fats or oils are often treated as pseudobinary systems (filling fat and coating
fat). Mixtures of importance to the migration of foreign oils and fat bloom are those
that form monotectics and eutectics, since these will have an effect on the solid fat
content (SFC) of the coating. A monotectic occurs when the SFC of a mixture is
less than that predicted by simple dilution alone, but still between that of the
constituent fats (Fig. 10.3). Monotectics are typical of nut oil–hard fat blends
(often incorrectly referred to as eutectics). Eutectics are formed when constituent
fats differ in molecular volume, shape or polymorph, but not greatly in melting
point. The result is a eutectic melting point that is lower than the melting point of
either of the constituent fats.
Some investigators have presumed a one-to-one correspondence between oil
migration and bloom formation (Altimiras et al., 2006) and some have even
measured bloom and interpreted the data in light of migration mechanisms
(Quevedo et al., 2005). However, the migration of filling oil and bloom of the
coating are two separate, albeit interrelated, phenomena. The migration of nut oils
or incompatible, eutectic-forming, fats increases the liquid phase through which
polymorphic transformations occur (Kahn and Rousseau, 2006; Smith et al.,
2007).
Assuming that bloom crystals grow by deposition of new TAGs onto the
exposed surface, numerous investigators have proposed that somehow the liquid
fraction migrates to the chocolate surface, whereupon the hard fraction it has
dissolved recrystallizes. The oft-repeated explanation is that the liquid is ‘pumped’
to the surface through cracks and pores. However, despite numerous attempts to
demonstrate this, little evidence exists to support such a mechanism. Rather than
growing by deposition of new material at the surface, crystal growth can occur
from below the surface, so that bloom crystals grow like mountains. This would not
require the migration of liquid oil to the surface and local gradients would drive
Product design and shelf-life issues: oil migration and fat bloom
193
100
90
Solid fat content (%)
80
õõ
õõ
õõ
70
60
50
õ
40
30
õ
20
10
0 õõõõõõ
0
10
õ
20
30
40
50
60
70
80
90
100
Fraction cocoa butter (%)
Fig. 10.3 Monotectic behavior of a cocoa butter–hazelnut oil blends at 21.1 ºC.
Straight solid line represents expected SFC from simple dilution.
diffusion of TAGs within the chocolate as outlined in Fig. 10.2. To the author’s
knowledge, no studies have been done to determine whether growth occurs by
addition to the surface of the bloom crystals or from beneath.
Polymorphic transformation
Bloom occurring during storage is always accompanied by a polymorphic transformation from βV to βVI (Lonchampt and Hartel, 2004). Van Mechelen et al.
(2006a,b, 2007) have recently shown this transformation to be a difference in the
stacking of neighboring ‘three-packs’ of mono-unsaturated triacylglycerols of the
Sat-UnSat-Sat type (e.g. POS and SOS) (Fig. 10.4). Transformation from βV→βVI
requires one three-pack to ‘flip over’, which would not be easy in the solid state,
but could easily be melt-mediated (van Mechelen et al., 2006a,b, 2007).
Just as oil migration per se does not cause quality deterioration, the rather subtle
transformation of solid cocoa butter from form βV to form βVI does not cause visible
bloom (Bricknell and Hartel, 1998). For the visual appearance of bloom on the
surface, this transformation must result in protruding crystals and, therefore,
crystal growth. Using atomic force microscopy, X-ray diffraction and differential
scanning calorimetry, Hodge and Rousseau (2002) demonstrated a strong correlation between an increase in surface roughness and the βV→βVI transition, although
some minimal value of roughness was required for the appearance of visual bloom.
The polymorphic transformation from βV→βVI preceded an increase in the whiteness index by 1–2 weeks (Sonwai and Rousseau, 2006).
194
Enrobed and filled chocolate, confectionery and bakery products
a
b
c
(a)
a
b
c
(b)
a
c
b
(c)
a
b
c
(d)
a
b
c
(e)
a
b
(f)
Fig. 10.4
(a)–(c): β2 (form V) packing of POS; (d )–(f): β1 (form VI) packing of SOS,
from van Mechelen et al. (2006a,b) with permission.
Product design and shelf-life issues: oil migration and fat bloom
195
Influence of non-fat particles
Surface bloom on undertempered chocolate may not actually be ‘fat’ bloom,
although its ultimate cause is an uncontrolled crystallization of fat. Kinta and Hatta
(2005a) found surface bloom on untempered chocolate to be largely sugar and
cocoa particles, apparently forced to the surface as it segregated from the crystallizing fat, an observation confirmed by Lonchampt and Hartel (2006), who also
reported that bloom on overtempered chocolate was most likely to be due to large
cocoa butter crystals.
Chocolate surfaces properly formed in contact with a mold are smoother and
glossier than those formed in contact with air (e.g. drops or enrobed pieces). In a
manner similar to stones in the ground that are worked to the surface through repeated
freeze–thaw cycles, contraction of the fat on cooling and solidification leaves behind
non-fat particles that produce a rougher surface than on a molded piece. The lack of
restraint at a free-formed surface permits fat crystals to grow freely outward. Melt–
recrystallization cycles can undo the effects of proper molding, resulting in as rough
a surface as if the piece were free-formed, with the roughness increasing with each
melt–recrystallization cycle. Melt–recrystallization can, in this way, causes a loss of
gloss (which is not necessarily synonymous with the onset of bloom).
Adenier et al. (1993) demonstrated that bloom did not form on surfaces in
contact with aluminum foil. While it has been suggested that this resulted from an
inhibition of oil migration to the surface, it is more likely that the aluminum foil
acted much as a mold does, physically preventing crystal growth from the surface.
Few studies mention if and how samples are packaged during storage and whether
or not packaging materials are in contact with the surface of the chocolate being
evaluated for bloom development.
In a study of bloom formation on chocolate drops that were one ingredient in a
‘trail mix’, Szlachetka (2007) determined that bloom appeared where peanut butter
drops, made with partially hydrogenated palm kernel oil (PKO), came in contact
with the chocolate. In this instance, the eutectic formed by the comingling of the
cocoa butter and PKO resulted in the dissolution of the surface fat and exposure of
non-fat particles, creating light spots.
10.3 Detection
Numerous analytical techniques are available for the detection of oil migration and
fat bloom, each with advantages and disadvantages. The experimental set up,
which is as important as the actual detection method, may even determine the
mechanism of migration. While model systems are preferable for investigating the
fundamental aspects of oil migration, actual products should be used to establish
shelf stability.
10.3.1 Oil migration
Oil migration may be observed directly by measuring the concentration of migrat-
196
Enrobed and filled chocolate, confectionery and bakery products
ing oils, or indirectly through its effect on product quality. The approach taken
depends largely on the goal of the investigation, that is a mechanistic study of oil
migration or an understanding of quality deterioration. A simple exchange of the
liquid phase of cocoa butter for liquid nut oil is not likely to result in major quality
deterioration. Recall, it is not the oil migration per se that is the problem, but the
consequences of that migration, such as softening or bloom.
In most published research, regardless of the analytical technique used to
quantify the migration of foreign fats or oils, a model system is employed such that
the migration occurs in one dimension. This is commonly accomplished by
layering chocolate over (or under) a ‘filling’. One can either measure the total
uptake of migrating oil in the chocolate or filling phase, or the spatially-resolved
concentration profile(s). The latter provides more detailed information about the
migration process, but requires either a technique capable of spatial resolution in
situ, or a means of separating layers of the samples physically before analysis.
Non-destructive in situ measurement generally requires advanced and expensive
instruments, but offers the opportunity to follow migration within a single sample
over time.
For in situ measurement, migration may be limited to a single dimension by
sequentially casting two layers in a cylindrical tube (Choi et al., 2007). However,
care must be taken so that the contraction of the chocolate on cooling does not leave
a gap at the edges that could draw in oil (and appear as capillary action). This
technique provides a well-defined contact area, good contact between the components and the layers can be made sufficiently thick so as to be considered ‘infinite’.
This approach is not suited to measuring the net uptake of oil over time, as the
layers are not easily removed from the tube. Instead, chocolate pieces may be
placed on a ‘bed’ of filling or filter paper (containing oil or not) in a Petri dish or
other suitable container (Ziegler and Szlachetka, 2005). To avoid edge effects,
chocolate pieces must be sufficiently large in length and width (diameter) relative
to the thickness. The sample must be easily separated from the filling for weighing,
which can cause problems in assuring good contact between the components.
If layers are to be separated, say for calorimetry, X-ray or compositional
analysis, the best technique is the ‘washer test’ of Talbot (1996). A steel washer
(2.5 mm thick) is fixed to a plastic base. Filling is deposited in the central hole
(1 cm diameter) and cooled. Five or more thin washers (0.5 mm thick) are stacked
on top of the first and chocolate is deposited in the central hole. The central hole of
the thin washers is slightly greater than that of the thick washer, so that when the
chocolate contracts, there is no gap (Fig. 10.5). For analysis, the chocolate layers
are separated from the filling and from each other using a thin razor blade. This test
most closely represents the enrobing of a prepared center, where liquid chocolate
is brought into contact with the filling and hence the effects of improper center
cooling can be studied. However, to simulate shell molding, the coating should be
solidified before contacting the filling. Destructive sampling, like the ‘washer
test’, facilitates the direct measurement of oil concentrations, but requires a
number of ‘identical’ samples that can be sacrificed over the storage time. By this
means, sample-to-sample variation is confounded with changes over time.
Product design and shelf-life issues: oil migration and fat bloom
197
Razor blade to separate layers
Thin washers
Chocolate
Filling
Thick washer
Plastic base
Fig. 10.5
Cross-sectional view of the washer test apparatus (Talbot, 1996).
The spherical shape of filled ‘truffles’ gave Ziegleder (2006) the opportunity to
observe oil migration in a simple one-dimensional geometry (radial), and also to
follow quality deterioration in a commercial product. However, for many commercial products, the geometry is quite complex and failure may occur owing to
preferential migration at corners, seams, edges or between impermeable layers
(Miquel and Hall, 2002).
As alluded to above, a critical detail that differentiates studies of oil migration
is whether the chocolate and ‘filling’ are brought in contact before or after the
chocolate is solidified (and the filling cooled). Oil will migrate rapidly into
tempered liquid chocolate in which greater than 90% of the cocoa butter is in the
liquid state. Enough oil can migrate prior to solidification of the chocolate to alter
the crystallization characteristics of the coating. Fig. 10.6 shows the extent and
effect of hazelnut oil migration into chocolate as it cools. In the absence of hazelnut
oil (open squares), chocolate hardens (the snap force increases) with cooling time,
but when brought into contact with hazelnut oil prior to complete solidification
(open circles), the chocolate is seen to soften even as it cools. Furthermore,
contraction of the solidifying fat can actually draw liquid oil into the coating
(Marty et al., 2005) and appear as ‘capillary action’. This has practical consequences (see Section 10.4.3).
Experiments can be conducted in such a way as to predetermine the mechanism
of oil migration. For example, Dibildox-Alvarado et al. (2004) placed semi-solid
samples consisting of interesterified hydrogenated palm oil and peanut oil (60:40)
on filter paper to monitor the loss of oil from the fat crystal network. In this
instance, the driving force for oil migration would be capillary forces within the
filter paper aided by gravity and opposed by capillary forces within the fat network.
In effect, Dibildox-Alvarado et al. (2004) measured the relative capillary pressure
of oil in the fat network to that in the filter paper’s fiber network, and as a
consequence, observed that draining of oil from the fat crystal network was slowed
Enrobed and filled chocolate, confectionery and bakery products
400
390
380
370
360
350
340
330
320
310
300
290
280
270
260
250
240
70
60
50
40
Hazelnut oil concentration (%)
Snap force (g)
198
30
20
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Time (hours)
Fig. 10.6 Migration of hazelnut oil into chocolate during cooling. Open squares, increase
in snap force as chocolate solidifies. Open circles, snap force of chocolate in contact with
hazelnut oil. Closed circles, amount of hazelnut oil migrated during cooling, from
Shetty (2004).
in rapidly cooled samples comprising small fat crystals. However, this may have
little relation to how this fat behaves in a composite confection.
A similar experimental set up was employed by Altimiras et al. (2006), but in
this case, the investigators placed a new, ‘dry’ filter paper in contact with simulated
‘chocolate’ (mixtures of cocoa butter and black sand) each time the paper was
weighed. The smaller the particle size of the sand used, the more cocoa butter
migrated, contrary to expectations for capillary action and the results of DibildoxAlvarado et al. (2004). Samples were stored at 30 °C, where particles are sufficiently
mobile to repack (settle) during the experiment. It is likely that settling of the
particle bed was greater for the smaller particles, excluding more cocoa butter.
They also followed changes in the whiteness index, which they assumed were
caused by fat crystal development (Altimiras et al., 2006). However, is it just as
likely that the increased whiteness was merely a result of exposure of the sand as
the fat retreated (like sand on a beach), as it appears that the cocoa butter migrated
through the lower surface (in contact with the filter paper), while the color was
measured on the upper surface.
Textural changes
The migration of oil between the individual components of a composite confectionery would be inconsequential if it did not bring about dramatic changes in
product quality. Alterations in texture are among the most detrimental changes
observed; the coating softens, the filling hardens and sensory contrast between the
Product design and shelf-life issues: oil migration and fat bloom
199
two is lost, having an impact on flavor perception. Hardness can be monitored by
sensory tests, but instrumental methods are preferred since for chocolate they are
easy, reproducible and highly correlated with human perception. Furthermore,
hardness is directly correlated to solid fat content (SFC), so techniques measuring
SFC, such as calorimetry or nuclear magnetic resonance, provide useful information as well.
Ali et al. (2001) used maximum penetration force to follow softening of filled
dark chocolate over time. Snap force, determined using a three-point bend apparatus, similarly declined as oil migration proceeded (Shetty, 2004). Softening
(decrease in SFC) and polymorphic transitions (change in melting point) have been
followed simultaneously using differential scanning calorimetry (DSC) (Ziegleder,
2006). Oil migration has also been followed using low-resolution nuclear magnetic resonance through its effect on SFC (Shetty, 2004) and relaxation times
(Walter and Cornillon, 2002).
Nuclear magnetic resonance imaging (MRI)
Nuclear magnetic resonance imaging (MRI) has been employed by several groups
to follow oil migration into chocolate (Guiheneuf et al., 1997; Miquel et al., 2001;
Miquel and Hall, 2002; Walter and Cornillon, 2002; Deka et al., 2006; Choi et al.,
2005, 2007). The advantages of MRI include the ability to measure migration nondestructively in situ and, therefore, follow the process in a single sample, avoiding
problems of sample-to-sample variation. Conventional spin-echo MRI detects
signals from liquid lipid protons only (Guiheneuf et al., 1997), and hence it is an
indirect measure of oil migration. In fact, it measures only the migration which
results in a change in the solid fat content. The change in the amount of liquid phase
during migration is not a direct measure of the amount of oil that has infiltrated the
chocolate. Two- or three-dimensional MRI permits the investigation of migration
in actual commercial products (Miquel and Hall, 1998; Miquel et al., 1998; Miquel
and Hall, 2002), but the spatial resolution (generally hundreds of micrometers)
may not be sufficient to generate a concentration profile within very thin coatings.
The spatial resolution of MRI is sufficient to provide insight into the location of
migration in complex products, for example between wafers (Miquel and Hall,
2002).
MRI can be made semi-quantitative by calibration of the signal intensity with
the liquid oil content and the liquid oil content with the content of migrating oil
(Miquel et al., 2001; Deka et al., 2006).
Direct measurement of oil composition
Natural fats and oils are a complex mixture of triacylglycerols. The observation of
oil migration by chemical analysis requires a difference in either the fatty acid or
triacylglycerol composition of the two fats. Nut oils are often rich in unsaturated
fatty acids (oleic, linoleic and linolenic), milk fat contains short chain fatty acids
not generally found in other natural fats and the ‘lauric fats’ are so named because
they contain high levels of lauric acid. Hydrogenated fats may contain unique trans
fatty acids. Analysis of triacylglycerols directly requires less preparation than
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quantization of free fatty acids, usually as fatty acid methyl esters. Buchgraber et
al. (2004) provide an excellent review of triacylglycerol profiling using chromatographic techniques. The most commonly used techniques for quantifying oil
migration are gas–liquid chromatography (GLC) or high-performance liquid
chromatography (HPLC).
Ali et al. (2001) followed oil migration into plain chocolate from a filling
comprising palm mid fraction (PMF) and coconut oil (CNO). Cocoa butter (CB)
was composed largely of TAGs with 50, 52 and 54 carbons (C50, C52 and C54),
with C54 essentially absent from PMF or CNO. Coconut oil contained TAGs in the
range C32–C40, which were absent from either CB or PMF. Adenier et al. (1993)
analyzed triacylglycerols by thin layer chromatography (TLC) and constituent
fatty acids by GLC to establish the counter diffusion of cocoa butter TAGs into a
praline filling. Ziegleder et al. (1996a,b) employed the triolein [OOO] to 1palmitoyl-2-oleoyl-3-stearoyl-glycerol [POSt] ratio as determined by HPLC to
follow oil migration in between chocolate and nougat.
Szlachetka (2007) used Fourier-transform infrared (FTIR) microscopy to follow hazelnut oil migration into cocoa butter. A peak located at 3006 cm–1 in the
FTIR spectra, corresponding to the carbon–hydrogen stretch of a hydrogen bound
to a alkene (C=C), was much more pronounced in hazelnut oil than in cocoa butter
owing to the higher concentration of unsaturated fatty acids (Fig. 10.7). The
hazelnut oil concentration was obtained by integration of this peak from 3029 to
2987 cm–1 and comparison with a standard curve. In this manner, hazelnut oil
migration into cocoa butter, as well as, countermigration of cocoa butter into the oil
was followed over time (Fig. 10.8). Fundamentally, this technique provides the
same information that is obtained by an analysis of iodine value, but samples
require little preparation and, with the proper physical set up, samples can be
viewed in situ.
Dyes and tracers
In every case where dyes or tracers are added to the liquid phase in an attempt to
follow oil migration, the underlying assumption is that the dye migrates at the same
rate as the oil. This is rarely a sound assumption. For example, Marty et al. (2005)
observed the migration of Nile red, with a molecular weight less than half that of
triolein, into cocoa butter ahead of the peanut oil (oleic acid). Furthermore,
quantification of the dye, when done spectrophotometrically, requires strict adherence to Beer’s law and keeping dye concentrations within the linear range of
response throughout the sample is difficult.
X-ray diffraction
X-ray diffraction does not measure oil migration per se, but can be employed to
follow changes induced by oil migration, for example a decrease in SFC or
polymorphic transformations. Some investigators have followed bloom assuming that the rate of polymorphic transitions was determined by migration
kinetics.
Product design and shelf-life issues: oil migration and fat bloom
201
1.20
1.00
0.80
0.60
Absorbance (%)
0.40
0.20
0.00
1.20
1.00
0.80
0.60
0.40
0.20
0.00
3800
3400
3000
2600
2200
1800
1400
1000
Wavenumber (cm–1)
Fig. 10.7 FTIR spectra for cocoa butter (top) and hazelnut oil (bottom) showing the
peak at 3006 cm–1 used to quantify hazelnut oil concentration (Szlachetka, 2007).
Integrated intensity (HO oil band)
5.75
42.5 h
4.75
3.75
2.75
1.75
0h
0.75
–0.25
0
50
100
150
200
250
300
350
Distance (µm)
Fig. 10.8 Hazelnut oil migration into cocoa butter as a function of time. The oil–fat
boundary is at 50 µm (Szlachetka, 2007). Dashed line is cocoa butter–oil interface. Arrow
indicates increasing migration time.
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10.3.2 Fat bloom
Some investigators limit the definition of bloom to surface defects and the
influence on appearance alone. However, recrystallization in the interior may be
the limiting factor for shelf life, especially in products where surfaces are protected
by packaging. The transformation of cocoa butter from form βV to βVI during
storage may cause changes to melt and flavor release, even if it does not affect the
appearance.
An important detail, not always mentioned by investigators, is whether or not
the surface being observed was free-formed or crystallized in contact with a mold
and, if so, what kind of mold and at what temperature. It should also be stated
whether the sample was stored within a package (e.g. a plastic bag) that could
potentially make contact with the surface.
For fundamental investigations of recrystallization, Haghshenas et al. (2001)
developed a procedure for measuring the exchange rate of triacylglycerols between the dissolved and solution state. This test could be adapted to follow the
movement of TAGs from one crystal to another. Accelerated bloom tests involve
cyclical changes in temperature, typically in the temperature range between 20 and
30 °C, with the time that the test is kept at the high temperature being 8–12 hours
for the convenience of the investigators. The relationship between these accelerated tests and the stability of products in the marketplace is qualitative in nature,
good for comparisons of one formula with another, but generally not predictive of
the actual shelf life. It is likely that the mechanism of bloom formation operating
at constant temperature, crystal growth from the beneath the surface, is augmented
by surface roughening caused by particle segregation when the temperature is
cycled.
Surface color or gloss
Since the most obvious defect resulting from fat bloom is a grey-white cast on the
surface of the confection, measurement of the optical properties of the piece is a
direct assessment of quality. Surface color can be measured via a sensory panel or
instrumentally. If appearance is measured by a sensory panel, it is important to
have visual references, a panel of sufficient size and ‘blind’ presentation of the
samples to the panel (coded samples so that the panelists are unaware of the
treatment). It is best not to have researchers directly involved in the evaluation to
prevent bias. Unfortunately, there are numerous studies reporting the visual onset
of bloom, with little or no description of how this assessment was done, by whom
or under what conditions.
Briones et al. (2006) provide an excellent comparison of several techniques for
the instrumental determination of color, gloss and surface roughness of chocolate,
and clearly demonstrate that the surface roughness plays a decisive role in the
visual quality. Generally, surface color is measured with some kind of reflectance
spectrophotometer or colorimeter, although ‘glossmeters’ have been developed.
The spectral characteristics are often reported in L*, a*, b* colorspace where L* is
the lightness and a* and b* are the color-opponent dimensions, although sometimes the asterisk is omitted. Lohman and Hartel (1994) used the whiteness index,
Product design and shelf-life issues: oil migration and fat bloom
203
WI, (equation 10.4) to ‘amplify’ the whiteness of fat bloom from the other color
components of chocolate:
WI = 100 – [(100 – L2) + a2 + b2]0.5
[10.4]
When assessing appearance either instrumentally or by sensory methods,
proper and consistent lighting is required. Spectrophotometers and colorimeters
provide an average color value over a sampled area. This presents a sampling
problem, since bloom is a stochastic process, appearing sporadically in unpredictable places. Briones et al. (2006) demonstrated the use of visual imaging and image
processing to determine color and visual texture of the entire surface of chocolate
samples. Unless large areas can be sampled repeatedly, several randomly selected
spots should be sampled from a number of replicate pieces during each sampling
period to minimize sampling error. A polymorphic transition may or may not be
responsible for the development of visual bloom. Generally, the only way to follow
crystal transformations unambiguously is with X-ray diffraction.
X-ray diffraction
Fat bloom occurring on long-term storage or with oil migration is associated with
a polymorphic transition from the βV to βVI form. This transition may be followed
using differential scanning calorimetry, assuming a melting point characteristic of
the polymorphic form, but the only absolute technique is to observe the transition
using X-ray diffraction. For chocolate, unlike cocoa butter alone, this requires the
additional step of separating the signal from the crystalline fat phase from that of
crystalline sugar. This can be done by dissolving the sugar into an aqueous solution
(Cebula and Ziegleder, 1993), or by obtaining difference spectra between solid and
molten chocolate (Kinta and Hatta, 2005a,b).
Surface roughness and atomic force microscopy
Bloom development has been followed by imaging topological features in the size
range of interest (below 1 µm and up to about 10 µm) using atomic force
microscopy (AFM) (Smith and Dahlman, 2005; Rousseau, 2005; Sonwai and
Rousseau, 2006). AFM yields a direct measure of surface roughness and actual
dimensions of features in three dimensions (3D) (unlike scanning electron
microscopy which reduces things to two dimensions). However, only very small
areas can be sampled and it is difficult to sample the same area over the extended
time periods required for the development of bloom. Like microscopic techniques
in general, the small sampling area of AFM means that it is difficult to assure that
the sample chosen is truly representative of the entire surface and free from
artifacts. This limitation appears to have been overcome somewhat by Quevedo et
al. (2005), who used a scanning laser microscope to determine surface roughness,
but the resolution of the technique was only 1 µm.
In addition to nanometer resolution, when operated in tapping mode, AFM can
provide information on the mechanical properties on the sample and, in theory,
differentiate crystalline regions from amorphous or liquid regions. However, it
does not provide compositional analysis. Kinta and Hatta (2005a,b) determined
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Enrobed and filled chocolate, confectionery and bakery products
the composition of bloom using scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS). Carbohydrate (sugar and cocoa) was
differentiated from fat through the carbon-to-oxygen ratio (high for fat, lower for
carbohydrate).
10.4 Optimizing product quality in relation to oil migration
and fat bloom
10.4.1 Cocoa butter vs. confectionery coatings
Cocoa butter is not the only fat that undergoes bloom. Any natural fat can
potentially recrystallize at temperatures where it exists in a semi-crystalline state,
with polymorphic fats even more susceptible to bloom, especially when crystallized in a polymorphic form of lower stability. Smith et al. (2004) investigated
bloom formation in compound chocolate coatings containing palm kernel stearin
and hydrogenated palm kernel stearin and demonstrated that bloom formation was
not simply due to segregation between cocoa butter and the lauric fats, but was
consistent with published phase diagrams. Bloom crystals were selectively enriched in CB TAGs or palm kernel TAGs depending on temperature. In all cases,
bloom was fully solid and had a higher melting point than the bulk lipid phase.
10.4.2 Tempering
Good temper is prerequisite of a long shelf life. Recrystallization (i.e. bloom) will
be enhanced if unstable polymorphs are formed or if tempering results in a wide
crystal size distribution. Changes in crystal size distributions throughout the
production day can result in varying resistance to bloom. Although proper temper
is thought to impede oil migration, Miquel et al. (2001) and Choi et al. (2005)
found this not to be the case. Szlachetka (2007) found oil migration to be slower
through untempered chocolate in the α form than through well-tempered chocolate. Seeding chocolate with fine crystals of the βVI polymorph can slow bloom by
removing one of the driving forces behind recrystallization.
10.4.3 Cooling and solidification
The uniform crystal size distribution initiated by tempering must be maintained
throughout cooling for maximal shelf stability. Nucleation of unstable polymorphs
in the cooling tunnel must be avoided. Extremely rapid cooling, that is, cold
stamping technology (see Chapter 19), results in a fat phase structure that appears
to resist bloom. Differences in shelf stability could be expected between shellmolded (cold stamping or otherwise) pieces and products manufactured by
‘one-shot’ depositing or hand dipping, since in the latter cases the chocolate is
brought into contact with the filling in the liquid state.
Miquel et al. (2001) showed that a thermal treatment consisting of 24 hours at
Product design and shelf-life issues: oil migration and fat bloom
205
Table 10.1 Potential strategies for controlling oil migration (Dea, 2004; Timms, 2002;
Ziegleder, 1997)
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Reduce chocolate particle size.
Temper chocolate well.
Use thicker chocolate coating.
Double enrobe with cooling in between (re-enrobe already bloomed product).
Increase the ratio of coating to filling.
Optimize shape to minimize thin spots.
Use dark chocolates made with hard butters.
Minimize oil content of filling.
Use harder fats in the filling.
Process filling for optimal fat structure.
Add starch to fillings.
Use structuring fats for fillings.
Use compatible fats for filling and coating.
Use barrier fats between chocolate and nuts/fillings.
Use protective glaze layers between nuts and chocolate.
Use compound coating instead of chocolate.
Store product frozen or refrigerated.
30 °C followed by 24 hours at 4 °C reduced the overall softening effect that
hazelnut oil migration had on chocolate, similar to the effect of ‘presaturation’ of
hazelnut oil with cocoa butter by Ziegler and Szlachateka (2005) illustrated in Fig.
10.1. Ziegleder (2006) reported that despite the high level of ‘free oil’ in a hazelnut
nougat filling made with cocoa butter, there was almost no softening of a truffle
shell over a one-year period. In comparison, fillings formulated with milk fat or
hydrogenated coconut oil, but without cocoa butter, softened the chocolate shells
dramatically.
10.4.4 Optimal storage and transportation
For most present day formulations, shelf life is longest when product is stored at a
constant temperature below 18 °C and generally the cooler the better. There is a
maximum in the recrystallization rate–temperature relationship. Timms (2002)
puts this maximum at 18–22 °C for milk chocolate and 18–26 °C for dark
chocolate.
10.4.5 Strategies for oil migration
Table 10.1 summarizes the strategies that have been proposed for mitigating the
worst effects of oil migration. Perhaps somewhat counterintuitively, higher fat
coatings should retard the deleterious effects of oil migration, as the migrating oil
would be saturated in a hard fraction sooner. Unfortunately, while greater solubility may inhibit the rate of bloom formation (Matsuda et al., 2001), it may
exacerbate the detrimental effects of oil migration (unless the filling is presaturated
with cocoa butter).
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Enrobed and filled chocolate, confectionery and bakery products
10.4.6 Anti-bloom composition
The substitution of illipé fat (Shorea stenoptera) for 15% of the cocoa butter
provided bloom resistance (delayed onset) for shell-molded dark chocolate truffles
(Ali et al., 1998), apparently owing to its higher StOSt/POSt ratio. Glycolipid
fractions from pumpkin have shown anti-bloom properties (Nakae et al., 2000).
Sonwai and Rousseau (2006) demonstrated that a cocoa butter equivalent
(Coberine®) delayed the onset of bloom in tempered cocoa butter by 1–2 weeks at
25 °C. These same authors observed a decrease in SFC from a high of ≈71% at
week 3 to ≈67% at week 25 for cocoa butter stored at 25 °C. SFC was measured by
low-resolution pulsed nuclear magnetic resonance (NMR). While the authors
suggested that heat released on further crystallization during the storage period
could be responsible for the drop in SFC, something that seems contradictory at
face value, it is more likely that liquid TAGs trapped within the solid matrix were
‘seen’ as solid by the NMR (much like bound water) and so they were excluded
from the crystal network registered as liquid oil.
Smith et al. (2008) formulated fillings containing hazelnut oil, hardstock and
the antibloom fat Prestine®. The antibloom fat migrated with the nut oil and
inhibited the βV→βVI transformation, but the effect of oil migration on texture was
not reported. Readers are directed to the review by Lonchampt and Hartel (2004)
and to the patent literature for further information on antibloom compositions.
10.5 Future trends
Most published research focuses on the chocolate coating, with much less attention
paid to the nature of the filling. A more holistic approach to product design is
required, hence there is a need to see oil migration as a case of interphase mass
transfer. It is apparent that not simply the amount, but the properties of the liquid
phase are important and a better understanding of the intersolubility of
triacylglycerols should be sought. Research on the influence of emulsifiers on
triacylglycerol solubility and crystallization is a promising opportunity. Since the
composition of the filling is not as constrained by regulations as that of the
chocolate, more work should be conducted on designing suitable fillings.
10.6 Sources of further information
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ings 56th PMCA Production Conference, Hershey, PA, April 8–10, pp 58–69.
(2009). Industrial Chocolate Manufacture and Use, 4th edition, Blackwell
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BECKETT, S.T.
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10.7
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MATSUDA, H., YAMAGUCHI, M. AND ARIMA, H. (2001). ‘Separation and crystallization of
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Systems, N. Garti and K. Sato (eds), Marcel Dekker, New York, Chapter 14, pp 485–503.
MIQUEL, M.E. AND HALL, L.D. (1998). ‘A general survey of chocolate confectionery by
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MIQUEL, M.E. AND HALL, L.D. (2002). ‘Measurement by MRI of storage changes in
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migration of lipids in composite chocolate measured by magnetic resonance imaging’.
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NAKAE, T., KOMETANI, T., NISHIMURA, T, TAKII, H., AND OKADA, S. (2000). ‘Effect of
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11
Product design and shelf-life issues:
moisture and ethanol migration
Geoff Talbot, The Fat Consultant, UK
Abstract: The movement of moisture and alcohol from one phase to another in multicomponent food products is a significant cause of textural change and spoilage. Alcohol
migration is mainly a problem in liqueur-filled chocolates and can result in the collapse
of the chocolate shell. Moisture migration is common in many bakery products where the
cereal-based component (biscuit, cake, wafer etc) is in contact with a phase of higher
water activity (caramel, jam, ice cream, for example). Moisture moving from the wet
phase to the dry phase causes detrimental textural changes to occur in both phases. This
chapter will discuss the diffusion mechanisms by which moisture and alcohol migrate
and then focus on potential solutions to both problems. These predominantly centre
around the use of barrier layers within the product to separate the moist and dry components. Although protein and carbohydrate barriers will be mentioned, the main focus will
be on barriers based on more hydrophobic materials such as fats and waxes.
Keywords: alcohol migration, chocolate, diffusion, fats, liqueurs, moisture barriers,
moisture migration, permeability, tortuosity, waxes.
11.1 Introduction
As food products become more complex, manufacturers try to include as many
taste and textural sensations as they possibly can in one product. The result is often
a combination of ingredients and components that give great sensory properties to
the product but that have great difficulty in coexisting with each other. In the
previous chapter, the problem of fat migration between two phases of differing fat
compositions was addressed. In this chapter we shall look at the similar problems
of moisture and ethanol (alcohol) migration.
Enrobed and filled products are, by definition, products with at least two phases,
212
Enrobed and filled chocolate, confectionery and bakery products
coating and filling, so the problem of migration is present in even the simplest of
such products. When we start to bring in multicomponent, multitextured centres,
the problem becomes ever more complex. Moisture migration can take place
between two components when the water activities of these two components are
unequal. Examples of this in the product categories being considered in this book
are when cereal-based components – biscuits, wafers, crispy inclusions – are in
close contact with higher water activity ingredients such as jam, caramel, toffee,
ice cream and so on. Moisture moves from the high water activity component into
the lower water activity component resulting in a drying out of the moist component and an increase in softness or sogginess of the crisper component. The loss of
desirable texture in both phases eventually makes the product unacceptable.
However, it is not always necessary for there to be a crisp cereal-based
component present for moisture or, for that matter, alcohol migration to be a
problem. If a centre containing a lot of water (e.g. a short shelf life cream-based
centre or a low-fat centre based on emulsion technologies) is encased in chocolate,
water from the centre can begin to dissolve sugar in the chocolate shell, thus
weakening the chocolate shell. In the same way, alcohol from a liqueur centre can
dissolve sugar, again causing a weakening of the shell but also a release of cocoa
powder from the shell into the liqueur. This affects the flavour of the liqueur centre
and gives it a ‘muddy’ appearance.
Before looking at potential solutions to the problem, we need to have at least a
background knowledge of how these components migrate and how we can
measure the degree of migration. This chapter will then move on to look at
potential solutions to the problem. Although these are predominantly lipid-based
(i.e. fat or wax barriers) other components such as protein and carbohydrate have
also been studied as moisture barriers. Finally, the problem of alcohol migration
from liqueur centres will be considered before looking at what the future trends and
developments in this area may be.
11.2 Mechanism of moisture migration
Migration of moisture from one phase to another in a multi-component product is
essentially a diffusion process in which moisture molecules migrate from a
component of higher water activity to one of lower water activity until a thermodynamic equilibrium is reached. That equilibrium does not necessarily mean that
the water concentration in the two phases is equal but that the water activities of the
two phases are equal.
In addition to migration resulting from this process of diffusion, there is also the
potential for moisture to move within a product as the result of capillary flow, that
is, if there are holes or cracks in, for example, a biscuit then moisture can move to
fill these.
11.2.1 Diffusion mechanisms
Moisture migration resulting from diffusion (be it unobstructed or through a
Product design and shelf-life issues: moisture and ethanol migration
213
barrier film) is controlled by a combination of Fick’s Law (equation 11.1) and
Henry’s Law (equation 11.2):
J = –D (δc/δx)
[11.1]
where J is the flux (rate of flow per unit area), δc/δx is the concentration gradient, c is the concentration (moles cm–3) and D is the mutual diffusion coefficient
(cm2 s–1).
c = SP
[11.2]
where c is the concentration, S is the solubility coefficient and P is the applied
pressure (mm Hg).
When a barrier film is used to minimise the rate of moisture migration, it is
necessary to know what is its permeability. Combining Fick’s law and Henry’s
Law allows us to define an equation (equation 11.3) which then includes a term for
the permeability of such a film:
dw/dt = K/X (A(p1–p2))
[11.3]
where dw/dt is the rate of transport of water gained or lost per day, A is the area of
contact, p1 and p2 are the water vapour pressures on each side of the film and X is
the thickness of any barrier film. The term, K/X is the permeability of the film
expressed in g mm m–2 day–1 kPa–1 (SI units) or, more commonly, in g mil m–2 day–1
mmHg–1 [1 mil is one-thousandth of an inch]. The SI units can be obtained from the
more commonly used units by multiplying these by 0.195016. Permeability takes
into account the thickness of the barrier, whereas permeance does not include this
thickness term. Permeance is the permeability of a barrier divided by its thickness.
Since the most usual way of reducing the rate of moisture migration within a
product is to place a barrier film between the wet and the dry phases of the product,
it is instructive to consider how moisture might still be able to move through that
film. As will be seen later, the most common form of moisture barrier is lipid-based
(usually triglyceride- or fat-based, but occasionally wax-based). The reason for
this is that water has a limited solubility in fats and waxes, but it is a finite solubility.
Assume a film of liquid vegetable oil was being used as a barrier in a product
(see Fig. 11.1). Water on the wet side of the film will migrate into the film until the
film is saturated, that is until it has dissolved as much water as it is able to do. Once
this situation has been reached, molecules of water in the film are then able to
migrate out of the oil film and into the dry phase of the product. For every molecule
of water that leaves the barrier film into the dry phase of the product another
molecule enters the film from the moist phase of the product to maintain the
saturation of the film with water.
According to Formo (1979), the solubility of water in an oil such as winterised
cottonseed oil is 0.141% at 32.2 °C. Because the solubility of water in triglycerides
is very low, even a liquid oil film such as this will have some barrier effect. The
question then arises as to how can this barrier effect be enhanced. If we consider
again equation 11.3, increasing the film thickness is one way of reducing the rate
of transport of water. Simply doubling or tripling the thickness of the film is
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Enrobed and filled chocolate, confectionery and bakery products
‘Wet’ phase
Fig. 11.1
Barrier
‘Dry’ phase
Moisture migration as a result of diffusion.
usually not possible because of the desire to keep the visual nature of any barrier
film at a minimum. There is a second option, however, tortuosity.
11.2.2 Tortuosity
In simple terms, tortuosity is placing obstacles in the way. The distance between
two cities by air is usually much less than the distance between the same two cities
by road. This is because, by road, you have to go round obstacles such as fields,
rivers, houses and so on. In the same way the distance from one side or a barrier
film to another can be increased by placing obstacles in the way, in other words, by
increasing the tortuosity. These obstacles can be crystals of solid fat or non-fat
solids such as sugar, cocoa powder and so on. Examples of the positive use of
tortuosity to reduce the permeability of a barrier film will be given in later sections
of this chapter.
11.3 Measurement of permeability
There are essentially three ways of measuring the permeability of a barrier, two of
which are manual methods requiring periodic weighings. The two manual methods
are (a) a dry-cup and (b) a wet-cup method. The migration cell used in the dry-cup
method is shown in Fig. 11.2. This consists of an aluminium dish filled with a
desiccant such as silica gel. A disc of porous card which is either saturated with the
barrier to be examined, or has a similar sized disc of barrier bonded to it, is laid on
the shoulders of the cell and sealed in place with a mixture of microcrystalline wax
and plasticizer. There are also some gravimetric cells that clamp a sealing ring
made of either rubber or plastic on either side of the barrier to hold it in place. The
whole system is then placed into an atmosphere of a fixed relative humidity. This
can most easily be achieved by putting the cells into a desiccator in which there is
Product design and shelf-life issues: moisture and ethanol migration
Microcrystalline wax and
plasticiser seal
215
Porous card
saturated with fat
Desiccant, e.g.
silica gel
Aluminium dish
Fig. 11.2
Permeability measurement using the manual dry-cup method.
Table 11.1 Relative humidities of saturated salt solutions (adapted from http://
www.omega.com/temperature/z/pdf/z103.pdf)
Salt
Lithium chloride
Potassium acetate
Magnesium chloride
Potassium carbonate
Magnesium nitrate
Sodium chloride
Potassium chloride
Potassium nitrate
Potassium sulphate
10 °C
20 °C
30 °C
11.3
23.3
33.5
43.1
57.4
75.7
86.8
96.0
98.2
11.3
23.1
33.1
43.2
54.4
75.5
85.1
94.6
97.6
11.3
21.6
32.4
43.2
51.4
75.1
83.6
92.3
97.0
also a saturated salt solution that gives a particular relative humidity (Table 11.1).
Some of these are quite independent of temperature, while others vary quite
considerably with temperature.
Moisture from the atmosphere inside the desiccator will gradually migrate
through the barrier on the card and into the desiccant. The rate at which this occurs
can be measured by weighing the cells at intervals and using this to calculate the
permeability.
The wet-cup method is very similar except that the saturated salt solution is
placed inside the migration cell and the desiccant is in the desiccator. Moisture now
moves from the cell and this therefore loses weight. Again regular weighings
enable the permeability to be measured.
The third method is an instrumental one and directly measures the water vapour
transmission rate (WVTR). The example shown in Fig. 11.3 is of the cell used in
the Versaperm WVTR instrument (Versaperm Limited, B940-H41 Popjak Road,
Sittingbourne Research Centre, Sittingbourne, Kent ME9 8PS, United Kingdom).
The principle is very similar to the wet-cup method. A dish of water or saturated
salt solution is placed in a cell above which the sample is sealed. Dry nitrogen is
passed across the top of the sample and an electrolytic cell measures the moisture
216
Enrobed and filled chocolate, confectionery and bakery products
Dry N2
Electrolytic cell
Seal
Barrier
Fig. 11.3
Water
Support
Current gives direct
measure of water
vapour transmission rate
Instrumental direct method – Versaperm WVTR (source: K W Smith,
Unilever Research).
present in the exiting gas. There are other similar instrumental methods in use in
which the moisture in the gas stream is detected by other means, such as by using
infrared. Using a fixed sample area and a known flow rate for the gas allows the
instrument to calculate the WVTR in g m–2 day–1.
Having simply a lipid film is all but impossible both because it is extremely
difficult to mould, transfer and seal such a film within the apparatus without
damaging it and because doing this would restrict us to fairly high solid fat content
films. So, irrespective of which method is being used, it is necessary to have some
form of support for the lipid barrier. For this reason lipid barriers are generally
painted as evenly as possible on a thin permeable card. The thickness of the barrier
is calculated by weight difference before and after application. The permeability of
the card itself is so high that the instrument is unable to measure it. This means that,
to all intents and purposes, the permeability which we measure is the permeability
of the lipid film. Because the thickness of the barrier layer is included as a function
within the permeability units, the permeability (as a number) should be independent of the barrier thickness.
In general, instrumental methods are much quicker than the gravimetric manual
methods but have the disadvantage that only one measurement can be made at a
time. With the manual methods, however, many cells can be in use at the same
time.
11.4 Reducing moisture migration
The most common way of reducing the extent of moisture migration is to apply a
barrier film between the moist and dry phases. By definition this barrier film must
have a low permeability in order to minimise the rate of moisture movement.
Lipids in general are perhaps the mostly widely researched type of barrier. Of
these, the lowest permeability is generally found with waxes. Waxes, though,
suffer from (a) high melting points which have an effect on both application
conditions and sensory properties and (b) a white, candle-like appearance on the
Product design and shelf-life issues: moisture and ethanol migration
217
product. For these reasons, they have generally been used in combination with
other lipids (see Section 11.4.2). Fennema et al. (1993) evaluated some other lipid
materials and found that beeswax, in combination with an acetylated monoglyceride,
has a permeance of 0.00369 m s–1 × 10–3 compared with a permeance of 0.00195
m s–1 × 10–3 for beeswax alone. The best of the non-wax containing systems they
looked at was stearoyl alcohol with a permeance of 0.034 m s–1 × 10–3.
Although some materials which would not be considered to be part of the
normal food chain have been evaluated as moisture barriers, the trend today is to
reduce the number of additives in food as much as possible. This means that
barriers composed of what might be considered ‘normal’ food ingredients are
much more likely to find acceptability. Of these, fats are the most hydrophobic and
are the ones which generally find the greatest degree of acceptance. This section
will, therefore, dwell mainly on the use of fats as the basis of moisture barriers but
will also mention work that has been carried out on proteins and carbohydrates as
moisture barriers.
In the context of fats and, especially in a book that is dealing with enrobing of
chocolate, the use of barriers in which non-fat components are dispersed within the
fat phase (e.g. chocolate) will also be discussed.
11.4.1 Fat barriers
Fats have a long history of use in minimising moisture movement. For example,
‘larding’ was a process of coating food in fat, used in 16th century England to
minimise moisture loss (Labuza and Contreras-Medellin, 1981). It has already
been mentioned that even a liquid vegetable oil will have some moisture barrier
properties. There are two basic ways in which such a barrier could be improved.
The first way is to increase the path length of the migrating moisture by increasing
the thickness of the barrier or, more practically, introducing tortuosity into the
barrier film, that is by introducing obstacles to the movement of the water. The
second way is to have less moisture present within the barrier layer. Since the
moisture moves through the film by diffusion and this is essentially carried out by
diffusion of water in solution in the liquid oil phase of the barrier through the
barrier, less moisture would migrate through the barrier if there were less moisture
dissolved in the barrier. We are unable to change the solubility of water in the oil
phase, but we can reduce the amount of liquid oil present in the barrier film, thereby
reducing the amount of water dissolved at any one time. The two options then are
to either (1) increase the film thickness or, at least, the diffusion path length, or (2)
reduce the amount of water in the film by reducing the amount of liquid oil present.
At first sight these two ways seem to be contradictory to each other but both can be
achieved by simply increasing the solid fat content of the fat used in the barrier
layer.
Assume that we have a barrier of about 250 µm thick. This is a common
thickness for commercially used fat barriers. Moving from a barrier containing no
solid fat to one containing 50% solid fat would mean only half the amount of liquid
oil is present. This means that only half the amount of water is present at any one
218
Enrobed and filled chocolate, confectionery and bakery products
Permeance
(g m–2 day–1 mmHg–1)
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
Liquid oil (%)
Fig. 11.4
Effect of solid fat content on permeance.
time, but the barrier thickness is the same – 250 µm. The path length, however, has
increased to considerably more than 250 µm because the water molecules now
have to move further to get to the other side of the barrier, now having to
circumnavigate all the solid fat crystals. Increasing the solid fat content further to
80% means that only 20% of the original moisture content is present in the barrier
layer and there are even more solid fat crystals present as obstacles to moisture
migration. There is, then, a general relationship between the liquid oil content of
the barrier and its permeance (Fig. 11.4).
Because of this, different fats have different permeabilities. Tripalmitin which
is effectively 100% solid at 27.5 °C has a permeability of 0.194 g mm m–1 d–1 kPa–1,
whereas anhydrous milk fat which contains some liquid oil at 24.9 °C has a
permeability of 0.886 g mm m–1 d–1 kPa–1 (Shellhammer and Krochta, 1997).
Talbot (1991) evaluated the permeability of a wide range of fats of differing
types and, in particular, differing fatty acid chain lengths, in the model dry-cup cell.
He found that, while there was this general relationship between the amount of
liquid oil in the fat barrier and its permeance, oils and fats also fell into three broad
sub-groups (Fig. 11.5). At high liquid oil contents (greater than about 80% liquid
oil) all fats behave roughly the same. However, as the fat phase becomes increasingly higher in solid fat, a difference is seen between short-medium chain length
fats and long-chain length fats, notably between fats rich in C8–C14 fatty acids and
those rich in C16–C18 fatty acids. The shorter chain length systems have a lower
permeance for a given solid fat content. In this group of fats are those based on
palm kernel oil, coconut oil and cow’s milk fat, both the oils themselves and
hydrogenated and fractionated modifications of the oils. In the longer chain fatty
acid group are oils such as palm oil, cocoa butter, together with hydrogenated
liquid oils like rapeseed and soyabean oil.
When a range of oils of these various types was then evaluated on biscuits, the
same effects were seen (Fig. 11.6). The least effective barrier was palm oil which
not only contained 75% liquid oil under the test conditions but was also a longer
chain fat. Then came palm kernel oil, which contained less liquid oil (60%) but
Product design and shelf-life issues: moisture and ethanol migration
219
Permeance
(g m–2 day–1 mmHg–1)
2.5
Oils
2
1.5
1
C16-C18 fats
0.5
C8-C16 fats
0
0
20
Fig. 11.5
40
60
Liquid oil (%)
80
100
Effect of fatty acid chain length on permeance.
Moisture gain
(% initial weight)
1.6
1.4
Palm oil
1.2
Palm kernel oil
Cocoa butter
1
0.8
Hardened non-lauric
0.6
HPKS
0.4
0.2
0
0
5
10
15
20
Weeks storage
Fig. 11.6
Effect of fat type in a barrier on moisture uptake of biscuits.
which was a shorter chain length fat. Best of all was a fully hardened palm kernel
stearine which had both a shorter chain and contained almost no liquid oil.
Many of the fats that have been used industrially as moisture barriers have been
based on hydrogenated vegetable oils. Unfortunately, although their barrier properties are excellent and they are easy to use and apply, the fact that they have been
hydrogenated has, in recent years, raised some questions about their use. In
themselves, they do contain significant levels of trans fatty acids and could,
therefore, be some cause for concern. However, it is important to consider the
product as a whole and that the contribution that the barrier layer makes to the
whole product in terms of percentage weight is quite low, so, even a hydrogenated
fat barrier would contribute only a small amount of trans fatty acids to the total
product. Nevertheless, non-hydrogenated alternatives have and are being developed. The issue of how polymorphism affects moisture barrier properties is
considered below in Section 11.4.1.Chocolate barriers, but polymorphic fats rich
in SUS (saturated-unsaturated-saturated) triglycerides have been used as moisture
barriers. A more recent development by Asama et al. (2007) discloses the addition
220
Enrobed and filled chocolate, confectionery and bakery products
of the asymmetric version (SSU) of this type of triglyceride at levels of between
15% and 50% to an SUS-based material. This will undoubtedly have an effect on
the polymorphic nature of the barrier.
Non-fat inclusions in fat-based barriers
When a fat is applied in a molten state to a porous substrate such as a biscuit or
cake, a significant proportion of the fat is absorbed by the substrate before it has the
chance to crystallise on the surface and form a good, integral barrier layer. This has
the effect of reducing the barrier properties. One way of reducing the degree of
absorption of the barrier into the substrate is to shock-cool the barrier coating.
Unfortunately, this often has the effect of producing stresses and cracks in the
coating. While these are usually very small and often not apparent to the naked eye,
they are sufficient to start to allow moisture to migrate through them. In time,
enough moisture will have migrated through these small cracks to make the biscuit
beneath start to expand. This then makes the cracks larger and moisture passes
through at an increasing rate. Shock-cooling of the barrier layer is, therefore, not
recommended.
Talbot (1991) found that adding powdered sugar to the fat barrier increased its
viscosity sufficient for a thin layer to still be produced but with reduced absorption
into the biscuit or cake beneath. One of the major problem areas associated with
moisture migration into enrobed biscuits is when there is a layer of caramel in
contact with the biscuit. This is found generically in caramel wafer products but
also in some chocolate-coated caramel biscuit countlines. Non-fat inclusions in the
barrier used in this type of product were investigated. Adding, for example, 50%
powdered sugar to a palm kernel oil based barrier used on biscuits approximately
halved the rate of moisture uptake by the biscuits when stored at a relative humidity
(RH) of 56% to simulate the water activity of caramel (Fig. 11.7). In an attempt to
make the barrier look more like chocolate, the non-fat inclusion part was modified
to include 15% low-fat cocoa powder (i.e. the barrier was composed of 50% palm
kernel oil, 35% powdered sugar, 15% low-fat cocoa powder). When this was used,
the degree of moisture uptake into the biscuit increased until it was almost the same
as with the 100% fat barrier. The reason for this can be found by comparing the
relative adsorption isotherms of cocoa powder and sugar. At a water activity of
0.5–0.6, cocoa powder adsorbs more water than does icing sugar (Iglesias and
Chirife, 1983). These relative effects of sugar and cocoa powder on permeability
were also observed by Ghosh et al. (2005).
Loh et al. (2004) have patented the addition of microparticulated high melting
lipids such as saturated fatty acids, glycerol mono-, di- and tri-stearate, calcium
and magnesium stearate to lower melting vegetable oils as a means of improving
their performance as moisture barriers. Although arguably these are still lipids,
their use is more as particulate additives than as a component of the continuous fat
layer.
Chocolate barriers
One of the problems that users of barriers have to deal with is whether the barrier
Product design and shelf-life issues: moisture and ethanol migration
221
Moisture gain
(% initial weight)
2.5
2
PK
1.5
PK/sugar
1
PK/sugar/cocoa
0.5
0
0
Fig. 11.7
5
10
15
Weeks storage
20
Effect of non-fat solids in fat-based barriers on biscuits.
should be visible or not. Ideally, the consumer should not realise that a barrier is
being used and therefore there is a requirement for it to be thin and clear and, hence,
invisible. Sometimes, though, it is possible to make a virtue out of the visibility of
the barrier. A good example of this is the use of a chocolate-like barrier layer on the
inside of filled ice cream wafer cones. Consumers think it is just a pleasant part of
the product, they expect to see it there and, more than that, they expect to find a
small ‘plug’ of the barrier at the bottom of the cone. Many of them probably do not
realise that it has the function of reducing the degree of moisture migration from
the ice cream to the cone. This brings us to the question of whether to use real
chocolate in the kind of application where the barrier will be visible or to use a
chocolate-flavoured (i.e. cocoa powder-coloured) coating.
The polymorphic form of the fat barrier can have an influence on its properties,
although there are conflicting results here. Kester and Fennema (1989a) found that
the α form of a barrier of fully hydrogenated soyabean and rapeseed oils had a
lower permeability than did the β' form even though the β' form would have had a
denser crystal structure. A comparison of tempered and untempered cocoa butter
(Smith KW, unpublished), however, showed that the untempered form had a
permeability about 13 times greater than did the tempered form. This is critical if
a moisture barrier based on real chocolate is to be used.
Although the study did not look at whether the permeability of untempered
cocoa butter was so high because it changed its polymorphic form on storage and,
in so doing, caused structural changes that allowed moisture to pass through more
easily, this would be a possible scenario. If that were the case, then a chocolate
barrier ought to be used in a tempered state (except, perhaps, if being used in a
frozen confectionery product where, at –20 °C, it would not transform into another
crystal form). The problem with this is that tempered chocolate has a viscosity
some two to three times greater than untempered chocolate and so the thickness of
the barrier layer is likely to be greater than would be considered optimal. Although
a thick layer would benefit the product in terms of reducing moisture migration, it
would have considerable added cost implications to the product.
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Enrobed and filled chocolate, confectionery and bakery products
Table 11.2 Water vapour permeabilities of commercially available barriers compared
with chocolate (adapted from Bourlieu et al., 2006)
Barrier
Beeswax
Beeswax/acetoglyceride 2
Dark chocolate
Barrier fat 2
Milk chocolate
Beeswax/acetoglyceride 1
White chocolate
Barrier fat 1
Acetoglyceride
Permeability
(10–12 mol m–1 s–1 Pa–1)
(0–100% RH)
Average barrier
thickness (µm)
0.88 + 0.30
0.93 + 0.11
2.57 + 0.38
4.76 + 2.02
4.94 + 1.90
5.63 + 0.99
5.79 + 0.10
6.22 + 0.98
6.3 + 0.90
303
312
680
321
681
300
664
297
200
The water vapour transmission rates (WVTR) of dark chocolate barriers under a
range of conditions were studied by Biquet and Labuza (1988). They found that the
greater the water activity gradient from the dry material to the moist material the more
water vapour passed through the film. For example, at a water activity gradient of 0.00–0.33, the WVTR was 1.20 g d–1 m–2, but this increased to
3.21 g d–1 m–2 when the water activity gradient was 0.00–0.808. The amount of water
vapour being transmitted through the barrier was also temperature dependent. At
10 °C and 20 °C the WVTR was 3.34 g d–1 m–2 and 3.21 g d–1 m–2, respectively with
a water activity gradient of about 0.00–0.80. At 26 °C, however, the WVTR
increased dramatically to 10.38 g d–1 m–2. This would most probably have been due
to a combination of a greater level of liquid oil in the fat phase of the chocolate at
26 °C coupled with a greater potential for polymorphic changes to occur.
Bourlieu et al. (2006) compared different types of chocolate with two commercially available fat-based barriers, different commercially-available combinations
of beeswax and acetoglyceride, and beeswax and acetoglyceride separately. One
of the commercially available barrier fats (barrier fat 2) had a much higher contact
angle with water than any of the other barriers. This is generally an indication of
high hydrophobicity and it was even higher than the values normally quoted for
paraffin-wax coated paper. This perceived benefit did not, however, come through
as strongly in its water vapour permeability measurements (Table 11.2). The
lowest permeabilities were found with the beeswax and one of the beeswax/
acetoglyceride combinations (wax-based barriers are discussed in more detail in
Section 11.4.2). The three types of chocolate had surprisingly low permeabilities
but the films used were about twice as thick as with the other barriers. When the
water vapour permeability for an RH range of 0–70% was calculated, both milk
and white chocolate were considerably higher than the other barriers, although
dark chocolate was better.
Application of fat-based barriers
In theory, there are a number of ways of applying a barrier to a substrate. The main
Layer thickness (mm) (± 1SD)
Product design and shelf-life issues: moisture and ethanol migration
223
3.5
3
2.5
2
1.5
1
0.5
0
100% fat
Fig. 11.8
75/25 fat/icing
sugar
50/50 fat/icing
sugar
35/65 fat/icing
sugar
Barrier layer thicknesses from enrober.
ones that have been used in practice are (a) spraying, (b) enrobing and (c) brushing.
If we consider these in reverse order, brushing is usually the least successful and,
potentially, the most labour-intensive unless biscuits, for example, pass on a belt
beneath a brush that is continually fed with the barrier material. The problem with
brushing a barrier on to, say, a biscuit is that there will be an uneven thickness with
microscopic peaks and troughs in the barrier layer. Moisture will be able to migrate
more quickly through the thinner parts of the barrier and there is then the possibility
that expansion of the biscuit caused by moisture ingress will result in cracks in the
these parts of the barrier, thus accelerating migration. In fact, Talbot (1991) found
that biscuits coated with fat/sugar barriers by brushing took less than 1 week to
increase in moisture by 1% whereas similar biscuits in which the barrier was
applied by enrobing took more than 20 weeks to reach the same level of moisture
uptake.
Enrobing (using a conventional type of chocolate enrober) can be used both
with 100% fat barriers as well as with barriers containing non-fat solids such as
sugar and cocoa powder. The advantages of using an enrober are (a) that it is
equipment that is often already available where multi-component biscuit and cake
products are being produced, and (b) it is particularly useful in applying barriers
where the fat content is less than 50% (e.g. chocolate). It does, though, produce a
thicker – and more apparent – barrier layer than would be achieved by, for
example, spraying (see Fig. 11.8).
Spraying is usually the method of choice for applying fat-based barriers and
comes in two main types – spinning-disc and nozzle sprays. In spinning-disc
sprays, the barrier material is directed on to a rapidly rotating disc. The speed of
rotation of the disc is such that the barrier material is flung off the disk in a fine mist.
Baffles can be used to control the amount and direction of this mist downwards on
to a belt moving beneath the discs. Biscuits, for example, move on the belt under
the disc spray and are coated with a thin film (typically about 250 µm) of barrier.
Spinning-disc sprays are most useful for coating flat products such as biscuits and
cakes but are also used for coating other food products such as pizza bases. Any
surplus spray passes through the mesh belt and is recirculated back to the spray
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Enrobed and filled chocolate, confectionery and bakery products
discs. Nozzle sprays are used where the substrate to be protected is more conical,
for example, ice cream cones, pastry tarts and so on. Here, the cones or tarts pass
under the nozzle in an indexed way and stop while the barrier is sprayed into them
before moving on to allow the next one to be sprayed. This means that, unlike
spinning discs, there is generally no or minimal overspray.
Irrespective of the method used to apply the barrier, the temperature of the
barrier itself should be approximately 10 °C above the melting point of the fat
phase. After application of the barrier it should be crystallised by cooling in as
gentle a way as possible within the constraints of factory throughput. Certainly, for
reasons described earlier, shock-cooling of the barrier should be avoided.
11.4.2 Wax-based barriers
Just as fats have a long history of use in terms of protecting foods against both
moisture loss and moisture gain, so waxes have also been used for these purposes.
Wax coatings are often seen, for example, on fruits such as lemons and apples and
on vegetables such as cucumbers and peppers (Guilbert, 1986). Whilst these
coatings help to reduce moisture loss, they can also have other desirable or even
undesirable side effects. For example, too much wax as a barrier on lemons can
allow fermentation of the fruit to occur; coating some vegetables can affect the rate
of respiration resulting in off-flavour development. Thin wax-based coatings are
often applied to nuts, raisins and some confectionery products to give them a glaze
and to stop them sticking together. Frozen meat and fish are sometimes coated in
barriers to prevent oxidation, dehydration and freezer burn. And, finally, the use of
wax coatings on cheeses such as Gouda and Edam is well-known.
In discussing fats as moisture barriers, the point was made that there was a
general relationship between the liquid oil content of a barrier film and its
permeability. There is, however, a limit to how far we can go in increasing the solid
fat content before we reach a point of no improvement. In theory that point would
be when we have a barrier containing 100% solid fat. Ignoring the obvious
difficulties of applying a barrier with that high level of solid fat and of the potential
sensory problems associated with its melting point, the question arises – is this as
far as we can go in terms of reducing permeability? If we were just to use
triglycerides in the barrier, then the answer is probably ‘yes’ and the reason for this
is due to the way in which fats crystallise. A barrier based on a hydrogenated
vegetable fat, for example, will crystallise in a spherical form known as spherulites
(as depicted schematically in the left hand part of Fig. 11.9).
If, instead of crystallising in this form, we could force the fat to crystallise in flat
plate-like crystals (such as those depicted in the right hand part of Fig. 11.9) then
we would increase the path length of moisture movement further by increasing the
tortuosity of the barrier system. This is where waxes in the barrier can help.
Waxes are esters of long-chain alcohols with long-chain fatty acids – long, in
both cases, meaning 16 or more carbon atoms. We can give a ‘carbon number
distribution’ to the waxes by adding the numbers of carbon atoms in both the fatty
acid and alcohol chains. As far as use in food products is concerned we can divide
Product design and shelf-life issues: moisture and ethanol migration
Spherultic crystals
Fig. 11.9
225
Flat, plate-like crystals
Tortuosity (source: K W Smith, Unilever Research).
waxes into three main groups depending on their source: mineral, animal and
vegetable.
The main mineral wax is paraffin wax and, although it is approved for use as a
food coating on, for example, citrus fruits, it is not generally used in foods as a
moisture barrier. Indeed, there has, over the past 10–15 years, been a strong move
away from the use of mineral hydrocarbons in foods, prompted both by legislative
changes and consumer demands.
Of the animal-sourced waxes used as a food coating, beeswax is probably the
most important. This is produced by honey bees during the construction of their
honeycomb cells. It has GRAS (generally recognised as safe) clearance by the US
Food and Drug Administration and can be used at levels of below 0.1% on a range
of confectionery products.
As far as food products are concerned, the use of waxes from vegetable sources
is far more common, with candelilla wax, carnauba wax and rice bran wax being
widely used. Candelilla wax is found in the Euphorbia species in Texas and
Mexico and although it does contain some wax esters, it is mainly composed of
hydrocarbons (Bennett, 1975). Carnauba wax is found in the Copernica Cerifera
‘Tree of Life’ in Brazil and is almost totally wax esters (Bennett, 1975).
Other, more common oils, such as sunflower oil, rapeseed oil, grapeseed oil and
maize oil also contain some wax esters, although they themselves are, of course,
mainly composed of triglycerides. The wax content of some of these oils –
sunflower oil is a good example – is such that they need to be ‘winterised’ before
bottling, to ensure good clarity.
The carbon number distribution of the wax fractions of these oils (Fig. 11.10)
differs considerably with carnauba wax having the longest chains and grapeseed
oil wax the shortest. The waxes from sunflower oil and rapeseed oil are very similar
in their carbon number distribution.
Although such waxes can be used on their own as barriers within foods, they are
more generally used in combination with other lipids such as triglycerides and
acetylated monoglycerides. One of the main reasons for this is that, when produced
as thin layers, waxes have a tendency to crack and therefore let moisture through.
Indeed, the moisture barrier developed by Danisco under the name of the
226
Enrobed and filled chocolate, confectionery and bakery products
30
25
Carnauba
Carnauba
Rice
Ric e Bran
B ran
Maize
M aiz e
20
S unflower
Sunflower
Rape
Rape
% 15
Grapesseed
eed
Grape
10
5
0
40
42
44
46
48
50
52
54
56
58
60
62
Carbon
Fig. 11.10
Carbon number distribution of common vegetable waxes.
Table 11.3 Water vapour permeabilities of common waxes at 25 °C and an RH
gradient of 100–0% (adapted from Donhowe and Fennema, 1993)
Barrier film
Candelilla wax
Paraffin wax
Carnauba wax
Microcrystalline wax
Beeswax
Acetylated monoglycerides
Permeability
(g m–1 s–1 Pa–1 × 10–12)
0.18
0.22*
0.33
0.34
0.58
23.2–62.1*
*Data from Lovegren and Feuge (1954).
Grindsted™ Barrier System is made up of a blend of acetoglyceride and beeswax.
In this case the wax component lowers the permeability of the barrier while the
acetoglyceride gives some physical flexibility.
Although acetoglycerides themselves have been used as moisture barriers, their
effectiveness is much less than that of waxes, as is evidenced by work reported by
Donhowe and Fennema (1993). Table 11.3 compares the water vapour
permeabilities of various waxes with that of acetylated monoglycerides.
Considering, though, blends of triglycerides and waxes we can take, for
example, the triglyceride-based barrier fat A (typical of a commercially available
moisture barrier fat) as a starting point. This has a permeability of 3.8 g mil m–2
d–1 mmHg–1. The permeabilities of most waxes are considerably less than this and
blending them with barrier fat A resulted in a decrease in permeability (Fig. 11.11).
The most effective of these was a concentrate of sunflower wax. Wax is present in
sunflower oil at levels of between 0.02% and 0.35% and is removed by a process
Product design and shelf-life issues: moisture and ethanol migration
227
Permeability
(g mil m–2 day–1 mmHg–1)
4
3.5
Candelilla wax
3
Rice bran wax
2.5
2
Carnauba wax
1.5
1
Sunflower wax
concentrate
0.5
0
0
3
4
5
10
Level of addition
Fig. 11.11
Reduction permeability by adding vegetable waxes to barrier fat A.
of winterisation. This is a dry fractionation process which separates the waxy
residue formed when the oil is held at low temperatures to produce a clear oil
suitable for bottling. The remaining waxy residue contains between 1% and 10%
wax, the rest being sunflower oil. If it is further concentrated up to about 50%, it
has a permeability of just under 0.5 g mil m–2 d–1 mmHg–1. When added at a level
of 10% to barrier fat A, the permeability of the fat is reduced from 3.8 g mil m–2
d–1 mmHg–1 to less than 1 g mil m–2 d–1 mmHg–1 (Talbot et al., 2005).
Averbach (1992) found similar effects when he blended 0.5% rice bran wax with
a partially hydrogenated blend of soyabean and palm oils. The permeability decreased from 1.30 × 10–9 g cm–2 s–1 cmHg–1 cm to 0.07 × 10–9 g cm–2 s–1cmHg–1 cm.
11.4.3 Protein barriers
The main benefit of using proteins as barriers is that they exhibit very good filmforming properties. Unfortunately, their moisture barrier properties do not always
match up. Gelatin, for example, can produce strong, clear films but its permeability
is quite high. Zein (a protein extracted from corn gluten) has been widely studied
as a protein-based moisture barrier because it does show some good barrier
properties but, unfortunately, it has a very poor flavour that has generally prevented its use. Nevertheless it was patented by Cosler (1957) as a means of
preventing hard candies from sticking together as a result of moisture absorption.
Other proteins such as albumin and casein have also been evaluated but have very
poor barrier properties.
It has been found, however, that incorporating either beeswax or carnauba wax
into films based on whey protein isolate and glycerol improves the hydrophobic
nature of the film while also having a plasticising effects (Talens and Krochta, 2005).
11.4.4 Carbohydrate barriers
Although references to barriers containing different forms of cellulose are made in
228
Enrobed and filled chocolate, confectionery and bakery products
this chapter (particularly with regard to dual-layer barriers in Section 11.4.5), the
use of carbohydrates as moisture barriers is not widespread, not least because they
generally have quite a high permeability to moisture. They are more often used as
an additive to a lipid-based moisture barrier. An exception to this is a bake-stable
moisture barrier developed by Haynes et al. (2004) in which a crystalline carbohydrate is blended with a highly crystalline fat and a crystalline food fibre. The
carbohydrate is selected from various mono- and disaccharides as well as cellulose
derivatives. The crystalline fat is selected from fats such as coconut, palm kernel
and palm oil, while the food fibre is derived from sources such as wheat, oat, corn
and so on. The barrier is claimed to reduce moisture migration in baked products
such as pizzas and pies as well as in ice cream sandwiches and multi-layered
yoghurt products. Other workers have studied barriers based on different starches,
dextrins and corn syrups and the use of alginates or calcium salts of carrageenan to
reduce moisture loss from products.
11.4.5 Dual-layer barriers
In many ways, having two layers, each being composed of a different barrier
material, makes a lot of sense. For example, a highly impermeable but inflexible
barrier such as that based on a wax could be protected against cracking by a second
layer of material with reasonably good barrier properties and excellent flexibility
(such as a protein film). Although considerable research has been carried out in the
area of dual-layer barriers these have generally not been taken up industrially. The
reason for this is that including even one barrier layer adds complexity to the
process; adding two of different types and application conditions generally makes
the whole process far too complex to be commercially feasible.
Kester and Fennema (1989b) found that laminating a layer of beeswax to a film
of methylcellulose or hydroxypropyl methylcellulose and palmitic and stearic acids
considerably reduced the permeability to water vapour from 1.4 g mil m–2 d–1
mmHg–1 down to 0.3 g mil m–2 d–1 mmHg–1. A multi-layer barrier system was
invented by Gaonkar et al. (2004) and consists of a fat-based layer coupled with a
flexible hydrophobic layer based on a range of waxes and lipid-based emulsifiers.
11.4.6 Balancing water activities
Although reducing the water activity of the moist phase to a level closer to that of
the dry phase is, in theory, a way of reducing moisture migration because it
eliminates the driving force for migration to occur, it does have very limited
application. To get a significant reduction in water activity by the addition of such
components as sugars, salt or glycerol or by reducing the water content of the moist
phase would have such profound changes on texture and taste as to make this an
almost unworkable solution to moisture migration.
Product design and shelf-life issues: moisture and ethanol migration
229
11.5 Alcohol (ethanol) migration
The main product category in which alcohol migration is an issue is in chocolatecoated liqueurs. In these products, the centres are rich in both alcohol and water,
making them doubly problematic in terms, particularly, of chocolate shell stability.
Unlike migration of moisture between dry and wet phases of a multicomponent
product, the main issue with chocolate liqueurs (and, indeed, with any chocolate
centre with a high level of free water) is that the alcohol and/or water dissolves
sugar from the chocolate shell. This has two detrimental effects. First, it causes the
chocolate shell to swell thus weakening it until, in extreme cases, the shell
completely collapses. Usually, by that time, any alcohol that was in the centre has
evaporated through cracks in the chocolate shell. Second, the dissolution of sugar
from the chocolate shell releases other non-fat components from the shell such as
cocoa powder. When these then mix with the liqueur they change the overall
flavour profile of the centre making it more difficult to distinguish one liqueur from
another.
11.5.1 Types of liqueur
There are two main types of chocolate liqueur, those with a sugar crust and those
without. Liqueurs with a sugar crust are produced by starch moulding. Sugar is
dissolved in the liqueur centre until a supersaturated solution is produced. This is
then poured into moulded depressions, often in the shape of a bottle, in a tray of
moulding starch. This is stored to allow the sugar to crystallise out of solution and
form an outer crust in the shape of the starch mould. When enough sugar has
crystallised to give a thick crust, the sugar-encased liqueur centres are removed
from the starch and are then passed through a conventional chocolate enrober to
coat them with chocolate.
Production of liqueurs without a sugar crust is more difficult and these are
perceived as being of a higher quality. These are produced by filling an empty
chocolate shell with the liqueur centre and then very carefully backing off the filled
shell with more chocolate ensuring that a good seal has been made between the
shell and the base. The problems of alcohol migration are mainly seen in these
types of liqueur because the sugar-crusted liqueurs are (a) protected by the sugar
crust and (b) sufficiently saturated in sugar not to dissolve any more from the
chocolate shell.
11.5.2 Minimisation of alcohol migration
There are two main routes to minimising the effects of alcohol migration:
• Use a barrier coating between the shell and the liqueur.
• Modify the composition of the chocolate to make it less susceptible to attack by
alcohol.
Linke (1999) evaluated five different barrier fats:
230
Enrobed and filled chocolate, confectionery and bakery products
• a cocoa butter improver (essentially a cocoa butter equivalent (CBE) that is
•
•
•
•
harder than cocoa butter)
a non-temper cocoa butter substitute
a fractionated cocoa butter
cocoa butter powder in form βV
‘a high-melting special fat with a specific fatty acid and triglyceride composition’ – but no indication from Linke’s paper (other than the name barrier fat 01)
as to what its exact composition might be.
Since subsequent references in Linke’s paper refer only to barrier fat 01, it is
assumed that this performed better in his initial tests than the other four barrier
fats. Linke concludes that if these types of product have a liquid centre, the use
of a barrier fat is the only recommendation. However, the application of a
barrier to a liqueur-filled chocolate shell is not easy to achieve. First, the inside
of the chocolate shell needs to be sprayed with the barrier before filling with
liqueur. Then, to protect the chocolate base, a spray of barrier needs to be
applied to the top of the liqueur filling before crystallising and then backing off
with the final chocolate layer. Because of these problems, making changes to the
chocolate itself becomes more attractive – if they work!
Linke focuses on the emulsifier content of the chocolate, arguing that lecithin, in particular, acts as a kind of conduit for the transfer of alcohol (and
water) from the centre into the chocolate. This theory is given some support by
the observation that a chocolate shell containing no lecithin shows good stability
to alcohol when stored at 26 °C. However, without any emulsifier present it
would not be possible to produce such shells on a factory scale because of the
high viscosity and yield value. Adding 0.2% lecithin to the chocolate increased
the degree of attack by alcohol, adding further credence to Linke’s theory, but
the effect when 0.4% lecithin was present was not as bad! He also studied the
use of polyglycerol polyricinoleate (PGPR) as the emulsifier in chocolate. This
is known to reduce considerably yield values of chocolate. The addition of 0.2%
PGPR gave a similar effect to an emulsifier-free chocolate, while 0.4% PGPR
gave a worse result. Linke’s best results were achieved by combining a chocolate containing 0.3% lecithin and 0.1% PGPR with a layer of barrier fat 01. With
this combination the chocolates showed no structural changes over 70 days at
26 °C.
A further modification that can be made to the chocolate which was not
studied by Linke but which is suggested as a result of the author’s own experience is to include 5% cocoa butter improver (CBI) in the chocolate. A CBI is a
vegetable fat similar to a CBE but harder. It has the effect of increasing the solid
fat content and heat resistance of chocolate and this level of use is enough to
give good structural stability to the chocolate and to reduce the degree of
interaction between the chocolate and the liqueur. It is, though, only applicable
in those countries which permit the use of vegetable fat in chocolate. This level
and this type of vegetable fat does fully conform to the requirements of the 2003
EU Chocolate Regulations.
Product design and shelf-life issues: moisture and ethanol migration
231
11.6 Future trends
Many of the moisture barrier fats that have been used commercially are based on
partially hydrogenated vegetable oils. Because these are being replaced in many
countries by non-hydrogenated oils, the development of good barrier systems
without the use of hydrogenation (and which are non-polymorphic and do not need
to be tempered) is of great importance.
The use of waxes in combination with other materials (triglycerides,
acetoglycerides etc) is likely to be one route to achieving this. The application
temperature of such systems is, however, quite high (typically 70–80 °C) making
it necessary to have good spray systems that will maintain these temperatures
through heated spinning discs or heated nozzles without blocking. The use of
multi-layer barriers may well also become more widespread as better combinations
of barriers and easier ways of applying them to products become available.
11.7 Sources of further information and advice
The major manufacturers of speciality oils and fats (for example, Loders Croklaan,
The Netherlands; AAK, Denmark, Sweden and the UK) all supply fats for use as
moisture barriers and can give information and advice that is tailored to specific
applications. Geoff Talbot (The Fat Consultant) also has wide experience in the
development and application of fat-based barriers and can advise on specific
problems.
Review papers and chapters covering the subjects of moisture and alcohol
migration can be found in the following references:
GHOSH V, ZIEGLER GR AND ANANTHESWAREN RC
(2002). ‘Fat, moisture, and ethanol
migration through chocolates and confectionery coatings’, Criti. Rev. Food Sci. Nutr.,
42(6), 583–626.
SHELLHAMMER TH AND KROCHTA JM (1997). ‘Edible coatings and film barriers’, in Lipid
Technologies and Application, Gunstone FD and Padley FB (eds), Marcel Dekker, New
York.
11.8 References
ASAMA K, FUJINAKA M, KIDA H
(2007). Fat-and-oil Compositions for Inhibiting the
Migration of Water in Food and Foods Made by Using the Same. European Patent
1787521 A1.
AVERBACH BL (1992). Edible moisture barrier. US Patent 5,130,150.
BENNETT H (1975). Industrial Waxes. Chemical Publishing, New York.
BIQUET B AND LABUZA TP (1988). ‘Evaluation of the moisture permeability characteristics
of chocolate films as an edible moisture barrier’, J. Food Sci., 53(4), 989–98.
BOURLIEU C, GUILLARD V, POWELL H, VALLÈS-PÀMIES B, GUILBERT S AND GONTARD N
(2006). ‘Performance of lipid-based moisture barriers in food products with intermediate
water activity’, Eur. J. Lipid Sci. Technol., 108 ,1007–20.
COSLER HB (1957). Method of Producing Zein-coated Confectionery. US Patent 2791509.
DONHOWE IG AND FENNEMA O (1993). ‘Water vapor and oxygen permeability of wax films’,
JAOCS, 70(9), 867–73.
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Enrobed and filled chocolate, confectionery and bakery products
FENNEMA O, DONHOWE IG AND KESTER JJ
(1993). ‘Edible films: barriers to moisture
migration in frozen foods’, Food Australia, 45(11), 521–5.
FORMO MW (1979). ‘Physical properties of fats and fatty acids’, in Bailey’s Industrial Oil and
Fat Products, Swern D (ed.). Vol.1, 4th edition, p 215.
GAONKAR AG, HERBST L, CHEN W, KIM DA (2004). Multilayer Edible Moisture Barrier for
Food Products. US Patent Application 20040197459.
GHOSH V, ZIEGLER GR AND ANANTHESWAREN RC (2005). ‘Moisture migration through
chocolate-flavored confectionery coatings’, J. Food Eng., 66, 177–86.
GUILBERT S (1986). ‘Technology and application of edible protective films’, in Food
Packaging and Preservation: Theory and Practice, Mathlouthi M. (ed.). Elsevier Applied
Science, London.
HAYNES L, ZHOU N, SLADE L, LEVINE H AND CHAN W (2004). Edible Moisture Barrier for
Food Products. US Patent Application 20040197446.
IGLESIAS HA AND CHIRIFE J (1983). Handbook of Food Isotherms. Academic Press, New
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KESTER JJ AND FENNEMA O (1989a). ‘The influence of polymorphic form on oxygen and
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1383–9.
LABUZA TP AND CONTRERAS-MEDELLIN R (1981). ‘Prediction of moisture protection
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LOH J, ALMENDAREZ M, HANSEN T, HERBST L AND GAONKAR AG (2004). Edible Moisture
Barrier for Food Products. US Patent Application 20040101601 A1.
LOVEGREN NV AND FEUGE R (1954). ‘Food coatings, permeability of acetostearin products
to water vapor’, J. Agric. Food Chem., 2, 558.
SHELLHAMMER TH AND KROCHTA JM (1997). ‘Edible coatings and film barriers’, in Lipid
Technologies and Applications, Gunstone FD and Padley FB (eds), Marcel Dekker, New
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TALBOT G (1991). ‘Putting the lid on moisture migration’. Candy Industry, January, 53–6.
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E239–E243.
12
Shelf-life prediction and testing
P. J. Subramaniam, Leatherhead Food International, UK
Abstract: This chapter covers the important considerations that need to be taken into
account when setting up shelf life and accelerated shelf-life tests and discusses specific
shelf-life issues associated with chocolate confectionery products. The different tests
used for assessing sensory changes are covered, together with specific methods found to
be useful for praline, biscuit and wafer products. The importance of choosing testing
regimes appropriate to products and considerations concerning sample handling are also
covered. The sensory results of shelf life and accelerated shelf-life tests on chocolate
products are also given.
Key words: accelerated shelf life, biscuit, chocolate, confectionery, flavour, praline,
sensory changes, shelf-life, staleness, texture, visual, wafer.
12.1 Introduction
All product manufacturers and retailers know the importance of accurate measurement of shelf life. Without this information it is difficult to ensure that products are
safe for consumption and are consumed at the highest quality possible to satisfy
consumer expectations. Therefore, in determining the overall shelf life of a
product, both the safety and quality aspects need to be considered. Shelf life has
been defined in various ways but a useful definition is that given by the Institute of
Food Science and Technology (IFST, 1993) as the period of time when the
product:
• remains safe
• is certain to retain desired sensory, chemical, physical and microbiological
characteristics
• complies with any label declaration of nutritional data
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Enrobed and filled chocolate, confectionery and bakery products
when stored under the recommended conditions. A more recent document (ASTM
E 2454-05, 2005), the Standard Guide for Sensory Evaluation Methods to Determine the Sensory Shelf Life of Consumer Products defines shelf life in terms of
sensory aspects as:
• the time period during which the product’s sensory characteristics and performance are as intended by the manufacturer;
• the product is consumable or usable during this period, providing the end-user
with the intended sensory characteristics, performance, and benefits.
Low-moisture foods such as chocolate and sugar confectionery are inherently
stable at ambient conditions and therefore have relatively long shelf lives of 3–18
months (Subramaniam, 2000). Testing the shelf life of such products is a long and
laborious task, which can delay the commercialisation of new products. The
confectionery industry is therefore seeking ways of shortening the test period for
ambient stable products and of identifying accelerated shelf-life test methods,
including rapid instrumental methods, which can predict the shelf life within a
short time.
The most important quality parameter driving consumer acceptance, is of
course, sensory quality, relating to how the product looks, feels and tastes.
However, additional parameters also need to be satisfied, based on the claims made
for the product. For fortified confectionery, it is important to ensure that the
product composition at the end of shelf life still satisfies any claims and label
requirements, for example vitamin and mineral levels. Therefore shelf life encompasses many different aspects of product quality and performance.
The measurement of the rate of change of quality parameters as part of shelf-life
tests can be carried out relatively easily, but deciding the cut-off points for specific
quality parameters against which shelf life can be determined is more difficult,
particularly for confectionery products where food safety is not compromised
during shelf life. In these cases, the shelf life is set based on a combination of
scientific data from shelf-life studies and the views of marketing personnel and
based on company policy (Kilcast and Subramaniam, 2000). It is important that
any decisions and recommendations made with regard to the shelf-life tests and
quality control must have the support of all senior management (Thursby, 1974)
This chapter focuses on the methods used to assess and predict shelf life,
particularly of chocolate products. Although fat bloom is the main cause of
deterioration of chocolate and filled chocolate products, the issues of fat migration,
bloom development and control of fat bloom are covered in other chapters and
therefore will not be covered here. Instead, the focus of this chapter will be the
sensory, physical and chemical changes affecting the shelf life of chocolate
confectionery products.
12.2 Shelf-life testing methods
The measurement of shelf life requires first an understanding of all quality
Shelf-life prediction and testing
235
attributes that change during product storage. The key quality factors that limit the
shelf life of the product need to be identified from this information and the critical
levels of change of those different attributes causing product failure or significant
quality loss must be determined. Generally, confectionery products, because of
high levels of sugar and relatively low moisture contents, tend to be microbiologically stable, although a few osmophilic yeasts associated with fruits and nut meats
can ferment syrup concentrations above 75% (Richardson, 1980). The shelf life
therefore is based on the loss of specific sensory quality parameters. Quite often it
can be difficult to define the end point values for specific sensory characteristics
because a level of change that one consumer feels is unacceptable may still be
regarded as acceptable by another. Shelf life is determined by scientific tests but
the changes seen must always be related to consumers’ expectations. Converting
the consumer expectations of quality to accurately measurable scientific parameters can be difficult. This is the aim of the instrumental, physical and chemical
tests used as part of a shelf-life study. The cut-off limits of change, in particular
quality attributes, are often therefore set based on a consensus of opinions and, in
some companies, the views of only a small group of experienced personnel, rather
than the result of large groups of taste panels (Thursby, 1974).
The use of a scientific approach to shelf-life measurement is important in setting
the test methods and the critical limits needed to reduce inaccuracies in shelf-life
assessment. Shelf-life tests are carried out for different purposes. When used
during product development, shelf-life tests can be started as soon as the very first
samples are approved, even though further changes in formulation will be necessary (Barnett, 1980). They are often used for the purpose of assessing the success
of formulation modifications and processing refinements carried out as part of a
cost cutting exercise, or where a new market demands an extension of the shelf life
of existing products. In these cases, a comparison of the behaviour of the old
product (with a known shelf life) with the newly modified product under the same
test conditions, perhaps even under accelerated conditions, will help to determine
if the shelf life has been altered. Shelf-life tests must be carried out through direct
methods where representative samples of products (ideally production samples)
are subjected to realistic storage conditions that mimic the distribution cycle for the
product. Table 12.1 gives the typical steps involved in setting up a sequential shelflife test. In such tests, samples placed in storage will be removed sequentially at set
intervals and assessed for changes in quality using sensory tests and appropriate
physical and chemical tests that measure specific quality parameters until a time
when the product is deemed to be unacceptable.
Other test designs can also be used, using staggered sampling techniques, which
allow the direct comparison of the quality change in products stored for different
lengths of time. The advantages and disadvantages of the different designs are
discussed by Kilcast and Subramaniam (2000). Whatever the sampling design, the
storage test conditions need to be chosen carefully and a good understanding of the
storage, handling and climatic conditions of the markets in which the product will
be sold is essential to the accuracy of shelf-life tests. The test conditions should be
chosen based on the distribution cycle for the product. Commonly used shelf-life
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Enrobed and filled chocolate, confectionery and bakery products
Table 12.1 Steps in setting up shelf-life tests
Step Shelf-life testing considerations
1
2
3
4
5
6
7
8
9
10
11
12
Consider all changes occurring in the product based on past experience or the
behaviour of similar products on the market.
Identify critical changes to be measured.
Identify storage test conditions based on product cycle.
Identify sensory, chemical and physical techniques for measuring level of
attributes.
Decide packaging for the samples to be tested.
Decide the test intervals based on estimated or target shelf life (typically 2-week
intervals for 3–4 month shelf life; one month intervals for 6–12 month shelf life; 2month intervals for 12–18 month shelf life).
Prepare representative samples of the products for testing. Products may need to be
stabilised for 1–2 weeks before putting through storage tests. The number
produced should be considerably more than the calculated number of samples
required for testing at every interval set.
Set up storage unit(s) and monitor conditions and adjust until unit is stable.
Place samples in the storage unit and assess samples for time 0 point.
Remove samples from storage and assess for quality changes at each interval until
end of test.
Compare data collected at each interval against cut-off limits for consumer
acceptance.
Determine shelf life for product based on a discussion of the times to reach the cutoff points for specific quality attributes.
testing conditions which mimic ambient market conditions are 38–40 °C/80–90%
relative humidity (RH) for tropical climates and 20–25 °C/50–70% RH for temperate conditions. Products with an expected shelf life of 12 to 18 months are
sampled at 1–2 month intervals to measure shelf life.
12.2.1 Shelf-life limiting factors
In order to determine the shelf life of a product, it is important to understand the
relationship between different factors affecting its shelf life. The main factors
affecting shelf life are product composition/structure, packaging and the distribution and storage conditions. Product factors such as composition, raw material
quality, product structure, moisture content, water activity, fat content, liquid fat
content, pH and sensitivity to oxygen are all important intrinsic factors affecting
shelf life of confectionery (Subramaniam, 2000). The processing conditions used
will also influence these product characteristics. Product structure, such as the
surface smoothness and porosity of the product, plays important roles in determining product stability in both single and multi-component confectionery products,
where fat and moisture migration are important mechanisms of deterioration. In
products such as chocolate-coated biscuits, structural changes have been found to
be important in determining the rate of fat migration. Although fat migration to a
large extent is determined by the type of fat and the fat content of the biscuit and
chocolate components, factors such as biscuit density and the surface texture also
Shelf-life prediction and testing
237
influence the result. The greater the density, and the rougher the surface of a
biscuit, the greater the tendency for fat migration. Although high storage temperatures can increase the rate of fat migration, the direction of the migration may be
different based on the storage temperature.
Packaging has a significant role in determining the shelf life of confectionery.
Good barrier properties, particularly to moisture, can be used to improve shelf life
(Beehler, 1982). The maximum moisture loss or gain and oxygen ingress which
cause a quality change, can be used to determine the barrier properties required for
a product. The permitted moisture gain is 5% and the maximum oxygen ingress is
5–15ppm for nuts and snacks according to Robertson (1991). The permeability
characteristics of packaging used to influence shelf life of products will play an
integral role in shelf-life trials. As far as possible shelf-life tests should be carried
out in the final packaging format to be used. Stability tests can be carried out on
products packaged in perforated packaging, if the direct effects of humidity or
oxygen on product stability need to be determined. Perforated packaging is
normally used in accelerated shelf-life tests rather than conventional shelf-life
tests, to accelerate moisture movement between product and environment or vice
versa, whilst protecting the samples from dust and so on. Therefore the importance
of choice of packaging for shelf-life tests cannot be overemphasized.
The use of storage conditions representative of market environments is important for shelf-life study. Environmental factors such as temperature, humidity,
oxygen and light will affect the shelf life. The relative effects of these factors will
vary depending on the product and packaging characteristics. A common problem
is that shelf-life studies are often carried out under carefully controlled environmental conditions that do not reflect reality, especially once the product leaves the
factory and goes into a retail environment and then into homes. It is therefore
important that manufacturers have a good understanding of the behaviour of
products under realistic environmental conditions. The storage conditions chosen
for shelf-life testing should not be the ideal for the product, but allow for some level
of abuse seen during the product life cycle.
12.2.2 Sensory test methods
Sensory tests are the most important tests to be carried out during a shelf-life study
to assess the changes in perceived product attributes during storage. The changes
in the attributes will relate directly to the stability of the product. If the sensory
changes are not caused by microbial growth and spoilage, as in the case of most
confectionery, the degree of change in sensory characteristics has to be directly
related to product acceptability. Appropriate sensory tests need to be used to assess
different aspects of shelf life. The ASTM has produced a guide that is useful for
sensory shelf-life testing (ASTM, 2005).
Both analytical and hedonic sensory tests can be used to gain knowledge about
product stability. Analytical tests (such as difference tests and descriptive tests ) are
useful to identify and measure changes in a product. Difference tests (e.g. paired
comparison, duo-trio and triangle tests) are used to compare two products for sensory
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Enrobed and filled chocolate, confectionery and bakery products
differences. These tests are sensitive but will only provide a limited amount of
information on the sensory changes occurring during storage. Descriptive tests, for
example product profiling, measure changes in the individual attributes of products.
Results from such tests can be correlated with instrumental methods that measure the
same or a similar attribute (e.g. colour or texture characteristics) allowing quantification of the sensory changes. The quantitative profile methods use trained sensory
panels to measure the level of intensity of individual attributes and are therefore able
to give more information than difference tests.
Quantitative descriptive analysis (QDA) is the most commonly used method
where the data produced can be statistically analysed and presented in a visual form
(Kilcast, 2000). Example of glossaries established for shelf-life testing of milk
chocolate and chocolate-coated praline are shown in Tables 12.2 and 12.3,
respectively. these glossaries are derived by trained sensory panels after assessing
a range of similar products of different ages and discussing the perceived attributes. The attributes are scored on scales (e.g. an unstructured line corresponding
to a scale of 0–100 could be used). The orientation of the anchors (end points) for
individual attribute scales reflect the anticipated direction of change in the attribute
on storage. Samples can be presented as identified controls at the beginning of the
Table 12.2
Glossary of terms for milk chocolate
Attribute
Appearance
Colour
Gloss
Definition
Milk chocolate colour, assessed
on upper surface
Amount of shine, or gloss, assessed
on upper surface
Anchorsa
Position of
control on
scale 0–100b
Light-to-Dark
20
Not-to-Very
20
Texture
Hardness 1st bite Amount of force required to break
Not-to-Very
sample
Crumbliness
Way in which sample breaks into
Not-to-Very
small pieces
Smoothness
Feeling on tongue and palate, where a Not-to-Very
powdery sample is not smooth
Waxy
Slippery sensation on teeth
Not-to-Very
Cloying
Way in which the sample adheres to
Not-to-Very
the teeth and the mouth
Meltdown rate
Speed of meltdown in the mouth
Slow-to-Fast
Flavour
Flavour impact
Milk chocolate
Stale
Speed of flavour development
Flavour of milk chocolate
Flavour of old chocolate
Slow-to-Fast
Not-to-Very
Not-to-Very
20
10
30
20
20
30
20
30
10
a
The orientation of the scale reflects the direction of the anticipated change on storage and an increase
in attribute relates to an increased score.
b
This number indicates the fixed position of the control sample decided in discussion sessions prior to
the test.
Shelf-life prediction and testing
239
Table 12.3 Glossary of terms for chocolate-coated pralines
Attribute
Appearance
Chocolate colour
Gloss
Texture
Density
Crumbliness
Smoothness
Meltdown rate
Flavour
Chocolate
Nutty
Stale
Other off
Anchorsa
Position of
control on
scale 0–100b
Milk chocolate colour, assessed on
upper surface
Amount of shine, or gloss, assessed
on upper surface
Light-to-Dark
20
Not-to-Very
30
Solid state of sample where a highly
dense sample has a texture similar
to fudge
The extent to which the sample readily
breaks into small pieces
Feeling on tongue and palate, where a
powdery sample is not smooth
Speed of meltdown of sample
Low-to-High
10
Not-to-Very
10
Not-to-Very
30
Slow-to-Fast
30
Flavour of milk chocolate
Flavour of mixed ground nuts
Old flavours not associated with
fresh pralines
Other off flavours e.g. chemical
Not-to-Very
Not-to-Very
Not-to-Very
30
30
0
Not-to-Very
0
Definition
a
The orientation of the scale reflects the direction of the anticipated change on storage and an increase
in attribute relates to an increased score.
b
This number indicates the fixed position of the control sample decided in discussion sessions prior to
the test.
session. In this case, the position of the control is marked by the sensory assessors,
by way of consensus, on the scale so that test samples can be scored relative to the
control as shown in Tables 12.2 and 12.3.
The hedonic tests (such as preference tests and acceptability tests) measure the
level of consumer liking and perception of quality. These tests can be useful in
determining the end points for shelf life, when consumer acceptability falls
sharply. QDA tests on the same products can then be used to measure the level of
change in particular attribute(s) to identify the important changes which make the
product unacceptable to the consumer. A correlation of both types of tests is often
required to measure and then decide the shelf life of products. The final decision
on the end point and shelf life will often be a commercial one (Kilcast and
Subramaniam, 2000). Hedonic tests use consumers to carry out the assessments,
with tests at a central location, at home in the form of home usage tests or anywhere
where the consumer can access the internet. Products are commonly scored on a
category scale as in the example below:
1. like extremely
2. like very much
3. like moderately
240
4.
5.
6.
7.
8.
9.
Enrobed and filled chocolate, confectionery and bakery products
like slightly
neither like nor dislike
dislike slightly
dislike moderately
dislike very much
dislike extremely
Hedonic tests provide a direct measure of consumer acceptance but are expensive
as they are carried out with many consumers to represent the market.
12.2.3 Other methods for measuring physical and chemical changes
Physical and chemical tests are useful in measuring the primary factors that cause
deterioration of a product under normal storage conditions. The results of instrumental tests can be correlated with sensory results and are often used to set critical
limits for product deterioration. Some commonly used tests are described.
Moisture content
The texture of all confectionery products containing water is mainly determined by
the moisture content (Mansvelt, 1973). The moisture content of products can be
determined by appropriate tests such as oven and vacuum-oven drying and Karl
Fischer titration. In a shelf-life study, the moisture content of the product can be
correlated with the level of specific sensory attributes (e.g. texture in wafer and
biscuit products) to set the critical limits for moisture gain or loss during storage.
The rate of moisture loss/gain leading to significant changes in the sensory
characteristics can be used as the basis for shelf-life prediction. The critical
moisture content for wafers can be as low as 1% (Subramaniam et al., 1997). In soft
nougat centres with 8–10% moisture, an increase or decrease in moisture of 1% is
said to make a significant difference to texture (Mansvelt, 1973). The changes in
water content also induce crystallisation of some of the sugar present, which can
then compromise the microbial stability of the product. In the case of multicomponent products, the individual components need to be analysed separately in
order to study moisture movement between components. In certain multi-component products, it is interesting to note that changes in texture can occur without the
loss or gain of water by the product.
Water activity
Water activity (Aw) is an important property of foods and relates to the equilibrium
relative humidity (ERH) of products (Aw × 100 = ERH). The ERH of a product is
the humidity at which a product will neither gain nor lose moisture. The difference
between the equilibrium relative humidity (ERH) of the product and the relative
humidity of the storage environment is the driving force for moisture movement
between the product and the environment. Products with a higher ERH than the RH
of the environment (e.g. fondants, marzipan) will dry out during storage. However
products with an ERH lower than the RH of the environment (e.g. sugar glass,
Shelf-life prediction and testing
241
Table 12.4 Commonly used methods of instrumental texture measurement
Test
Product
Attributes measured
Three-point bend
Snap
Softening
Staleness
Crumbliness
Crunchiness
Firmness
Firmness
Shear
Chocolate
Biscuit
Wafer
Chocolate
Biscuit
Jelly products
Praline
Toffee
Gums
Toffee
Cereal
Extrusion
Caramel/toffee
Compression
Cut test
Incisor
Firmness
Hardness on first bite
Toughness
Firmness
Toughness
Stickiness
biscuits, wafers) will pick up moisture during storage. An ERH difference of more
than 2% between two components or between product and environment will cause
moisture movement (Cakebread, 1976).
Moisture can also move within the product if components of the product differ
in ERH, as is often seen in multi-component products (e.g. chocolate-coated
biscuits containing water-based fillings). The greater the difference in the ERH
between adjacent components (such as the biscuit and the filling), the greater will
be the tendency for moisture to migrate and the shorter the shelf life. The
measurement of water activity used to be a long and laborious process involving
storage of samples in sealed glass jars over different saturated salt solutions to
create a range of humidities. The measurement can now be made using water
activity meters that produce results within ten minutes. There are many practical
considerations during ERH measurement and these are given in detail by Bell and
Labuza (2000).
Texture measurement
Instrumental measurements are very useful in measuring changes in texture during
storage of products. If the parameters of the texture measurement are chosen
carefully, a high level of correlation can be obtained with the sensory results. Many
different methods have been devised and tested to measure different aspects of
sensory texture. These include the relatively simple force deformation techniques
(Lu and Abbott, 2004) and acoustic/sound measurement techniques (Duizer,
2004) using texture analysers, to more complex techniques such as near infrared
(NIR) diffuse reflectance (Millar, 2004) and nuclear magnetic reflectance (NMR)
and magnetic resonance imaging (MRI) as described by Thybo et al. (2004). Many
studies have been conducted to determine the best tests for measuring the texture
of specific products. Table 12.4 lists commonly used instrumental texture methods
to measure different texture attributes.
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Enrobed and filled chocolate, confectionery and bakery products
Colour and gloss measurement
The appearance characteristics of products are known to have a significant
influence on the acceptability of foods. Attributes which affect overall appearance
include colour and gloss, particularly in chocolate products (Subramaniam and
Groves, 2001). Colour and surface appearance has been shown to affect the results
of chocolate flavour in taste panel calibration tests (Musser, 1973). Loss of colour
can occur during storage as a result of the effect of temperature and light. The latest
trend is to substitute artificial colours in confectionery products with natural
colours which are generally less stable. The loss of colour or development of
darker colour (often because of Maillard browning reaction) can reduce acceptability and must be assessed as part of product acceptance during shelf-life testing.
For example, in nougat and fondant product, the centre can change from a white
colour to yellow/brown (Mansvelt, 1973) as a result of Maillard browning. Colour
can be easily measured using colorimeters and the instrumental values correlated
with sensory acceptability as part of shelf-life assessment.
Gloss levels of products can be measured by determining the amount of light
reflected from the surface using a gloss meter, which is said to measure gloss
independent of colour (Smith, 1999). The nature of the reflection is dependent
on the characteristics of the surface (Musser, 1973). A smooth surface causes a
mirror or specular type of reflection and leads to a high level of gloss. However,
rough surfaces scatter the reflected light, resulting in a lower level of total
reflection (termed diffused reflection) causing the product to appear dull.
Changes in the surface characteristics as the product ages, for example bloom
development, can be a shelf-life limiting factor. In shelf-life tests, instrumental
gloss and colour measurements have been found to correlate with bloom development (Subramaniam et al., 1997, 2005a). Shelf-life studies have raised many
questions about how the numerical values relate to visual gloss. The perception
of gloss and the levels considered by consumers to be the ideal for different
chocolate products have not been fully investigated. Traditionally, high gloss
was considered to be related to high quality. However, chocolate products with
very high levels of gloss are sometimes considered to be less acceptable (Fillion
et al., 2001). Therefore, the instrumental results of gloss measurements need to
be interpreted carefully.
Rancidity
Oils and fats deteriorate through oxidative (reaction of unsaturated fatty acids with
reactive molecules such as oxygen) and hydrolytic rancidity (chemical or enzymic
hydrolysis liberating fatty acids from triglycerides) giving rise to off-flavours and
off-odours. Hydrolytic rancidity gives rise to ‘soapy’ off-notes in systems containing lauric fats and promotes deterioration by direct oxidation (Kristott, 2000; Matz,
1976). Oxidative rancidity causes food spoilage by fat deterioration causing
pungent or acrid odours and is the most important of the two with respect to product
acceptability (Labuza, 1982). The quality assessment of fats and oils involves both
sensory and chemical tests. The chemical tests are based on either quantifying
the triglyceride and fatty acid decomposition products, or measuring volatile
Shelf-life prediction and testing
243
Colour
80
Stale
70
Gloss
60
50
40
Milk chocolate
Hardness on 1st bite
30
20
10
0
Flavour impact
Crumbliness
Meltdown rate
Smoothness
Cloying
Week 0
Fig. 12.1
Waxy
Week 16
Week 75
Effect of storing milk chocolate at 5 °C.
decomposition compounds in the headspace of closed oil containers. At least two
different tests are required to assess freshness of oils and fats (Kristott, 2000).
The most common tests are the measurement of peroxide value, anisidine value,
free fatty acid content, total oxidation (Totox) value, thiobarbituric acid (TBA) and
extinction at 230 and 270 nm (Kristott, 2000). Infrared spectroscopy is also
suggested (Gordon, 2004). However, correlation of specific test values to the level
of off-flavours and odours as assessed by a sensory panel is essential for individual
products in order to relate instrumental results accurately to the level of rancidity
and overall acceptability. More information on the influence of fats and the issues
of fat deterioration are covered in greater detail in other chapters.
12.3 Sensory changes during storage of chocolate
confectionery
A number of studies have been conducted to determine the sensory changes
occurring in both dark and milk chocolate products during storage under different
conditions (Subramaniam et al., 1997, 2005a). The effect of storage conditions on
milk chocolate characteristics is shown in Figs 12.1 to 12.3. The results show that
storage at 5 °C for 75 weeks does not significantly change the sensory quality of
milk chocolate and is therefore a suitable temperature to store chocolate products
244
Enrobed and filled chocolate, confectionery and bakery products
Colour
80
Stale
70
Gloss
60
50
40
Milk chocolate
Hardness on 1st bite
30
20
10
0
Flavour impact
Crumbliness
Meltdown rate
Smoothness
Cloying
Waxy
Week 0
Fig. 12.2
Week 16
Week 75
Effect of storing milk chocolate at 20 °C/50% RH.
Colour
80
Stale
Gloss
70
60
50
40
Milk chocolate
Hardness on 1st bite
30
20
10
0
Flavour impact
Crumbliness
Meltdown rate
Smoothness
Cloying
Week 0
Fig. 12.3
Waxy
Week 10
Week 16
Effect of storing milk chocolate at 24 °C/70% RH.
Shelf-life prediction and testing
245
90
80
not–very
70
60
50
40
30
20
10
0
W0
W2
W4
W6
W8
W10 W12 W16 W29 W37 W48 W57 W65 W75
Storage time (weeks)
Sample 5°C
Fig. 12.4
Sample 20°C/50% RH
Sample 20°C/70% RH
x Sample 24°C/70% RH
Loss of milk chocolate flavour in a milk chocolate stored under
different conditions.
to be used as reference samples during shelf-life tests. Storage at 20 °C/50% RH,
which simulates normal ambient storage, for the same length of time significantly
changes both flavour and texture characteristics. Storage at 24 °C/70% RH for 16
weeks produced the same trend in changes as at 20 °C/50% RH, suggesting that the
former conditions can be used as an accelerated test for shelf-life prediction of
chocolate. The following sections will focus more closely on changes in specific
flavour and texture attributes of confectionery products. Both changes in texture
and flavour are significant during storage.
12.3.1 Flavour changes
Three main types of flavour changes are common during storage (Subramaniam,
2007):
1. flavour loss leading to weaker flavours in open textured and porous products
e.g. fondant, compressed tablets and panned goods;
2. staleness development caused by oxidation of flavour components, especially
essential oils, e.g. mints, citrus;
3. development of rancidity caused by fat oxidation.
Changes in flavour attributes have been measured during the storage of milk
chocolate under different storage conditions using trained sensory panels
(Subramaniam et al., 2005a). The loss of chocolate flavour and the development of
stale flavour were the significant changes seen and these changes were found to
occur gradually throughout storage. The rate of loss of chocolate flavour and
development of stale flavours in milk chocolate can be seen in Figs 12.4 and 12.5,
respectively. The results show that the changes produced at 20 °C/50% RH over 75
246
Enrobed and filled chocolate, confectionery and bakery products
Fig. 12.5
Development of stale flavour in milk chocolates stored under
different conditions.
weeks are similar to the flavour changes seen over 16 weeks at 24 °C/70% RH,
demonstrating that the latter could be used to accelerate flavour changes in
chocolate.
The origin and development of stale flavours in chocolate has been the subject
of many debates by chocolate manufacturers. Staleness appears to take different
forms and has even been found to fluctuate depending on storage conditions.
Moisture was thought to play a role in this process. Certain stale flavours in
chocolate were thought to be reversible to some degree and able to be reduced or
even eliminated by remelting and moulding chocolate, allowing the recycling of
chocolate products. Little is still known about the origins of the stale notes and
whether ingredients may be the source of the problem. One study focusing on
staleness development in milk chocolate showed that stale or aged milk chocolates
had a harder texture than fresh samples (Fig. 12.6.), which seemed to relate to
changes in the microstructure (Subramaniam et al., 2005b). The fat continuous
matrix in the fresh chocolate was thought to change to a sugar–protein continuous
matrix during ageing. It is possible that the formation of such a matrix may be
responsible for the change (loss) in the chocolate flavour noted in aged chocolates.
Another possibility may be that flavours are masked by the formation of a rigid
network, which then is perceived as a loss of flavour on ageing. Although fresh and
stale milk chocolate samples were tested by gas chromatography–mass spectrometry
(GC–MS), the study was not able conclusively to identify common markers for
Shelf-life prediction and testing
247
Force to penetrate 4 mm (g)
6000
5000
4000
Fresh
Stale
3000
2000
1000
0
A
B
C
D
Chocolate
Fig. 12.6 Comparison of hardness of ‘fresh’ and ‘stale’ variants of four different milk
chocolates showing that the fresh chocolates are in general softer than the stale chocolate.
staleness in products of different composition. However, the products of oxidation
were found to be higher in some of the stale products.
12.3.2 Texture deterioration of chocolate, wafer, biscuit and praline
The smoothness of chocolate is an important quality attribute. The progression
of fat bloom is commonly associated with a loss of smoothness and an increase
in crumbliness. The loss of smoothness of milk chocolate under different storage conditions is shown in Fig. 12.7. The results showed that storage at 5 °C
retains milk chocolate texture in a smooth state but storage at 20 °C and 24 °C
causes a loss of smoothness on storage, the loss being accelerated at the higher
temperature.
Wafer, biscuit and praline are common components in chocolate products.
Texture is an important attribute for these products and can significantly influence
shelf life. The textural changes occurring during the ageing of these components
under different storage regimes have been measured (Kilcast and Subramaniam,
1998). In the case of wafer, the three-point bend/snap test measuring peak force,
peak area and the break distance were useful indicators of textural quality. Break
distance was found to relate to stale texture development, which caused the wafer
to become less crispy and more pliable. The reduction of crispness in wafer as a
result of the development of staleness was also reflected in the peak force and area
results, which increased as a rubbery/chewy texture developed on storage. Increase in moisture content of wafer samples during storage correlated with an
increase in the break distance and highlighted the importance of preventing
moisture absorption.
The biscuit product used in this study was an open structured, slightly crumbly
textured oatmeal biscuit with a high fat content of 19.6%. Texture tests found that
the number of fractures as measured during the hardness test was a good indicator
248
Enrobed and filled chocolate, confectionery and bakery products
80
75 ✱
not–very
70
65
✱
60
✱
55
✱
✱
50
✱
✱
✱
45
40
W0
W2
W4
W6
W8
W10 W12 W16 W29 W37 W48 W57 W65 W75
Storage time (weeks)
Fig. 12.7
Loss of smoothness in milk chocolates stored under different conditions.
of crumbliness. A significant decrease in the number of fractures suggested a
decrease in crumbliness as the biscuit aged. The break distance measurement in a
snap test was not found to be a good measure of the textural changes occurring
during the staling of biscuits. Moisture migration is the important mechanism
causing sensory changes in dry products such as wafer and biscuit. In chocolatecoated variants, moisture would move by diffusion through the chocolate, but, if
the coating is incomplete, moisture movement will be through the cracks and holes
in the coating, accelerating moisture absorption and reducing shelf life.
In the case of praline, a cut test was found to be useful in measuring the changes
in texture during storage. The peak force was found to relate to the surface hardness
of the samples and the peak area to the firmness of the bulk product. Praline
samples stored at 5 °C and 20 °C showed some softening of the surface of the
samples prior to further hardening on storage. However, at 28 °C/70% RH, praline
samples developed a crust on the surface, perhaps owing to the absorption of
moisture and showed a loss of smoothness. The sensory changes seen in a
chocolate-coated praline during storage related to moisture and fat migration.
12.3.3 Visual changes
Colour and gloss are the two main visual characteristics of chocolate. The factors
that affect colour of chocolate include the cocoa characteristics (type and roasting
temperature, alkalising); milk powder type and level; particle size and tempering.
The factors important for gloss are tempering and cooling, moulding or enrobing
and age (Voltz and Beckett, 1997). Changes in gloss and colour can be indicators
of loss of quality. The onset of bloom development on chocolate can be monitored
by measuring changes in colour and gloss. Subramaniam et al. (1997) found that
gloss assessed by a trained sensory panel correlated reasonably well with
Shelf-life prediction and testing
249
260
240
õ
¸
Gloss units
220
¸
õ
õ̧
200
õ
¸
¸
õ
¸
¸
õ
õ
180
¸
¸
¸
õ
õ
160
140
õ
120
100
0
1
2
3
4
5
6
7
8
9
Storage time (weeks)
¸
Filling A
õ
Filling B
Filling C
Fig. 12.8 Effect of level of hazelnut oil in filling on gloss during storage of filled
chocolates at 24 °C (fillings A, B and C had 20%, 32% and 40% hazelnut oil, respectively).
instrumental measurements from a gloss meter. The measurement parameters used
on the gloss meter can influence the results obtained and need to be chosen based
on product dimensions. Instrumental gloss measurement is a useful way to study
the progression of bloom and has been used to measure the performance of antibloom filling fats and the effect of hazelnut oil on migration-induced bloom on
chocolate (Subramaniam and Groves, 2003). The surface gloss of samples containing fillings with 20%, 32% and 40% hazelnut oil (fillings A, B and C,
respectively) stored under accelerated test conditions shows clearly how hazelnut
oil accelerates bloom development (Fig. 12.8). Bloom was first noted on samples
A, B and C after 7–8 weeks, 2–3 weeks and 1–2 weeks, respectively when stored
at 24 °C. Gloss is measured in arbitary gloss units, a value of 275 units being
associated with a polished black tile. It can be seen that a small change of about 20
units can be linked with early stages of bloom development. Interestingly, the gloss
meter is able to capture how the gloss level increases for the high hazelnut oil
product (sample C) at certain points in the storage because of migration of nut oil
on to the chocolate surface. This shows the importance of visual assessment
alongside the instrumental measurement of colour and gloss to interpret the causes
of visual changes in stored samples.
12.4 Shelf-life prediction
Shelf-life prediction is increasingly becoming an important part of any new
product development and because of improved controlled storage testing facilities
in more recent times it is seen as a real possibility by companies. Shelf-life
prediction will never be able to replace shelf-life testing, but it is a useful tool to
have available where commercial decisions have to be made within time con-
250
Enrobed and filled chocolate, confectionery and bakery products
straints for product launch. This section will cover the important aspects of
accelerated shelf-life testing.
12.4.1 Accelerated shelf-life testing (ASLT)
ASLT aims to accelerate the rate of deterioration of the product without altering
the mechanisms or order of changes seen in the product under normal storage
conditions. In any ASLT it is important that no new changes are brought about by
the testing conditions which are designed to force the product to age quickly.
ASLTs are particularly useful in predicting the shelf life of ambient-stable products such as confectionery which have long shelf lives. It should be noted that
ASLTs cannot be used if microbial growth occurs in the products. These tests are
designed solely to accelerate physicochemical changes. Products spoiling because
of microbial growth have other appropriate tests for prediction of microbial
growth. The principles of ASLT are covered in detail by Mizrahi (2000 and 2004).
Although ASLTs are extremely useful and have their place, there are many
limitations which need to be considered in using these tests (Robertson,1991). A
good understanding of the product under study is needed before accelerated tests
can be set up to make sure that tests are carried out as accurately as possible to
predict shelf life. In their simplest form, ASLTs are useful as comparative studies
in which the rate of change of specific characteristics of a new product is checked
against that of an existing similar product of known shelf life.
Accelerated shelf-life tests (ASLT) are used for many different purposes:
•
•
•
•
•
prediction of shelf life
assessment of product stability in a short period of time
abuse testing of products
troubleshooting of instability problems
formulation screening at initial stages of product development.
12.4.2 Testing regimes
The storage conditions used to accelerate the deteriorative process depend on the
characteristics of the products. The test conditions for any accelerated tests must
ensure that the changes induced are only those that are caused under the normal
storage conditions. For dark chocolate, the temperature limit will be close to 30 °C
and for milk chocolate 24 °C, as higher temperatures will cause the fat to melt
inducing changes that are caused by abuse rather than because of ageing. The exact
conditions used for ASLT should be chosen based on product stability characteristics, typical climatic conditions during distribution and retail storage. Table 12.5
gives some ASLT conditions used for confectionery products (adapted from
Subramaniam, 2007).
As discussed earlier in this chapter, packaging is an important factor to consider
in any shelf-life test. This includes accelerated tests, where products will be often
stored at high temperatures and humidity. It is important to undertake these tests in
Shelf-life prediction and testing
251
the final packaging format. Products in their secondary outers can be tested to
ensure that they are to the required standard. A common test for sugar confectionery items packaged in outer cartons will be that they show no significant change for
16 weeks at 25 °C/60 % RH. Barnett (1980) suggested an accelerated test where
packaged products are alternated daily between storage temperatures of
26.7 °C(80 °F) and 15.6 °C (60 °F) for 6–12 weeks. One week under these
conditions was thought to equate to one month of normal storage for most fatbased confectionery products and those containing nuts.
12.4.3 Sample handling
The same issues of sample handling in shelf-life tests apply also to ASLT. Sensory
tests are vital for both shelf-life testing and ASLT. Sensory tests require that
reference samples are retained for comparison with aged samples produced at each
storage test interval. These reference samples should be equivalent to fresh
samples of the product. How to maintain the freshness of the reference sample has
been a long standing debate. Some believe that chocolate products can be frozen
and presented after thawing at each point. However, others suggest that freezing
induces changes that can be noticed by a sensory panel, in particular relating to
flavour. In general it has been found that storage at 5 °C can be used to arrest
changes occurring in chocolate under normal storage and has been used widely in
many studies (Subramaniam et al., 1995, 2005a). However, chocolate samples
have also been frozen successfully for chemical analysis at a later date.
Table 12.5 Accelerated shelf-life testing conditions for confectionery (adapted from
Subramaniam, 2007)
Product
Deteriorative change
Typical ASLT conditions
Dark chocolate
Milk chocolate
Chocolate
Chocolates with fatty filling
Sugar glass
Toffee
Gums and jellies
Sweets with natural colours
Biscuits/wafers
Bloom
Bloom
Staleness
Fat migration
Moisture pick up
Graining and cold flow
Drying out
Colour fading
Staleness
24–28 °C
24 °C
24–28 °C/70% RH
24 °C
25 °C and 50% RH
25 °C and 70% RH
25 °C/50% RH
25°C + relevant humidity + light
28 °C/70% RH
12.5 Future trends
Shelf-life testing will always be required to test and verify the safety and stability
of products and sensory tests will always remain as a vital part of any study.
However, manufacturers are under greater demands to release products on to the
market more quickly before shelf-life tests are completed. This is particularly the
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Enrobed and filled chocolate, confectionery and bakery products
case for confectionery products which show a high turnover of product formats
and new developments. For this reason ASLTs are increasingly being used as part
of the decision making on product stability. If these are to be used with a high level
of confidence, further work is required to develop validated tests with proven
relationships of stability under normal ambient and ASLT conditions. The use of
rapid physical and chemical tests which can predict shelf life will be an important
future development for the industry. One important aspect of this is the correlation
of sensory data with chemical and physical data produced by different techniques.
Unfortunately no instrument can be as all encompassing and sensitive as the
human palate. This means that sensory testing and relating quality changes to
consumer acceptability will always be expected to remain the core of any future
shelf-life tests.
12.6 Sources of further information and advice
A vast amount of published information exists on shelf-life assessment of different
food products. However, many of these approach the subject in a theoretical
manner rather than from a practical basis. All those who have set up shelf-life trials
will understand that there are many practical considerations in carrying out such
tests. Unfortunately very little data exists on this aspect of the subject, except in the
much older publications which do offer some important information and advice
not found in later publications. Much research is still required on ASLT of different
aspects of product quality. The most useful published information is provided by
Mizrahi (2000 and 2004) as given in the reference section. However, there are a
number of comprehensive books on shelf-life testing which can be combined with
confectionery specific books and these are listed as follows:
• Labuza, TP (1982). Shelf-life Dating of Foods, Food and Nutrition Press,
Westport, CT.
• Charalambous, G (1993). Shelf-life Studies of Foods and Beverages – Chemical, Biological, Physical and Nutritional Aspects, Elsevier Science, Amsterdam.
• IFST (1993). Shelf-life of Foods – Guidelines for its determination and Prediction, Institute of Food Science & Technology, London.
• Man, CMD and Jones, AA (1995). Shelf-life Evaluation of Foods, Blackie
Academic & Professional, an imprint of Chapman and Hall, London, UK.
• Kilcast, D and Subramaniam, PJ (2000). The Stability and Shelf-life of Food,
Woodhead Publishing, Cambridge UK.
• Steele, R (2004). Understanding and Measuring the Shelf-life of Food,
Woodhead Publishing, Cambridge UK.
• Beckett, ST (2009). Industrial Chocolate Manufacture and Use, 4th edition.
Blackwell Science Ltd, London, UK.
• Minifie, BW (1980) Chocolate, Cocoa and Confectionery: Science and Technology, 2nd edition, AVI publishing, Westport, Conneticut.
Shelf-life prediction and testing
253
12.7 Acknowledgements
Leatherhead Food International holds the copyright to all figures and tables used
in this chapter and these should not be reproduced without permission.
12.8 References
ASTM E 2454-05 (2005). Standard Guide for Sensory Evaluation Methods to Determine the
Sensory Shelf Life of Consumer Products, USA.
(1980). ‘New products-production’, Manufacturing Confectioner, 60(6), 87–
91.
BEEHLER DC (1982). ‘The effect of packaging on candy bar shelf-life’, Candy Industry, 35–
8.
BELL LN AND LABUZA TP (2000). Moisture Sorption – Practical Aspects of Isotherm
Measurement and Use, 2nd edition. American Association of Cereal Chemists, St Paul,
USA.
CAKEBREAD SH (1976). ‘Ingredient migration in composite products’, Confectionery Production, 42(5), 26–37.
DUIZER LM (2004). ‘Sound input techniques for measuring texture’ , in Texture in Food
Volume 2: Solid Foods, Kilcast D (ed.), CRC Press, Boca Raton, pp146–66.
FILLION L, ARAZI S, LAWSON S AND KILCAST D (2001). Gloss Perception and its Importance
in Food Products: an exploratory study, LFRA Research Report, Leatherhead Food
International.
GORDON MH (2004). ‘Factors affecting lipid oxidation’, in Understanding and Measuring
Shelf-life of Food, Steele R (ed.), Woodhead Publishing, Cambridge, UK, pp 128–41.
IFST (1993). Shelf-life of foods: Guidelines for its Determination and Prediction, Institute of
Food Science and Technology (UK), London.
KILCAST D (2000). ‘Sensory evaluation methods for shelf-life assessment’, in The Stability
and Shelf-life of Food, Kilcast D and Subramaniam PJ (eds), Woodhead Publishing,
Cambridge, UK, pp 79–106.
KILCAST D AND SUBRAMANIAM PJ (1998). Shelf-life Prediction of Composite Chocolatebased Low-Moisture Products: Stage 1: critical evaluation of characterisation methods.
MAFF-LINK Project Report for Project No. AFQ1116.
KILCAST D AND SUBRAMANIAM PJ (2000). ‘Introduction’ in The Stability and Shelf-life of
Food, Kilcast D and Subramaniam PJ(eds), Woodhead Publishing, Cambridge, UK, pp
1–22.
KRISTOTT J (2000). ‘Fats and oils’, in The Stability and Shelf-life of Food, Kilcast D and
Subramaniam PJ (eds), Woodhead Publishing, Cambridge, UK, pp 279-310.
LABUZA TP (1982). ‘Shelf-life of fried snack foods’, in Shelf-life Dating of Foods, Labuza
TP (ed.), Food & Nutrition Press, Westport, Connecticut, pp 129–48.
LU R AND ABBOTT JA (2004). ‘ Force/deformation techniques for measuring texture’, in Texture in Food Volume 2: Solid Foods, Kilcast D (ed.), CRC Press, Boca Raton, pp 109–45.
MATZ SA (1976). Snack Food Technology, AVI publishing Company, Westport Connecticut.
MANSVELT, JW (1973). ‘Shelf-life of sugar confectionery’, Confectionery Production, 10,
542–9.
MILLAR S (2004). ‘Near infrared (NIR) diffuse reflectance in texture measurement’, in Texture
in Food Volume 2: Solid Foods, Kilcast D (ed.), CRC Press, Boca Raton, pp167–83.
MIZRAHI S (2000). ‘Accelerated shelf-life tests’, in The Stability and Shelf-life of Food,
Kilcast D and Subramaniam PJ (eds), Woodhead Publishing, Cambridge, UK, pp 107–28.
MIZRAHI S (2004). ‘Accelerated shelf-life tests’, in Understanding and Measuring Shelf-life
of Food, Steele R (ed.), Woodhead Publishing, Cambridge, UK, pp 317–339.
BARNETT CD
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Enrobed and filled chocolate, confectionery and bakery products
MUSSER JC (1973). ‘Gloss on chocolate and confectionery coatings’, 27th PMCA Production
Conference, Pennsylvania Manufacturing Confectioners’ Association, Centre Valley
PMCA, pp 46–50.
RICHARDSON T (1980). ‘Confectionery production’, The Manufacturing Confectioner, 12,
52–5.
ROBERTSON GL (1991). ‘Predicting the shelf-life of packaged foods’, Asian Food Journal,
6(2), 43–51.
SMITH G (1999). ‘New emerging technology in gloss measurement’, Innovations in Food
Technology, August, 44–5.
SUBRAMANIAM PJ (2000). ‘Confectionery products’, in The Stability and Shelf-life of Food,
EKilcast D and Subramaniam PJ (eds), Woodhead Publishing Limited, Cambridge, UK,
pp 221–48.
SUBRAMANIAM PJ (2007). ‘Determining shelf-life of confectionery products’, Manufacturing Confectioner, 87(6), 85–91.
SUBRAMANIAM PJ AND GROVES K (2001). A study of Gloss Characteristics of Chocolate
Coatings, Research Report 783, Leatherhead Food International.
SUBRAMANIAM, PJ AND GROVES K (2003). A Study of Anti-bloom Fats for Delaying
Migration-induced Bloom, Research Report 830, Leatherhead Food International.
SUBRAMANIAM PJ, ROBERTS CA, KILCAST D AND JONES SA (1997). Accelerated Shelf-life
Testing of Chocolate Products, Research Report No. 738, Leatherhead Food International.
SUBRAMANIAM PJ, LAWSON S, EELES M AND GROVES KHM (2005a). An Investigation of
Accelerated Shelf-life Testing Conditions for Milk Chocolate and Chocolate-coated
Pralines. Research Report No, 882, Leatherhead Food International.
SUBRAMANIAM PJ, PHELPS T, LAWSON S, GROVES KHM AND REID WJ (2005b). An Investigation of Staleness Development in Milk Chocolate, Research Report No. 878, Leatherhead
Food International.
THURSBY ML (1974). ‘Optimize the shelf-life of your products’, Candy and Snack Industry,
139(12), 34.
THYBO AK, KARLSSON AH, BERTRAM HC, ANDERSEN HJ, SZCZYPINSKI P AND DONSTRUP S
(2004) ‘Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) in
texture measurement’, in Texture in Food Volume 2: Solid Foods, Kilcast D (ed.), CRC
Press, Boca Raton, pp 184–204.
VOLTZ M AND BECKETT ST (1997). ‘Sensory of chocolate’, The Manufacturing Confectioner,
2, 49–53.
13
Controlling the rheology of chocolate and
fillings
M. Wells, formerly of Cadbury Trebor Bassett, UK
Abstract: This chapter begins by describing rheological terms, going on to discuss how
to measure the flow behaviour of chocolate and typical fillings such as liquid caramels,
cremes, fondants, truffles and pralines. Further sections then discuss the major recipe and
process parameters which influence the viscosity of chocolate and fillings and how these
can be controlled. Later sections discuss how to deal with specific practical issues which
arise when we make coated and filled products by different methods. The final section
considers how to deal with elastic behaviour.
Key words: Casson, chocolate viscosity, low shear rate viscosity, rheology of caramels,
tempered viscosity.
13.1 Introduction
If we are to make coated and filled confections that the consumer will repeatedly
purchase, it is vital that they are uniform in quality. This means that as well as
taking great care over the taste of the product we must also give careful attention
to certain physical characteristics as well. The proportion of coating to filling must
be consistent and the external appearances of the top surface and of the base need
to be acceptable to the eye. These are features which are influenced by the rheology
of the chocolate and the filling and it is the control of these that is the subject of the
present chapter.
Rheology is the study of the flow and deformation of materials. In very many
cases, at the point of manufacture, we will be dealing with liquid materials which
display irreversible flow when they are deformed. In these situations we will only
need a measurement of the viscosity of the material in a viscometer under carefully
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Enrobed and filled chocolate, confectionery and bakery products
defined conditions. In some situations however, the materials under discussion can
show a degree of recoverable elasticity characteristic of solids when they are
deformed. This behaviour needs to be considered. Thus Sections 13.2 to 13.4 of
this chapter deal with rheological terms and how to measure the flow behaviour of
chocolate and typical fillings. Sections 13.5 and 13.6 cover the factors which
influence the viscosity of chocolate and fillings. Sections 13.7 to 13.9 deal with
specific practical issues which arise when we make coated and filled products by
different methods. Section 13.10 considers how to deal with elastic behaviour and
the final section outlines sources of further information.
13.2 Defining rheological terms
We consider here the case where chocolate or filling is undergoing shear flow, that
is, where elements of the fluid are moving past each other and over a material
surface parallel to the direction of flow. There are two ways in which this could be
made to happen:
• a force, which might come from gravity or a positive displacement pump, is
moving the fluid past static surfaces, or
• a force is applied by moving the surface past a sample of the fluid.
We examine the second situation where a thickness x of fluid is entrained
between a fixed surface and a moving surface of area A to which a constant force
F is being applied to maintain a velocity V, as in Fig. 13.1.
It will be evident that the higher the fluid viscosity, the larger the applied force
Speed V
Force F
Moving surface: area
Fluid
Fixed surface
Fig. 13.1 Shear flow.
A
X
Controlling the rheology of chocolate and fillings
257
F will have to be to maintain the plate moving at a constant velocity V. To
determine the fluid viscosity we need to define a few important rheological terms.
These are shown in Table 13.1 which refers to the definitions in Fig. 13.1.
Shear stress measures the shear pressure being applied to the moving plate to
overcome the resistance of the fluid. Clearly the larger the contact area the higher
the shear pressure will have to be. The shear rate on the other hand defines the
velocity gradient in the fluid gap. In many situations where chocolate or filling is
being used, the shear rate is produced by forced movement of the fluid between
fixed surfaces. It is important to remember that in these cases high shear rate can
be produced in two ways: either by very rapid pumping between quite widely
spaced surfaces, or by slower pumping between narrow gaps. High shear rates can
develop in unexpected places, such as between a rotating shaft and its packing or
between the teeth of the gears in a pump.
Viscosity is a property of the fluid itself and measures the resistance to
movement. For simple fluids such as water, cocoa butter, even glucose syrup and
golden syrup, the viscosity is the same regardless of the shear rate. These fluids are
known as Newtonian fluids. Table 13.2 gives some idea of the enormous range of
viscosities which are possible from ‘fluids’ which are nominally Newtonian.
The vast majority of food materials are actually non-Newtonian fluids. This
means that their viscosity changes with the shear rate being applied. The most
common behaviour is so called pseudoplastic or shear thinning behaviour. This is
where the viscosity is reduced as the shear rate increases. This type of behaviour is
very common with fluids such as chocolate where the microstructure is a dispersion of micron and sub-micron-sized particles in a continuous fluid. The reason
for the change in viscosity with shear rate is believed to be due to some sort of
Table 13.1 Rheological terms
Term
Greek symbol
Shear stress
Shear rate
Viscosity
τ
γ·
η
Equation
τ = Force/area
γ· = Speed/distance
η = Shear stress/shear rate
Identity
SI unit
F/A
V/x
τ/γ·
Pa
sec –1
Pa s
Table 13.2 Newtonian food viscosities
Material
High boiled sweet
Toffee
Soft caramel
42DE glucose syrup
Golden syrup
Glycerine
Cocoa butter
Water
Temperature °C
Viscosity (Pa s)
20
20
20
40
20
20
40
20
1012
106
103
200
100
1
0.05
0.001
258
Enrobed and filled chocolate, confectionery and bakery products
Ordering in
shear field
Fig. 13.2
Ordering of particulate dispersion during shear thinning or pseudoplastic flow.
of ordering of the closely packed particles in the shear field, much as depicted in
Fig. 13.2. On account of this change of viscosity with shear rate it is vital always
to quote the viscosity for chocolate along with the shear rate at which it was
measured.
A rarer type of viscosity behaviour is so called dilatancy or shear thickening.
This is where the viscosity increases as shear rate increases. This is only seen in
chocolate at very high shear rates, beyond about 1500 s–1 and well beyond those
normally encountered in typical processes. Dilatancy is a result of disordering of
the closely packed particles in the shear field and a concomitant expansion. It
occurs when the shear forces are large enough to overcome interparticle forces
(Boersma et al., 1990). It becomes more significant when particles are closer
together, that is, with lower fat chocolates, particularly when they have a smaller
particle size. This type of behaviour is familiarly seen at the seaside when running
on damp sand: the faster we run the harder the sand appears to be.
We need at this point to enquire as to what shear rates might be important to us
in using chocolate or filling. The answer very much depends on what operation we
are carrying out. The solids particles in chocolate, left to stand without stirring, will
gradually sediment under the gravitational force. This is why chocolate left in the
hot stove always has a layer of fat on it after a few days. The shear rates achieved
by the particles in this operation are exceedingly small, estimated at 10–6 to 10–4
s–1, depending on the volume of solids in the chocolate dispersion. At the opposite
extreme, if we were using chocolate to spray on our moulds, the shear rate in the
spray head might be in excess of 103 s–1. Table 13.3 below outlines some typical
shear rates which might apply to confectionery.
Table 13.3 Shear rates in confectionery production
Operation
Sedimentation
Gravity drainage
Pumping/pouring
Spraying
Tasting
Range of shear rates
10– 6 to 10– 4
10– 1 to 1
1 to 102
103 to 104
1 to 106
Example
Unstirred chocolate
Enrobing chocolate
Pumping or depositing chocolate
Spray coating
Chewing, low; dispersing between
tongue and roof of mouth, high
Controlling the rheology of chocolate and fillings
259
13.3 How to measure the rheology of chocolate and fillings
13.3.1 Measurement of chocolate and fat-based fillings
The method used for measuring liquid chocolate and fat-based fillings is the same.
The method recommended here is a summary of Analytical Method 46, published
by the International Office of Cocoa, Chocolate and Sugar Confectionery (IOCCC,
2000; Aeschlimann and Beckett, 2000) with some significant differences, which
will be highlighted in their context.
The most generally useful instrument for viscosity measurements is the rotational viscometer with coaxial cylinders: Searle, with a rotating bob or Couette
with a rotating cup (Barnes et al., 1989). Either shear rate controlled or shear stress
controlled instruments can be used. The preferred bob is of the DIN pointed type,
not with polished steel as in the method, but roughened with vertical scores of ~0.5
mm depth and 2 mm apart to offset slippage at low shear rate (Barnes, 1995). The
ratio of bob diameter to cup diameter should be not less than 0.85, giving a gap
width of between 1 and 2 mm, more than ten times the largest particle diameter.
The set up is as depicted in Fig. 13.3.
The principle of the measurement is that rotation of the coaxial cylinders
produces a torque on the measuring head which is proportional to the shear stress.
The shear rate is determined by the speed of rotation and the gap between the cup
and bob. By choosing different rotational speeds the viscosity of the material in the
cup may be determined at different shear rates.
The details of the calculations are as follows. For a bob of height h, radius r,
rotating in chocolate, the shear stress τ at radius r is related to the torque T
experienced by the torsion head by the equation:
Fig. 13.3
Viscometer cup and bob.
260
Enrobed and filled chocolate, confectionery and bakery products
T
τ = ——–
2πr2h
[13.1]
In a coaxial cylinder viscometer, shear is experienced at the cup and bob
surfaces. It is conventional to quote the viscosity at a representative shear rate
which is the arithmetic average of that experienced by the two surfaces. If the bob
or cup is rotating at ω radians s–1 this representative shear rate is given by equation
13.2.
r2c + rb2
.
γrep = ———
ω
[13.2]
r2c – rb2
In most modern viscometers all the necessary calculations are done by the
software and shear stress, shear rate and viscosity values are displayed. The other
factor which we need to take account of is the percentage of the maximum torque
used for each measurement. Ideally the torque reading should be in the range 10–
90% of the full scale reading. Care needs to be taken in choosing the right geometry
to achieve this. Equation 13.1 tells us that the bob surface area will contribute
significantly to the overall torque. Contact with the manufacturer usually allows
the most appropriate bob and cup sizes for the chosen recipe to be obtained.
To ensure best practice in measuring chocolate viscosity, the reader is referred
to the published method for full information. The essential details to bear in mind,
however, can be summarised as follows.
• Cup and bob should be maintained at 40 °C before use.
• The sample should be free of air and at 40 °C before measurement starts.
• The measuring system should be accurately filled, so that the annulus between
the cup and bob is fully occupied with the fluid.
• The sample should be given the very minimum of pre-shear. I suggest no more
•
•
•
than 15 s at 5 s–1 to allow all the surfaces to be coated. Some chocolates are
deliberately made to a high viscosity specification by means of minimal
conching. Too much shear will alter what we have carefully made, that is,
provide additional conching.
Chocolate samples should be measured over the same shear rates and time steps
and preferably in the direction of increasing shear rate.
Liquid samples should be measured as soon as possible after manufacture. The
practice of leaving an unstirred sample for hours in the oven leads to a rise in
viscosity as re-aggregation of the particles occurs, especially if the moisture
content is over about 1%.
Solids samples should be melted in an oven at 45 °C (not 52–55 °C as in the
method) for 60 minutes, hand stirred for homogeneity and then placed in the
measuring system. This temperature is chosen because in the case of crumb
chocolates with moisture levels over 1%, significant viscosity increase can be
produced by holding at temperatures in excess of 50 °C.
Choice of shear rates
The chocolate industry in the main is wedded to the Casson method of measuring
Controlling the rheology of chocolate and fillings
261
chocolate flow (Seguine, 1990). This equation relates shear stress to shear rate by
the equation 13.3.
.
τ½ = τ½yield + η½plastic γ ½
[13.3]
Measurements are made over a range of shear rates from 5 s–1 to around 100 s–1 and
graphical extrapolations made to produce ‘yield value’ and ‘plastic viscosity’.
Little thought is given to what shear rates might be appropriate for the chocolate
being used. Long experience in the chocolate industry has indicated that the
following procedure works very well and is understood at every level of production.
1. For enrobing and shell making applications where chocolate drainage determines chocolate weight, viscosity specifications are made at a low shear rate
of 0.5 s–1. This correlates well with chocolate weight.
2. For moulding applications where chocolate is weighed into the mould and the
main concern is that the chocolate can be pumped into and out of the depositor,
viscosity is specified at a moderate shear rate of 7 s–1. This corresponds to shear
rates in pipe work and other pumped circuits.
3. If chocolate were to be sprayed, specifications would be set at much higher
shear rates, at say 100–200 s–1.
The benefit of this method of operation is that everybody understands the
concept of viscosity and the difference between low and high shear rates can be
seen by the relatively slow movement of chocolate during enrobing and its more
rapid flow during pumping. The concepts of plastic viscosity and yield value on the
other hand ‘are neither broadly nor generally very clearly understood’ (Seguine,
1988). The correlation between ‘yield value’ and low shear rate viscosity is
actually surprisingly good, as Fig. 13.4 shows.
What is however clear from the diagram is that with some formulations ‘yield
value’ can be zero or even negative. This latter situation is clearly nonsensical
and is caused by the chocolate displaying slight shear thickening behaviour, so
that the Casson equation is inapplicable. This problem is avoided when low
shear rate viscosity is used. It should also be added that measurement below the
so called ‘yield value’ using vane geometry to avoid slip, indicates that viscosity
is finite and levels off to a constant upper Newtonian plateau at very low shear
rate (Barnes, 2000: Chapter 11, Figure 1). It is evident that the ‘Casson yield
value’ is a mathematical anomaly resulting from extrapolation. It would avoid a
lot of confusion if the use of the Casson method for chocolate were eventually
abandoned.
Plastic viscosity has even more problems associated with it. Its numerical value
turns out to be significantly lower than any chocolate viscosity it is possible to
measure! It actually correlates well with a viscosity measured at 100 s–1. This is
clear from Fig. 13.5.
Since this shear rate rarely corresponds to any unit operations for finished
chocolate use, use of ‘plastic viscosity’ is not recommended.
262
Enrobed and filled chocolate, confectionery and bakery products
35
Casson yield value (Pa)
30
R 2 = 0.888
25
20
15
10
5
0
–5
0
20
40
60
80
100
120
140
Viscosity (Pa s) at 0.5 s–1
Fig. 13.4
Correlation between Casson ‘yield value’ and low shear rate viscosity.
13.3.2 Measuring viscosity of caramels and creme fondants
The same equipment is also suitable for the measurement of water-based cremes
and caramels. The only additional factors that need to be considered are:
• The sample needs to be protected against water loss during the measurement.
•
Viscometer manufacturers have a number of options for measuring viscosity
while minimising evaporative losses. These include a semi-enclosed system
containing a little tray for a salt solution of the correct equilibrium relative
humidity (ERH) to maintain the moisture at the product’s ERH.
Temperature control is even more vital than with chocolate as these systems are
in the ‘rubbery’ state where viscosity changes very significantly. The contrast
with chocolate can be seen in Fig. 13.6.
13.4 Typical chocolate flow curves
A typical viscosity versus shear rate flow curve for milk chocolate over a wide range
of shear rates is depicted in Fig. 13.7. A comparison with a universal flow curve and
the difference between smooth and rough bob surfaces is also demonstrated.
A number of important features are clear from this figure.
• At shear rates below about 10 s–1 chocolate is very shear thinning.
• As the shear rate reaches 100 s–1 and beyond chocolate approaches a Newtonian
plateau viscosity.
Controlling the rheology of chocolate and fillings
263
Casson plastic viscosity (Pa s)
7
6
R 2 = 0.9821
5
4
3
2
1
0
0
1
2
3
4
5
6
Viscosity (Pa s) at 100
Fig. 13.5
7
8
9
10
s–1
Correlation between Casson ‘plastic viscosity’ and high shear rate viscosity.
• At very high shear rates, as stated earlier, chocolate shows shear thickening
behaviour.
This is just one typical chocolate flow curve. If we consider the whole range of
chocolate formulations, two significant changes can be made to the above curve.
80
70
Viscosity (Pa s)
60
50
Caramel
40
30
20
Chocolate
10
0
40
41
42
43
44
45
46
47
48
49
50
Temperature (°C)
Fig. 13.6
Comparison between the change of viscosity with temperature of chocolate
(circles) and caramel (squares).
264
Enrobed and filled chocolate, confectionery and bakery products
Measure
at 0.5 s–1
Measure
at 7 s–1
100000
?
Viscosity (Pa s)
10000
1000
õ õ
Chocolate with
rough bob
õ
õ
100
10
1
0.00001 0.0001
õ
õ
õ
õ
õ
Chocolate with
smooth bob
0.001
0.01
0.1
õ
õõ
1
õõ
õõ
10
õ õõõ
100
1000
10000
Shear rate (s–1)
Fig. 13.7 Comparison of universal flow curve and chocolate flow curves. Notice that less
slip and higher viscosity achieved with the roughened bob. Observe the expected lower
Newtonian plateau and dilatancy at very high shear rates.
The position of the curve on the y axis (viscosity) can show considerable variation,
the main contributing factor being the fat content of the chocolate. The second
change is the position of the upper Newtonian plateau on the x axis (shear rate).
With high levels of polyglycerolpolyricinoleate (PGPR) emulsifier, the Newtonian
plateau moves to much lower shear rates. The effect of these two major changes is
clear in Fig. 13.8.
1000
Standard chocolate, 30% fat
Viscosity (Pa s)
High fat chocolate, 35% fat
High PGPR chocolate
100
10
1
0.1
1
10
100
Shear rate (s–1)
Fig. 13.8 Range of possible chocolate flow curves. When high PGPR levels are used,
near Newtonian behaviour is evident from a shear rate of about 3 s–1 and above.
Controlling the rheology of chocolate and fillings
265
The major features of these flow curves can actually be fitted better using the
Sisko equation [13.4] below rather than the Casson equation. This equation defines
the steep slope at the low shear rate end of the curve and also the approach to a
Newtonian plateau viscosity ηinf:
η = ηinf + Kγ· n–1
[13.4]
This equation is the high shear rate limit of the more general Cross model [13.5]
which has both upper and lower Newtonian limiting viscosities as depicted in Fig.
13.7
η – ηinf
1
———– = ————
η0 – ηinf
1 + (Kγ· )m
[13.5]
13.5 Factors affecting chocolate rheology
Molten chocolate is a very high volume fraction dispersion of solid particles (size
typically from 0.1 to 40 µm) in liquid fat. The disperse phase is simplest in the case
of dark chocolate and more complex in milk and white chocolates where milk
proteins are involved and some of the sugars can be in the amorphous rather than
the crystalline state. The key factors which determine the viscosity of chocolate
are:
• the volume fraction of dispersed solid particles
• the forces of interaction between the particles.
A typical milk chocolate of 30% fat has a solids volume fraction φ of 57.5%. It
is clear that dispersing this volume of solids in a minority of liquid is not a trivial
task. Initial mixing tends to provide a dispersion of liquid fat droplets in a solid
matrix – the structure of so called ‘refiner flake’ after five-roll refining. The task of
the chocolate maker is first to invert this phase and second to release fat that is
trapped in particle aggregates. This task is greatly assisted if the chocolate maker
is able to use chocolate emulsifiers which reduce the strength of the particle–
particle bonds.
13.5.1 Effect of chocolate conching
The task of chocolate conching is primarily one of providing sufficient mechanical
work to disperse the solids particles thoroughly in the fat phase and to reduce the
size of the particle agglomerates. Figure 13.9 indicates how chocolate viscosity
relates to applied energy per tonne.
Two things are evident from this graph.
266
Enrobed and filled chocolate, confectionery and bakery products
Fig. 13.9
Effect of conching work input on chocolate viscosity for two chocolate
recipes: 29.5% fat (closed circles), 27.5% fat (open circles).
• Recipe control within strict fat limits is essential. A drop of 2% in fat content
•
means that three times as much energy is needed to achieve the same viscosity.
Adequate dispersion becomes increasingly hard as the particles move closer
together.
At least 40 kWh tonne–1 was needed for the 29.5% fat chocolate before some
sort of plateau viscosity was reached.
13.5.2 Effect of fat content
As we suggested above, reducing fat content significantly increases chocolate
viscosity. The expected result of adding a volume fraction φ of solid to a
continuous fat phase with a viscosity η0 (which will contain cocoa butter and
optionally butter fat and vegetable fat) is given by the Einstein equation [13.6]:
η = η0(1 + [η]φ)
[13.6]
where [η] is called the intrinsic viscosity which, for perfect non-interacting
spheres, is calculated as 2.5. It transpires that this equation only applies at extreme
dilution when φ is in the 1–5% range. At the sort of volume fractions we use with
chocolate, there is considerable crowding of particles and the intrinsic viscosity
takes a much larger value because particles are aggregated and continuous fat
phase is lost within these aggregates. The so-called Krieger–Dougherty equation
[13.7] proves much more suitable for explaining the behaviour of high volume
fraction dispersions such as chocolate (Barnes, 2000):
Controlling the rheology of chocolate and fillings

φ  –[η]φ
η = η0 1 – —– 
φmax 

max
267
[13.7]
Here the symbols apply as before, but φmax refers to the maximum amount of
solid that can be close packed together, at which point the dispersion viscosity
becomes infinite. This equation has been applied to chocolates at shear rates from
0.2 to 100 s–1. The fitting parameters below have been applied to milk chocolate
viscosity at 40 °C and a shear rate of 7 s–1.
• η0, continuous fat phase viscosity: 0.049 Pa s
• [η], intrinsic viscosity: 5.0
• φmax, maximum packing fraction: 0.735
The volume fraction of chocolate solids has been calculated assuming a value
of 897 kg m–3 for the mixed fat density and 1555 kg m–3 for the milk chocolate
solids. These values will obviously fluctuate depending on the chocolate formulation.
By simple manipulation we can then produce a very useful plot of viscosity
against fat content rather than solids volume fraction. Figure 13.10 shows examples
for two types of milk chocolate and the theoretical expectation for non-interacting
steel balls.
This figure illustrates the increasingly steep rise in viscosity as fat is removed
and we approach the maximum packing fraction. This type of plot is very useful for
predicting the quantity of fat required to change from one recipe to another.
Fig. 13.10 Viscosity versus fat content. The continuous lines are Krieger–Dougherty fits
to the experimental data: closed circles and squares. Notice that high PGPR recipes can be
made with 5% less fat at the same viscosity.
268
Enrobed and filled chocolate, confectionery and bakery products
Table 13.4 Chocolate emulsifiers permitted within the EC
Code
Description
E322
Lecithin
Permitted
dosage
Comments
Quantum satis Soya most freely available;
sunflower, rapeseed and corn
less available. Adverse
flavour in some chocolates
E 442
Ammonium phosphatides (YN) Up to 1%
Deodorised rapeseed oil base.
Flavourless
E472(c) Citric acid esters of mono
Quantum satis New emulsifier for chocolate
and diglycerides
available since 2005.
Flavourless
E476
Polyglycerolpolyricinoleate
Up to 0.5%
Much improved in effective(PGPR)
ness over last 10 years.
Flavourless
E492
Sorbitan tristearate
Up to 1%
Rarely used except sometimes as bloom inhibitor.
13.5.3 Effect of emulsifier choice and dosage
Before World War II, typical milk chocolates had to be made with fat contents of
around 36% to achieve acceptable fluidity. The use of chocolate emulsifiers allows
typical milk chocolates to be made at a 30% fat level, with considerable savings in
cost and calorie content. Emulsifiers can thus be regarded as ‘super fats’ equivalent
to 10–12 times their own weight of fat. The list of materials now allowed within the
EC is shown in Table 13.4.
These emulsifiers work by adsorbing onto the surfaces of dispersed solids and
providing a repulsive steric barrier that prevents particle–particle aggregation. The
most effective of these is PGPR which has the highest molecular weight and
therefore can provide a longer range repulsive force than the other materials. The
relative effectiveness of three of these emulsifiers at low shear rate can be seen in
Fig. 13.11.
The most common method of using soya lecithin (SN) or YN emulsifiers is to
keep them back to the very last stage of conching. This allows the chocolate maker
to maximise work input during the dry stage of conching and achieve low viscosity
when emulsifiers are added at the end. This procedure is very frequently used with
batch conching.
Some manufacturers who use continuous conches prefer to use part of the
emulsifier in pasting and refining. This limits the torque experienced by the conche
motor and allows optimum chocolate throughput to be obtained. The majority of
the emulsifier is still added in the last section of the conche to achieve the required
viscosity reduction. PGPR is nearly always added at the last stage of conching. It
is so effective that accurate dosing is essential. Overdosing can lead to serious
problems if the chocolate’s end use demands pattern formation.
The data displayed in Fig. 13.11 shows that it is not necessary to use SN or YN
Controlling the rheology of chocolate and fillings
269
350
Viscosity (Pa s) at 0.5 s–1
300
250
200
150
100
50
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Added emulsifier (%)
Fig. 13.11 Effect of chocolate emulsifiers on chocolate viscosity at a low shear rate:
soya lecithin (closed circles), YN (ammonium phosphatides) (open squares), PGPR
(closed triangles).
above about 0.5%; PGPR addition to this would normally be no higher than around
0.3%, and often much lower than this. An exception to these rules applies in the
case of ice-cream coating. The effect of the cold temperature and moisture present
during enrobing means that it is very useful to have quite high levels of PGPR, as
well as high fat contents, to prevent excessive coating loads at the very low ice
cream temperatures.
13.5.4 Effect of particle size
The size of the particles in chocolate has a significant impact on viscosity,
particularly on the low shear rate viscosity or apparent yield value. This is because
at the same solids volume fraction, smaller particles will on average be closer
together and the attractive van der Waals force between particles will be greater.
More of the fat continuous phase will tend to be trapped in aggregates so that the
apparent solids volume fraction will be higher, particularly at low shear rates. The
size of the effect can be seen in Fig. 13.12.
It should be pointed out that this large effect is most pronounced where most of
the ingredients are added as fat free powders. If, as in the case of milk crumb-based
chocolates, the fat is trapped in pools within the crumb, a much smaller effect is
seen. In this case it is clear that as size reduction is improved so the amount of fat
released from the crumb solids to the fat continuous phase increases. In this type of
system we found that a reduction in the 84% ile size from 50 µm to 15 µm only
reduced low shear rate viscosity from 95 to 60 Pa s: a very much smaller effect.
270
Enrobed and filled chocolate, confectionery and bakery products
Viscosity (Pa s) at 0.5 s–1
1000
100
10
1
1
10
100
% over 20 µm (chocolates) mean size in µm (sucrose)
Fig. 13.12 The effect of particle size on chocolate viscosity for: sucrose in fat (triangles),
30% fat milk powder chocolate (squares), 32% fat milk powder chocolate (circles).
13.5.5 Effect of moisture content
Moisture has a particularly significant deleterious effect on low shear rate viscosity. It is believed that the effect is a result of syrup at the surface of particles creating
a kind of ‘house of cards’ three-dimensional matrix among the particles, giving a
Fig. 13.13 Moisture and chocolate: (a) effect of moisture on low shear rate viscosity;
(b, next page) amount of extra fat needed to compensate for the higher viscosity.
Controlling the rheology of chocolate and fillings
271
Fig. 13.13 continued
significant degree of ‘solid-like’ behaviour to the chocolate (Harris, 1968). Figure
13.13 demonstrates both the effect on low shear rate viscosity and the additional fat
that would be necessary to offset the enhanced viscosity.
Because of the large effect of moisture, it is preferred to control moisture during
conching to around 0.8%. Large variations in the incoming ingredients will be the
cause of significant difficulty in achieving this sort of specification.
13.5.6 Effect of temperature on viscosity
We have seen that the viscosity of a dispersion like chocolate is related to the
volume fraction of solids present by an equation of the Krieger–Dougherty (KD)
type (Section 13.5.2). This equation can be expanded by the binomial theorem to
give a simpler format:
ηdispersion = ηsolvent(1 + k1φ + k2φ2 + k3φ3 + …)
[13.8]
This indicates that the chocolate viscosity ought to be directly related to the
solvent viscosity, in this case the viscosity of cocoa butter plus associated fats.
Measurements show that the change in the viscosity of fats follows the Arrhenius
equation [13.9].
B
—–
η = Ae RT
[13.9]
where R is the gas constant, T is the absolute temperature and A and B are constants.
At a moderate shear rate of 7 s–1, chocolates appeared to show Arrhenius behaviour
except that there were significant deviations from the value obtained for cocoa
butter itself. This is shown in Table 13.5.
It is evident that although chocolates give quite good Arrhenius plots, it is
impossible to apply a universal correction factor, allowing measurement at one
272
Enrobed and filled chocolate, confectionery and bakery products
Table 13.5 ‘Arrhenius’ behaviour of cocoa butter and milk chocolates
Product
Cocoa butter
Chocolate 1
Chocolate 2
Chocolate 3
Chocolate 4
Slope B/R
Difference from cocoa butter (%)
3295
2406
3192
2593
2831
0.0
27.0
3.0
21.0
14.0
temperature to be reliably converted to viscosity at, say, 40 °C. This warning
applies even more to measurements made at low shear rates. The most significant
factor here appears to be the moisture content of the chocolate and the presence or
absence of emulsifiers. The following features are found at low shear rate.
• If moisture contents are around 0.7% or below, chocolate viscosity drops by
•
•
around 25% as temperature rises from 40 to 55 °C. Above this temperature there
is a slight increase.
If moisture contents are 1% or above, viscosity starts to increase as soon as the
temperature reaches 45 °C, with a particularly steep incline above 60 °C.
Addition of 0.2% or more of PGPR seems to alleviate most of the viscosity
increase.
We would not expect the KD equation to work reliably at low shear rate where
particle interactions play such an important role in determining the viscosity.
Measurements seem to indicate that one of the reasons why the viscosity increases
with temperature is that emulsifier desorbs from the particle surfaces at higher
temperatures. These changes with temperature, not surprisingly, are found to be
largely reversible.
13.5.7 Effect of tempering on chocolate viscosity
The amount of seed crystal added to chocolate during the tempering cycle is only
of the order of 1–5%. We have consistently found that degree of temper has a
relatively unimportant influence on tempered viscosity. There are other parameters which are much more important. The most significant of these is the
temperature at which the chocolate is held after tempering. The melting point of
form V (βV) cocoa butter has various values in the literature from 33.8 to 30.7 °C.
To prevent melting out of the form V seeds created during tempering, it is normal
to hold tempered milk chocolate particularly at temperatures below this critical
point. The rate at which milk chocolate thickens is very significantly affected if this
temperature is too far below this figure. Figure 13.14 shows how rapidly tempered
chocolate thickens up in the temperature range 29–30.5 °C. We recommend
holding milk chocolate as close to 30 °C as possible after tempering.
Two other factors that affect viscosity after temper should also be mentioned.
The first of these concerns the water temperatures used to cool the chocolate during
the continuous tempering cycle. The lower this temperature is, the higher will the
Viscosity increase after 2 min standing (%)
Controlling the rheology of chocolate and fillings
273
90
80
70
60
50
40
30
20
29–30% fat
milk chocolates
High fat
milk chocolates
Dark
chocolates
10
0
–10
28.5
29.0
29.5
30.0
30.5
31.0
31.5
32.0
32.5
33.0
Chocolate temperature (°C)
Fig. 13.14 Tempered viscosity change on standing. Tempered viscosity measured at shear
rate of 0.5 s–1 in an ‘infinite sea’ of chocolate at time zero and after 2 minutes standing;
percentage change in this time is calculated and presented on the y-axis against the measured
temperature of the tempered chocolate on the x-axis.
tempered viscosity tend to be. Newer continuous temperers have much improved
heat transfer characteristics which mean that tempering can be achieved with water
temperatures in the range from 15 to 18 °C. The second factor concerns the
residence time for the chocolate in the temperer. It is advisable to keep the
throughput through a temperer within narrow bands. Tempered viscosity can be
unreliable if the throughput has been turned down significantly and chocolate has
stayed in the cooler sections of the temperer for much longer than normal.
Tempered milk chocolate treated in the way described above should have a
viscosity some 10–25% higher than the untempered chocolate measured at 40 °C.
13.6 The rheology of fillings
In considering the rheology of fillings we must first examine their recipes and
microstructure. There are differences and similarities between the three types and
we will deal with them in turn.
13.6.1 Caramel structure and rheology
Caramels, like chocolate, are dispersions but with very different continuous and
disperse phases and in very different proportions. The continuous phase of a
caramel is a concentrated water solution of sugars, while the disperse phase
involves milk proteins and droplets of milk and vegetable fats. Table 13.6
compares a hard toffee caramel which could be enrobed with a liquid caramel
which could be used for a filled unit.
274
Enrobed and filled chocolate, confectionery and bakery products
Table 13.6 Typical caramel formulations
Hard toffee
Continuous phase
Water
Sucrose
Lactose (from milk)
Glucose syrup + invert
Salt+emulsifers+acidity regulators
Disperse phase
Milk proteins
Butter and vegetable fats
6.0
38.0
4.0
30.0
2.0
4.0
16.0
(Total)
80.0
20.0
Filling
caramel
14.0
15.0
2.0
45.0
2.0
2.0
20.0
(Total)
78.0
22.0
This table suggests that the rheology of caramels will be different from that of
chocolate. Whereas with chocolate the difficulty in manufacture is all about
dispersing a large amount of solid in a minority of liquid fat, with caramel the
disperse phase only makes up 20% or so by weight and 28% by volume. The
dispersion process is relatively straightforward in caramel making compared with
the difficulty of getting the correct final moisture content and right level of
caramelisation. Talking in very rough terms, controlling the rheology of caramels
is largely about controlling the viscosity of the continuous phase and this in turn is
dependent, among other things, on temperature and moisture content. There are, of
course, significant contributions from the fat and protein in the disperse phase, but
these are more important in the cold flow characteristics of the product than in its
behaviour when it is hot and flowing.
The first key point to make is that liquid caramels show very much less shear
thinning behaviour than chocolate. This can be clearly seen in Fig. 13.15.
The shear thinning region of a flow curve where log viscosity or log shear stress
against log shear rate is linear is known as the power law region. In this region of
the flow curve, the relationship between shear stress and shear rate follows
equation 13.10,
τ = Kγ· n
[13.10]
where n, the power law index describes the slope of the line in this shear rate region
and K is called the consistency constant. For a Newtonian fluid, n will have a value
of 1.0. A very shear thinning fluid like chocolate can have an n value as low as 0.17.
Typical values for caramels are much closer to 1, typically 0.7 to 0.85. What is also
clear from Fig. 13.15 is that at pumping shear rates caramels tend to be much more
viscous than chocolate. This needs to be taken account of in sizing pumps, pipe
work and depositor nozzles to minimise pressure drop.
The second key point about caramels is how very sensitive the viscosity is to
temperature and moisture levels. This is evident in Fig. 13.16.
To put numbers to the effects, the viscosity of caramel increases by 14% for
every degree C drop in temperature. A 14% increase in viscosity also occurs for
every 0.2% reduction in moisture content. These larger changes happen because
Controlling the rheology of chocolate and fillings
275
1000
Viscosity (Pa s)
Creme
100
Caramel
10
Chocolate
1
0.01
0.1
1
Shear rate
10
100
(s–1)
Fig. 13.15 Flow curves of chocolate (closed circles), soft caramel (open circles) and
liquid creme (closed triangles) compared over a wide shear rate range.
the continuous syrup phase of caramels is in the so-called rubbery state. This is an
intermediate state between the glass transition (typically at –35 °C for a caramel
with 14% water) and the upper solution temperature (typically at 60 °C). Between
these two regions, viscosity is expected to vary much more steeply than the simple
Arrhenius change of 2–3% per °C.
What effect does the disperse phase have on caramel rheology? The type of
protein has an important effect in hard enrobed caramels on the ‘cold flow’
characteristics. Casein-type milk proteins provide a degree of three-dimensional
ordering of the disperse phase, giving ‘stand up’ characteristics which are lacking
when the cheaper whey proteins only are used. The crystallisation behaviour of the
toffee fats is also important in determining the cutting behaviour of hard caramels,
but a discussion of this is outside the scope of this chapter.
13.6.2 Structure and rheology of cremes and fondants
A creme has a slightly simpler microstructure than a caramel. It is essentially a
dispersion of sucrose (and sometimes dextrose) crystals in a continuous phase of
concentrated sugar syrup solution whose composition and behaviour is similar to
that found in liquid caramels. The name ‘creme’ is given to a composition that is
liquid at room temperature. This recipe is used in filled chocolates. Fondants
generally are solid at room temperature, have less moisture and more crystalline
sugar in them, and are used to make enrobed rather than shell-deposited units.
As far as their rheology is concerned, cremes behave in a very similar way to
caramels. This is not surprising because cremes also have a continuous phase made
276
Enrobed and filled chocolate, confectionery and bakery products
1000
35 °C caramel at 4 s–1
Viscosity (Pa s)
40 °C creme at 4 s–1
100
10
12.5
13
13.5
14
14.5
15
15.5
16
16.5
Moisture (%)
Viscosity (Pa s)
1000
100
10
14% moisture caramel at 4 s–1
12% moisture creme at 0.5 s–1
1
35
40
45
50
55
60
Temperature (°C)
Fig. 13.16 Change in caramel and creme viscosity with moisture and temperature: top,
effect of changing moisture at a fixed temperature; bottom, effect of changing temperature
at a fixed moisture content.
of a concentrated sugar solution, generally containing sucrose, invert sugar and
glucose syrup of some type. The only difference is that changing the temperature
alters the quantity of dispersed sugar crystals as the solubility of the sugars changes
with temperature. No such change occurs when a caramel is heated. The volume
fraction of dispersed sugar crystals in a liquid creme is difficult to determine,
although calculations based on the known saturated solubilities of the sugar
50
25
45
24
40
23
35
22
30
21
25
20
20
19
277
Moisture in continuous phase (%)
Crystalline sucrose in dispersion (%)
Controlling the rheology of chocolate and fillings
18
15
10
11
12
13
14
15
16
17
18
19
Total moisture (%)
Fig. 13.17 Effect of water addition to creme: the percentage of crystalline sucrose in
the disperse phase (closed circles); the moisture content of the continuous syrup phase
(open circles).
components using the so called Grover equation (Grover, 1947) allow estimates to
be made. The effect of water addition to a creme whose starting recipe is 60%
sucrose, 15% invert sugar solids, 15% 42DE glucose syrup and 10% water is
shown in Fig. 13.17.
It is clear from this that the expected disperse phase volume is higher than for
caramels and that addition of water affects the expected crystal phase level
substantially. An inspection of Figs 13.15, 13.16 and 13.17 shows that cremes do
indeed behave like caramels, the slightly enhanced sensitivity to both temperature
and moisture being a result of the rather higher disperse phase solids concentration.
13.6.3 Structure and rheology of truffles and pralines
There are a number of definitions of both truffle and praline, depending on country
of origin and whether the confection is designed for long or short shelf life. For our
purpose we have taken a truffle to be mixture of dark, milk or white chocolate with
a soft fat, which is either butter fat or a vegetable fat, tailor made to have the low
melting point characteristics of butter fat. We assume that manufacturers would
wish to steer away from recipes containing water introduced from cream. The
microbiological risk associated with such a material, to say nothing of the control
of the rheology, would preclude any recommendation here. A praline, on the other
hand, we have taken to be a finely divided roast nut paste containing optional
additions of either chocolate itself or an equivalent mixture with finely divided
sugar, cocoa powder and or milk powder.
278
Enrobed and filled chocolate, confectionery and bakery products
Viscosity (Pa s)
1000
Milk chocolate
100
Truffle
10
1
0.1
1
10
Shear rate
Fig. 13.18
100
(s–1)
Comparison of truffle (open circles) and milk chocolate (closed circles)
flow curves.
In structural terms, truffles and pralines are essentially dispersions of solid
particles in a low melting fat continuous phase. It is not surprising, therefore, that
in rheological terms both truffles and pralines behave like chocolate. Figure 13.18
compares the flow curve of a truffle with that of a standard milk chocolate
containing 30% fat.
It is clear from this figure that the truffle behaves in a very similar fashion to
milk chocolate but with a high fat content. All the factors that affect chocolate
viscosity, described in Section 13.5, can be taken as applying in general to truffles
and pralines. We shall not need, therefore to provide any separate discussion of the
rheology of truffles and pralines.
13.7 Issues with shell moulding
In this method of making filled confections, a shaped plastic mould is filled with
fluid tempered chocolate, inverted and shaken to allow excess chocolate to be
removed, scraped to remove excess chocolate from the mould surface and then
passed into a cooler either as it is, upside down, or in the open end up configuration
produced by re-inverting the mould. This sequence of operations is depicted in Fig.
13.19 (Talbot, 2004).
The key issues which need to be addressed in shell moulding of this kind are as
follows:
Controlling the rheology of chocolate and fillings
Fig. 13.19
279
Shell moulding: (a) empty mould, (b) fill with chocolate, (c) invert and
drain excess, (d) mould containing chocolate shell.
• Assuming that care has been taken of the degree of chocolate temper, it is
•
•
essential to keep tight control of the chocolate temperature at deposit. Ideally
this should be at least 30 °C for milk chocolate, but there will be a recipe
dependence. See comments in Section 13.5.7.
The mould temperature should be as even as possible and about 1–2 °C lower
than the chocolate temperature. The important thing here is to make sure that the
mould pre-heater is of sufficient capacity and quality of air flow to achieve an
even temperature. Cold and hot areas on the mould will lead to an uneven weight
distribution as tempered chocolate viscosity and drainage are so sensitive to
chocolate temperature.
The desired chocolate deposit weight will be determined by the initial tempered
chocolate viscosity, the chocolate and mould temperatures and also the mould
shaker settings which are the final control mechanism.
What is the relationship between chocolate viscosity and the weight of chocolate remaining after drainage? The thickness h of a chocolate film draining by
gravity down a vertical wall at distance x has been solved in the case of Newtonian
and power law fluids. The relationships are:
ηx ½
[13.11]
for a Newtonian fluid after t seconds, h = —–
ρgt
where g is the acceleration due to gravity and η is the viscosity.
K 1/n+1 x n/n+1
[13.12]
—
–
ρg
t
The author’s experiments have shown a very good correlation between the actual
weight and the calculated weight of enrobed chocolate assuming a power law
model. There was also an excellent correlation between actual weight and viscosity
measured at 0.5 s –1.
When chocolate is shaken, experiments indicated (Barigou et al., 1998) that the
viscosity of dark chocolate was lowered dramatically, becoming an almost
Newtonian fluid with a viscosity at 20 s–1 of half of its original value. With some
chocolates under certain conditions, a reduction of 80% of the original viscosity
was achieved. Drainage under these conditions was greatly increased.
for a power law fluid, h =
280
Enrobed and filled chocolate, confectionery and bakery products
Experiments involving vertical vibration in the author’s laboratory indicated
that the main controlling variable in assisting drainage was not the frequency or
amplitude of the sinusoidal vibration considered separately but a combination of
the two as described by the root mean square (rms) acceleration. This is normally
expressed in units of g, the acceleration due to gravity. In these terms the
acceleration is given by equation 13.13:
4π2 .af 2
rms acceleration/g = ——
g√2
[13.13]
where a is the amplitude of the vibration and f is the frequency. In vertical
vibration, drainage increased to a maximum around 3g acceleration with no
improvement in drainage being achieved at higher values. The correlation between
coated weight and viscosity at a particular shear rate indicated the following.
• At accelerations of 0–1 g, weight correlated very well to viscosity at shear rates
in the range 0.1–1 s–1.
• At higher accelerations the correlation between weight and viscosity was
poorer, being best at a shear rate of around 100 s–1.
Experience has shown that for shell moulding of small assortment units
weighing around 10 g, chocolates with tempered viscosity in the range 120–170
Pa s at 0.5 s–1 give very acceptable shells, controlled in modern shell plants by
horizontal shakers. For larger units, such as might be used to make Easter eggs,
much higher viscosity chocolate can be used.
13.8 Issues with enrobing
The issues just described for shell moulding apply equally well to enrobed
products. Additional key issues can be identified.
• Because enrobed units are free standing on a horizontal wire mesh, shaking to
•
•
•
•
remove chocolate is limited to less than 1g vertical acceleration otherwise the
units will leave the band! Horizontal acceleration is precluded, otherwise
adjacent rows merge together and units tip over.
Vertical acceleration tends to lead to unevenness across the band because the
flexibility of the band material leads to variable vibration amplitude across the
width.
For these reasons it is customary to add an air knife to the enrober to provide an
extra control for chocolate unit weight.
It is usual to pass the units through a shallow bath of chocolate (the so-called
bottomer) to coat the base of the unit which is not always adequately covered by
a vertical curtain of chocolate.
The final essential element of the enrober is the de-tailing spindle. Without this
device, units tend to develop unsightly feet at the base which give problems
especially in a high speed wrapper which is intolerant of what it sees as
oversized material. The high speed spindle removes these unwanted appendages.
Controlling the rheology of chocolate and fillings
281
With these control devices in place it is possible to use chocolate with a very
similar viscosity specification to that which is used for shell moulding.
If chocolate is being used to coat ice cream, the weight of deposit is affected by
the very cold centres. In this application, it is normal to use a formulation with very
much lower viscosities than is normal for countline or assortments unit enrobing.
A typical ice cream chocolate would have a fat content as high as 40%. In addition
it might well have an additional 0.2–0.3% PGPR in the recipe to provide protection
against the water in the ice cream increasing the recycled chocolate viscosity.
13.9 Issues with one-shot depositing
Producing a filled chocolate by shell moulding necessitates a quite complex
sequence of operations involving:
•
•
•
•
•
creating the correct weight of shell deposit,
solidifying it before the centre is added,
cooling the centre sufficiently rapidly to prevent it burning through the shell,
rewarming the mould to allow chocolate to be applied to the backs before it sets
on and in the moulds,
and finally cooling the total unit so that all the units demould before the mould
returns via the mould heater to the depositor.
One-shot depositing and moulding simplifies the procedure considerably but
adds to the complexity of production by adding a further rheological dimension to
the depositing operation. The method involves co-depositing chocolate and filling
in a co-extrusion nozzle which deposits chocolate as a ring around the filling
depositor (Fig. 13.20; Talbot, 2004).
Matzler (2000) has described how the viscosity of the chocolate and filling need
to be specified. The viscosity of the chocolate and filling need to be close at the
shear rate experienced during the depositing operation. Matzler recommends that
Fig. 13.20
One-shot moulding: (a) empty shell and co-depositor, (b) deposit chocolate
and filling together, (c) finished filled shell.
282
Enrobed and filled chocolate, confectionery and bakery products
during deposit the chocolate should move 96 mm in 10 s while the filling moves at
least 113 mm in the same timer period.
It is also important that the centre extrusion starts after the chocolate deposit and
finishes just before it. This allows the chocolate to finish uniformly on the outside.
A final point is that one-shot depositing only works with co-deposits at closely
matched temperatures, ideally with the chocolate slightly warmer than the centre.
13.10 Dealing with viscoelasticity
All the discussion above has assumed that chocolate and fillings can be described
as purely viscous fluids. This is only an assumption; most of the concentrated
materials we have been considering also have a degree of solid-like, elastic
behaviour. This reveals itself in chocolate depositing as a trailing tail of chocolate
hanging from the depositor nozzle. Provided the tail does not deposit on the land
between the mould impressions, this is not usually a problem. Of more concern is
the behaviour of the centre. A trailing deposit in this case can often spread over the
mould ‘lands’ and end up mixing in with the backing chocolate and adversely
affecting its viscosity and temperability. The dripping of the centre deposit in this
way is often misinterpreted. True viscoelasticity is dealt with by either a rapid suck
back in the depositor which breaks the thread, or by the action of the mould lifting
table where a sudden drop can achieve the same result. If the centre filling is very
Newtonian in its flow behaviour these actions have little effect; the fluid just
carries on flowing. The author has seen real problems will caramel fillings which
have been formulated to give low ERH, but produce a highly viscous virtually
Newtonian fluid.
13.11 Sources of further information and advice
Information relating specifically to the rheology of chocolate and fillings is
relatively sparse. The only books dealing with the subject as part of a general
introduction to chocolate and confectionery are those by Beckett (2009), Beckett
(2000) and Minifie (1980). The Minifie book is now rather out of date, but Beckett
(2009) is expected as a new edition in 2008. McKenna (2003) is in some ways a
more useful book, dealing as it does with the texture of semi-solid foods, with
examples from yoghurt, soup, food spreads and ice cream.
Leatherhead Food International (UK) has considerable information on all
aspects of confectionery and is a good source of literature on chocolate rheology.
Pennsylvania State University in the USA has a cocoa, chocolate and confectionery group as part of their food science department and have published many papers
involving chocolate science, including those specifically related to chocolate
rheology. Other useful sources of information come from ZDS, Solingen which is
the central college of the German confectionery industry and the Biscuit, Cake,
Chocolate and Confectionery Alliance (BCCCA) in London, now known as the
Controlling the rheology of chocolate and fillings
283
BCCC Sector Group of the Food and Drink Federation (FDF). The equivalent
grouping of confectioners in the USA is the Pennsylvania Manufacturing Confectioners Association (PMCA). These last three sources hold regular technical
conferences and rheology lectures come up on a regular basis.
(1999), ‘The yield stress – a review of ‘παντα ρει’ – ‘everything flows?’, J
Non-Newtonian Fluid Mech, 81, 133–78.
BRIGGS J.L. AND WANG T. (2004), ‘Influence of shearing and time on the rheological
properties of milk chocolate during tempering’, JAOCS, 81(2), 117–21.
GENOVESE D.B., LOZANO J.E. AND RAO M.A. (2007), ‘The rheology of colloidal and
noncolloidal food dispersions’, J Food Sci, 72(2), R11–R20.
KARNJANOLARN R. AND MCCARTHY K.L. (2006), ‘Rheology of different formulations of milk
chocolate and the effect on coating thickness’, J Texture Studies, 37, 668–80.
MONGIA G. AND ZIEGLER G.R. (2000), ‘The role of particle size distribution of suspended
solids in defining the flow properties of milk chocolate’, Int J Food Properties, 3(1), 137–
47.
SCHANTZ B. AND ROHM H. (2005), ‘Influence of lecithin-PGPR blends on the rheological
properties of chocolate’, Lebensm-Wiss u-Technol, 38, 41–5.
SERVAIS C. AND ROBERTS I.D. (2004), ‘Determination of chocolate viscosity’, J Texture
Studies, 34, 467–97.
WICHCHUKIT S., MCCARTHY M.J. AND MCCARTHY K.L. (2005), ‘Flow behaviour of milk
chocolate melt and the application to coating flow’, J Food Sci, 70(3), E165–E171.
BARNES H.A.
13.12 References
AESCHLIMANN J.-M. AND BECKETT S.T.
(2000), ‘International inter-laboratory trials to
determine the factors affecting the measurement of chocolate viscosity’, J Texture
Studies, 31(5), 541–76.
BARIGOU M., MOREY M. AND BECKETT S. (1998), ‘The shaking truth’, Int Food Ingredients,
4, 16–18.
BARNES H.A. (1995), ‘A review of the slip (wall depletion) of polymer solutions, emulsions
and particle suspensions in viscometers: its cause, character and cure’, J Non-Newtonian
Fluid Mech, 56, 221–51.
BARNES H.A. (2000), A Handbook of Elementary Rheology, Institute of non-Newtonian Fluid
mechanics, University of Wales.
BARNES H.A., HUTTON J.F. AND WALTERS K. (1989), An Introduction to Rheology. Rheology
Series, 3, Elsevier, Oxford.
BECKETT S.T. (ed.) (2009), Industrial Chocolate Manufacture and Use, 4th edition, Blackwell
Science, Oxford.
BECKETT S.T. (2000), The Science of Chocolate, RSC paperbacks, Cambridge.
BECKETT S.T. (2001), ‘Casson model for chocolate, friend or foe?’, The Manufacturing
Confectioner, March, 61–7.
BOERSMA W.H., LAVEN J. AND STEIN H.N. (1990), ‘Shear thickening (dilatancy) in concentrated suspensions’, AIChE Journal, 36(3), 321–32.
GROVER D.W. (1947), ‘The keeping properties of confectionery as influenced by its water
vapour pressure’, J Soc Chem Ind, 66, 201–205.
HARRIS T.L. (1968), ‘Fractional % of suitable surface-active lipids modify the flow of molten
chocolate’, SCI Monograph, 32, 108–22.
IOCCC INTERNATIONAL OFFICE OF COCOA, CHOCOLATE AND SUGAR CONFECTIONERY (2000),
Visocosity of Cocoa and Chocolate Products. Analytical method 46 – 2000. Available
from CAOBISCO, Rue Defacqz 1, 1000 Bruxelles, Belgium.
MATZLER A. (2000), ‘Latest information from the one shot technology or being creative with
284
Enrobed and filled chocolate, confectionery and bakery products
one shot technology’, Proceedings of ZDS Chocolate Technology 2000 Conference, Koln,
Germany, 12–14 December 2000.
MCKENNA B. (2003), Texture in food, Volume 1: Semi-solid foods, Woodhead Publishing,
Cambridge.
MINIFIE B.W. (1980), Chocolate, cocoa and confectionery: science and technology 2nd
edition, AVI Publishing, Westport, CT.
SEGUINE E.S. (1988), ‘Casson plastic viscosity and yield value, what they are and what they
mean to the confectioner’, The Manufacturing Confectioner, November, 57–63.
SEGUINE E.S. (1990), ‘Casson offers a new measure of viscosity’, Candy Industry, 155(2),
42–6.
TALBOT G. (2004), ‘Chocolate and compound moulding’, Kennedy’s Confection, October,
22–26.
14
Using microscopy to understand the
properties of confectionery products
Kathy Groves, Leatherhead Food International, UK
Abstract: Microscopy is an essential tool in understanding the relationship between
ingredients, processing and product properties such as texture, stability and sensory
properties. This chapter presents an initial overview of microscopy techniques, with
examples that illustrate their usefulness in products such as chocolate, confectionery,
bakery and ice cream. It then goes on to discuss chocolate and chocolate coating
microstructure and the relationship to properties such as stability, heat resistance and
gloss. The chapter concludes with short sections on future trends in microscopy and
further information available.
Key words: gloss, heat-resistant chocolate, microscopy of chocolate, microscopy of
coatings, microstructure of bakery, microstructure of chocolate, microstructure of
confectionery, stability.
14.1 Introduction
It is widely accepted that there is a strong relationship between the structure of food
and its texture, sensory and stability properties. The properties of the ingredients in
manufactured products and the processing of these to make the product will have
profound effects on the structure and hence the properties. The food industry has
drivers to develop new products or change processing equipment or ingredients
and these will affect the qualities of the product as experienced by the consumer.
A more recent development is that food structure research is now driven by the
need to enable the Industry to understand how to give the consumer what he or she
wants (Duran, 2004). It is important therefore to consider the structure of the
product when trying to understand differences in texture or sensory qualities and
the effects on these of changing ingredients or processing.
286
Enrobed and filled chocolate, confectionery and bakery products
The term ‘structure’ covers a wide range of sizes or levels which can be
examined by different techniques. Levels that can be considered are:
• Atomic/molecular: analysed by chemical techniques mainly but also now by
scanning probe microscopies;
• Small scale: structures of groups of molecules and aggregates of these, analysed
by electron microscopy mainly and covering the size range of 100 nm upwards;
• Intermediate: assemblies of aggregates and larger structures as well as products,
•
analysed by light microscopy mainly and covering the size range of about 1 µm
to several millimetres;
Macroscopic: products, assessed mainly by sensory science and the consumer
but in microscopy terms at the macrophotography level.
All these levels of structure are important when considering the structure of the
food and ideally all should be carried out so that they can be related to each other
to obtain the full picture. In practice, when considering the properties of foods,
selected techniques only are used as a matter of cost and time.
In this chapter the small scale and intermediate levels are mainly considered and
initially general microscopy techniques are discussed with reference to their
usefulness for ingredients, chocolate, confectionery, bakery products and ice
cream. This section is then followed by more specific examples of the use of these
techniques in understanding properties such as stability (bloom/staling), heat
resistance and appearance (gloss) in chocolate and coatings. At the end, a short
view of future trends in microscopy is given with advice for further reading.
14.2 Microscopy techniques and their uses
Food microscopy in its early stages was mostly concerned with the study of natural
food structures and the effect of processing on these. It used the techniques
available at the time which were light and electron microscopy. With the advancement in techniques, microscopy became more sophisticated with the new techniques
emerging in the medical and physical sciences being applied to food research. At
the same time, the microscopy of food moved on to look at the structures of
manufactured foods and the effects of processing on these. The aim of the research
was always to understand the relationship between structure and properties. The
whole sequence is dynamic, with new developments in microscopy techniques and
in food product development that push our understanding further.
An extra overlay on this is the development of closer working relationships
between food microscopists and experts in texture, rheology, sensory and process
and product development. This combination makes the interpretation of results in
all fields more meaningful. Finally, there is little point in carrying out this research
if it is not communicated to those at the sharp end in the industry and the findings
modified and applied to the manufacturing processes and the products made from
these. This is essential, since the behaviour of food in a full scale process is usually
nothing like the behaviour in a laboratory or pilot plant.
Microscopy to understand the properties of confectionery products
287
Fig. 14.1 Granulated sugar seen under the stereo light microscope Bar = 500 µm
(reproduced with permission of Leatherhead Food International).
There are very few books on techniques in food microscopy available, although
there are chapters in product publications that are useful. Good information on the
application of microscopy on various foods can be found in Food Microscopy
edited by Vaughan (1979) and on staining in a short publication by Flint (1994). A
more general overview of stains and techniques is given by Groves (2006) in a
chapter on the use of microscopy to study ingredient interactions in foods.
This section of the chapter will give an overview of the main microscopy
techniques currently used in many laboratories and illustrate how they might be
useful in food products.
14.2.1 Light microscopy
It is essential when looking at chocolate, confectionery or other food products to
start at a low magnification and work upwards. This places the structural features
found in the food in context with what the consumer or manufacturer will taste or
see by eye. Simple light microscopy techniques include the use of a stereo light
microscope. This gives good depth of field and an image that is recognisable to
non-microscopists. It is also the low magnification version of what is generally
seen in the scanning electron microscope. Its benefits are greater than would be
expected for the magnification used. For example, it can give information on
particle size, agglomeration and shape of ingredients, as well as visualisation of
gross crystallisation, bloom, thickness of coatings, aeration of confectionery
products and crumb structure of bakery products. Figures 14.1 and 14.2 illustrate
this aspect. They show the size and shape of sugar crystals and also a cut-through
of a filled chocolate showing the filling inside the chocolate shell is shown in Fig.
14.2. Changes on accelerated storage and contraction of filling, aeration and
crystallinity can be seen using this simple form of microscopy.
288
Enrobed and filled chocolate, confectionery and bakery products
Fig. 14.2 View through a filled chocolate under the stereo light microscope showing
structure of filling and gaps between filling and chocolate shell (reproduced with permission
of Leatherhead Food International).
In studies on the effect of anti-bloom agents on the development of chocolate
bloom, Subramaniam et al. (1999) and Subramaniam and Groves (2003) used the
stereo light microscope to determine when the bloom had formed and a macrolens
to photograph the appearance of the chocolate (Fig. 14.3). This was then followed
by scanning electron microscopy for a closer look at the bloom crystal shapes. In
a study on sorbitol powders and their functionality in chewing gum, Groves et al.
(1996) used a stereo light microscope to differentiate shape and size in different
sorbitol powders and these were related to their performance in chewing gum
products. These observations were combined with polarised light microscopy and
scanning electron microscopy to provide information on crystal structure within
the powder particles.
More information and increased magnification is obtained by using a transmitted light microscope. This is a powerful technique in the understanding of the
structure of foods and could be considered to give the lower magnification view of
what is seen in the transmission electron microscope. However, it is not always as
easy for non-microscopists to relate to images from this technique. As the light is
transmitted through the sample, it is necessary for the sample to be transparent. For
liquids or powders this is achieved by either placing a drop of the sample on a slide
or by dispersing the powder in a suitable mountant that will not dissolve it. Water,
glycerol and liquid paraffin are often used as mountants for foods.
For most foods, the light will not pass through sufficiently unless the foods are
squashed thinly on the slide or thin sections are cut using either a blade or
microtome. Squashing the sample can give useful information but care needs to be
taken that the effects of shear on the sample under pressure are taken into account
when evaluating the structure. For example, it would be acceptable to squash
Microscopy to understand the properties of confectionery products
Fig. 14.3
289
Samples under the stereo light microscope showing differences in gloss
(reproduced with permission of Leatherhead Food International).
chocolate to note the size of sugar crystals as long as the pressure did not break the
crystals. Squashing a filling can give very useful information on the size and
distribution of the ingredients and also on the viscosity as measured subjectively
under the microscope. Dispersing in a solvent is another possible approach for
obtaining a transparent sample where one component is of interest. This has been
successfully done with ice cream to measure ice crystal size, but combined with a
temperature controlled stage on the microscope to prevent the ice crystals from
melting. It has also been used to look at the role of milk proteins in chocolateflavoured coatings in a study by Dodson et al. (1984). In this research, the authors
compared the flavour, snap, structure and flow properties of the coatings to the
milk protein ingredients used in their manufacture. They combined light microscopy
with scanning electron microscopy and found that the viscosity of the coatings was
affected by the way that the milk powder particles broke down in manufacture,
which in turn was related to the original structure of the powder. Powder particles
with a more open structure broke down to give more smaller particles and a higher
viscosity.
Generally, however, some form of sectioning is necessary to obtain good detail
on the structure of solids. If the sample is firm, hand-cut sections with a blade can
be good enough to give sufficient information. However it is preferable to use a
microtome, as this will allow thin sections of about 5–15 µm to be cut and increase
the detail that is visible. Chocolate can be cut at refrigerator temperatures, but most
foods would need to be cut frozen and the effects of freezing, such as ice formation,
need to be considered. Again, this technique has been used successfully for many
foods including ice cream when combined with a temperature controlled stage. For
very high sugar systems, frozen sections are not usually possible.
An alternative technique is to embed the food in a medium to hold the sample.
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Paraffin wax used to be the embedding medium used for this, but now it is more
common to use a low viscosity resin such as the acrylic resin LR White. Water and
fat need to be removed to allow this technique to be used although this can cause
the collapse of the sample. Fixation in aldehydes to preserve the structure of any
protein is used to prevent too much distortion. There are also specialised fixative
protocols for starches and fats. The advantages of resin embedding are that much
thinner sections can be cut for light microscopy (2 µm is usual) and this allows
greater detail to be seen at higher magnification. In addition, the same resinembedded sample can be cut for transmission electron microscopy, giving a direct
comparison at the different magnifications. There are some who are concerned
about fixation of foods and the possible artefacts induced. Changes to the food
product or ingredient are caused during this process, however, by comparison of
structures between control and test samples the true nature of the differences in
structure can be deduced. In addition, comparison of the same samples, prepared
and examined using different microscopy techniques will confirm the differences
seen.
Once the sample is prepared for transmission light microscopy, the structure
can be viewed directly or staining or contrast techniques can be used to highlight
features and properties. Examples of the typical features of importance shown by
this technique include the size and distribution of air in powder ingredients, the
crystallinity of ingredients, especially sugar and sugar-free products, and the
overall structure of foods, with information on the interaction between different
components. The state of gelatinisation of starch grains in jellies, oil droplet sizes
in emulsions and caramels and interaction between sugar and protein in milk
chocolate are also seen using light microscopy. For bakery products, the development of gluten and the distribution of fat can be seen in sections of product under
the transmitted light microscope. For ice cream products, frozen sections or
dispersions of ice cream in suitable solvents can be used to determine the size of the
ice crystals present as long as a suitable temperature controlled stage is used with
the light microscope. Figures 14.4 and 14.5 show a milk powder dispersed in liquid
paraffin. The size and shape of the spray dried particles can be seen in Fig. 14.4 and
the same sample is viewed by crossed polarised light in Fig. 14.5. The crystalline
material (fat and some lactose) appears white in the powders examined by this
technique. The fat distribution and amount of crystalline lactose are thought to be
some of the important factors in the properties of milk powders in confectionery
products.
In a study on three ostensibly similar commercial confectionery gums, the use
of resin sections of the gels in the samples showed a strong relationship between
the sensory properties and the structures of these products (Subramaniam, 2000).The
sample with the highest elasticity showed a continuous gelatine gel structure, with
dispersed starch and sugar. The softest sample was starch continuous with gelatine
and sugar dispersed through it. The third product was a phase separated starch and
gelatine gel in sugar. This sample showed a rapid breakdown in the mouth related
to the separation of the hydrocolloids.
Microscopy to understand the properties of confectionery products
291
Fig. 14.4 Skimmed milk powder viewed by transmitted light microscopy, showing air
bubbles as black. Bar = 20 µm (reproduced with permission of Leatherhead
Food International).
Fig. 14.5 Skimmed milk powder as in Fig 14.4, viewed by polarised light microscopy
showing crystalline fat and sugar as white (reproduced with permission of Leatherhead
Food International).
14.2.2 Confocal scanning laser microscopy (CSLM)
Although it is a fairly expensive instrument, the confocal microscope has become
very widely used in food research. It is particularly useful for looking at the
distribution of fat and protein in foods but has also been successfully used for other
ingredients such as starch and cocoa solids. It is a fluorescence-based technique,
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 14.6 A sucrose-based chew viewed by confocal scanning laser microscopy
showing the fat distribution (white). Bar = 50 µm (reproduced with permission of
Leatherhead Food International).
which means that the sample is usually stained with a fluorescent dye. It is
sometimes considered to sit between the light microscope and the electron microscope in imaging terms. In fact it is complementary to both of these and gives
different information to that obtained from them. The sample is stained with a
suitable stain for one or more ingredients (or, if autofluorescent, imaged directly)
and the scanned image collected on the computer. Owing to the nature of the optics,
opaque thick samples can be imaged in a thin plane of focus very well. Therefore
an advantage of the technique is that it can look ‘inside’ samples so that thick
samples can be imaged with little preparation. In addition, the three-dimensional
nature of the structure can be viewed by focusing through the sample to obtain a
stack of several optical sections. These can then be added together to produce a
combined image using the computing power of the microscope. This allows the
distribution of ingredients to be demonstrated in the food in three-dimensions.
Additionally, time-lapse imaging of dynamic changes that take place in gelation or
on shearing can be obtained.
A typical image from a confocal microscope is shown in Fig. 14.6. This shows
the fat in a sugar-based pulled chew as a droplet emulsion, often associated with the
edges of the air bubbles. The fat is stained in the sample with Nile red and appears
white in the image. The air, sugar and water are unstained and appear black. Figure
14.7 shows the appearance of the fat in a lab-scale sorbitol-based chew. The size
and distribution of the fat is quite different from that in the sugar system. Eeles et
al. (2006) used confocal microscopy to look at the emulsion structure in pulled
chews. They reported that changing the sweetener affected both the texture and
also the emulsion structure, with changes in fat distribution increasing the shortness.
Reviews of the use of confocal microscopy for foods are given by Heertje et al.
Microscopy to understand the properties of confectionery products
293
Fig. 14.7 A sorbitol-based chew viewed by confocal scanning laser microscopy
showing the fat distribution (white). Bar = 50 µm (reproduced with permission of
Leatherhead Food International).
(1987), Vodovotz et al. (1996), and Dürrenberger et al. (2001). The technique has
been used to look a number of foods, including fat distribution in spreads (Clegg
et al., 1996) and protein and fat distribution in cheese and gelation of milk proteins
(Hassan and Frank, 1997; Auty et al., 2001).
14.2.3 Electron microscopy
The two main forms of electron microscopy are scanning electron microscopy
(SEM) where the beam is scanned across the surface of the sample and transmission electron microscopy (TEM) which transmits the beam through the (very thin)
sample. Both are conventionally used under high vacuum which means that the
water and other volatiles like fat need to be removed or ‘fixed’.
For SEM the images obtained are recognisable by non-microscopists and give
increased detail of the surfaces and inside particles and foods. If fat is present, this
either needs to be removed or fixed with a chemical such as osmium. A commonly
used alternative is to freeze the sample and examine under the SEM using a cryo
stage. This gives the added advantage that fat and water can be retained and
visualised. Fat and fat crystals can be seen easily using CryoSEM and the
technique has furthered understanding of bloom on chocolate. Water can also be
seen by using sublimation to remove the ‘free’ water while the sample is still
frozen. Areas of water are shown by an ice matrix of dissolved solids after the water
has sublimed off. CryoSEM is used frequently for products like ice cream,
emulsions and chocolate and is useful for both an understanding of the general
nature of the microstructure and also for interpreting changes on storage (Sargent,
1988). For example, in ice cream the development of air and aggregation of ice
crystals to form larger structures during storage can be followed, as well as the
ability to see the emulsion at the ice and air interface.
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 14.8 Full fat milk powder under the scanning electron microscope showing
internal structure (reproduced with permission of Leatherhead Food International).
A great deal of useful information can be obtained from conventional SEM
under high vacuum. Examination of different sorbitol powders under SEM showed
differences in crystal alignment and density that were related to the dispersion and
performance of the sorbitol in chewing gum and also to tableting (Groves et al.,
1996). Differences in the microstructures of ingredients such as milk powders can
be clearly seen using the SEM. An example of this is shown in Figs 14.8 and 14.9
where the difference in internal structure between full fat milk powder and
skimmed milk powder can be seen. Additionally, the removal of fat from milk
chocolate or refined and conched ingredients can show associations that have
formed between the sugar or sweetener and the milk protein.
The ability to form close associations between the milk protein and the sugar
appears to be related to the viscosity of the chocolate during manufacture. Recent
research on the performance of different milk powders in a chocolate model
system (Groves et al., 2008a) and also on the interaction of polyols with fat
(Groves et al., 2008b) has shown that an interaction does take place between milk
protein and sugar or sweetener during both refining and conching. This interaction
results in an aggregation of the milk protein with the sweetener. The extent of
aggregation is different with different sweeteners. During the conching process,
this aggregation continues to develop and the fat becomes trapped inside the
aggregates, sometimes resulting in very large increases in viscosity. Figure 14.10
illustrates this aggregation. This area needs further understanding in order to be
able to predict the effect of ingredient variability in chocolate manufacture.
Transmission electron microscopy (TEM) offers a different view of the structure of food products. In this, the sample is either chemically fixed or then
embedded in a resin (this is the usual approach), or prepared by negatively staining
Microscopy to understand the properties of confectionery products
295
Fig. 14.9 Skimmed milk powder under the scanning electron microscope showing
internal structure. (reproduced with permission of Leatherhead Food International).
Fig. 14.10 Scanning electron image of maltitol and cocoa butter refined together in a
chocolate model system. An aggregated lump of maltitol and fat can be seen (reproduced
with permission of Leatherhead Food International).
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Enrobed and filled chocolate, confectionery and bakery products
A
G
Fig. 14.11 Transmission electron image of a thin section through a gelatine-based
marshmallow showing the air bubbles (A) and gel between the bubbles (G). Bar = 200 nm
(reproduced with permission of Leatherhead Food International).
or freeze fracture. Early work on foods often used freeze fracture (Dodson et al.,
1984a; Lewis, 1981) but resin sections have become more typical in recent
research. TEM is relatively rarely used in food product research compared to SEM
and the images produced are more difficult to interpret for a non-microscopist.
However, it is a very powerful technique for looking at the fine detail of a food
product or ingredient and using the information to explain property differences.
Owing to the increased preparation needed, the results are often looked upon more
suspiciously as being the result of artefacts. Again, this is true to the same extent
with many non-microscopy techniques and should be given the same consideration as results from those more accepted techniques.
Examples of the uses of TEM in foods includes research into the structure of
proteins at interfaces of foams and emulsions. Studies on caramels have shown
differences in casein and whey protein distribution, at the fat droplet interface and
in the sugar phase, that relate to properties such as viscosity, cold flow, creaminess
and stickiness. In an extensive study of toffee properties, Dodson et al. (1984b and
c) reported that the structure of the milk protein at the fat interface was crucial to
the properties of the toffees in terms of texture and behaviour. Later studies by
Kalichowsky-Dong et al. (1998) and Eeles et al. (2002) showed that emulsifiers
affected the binding of the milk protein to the fat interface and subsequently the
emulsion stability. This resulted in changes in the stickiness and viscosity of the
toffees.
In whipped products, such as foamed jellies and marshmallows, the formation
of a protein film at the interface is important in order to provide a stable foam.
However, it is also necessary to stabilise the solution between the air bubbles in the
Microscopy to understand the properties of confectionery products
297
A
Fig. 14.12 Transmission electron image of a thin section through a whey-based marshmallow showing the air bubbles (A) and aggregated protein failing to gel between the
bubbles. Bar = 200 nm (reproduced with permission of Leatherhead Food International).
form of a gel, otherwise the foam will collapse with time. The use of the TEM has
been essential in understanding why some proteins are very successful at achieving
this and others less so (Eeles et al., 2006). An example of this aspect is shown in
Figs 14.11 and 14.12, where TEM has been used to look at the interface and gel
between the air bubbles in a marshmallow product. In Fig. 14.11, the marshmallow
was made with gelatine. This protein went to the interface to stabilise the air
bubbles (A) but also formed a gelatine gel between the bubbles (G). The properties
of the gel will determine the texture of the marshmallow. In Fig. 14.12 the product
was made with a whey protein isolate. In this situation, the whey protein stabilised
the foam at the interface (A) but was not in the correct structure to form a stable gel
between the bubbles, as it had become too aggregated. Changes to the formulation
and method of manufacture could be used to overcome problems like these, once
the reason for the product failure is understood.
TEM has been used to look at the close association between protein and
polysaccharides in gels (Lewis, 1995) and the resultant structures related to texture
and rheology. In addition, the role of ingredients in product properties has been
studied using this technique. In studies of the functional impact of milk powders in
chocolate manufacture, it was shown, using microscopy, that surface fat and
particle size had an important effect on the viscosity of the chocolate. TEM also
showed that roller refined milk powder particles had a dense structure, whereas
spray dried milk powder was more open and aerated. This difference meant that
during refining the spray dried milk broke into small fragments more easily, giving
a higher viscosity in the chocolate. This gave further insight into what is still a
difficult problem of predicting ingredient functionality.
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Enrobed and filled chocolate, confectionery and bakery products
14.2.4 Other microscopy techniques
Newer instruments such as the low vacuum SEM and the truly wet environmental
scanning electron microscope (ESEM) are becoming more widely used to look at
food products. Low vacuum SEM allows some oil to be present while imaging the
food, but little water. ESEM on the other hand, can vary the pressure inside the
sample chamber of the microscope so that fully wet samples can be imaged. Care
needs to be used to try and match the vapour pressure in the microscope with the
moisture of the food product, otherwise dissolution or, at the other extreme,
dehydration of components can occur. Images obtained by ESEM can be difficult
to interpret compared to conventional SEM. The ability to vary the vapour pressure
in the chamber of an ESEM gives the opportunity to carry out dynamic experiments involving wetting and drying of samples. The first published use of ESEM
on foods was by McDonough et al. (1993). They observed microstructural changes
in starch and movement of fat in corn tortilla chips after deep frying.
14.3 Relationships between the microstructure of chocolate
and coatings and their properties
Most foods are very complex structures that at first glance appear simple. Chocolate has an apparently simple structure in that it consists of a continuous phase of
cocoa butter with cocoa solids, sugar and lecithin suspended in this phase. Milk
chocolate additionally contains milk protein and milk fat, or other small amounts
of solids which are sometimes added. The properties of the cocoa butter are
complex and this has led to changes in the chocolate making process as the
properties have become understood. Microscopy has played a major role in this
understanding. Examples of the use of microscopy to understand the role of
ingredients such as milk have been given earlier in this chapter. The techniques
have also been used to investigate other properties, such as stability, heat resistance
and visual appeal or gloss. Examples of these are given in the next section.
14.3.1 Stability
Bloom
One of the first questions asked in chocolate shelf-life stability is about the stability
of the chocolate to bloom. Cocoa butter in chocolate is mostly crystalline at room
temperature but has very interesting thermal properties that give chocolate its
unique melt-in-the-mouth feel. It is well documented that cocoa butter is a
polymorphic fat, showing different crystalline forms each with a different melting
point spanning the range from approximately 0–36 °C (see Tables 4.2 and 4.3, in
Chapter 4). It is the control of the crystallisation of the cocoa butter to produce a
stable form of crystal that affects the textural and stability properties of the final
chocolate. The use of microscopy and X-ray diffraction techniques demonstrated
this polymorphism and the structural appearance of the different forms. The
Microscopy to understand the properties of confectionery products
299
Fig. 14.13 Surface of chocolate showing typical cocoa butter bloom. Viewed by coldstage scanning electron microscopy (reproduced with permission of Leatherhead Food
International).
formation of the dull bloom caused by cocoa butter was shown to be due to the
transition of cocoa butter to the most stable form βVI, but in the form of fairly large
crystals that gave the surface a dull appearance. The mechanism of the actual
bloom formation is still not completely understood. In pure chocolate, one hypothesis is that there is a phase separation of triglycerides which then migrate through
the chocolate and produce a new crystalline form of fat on the surface. The use of
atomic force microscopy to study bloom formation indicated that pores in the
surface of the chocolate might be involved in the mechanism. A recent review of
research into cocoa butter bloom is given by Groves and Subramaniam (2008) in
an article on the influence of ingredients on chocolate microstructure.
Temperature abuse, incorrect tempering or migration of non-cocoa butter oils in
fillings of enrobed chocolates are known to cause fat bloom. Enrobed products
such as nuts, biscuits and soft fillings often can show instability owing to migration
of oils through the chocolate causing the formation of classic cocoa butter bloom
crystals. Small pores or channels in the chocolate are thought to be the route for the
migration of these oils and edible barriers are often used to prevent this movement.
Efforts to prevent bloom also include the development of antibloom fats for
incorporation into chocolate, coatings and fillings. In a study of the effectiveness
of antibloom fats in delaying the onset of bloom, Subramaniam et al. (1999) found
that the bloom crystals formed varied in appearance depending on the antibloom
fat used. Certain antibloom fats produced long needle crystals that projected
several millimetres from the surface of the chocolate as well as more typical form
βVI crystals (Figs 14.13 and 14.14). There needs to be more study of these effects
to determine whether fractionation of the fat is taking place to produce new crystal
forms.
Staling
It is common for the industry to store chocolate after manufacture for a short time
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 14.14 Surface of chocolate containing an anti-bloom fat showing unusual bloom.
Viewed by cold-stage scanning electron microscopy (reproduced with permission of
Leatherhead Food International).
to allow the chocolate to ‘settle’ and become more stable in terms of texture. The
chocolate becomes slightly firmer and this is assumed to be the result of a change
in the crystallinity of the cocoa butter. However the possibility that a change takes
place in the sugar and milk protein in milk chocolate has been raised. As chocolate
ages, the texture can become harder and crumblier, develop flavour changes and be
described as becoming stale. The reasons for this are not clear but it is known that
some of these changes are reversible.
In a study on the development of staleness in milk chocolate, Subramaniam et al.
(2005) reported that naturally staled chocolates were harder than the fresh controls
and did not collapse to the same extent when defatted in a solvent. Under the
microscope, an increase in protein aggregation was seen in the stale chocolates and
also an increase in protein–sugar association. These differences were seen using
both light microscopy and confocal microscopy. The confocal microscope showed
the increase in protein–sugar association seen in the light microscope, but a threedimensional network was not observed. The possibility that an association between
sugar and protein takes place in chocolate during storage has been discussed as an
explanation for textural changes. It has been reported (Groves, 2005) that an
association is present in chocolate made from crumb but not to any extent in the
more typical dry mix chocolate. Therefore, it was interesting to see that an
association had taken place in a dry mix chocolate during staling. Sensory tests
showed a decrease in sweetness which could be due to the ‘shell’ of protein formed
around some of the sugar.
Subramaniam et al. (2005) also carried out an accelerated staling test on fresh
chocolate. The sensory and chemistry results were inconsistent compared to the
naturally staled samples, suggesting that either the accelerated test was not
sufficient to produce a similar effect or that the effects of accelerated storage were
Microscopy to understand the properties of confectionery products
301
different to natural storage. Under the microscope, the association between protein
and sugar was seen but to a much lesser extent, suggesting the accelerated test was
not sufficiently long enough. More research is needed into the staling aspect of
chocolate, particularly to link accelerated storage to natural storage.
14.3.2 Heat resistance
The natural melting profile for cocoa butter and the particle size distribution of the
sugar and other solids are important for the flavour and sensory properties of
chocolate. Chocolate will start to soften at about 28 °C and, given the natural
temperatures globally, it is apparent that these are in the range that will cause
unacceptable changes to chocolate. Therefore there is a strong interest in developing heat resistance in chocolate for a global market. It is important, however, to
maintain the creamy smooth melt-in-the-mouth properties as much as possible.
Attempts to produce heat resistant chocolate date back to Schmidt and Vogtl
(1919), who added water to increase the viscosity of the chocolate mass and make
a heat stable chocolate. This principle of increasing the viscosity of chocolate by
increasing the water content has been further developed over the years and is one
of the key techniques used in the production of heat-stable chocolate. Three
methods known to be used to achieve heat resistance in chocolate are:
• incorporation of high melting fats
• disruption of the continuous fat phase in some way
• incorporation of water in the form of an aqueous emulsion.
The methods developed might include more than one of these approaches so
that the overall sensory properties are similar to normal chocolate. They are all
described in a number of patents which have been reviewed by Subramaniam et al.
(1994).
High melting fats to add to the cocoa butter phase have been developed in
different ways and are known as either cocoa butter equivalents (CBEs), cocoa
butter replacers (CBRs), or cocoa butter improvers (CBIs). These are still being
developed, but restriction on their use by legislation or cost or for reasons of
reduced sensory properties means that alternative approaches are desirable.
Disruption of the continuous fat phase was attempted by trying to produce a
network structure of non-fat ingredients, such as sugar and milk protein. This was
achieved either by limiting the mixing of the fat during the conching stage or by
hydrating the sugar or milk powder in different ways. These techniques were
successful to different extents, each having advantages and disadvantages in terms
of heat resistance and appearance and sensory attributes.
A number of techniques for incorporation of water into the chocolate mass have
been proposed. These result in an increase in viscosity of the chocolate and have
been achieved by addition of water or a gelling agent. If the viscosity of the mass
is too high, it obviously will make moulding difficult or impossible. Therefore a
process where the water is incorporated without too much viscosity rise is
preferable. Different ways to achieve this have included use of sweeteners and
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 14.15 Confocal image of control chocolate stained to show protein as white. Spray
dried milk particles can be seen. Bar = 25 µm (reproduced with permission of
Leatherhead Food International).
Fig. 14.16 Confocal image of a heat-resistant chocolate stained to show protein as white,
sugar and fat are black. Crystals of sugar surrounded by protein can be seen. Bar =
25 µm (reproduced with permission of Leatherhead Food International).
polyols which are thought to interact with the fat, the addition of emulsions or foams
into the fat phase and the addition of water into pastes made with starches or gums.
As well as reviewing the patent literature in heat resistance in chocolate,
Subramaniam et al. (1994) also characterised the properties of several heatresistant chocolates made commercially and compared them with a standard
Microscopy to understand the properties of confectionery products
303
Fig. 14.17 Combined image of multiple confocal optical sections of area seen in Fig
14.16. Crystals of sugar surrounded by protein forming a loose three-dimensional network
can be seen. (reproduced with permission of Leatherhead Food International).
chocolate control. The aim of the work was to establish the relationship between
the structure of the product and the resulting characteristics such as heat resistance,
texture and sensory properties. Different microscopy techniques were necessary to
understand the structures of the products and analysis of the fat content and level
of solid fat, moisture, heat stability and sensory properties were carried out to
attempt to elucidate the mechanism by which the manufacturers had developed
heat resistance. The research was extensive, giving interesting results that shed
considerable light on the relationship between structure, heat resistance and
sensory properties. Two examples of the structures produced in the heat-resistant
chocolates were one which had a network structure of protein and sugar or polyol
present and one which had aerated foam which trapped the fat.
The chocolate with a three-dimensional network of protein and sugar or other
sweetener was described as ‘slightly gritty’ by a sensory panel, but particle size
analysis showed a typical chocolate size distribution. The reason for the discrepancy was seen by using the three-dimensional imaging ability of the confocal
microscope. The protein from the milk was clearly seen associated around crystalline material (sugar or polyol) (see Figs 14.15 and 14.16) when compared to a
standard chocolate. By collecting images in depth, these associations could be seen
to be linked together to form larger particles and a loose network (Fig. 14.17). It
was these larger particles that were detected by the sensory panel, but which broke
up in the particle sizer when the fat was removed.
The heat-resistant chocolate with a foam structure appeared to have a large
number of protein particles when examined by light microscopy and confocal
microscopy (Fig. 14.18). The use of TEM gave insight into the structure, revealing
a foam in the milk protein compared to the standard chocolate (Figs 14.19 and
14.20.) This illustrates both the complexity of chocolate products and also the
usefulness of techniques like TEM.
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 14.18 Confocal image of a heat-resistant chocolate made with a foam of protein
stained to show protein as white, sugar and fat are black. Many extra protein areas can be
seen. Bar = 25 µm (reproduced with permission of Leatherhead Food International).
Fig. 14.19 Thin section through a heat-resistant chocolate made with a foam viewed by
transmission electron microscopy, showing aerated or holey structure of protein and sugar.
Bar = 500 nm (reproduced with permission of Leatherhead Food International).
Microscopy to understand the properties of confectionery products
305
Fig. 14.20 Thin section through a standard control chocolate viewed by transmission
electron microscopy, showing typical structure of the milk protein. Bar = 500 nm (reproduced with permission of Leatherhead Food International).
14.3.3 Gloss
The final example in this section deals with chocolate coatings and visual appeal.
It is known that appearance characteristics have a significant influence on the
acceptability of foods. Attributes that are important in chocolate include colour,
shape and gloss. Colour and surface appearance have been shown to affect the
results of chocolate flavour in taste panel tests (Musser, 1973). Traditionally, high
gloss on chocolate was considered to relate to high quality of the chocolate and to
a certain extent this is still true. However, in a study of consumer attitudes to
chocolate appearance, Fillion et al. (2001) reported that very high levels of gloss
were sometimes considered as ‘artificial’ or ‘cheap’. Getting the gloss level correct
is therefore important to the industry. An understanding of the factors that affect
gloss is needed to enable this.
Most research has concentrated on the effects of tempering on gloss, but there
have also been studies on the cooling regime and speed as this is known to affect
gloss. Subramaniam and Groves (2002) carried out a study on the effects of fat
type, fat content and particle size on gloss, microstructure and hardness in
chocolate coatings. They reported that a reduction in particle size increased gloss
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 14.21 Cold-stage scanning electron microscopy of the surface of chocolate coating
made with palm kernel stearine showing the glossy surface appearance. Bar = 10 µm
(reproduced with permission of Leatherhead Food International).
Fig. 14.22 Cold-stage scanning electron microscopy of the surface of chocolate coating
made with hydrogenated palm kernel oil showing the dull surface appearance. Larger
crystals and areas of liquid fat are visible on the surface contributing to the dulling. Bar =
10 µm (reproduced with permission of Leatherhead Food International).
Microscopy to understand the properties of confectionery products
307
and hardness in the systems they studied. Previous research by Musser (1973) had
shown however, that if sufficient free fat was available at the surface, the particle
size did not significantly affect gloss. A decrease in particle size will increase the
viscosity of the coating, making handling and moulding difficult. Therefore there
is an optimum particle size that will give good gloss with best viscosity.
Results from the study by Subramaniam and Groves (2002) also showed that
the fat type affected gloss, both initially and after storage. Addition of hydrogenated palm kenel oil (HPKO) gave a high level of gloss initially but this faded or
dulled after a short time at 20 °C. The use of CryoSEM showed that initially a
smooth surface was produced with few visible crystals and that dulling with time
was associated with an increase both in crystallinity at the surface and also areas of
liquid fat (Figs 14.21 and 14.22). Coatings containing palm kernel stearine (PKS)
were harder than HPKO and retained gloss on storage. Under the microscope, the
surface was smooth but with small crystals visible which did not change with time.
The results from this study suggested that the size of the crystals at the surface was
an important factor in the gloss, but that the hardness of the fat and mix of solid to
liquid fat affected the retention of gloss with time.
14.4 Future trends
The future in terms of microscopy techniques will involve further development of
the environmental scanning electron microscopy area, together with development
of the tensile stage and shear effects related to dynamic structural changes in the
microscope. In addition, matching the ability to image structure together with some
form of analysis such as already exists with Fourier transform infrared and Raman
spectroscopy will be developed further with other imaging techniques. A major
area of study that is fairly undeveloped is the understanding of changes in the
mouth as foods are eaten and how these relate both to consumer liking and also to
texture as measured conventionally. Using this information will enable the industry to deliver more tailored product design and high quality flavour and texture
properties.
14.5 Acknowledgement
All images are reproduced with permission from Leatherhead Food International.
14.6 References
AUTY M A E, TWOMEY M, GUINE T P AND MULVIHILL D M
(2001). ‘Development and
application of confocal scanning laser microscopy methods for studying the distribution
of fat and protein in selected dairy products’. Journal Dairy Research, 68, 417–27.
CLEGG S M, MOORE A K AND JONES S A (1996). ‘Low-fat margarine spreads as affected by
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Part III
Processing, packaging and storage
15
Ingredient preparation: the science of
tempering
K. Smith, Unilever R & D, UK
Abstract: This chapter considers tempering from a scientific, rather than practical,
perspective. It begins by looking at the importance of tempering as it relates to product
quality, before climbing the steps to its understanding. Starting with the polymorphic
behaviour of triacylglycerols, it moves on the look at the specific behaviour of cocoa
butter, examines how tempering leads to the formation of stable seeds, then looks at how
the quality of temper is measured. Finally, comments are made on technologies that may
have an impact on tempering in the future.
Key words: chocolate quality, cocoa butter, polymorphism, tempering, temper measurement.
15.1 Introduction
It is every chocolatier’s desire to create a high quality chocolate bar, which will be
glossy, firm and break with a satisfying snap. These well-known characteristics of
chocolate are achieved through one of the most important steps in chocolate
manufacture: tempering. The tempering process is also responsible for the contraction of the chocolate when it is cooled (thus releasing it readily from the mould),
the fast and complete melting in the mouth and the good flavour release. In
addition, when carried out correctly, it can slow fat migration and recrystallisation
during storage (which could lead to bloom – a serious product defect).
Tempering is thus demanded by the desire for a shelf-stable, high quality
chocolate product and is necessary owing to the complex polymorphism of cocoa
butter. This chapter will look at the necessity of tempering and at the consequences
of not tempering. The need for tempering is dictated by the specific polymorphism
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Enrobed and filled chocolate, confectionery and bakery products
of cocoa butter, which will be described here, after exploring the polymorphism
and phase behaviour of triacylglycerols in general (expanding on the discussion in
Chapter 4). The changes that take place during the tempering process are also set
out, considering the crystallisation, polymorphic transformation and subsequent
cooling of the chocolate. Naturally, an important consideration is the measurement
of the degree, or quality, of temper, since this will determine the subsequent quality
and stability of the chocolate. This chapter will describe the principal measurement
method and why it works. Finally, it will briefly describe some of the less
conventional or new tempering processes that have been proposed.
15.2 Effects of tempering on quality
The processing stages of chocolate are: mixing the ingredients in the correct
formulation until a uniform mass is achieved; refining, where it goes through a
reduction in granularity such that 90% of the particles are below about 20–
25 µm; conching, during which the product is stirred and sheared at a controlled
temperature (50–65 °C) for several hours to develop the flavour by removing
undesirable volatiles; tempering or precrystallisation, the stage described in this
chapter; moulding (or enrobing) and cooling, where the tempered chocolate is
deposited in moulds and cooled until properly solidified; finally, the product
goes through the stages of demoulding and packing. Of all of these stages,
tempering is one of the most important, significantly affecting both physical and
organoleptic properties.
Thus, the production of top quality chocolate depends not only on raw materials
and their preparation, nor on the final solidification of the molten chocolate, but on
the key step in between, that of tempering. It is this process that encourages the
cocoa butter to solidify into the specific crystalline form needed to yield the gloss,
firmness, snap and bloom resistance that is desired (Bomba, 1993). If tempering is
neglected or carried out improperly, a number of problems may be encountered.
If undertempered chocolate is moulded, there may be little or no contraction
from the sides of the mould, resulting in difficulty in removing the chocolate from
the mould, an important step prior to packing! Contraction is due to the difference
in density between liquid and solid cocoa butter. However, as described later,
cocoa butter can crystallise in a number of different polymorphs, whose density
differs. If the cocoa butter does not crystallise into the correct polymorphic form,
the difference in density between the solid and liquid leads to insufficient contraction of the chocolate away from the sides of the mould. This causes difficulty in
demoulding and can leave the chocolate surface marked where it has been forcibly
removed from the mould.
Overtempered chocolate can also lead to difficulties in demoulding. In this case,
different factors play a part. First, more solid fat is present when the chocolate is
deposited in the mould. With less solid to crystallise, there is less contraction.
Second, the crystals tend to be larger and fewer. The hardness and contraction of
a chocolate develop toward the end of the cooling tunnel, as the final few percent
Ingredient preparation: the science of tempering
315
of the solid crystallises, forming bridges between the crystals (sintering). Fewer,
larger crystals imply fewer bridges between crystals and less contraction.
Undertempered chocolate can also appear dull and blotchy, lacking its desired
gloss. The glossy nature of well-tempered chocolate is due to the fine crystals
produced during cooling after tempering, when the cocoa butter is in the correct
polymorph. Larger crystals of less stable polymorphs can occur and some degree
of recrystallisation may also take place. Together with poor contraction from the
mould, this leads to dull and blotchy chocolate. Overtempered chocolate can also
give rise to poor gloss, since it often has fewer larger crystals and so gives rise to
coarser structure in the chocolate, with the resulting dullness.
After solidification, badly tempered chocolate may be soft, bending and breaking roughly rather than snapping cleanly. The hardness of a chocolate depends,
principally, on three factors: the proportion of solid fat present (solid/liquid ratio),
the shape (morphology) of the crystals and the degree of linking between the solid
fat crystals (network formation). At room temperature, the proportion of solid fat
present for the most stable (desired) polymorph can be quite similar to some of the
less stable (undesirable) polymorphs, although the least stable crystal forms will
have lesser amounts of solid. However, the number of crystals and the crystal
morphology will differ between polymorphs. Only the stable polymorphs will give
the correct network formation and thus produce a good, hard chocolate with a
satisfying snap.
Insufficiently tempered chocolate may melt too readily in the hand. This is due
to the lower melting point of less stable polymorphs. Finger temperature is just a
few degrees lower than mouth temperature. Thus, the desired polymorph is one
which has a melting point between that of hand temperature (typically 29–32 °C)
and mouth temperature (usually around 37 °C). Without tempering, crystallisation
does not occur into a stable form, resulting in a chocolate with a lower melting
point and sticky hands!
Finally, chocolate that has not been tempered will often bloom after a short
period of time. Cocoa butter that has crystallised into less stable polymorphic
forms will re-crystallise into more stable polymorphs. During this process, fat
moves to the surface and crystallises as a fine haze which lightens the chocolate
colour and may also appear as visible, white or pale specks. This occurs at a faster
rate at higher temperatures and can be accelerated by oil migration from other
components of the product (see Chapter 10).
Although poor tempering is often associated with the formation of fat bloom, it
is not the only cause (Lonchampt and Hartl, 2004). Nonetheless, tempering is
critical to the attainment of a high quality chocolate product.
15.3 Polymorphism and phase behaviour of triacylglycerols
Tempering is necessary because of the complex polymorphism of cocoa butter. In
this section, triacylglycerol (TAG) polymorphism in general is described (extending the section in Chapter 4), as a background to understanding that of cocoa butter.
316
Enrobed and filled chocolate, confectionery and bakery products
Tripalmitoyglycerol
Double chain length spacing
Triple chain length spacing
α
β'
H
O⊥
T
Hexagonal
Orthorhombic perpendicular
Triclinic parallel
Fig. 15.1
β
Schematic diagrams of a typical triacylglycerol (top), long (layer) spacing
views (middle) and basic polymorphic types (bottom).
Almost all fats are polymorphic in nature, having at least two common polymorphic forms. Each polymorph has a distinct crystal structure, which is reflected in
different physical properties, for example density, melting point, expansion coefficient, heat capacity, crystal shape and network formation. The only truly
unambiguous means of identifying polymorphs is X-ray diffraction, which directly relates to the crystal structure, although techniques that depend on the
melting point can be indicative of the polymorphic form, and vibrational techniques
(e.g. Raman, Fourier transform infrared spectroscopy (FTIR)) may also be used.
Polymorphism in fats is dominated by the long hydrocarbon fatty acid chains in
the triacylglycerols. Fig. 15.1 shows how each of these chains is arranged in a
zigzag shape and can be packed together in the crystal in many different ways. At
the top of the figure, a single molecule of the TAG tripalmitoylglycerol (tripalmitin
or PPP, indicating the fatty acids on the 1, 2 and 3 positions of the glycerol) is
shown. In the centre of the figure is shown the way in which TAG molecules can
pack together in a crystal, in double or triple chain length arrangements. These
characterise the so-called long spacings. Other structures are possible but these are
the principal ones.
Ingredient preparation: the science of tempering
317
Looking down on the ends of the hydrocarbon chains, the views at the bottom
of Fig. 15.1 will be seen. These show the so-called short spacing arrangements. In
general, three main polymorphs are recognised: α (alpha), β' (beta-prime) and β
(beta) in order of increasing melting point. Crystal forms with low melting point
are less stable and tend to transform into more stable forms, with higher melting
points. The speed with which polymorphic changes occur depends on the relative
stability of the crystal forms and the temperatures which they experience. In the α
phase, which is usually unstable, the orientation of the hydrocarbon zigzags is
pseudo-random, they are packed in a hexagonal arrangement and are orthogonal
(at right-angles) to the base plane.
In the β' polymorph, the hydrocarbon zigzags are orthogonal to adjacent chains
and in an orthorhombic arrangement, while the orientation with respect to the base
plane may be orthogonal or skew. The β polymorph has the hydrocarbon zigzags
packed parallel to each other in a triclinic form and the chains are usually skew to
the base plane. The β polymorph is usually the most stable.
Both β' and β polymorphs exhibit sub-phases where the overall structure is the
same but minor, significant, differences exist. These are denoted by a subscript, for
example. β'2, with the lower subscripts indicating greater stability and melting
point. Bringing all this together, β'2–2 would represent the second most stable betaprime polymorph, having a double chain length structure.
Although it has proved to be very difficult, it has been possible to determine the
complete crystal structure of the most stable (β) polymorph for a few TAGs. These
are the trisaturated mono-acid TAGs, such as tristearoylglycerol (StStSt) and
tripalmitoylglycerol (PPP). Essentially, this whole series has the same structure,
differing only in chain length (Van Langevelde et al., 1999). Trielaidoylglycerol
(EEE), the trans isomer of trioleoylglycerol (OOO), has a very similar structure to
the trisaturated TAGs (Culot et al., 2000).
Two other series of TAG crystal structures have been determined (Van
Langevelde et al., 2000; Sato et al., 2001). These are of the symmetric type
CnCn+2Cn (e.g. CLaC, C = capric, La = lauric) and the asymmetric type CnCnCn–2
(e.g. PPM, M = myristic). These TAGs are stable in the β' polymorph and show a
completely different structure to the monoacid TAGs (Hollander et al., 2003).
Figure 15.2 illustrates the different structures for these types of TAG compared to
that of the β polymorph of PPP (note the difference in the relationship between the
acyl chains at the three glycerol positions, i.e. for each molecule, which acyl chains
are adjacent to each other).
The principal TAGs in cocoa butter are 1,3-dipalmitoyl-2-oleoylglycerol (POP),
rac-1-palmitoyl-2-oleoyl-3-stearoylglycerol (POSt) and 1,3-distearoyl-2oleoylglycerol (StOSt), and the polymorphism of cocoa butter is greatly influenced
by them. For this reason, they have been extensively studied (e.g. Sato et al., 1989;
Rousset and Rappaz, 1996; Arishima and Sato, 1989; Arishima et al., 1991;
Koyano et al., 1989; Ueno et al., 1997; Mykhaylyk et al., 2007). These studies
have established the polymorphic phases for POP, POSt and StOSt, summarised in
Table 15.1.
Until recently, the precise crystal structures of POP, POSt and StOSt were
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Enrobed and filled chocolate, confectionery and bakery products
1
3
2
2
3
1
Tripalmitoyglycerol
(CnCnCn type)
2
3
3
2
1
1
2
3
1,3-dicaproyl-2-lauroylglycerol
(CnCn+2Cn type)
3
1 2 1
1,2-dipalmitoyl-3-myristoylglycerol
(CnCn–2Cn type)
Fig. 15.2 Schematic diagram showing the packing of triacylglycerol molecules in the β
form of PPP (top) and two different β' forms, CLaC (bottom left) and PPM (bottom right).
Numbers at the ends of the acyl chains indicate their position on the glycerol backbone.
Table 15.1 Polymorphic forms of POP, POSt and StOSt
POP
Polymorph
α
γ
δ
pseudo-β'2
pseudo-β'1
β2
β1
Melting
point (°C)
15.2
27.0
29.2
30.3
33.5
35.1
36.7
POSt
Polymorph
Melting
point (°C)
α
19.5
δ
intermediate
pseudo-β'
28.3
29.8
31.6
β
35.5
Compiled from Sato et al. (1989) and Arishima et al. (1991).
StOSt
Polymorph
Melting
point (°C)
α
γ
23.5
35.4
pseudo-β'
β2
β1
36.5
41.1
43.0
Ingredient preparation: the science of tempering
Proposed
319
Actual
Fig. 15.3 Schematic diagrams comparing one proposed structure (left) with the actual
structure (right) of 1,3-distearoyl-2-oleoylglycerol, a major component of cocoa butter
(from Peschar et al., 2004).
unknown although their general polymorphism was understood (i.e. double or
triple chain length spacing and α, β' or β). Knowledge of their structures is
important since the crystal structure of cocoa butter is highly dependent on them
and powder X-ray diffraction shows similarities to cocoa butter. Several structures
have been proposed for the β forms of StOSt, similar to that shown on the left of
Fig. 15.3. However, these proposed structures have been shown to be erroneous
(Peschar et al., 2004). The structure determined by this group for the β2 polymorph
of StOSt is shown on the right of Fig. 15.3.
Edible fats are a mixture of many TAGs, differing in chain length and
unsaturation. While each of these will have its own polymorphism, there is plenty
of scope for the formation of mixed crystals and for interactions between TAGs.
Mixed crystals, themselves, will have specific structures according to their unique
composition. Incorporation into mixed crystals is more likely where the TAGs
involved have similar chain lengths, symmetry and unsaturation. Thus POP, StOSt
and POSt (the major components of cocoa butter) will mix much better with each
other than with StStSt or PPP.
In natural fats, at most temperatures, there will be a mixture of solid and liquid
phases. Some TAGs will not contribute to the solid at all. These are usually the
more unsaturated, lower melting ones like rac-1-palmitoyl-2,3-oleoyl glycerol
(POO), rac-1-stearoyl-2,3-oleoyl glycerol (StOO) and trioleoyl glycerol (OOO)
(which, together, make up to 20% of cocoa butter). The mixture of these can act as
a solvent for other, higher melting TAGs that are predominantly present in the solid
phase, such as POSt.
If we consider a simple phase diagram (Fig. 15.4) in which there is complete
miscibility in both the liquid and solid phases, we can follow what happens on
cooling a mixture of two components, A and B. Cooling from the point labelled 1,
320
Enrobed and filled chocolate, confectionery and bakery products
A
B
1
Temperature
Liquid
+
Solid
2
3
Solid
5
4
0
20
40
60
80
100
B (%)
Fig. 15.4 Example of a simple, two-component phase diagram demonstrating continuous solubility in the solid phase. See text for description of the numbers and arrows.
where everything is completely liquid, the temperature falls until the liquidus line
(upper curve) is reached, at point 2. As the liquidus is crossed, crystallisation
becomes possible. The composition of the crystallising material is read off the
chart by taking a horizontal (isothermal) line across to point 3 and by dropping a
vertical line to the composition axis, that is in this case, about 73% B. Thus, the
solid is a mixture of both A and B, rather than purely the highest melting point
component, B. During subsequent cooling, the composition of the crystallised
material will follow the solidus line (lower curve) down to point 4, while the
composition of the remaining liquid will follow the liquidus line down to point 5.
The process described above assumes that the system remains at equilibrium at
all times and that there is sufficient time for the solid phase to maintain homogeneity. In practice, of course, this never happens; practical cooling processes are too
rapid and supercooling is always encountered. There often is insufficient time for
the solid phase to equilibrate to the thermodynamically stable composition.
The phase behaviour of binary combinations of fats need not be as simple as that
shown in Fig. 15.4. Many other, more complex, behaviours are possible (Rossell,
1967; Timms, 1984). If partial immiscibility occurs, as it commonly does with
TAGs, a situation similar that shown in to Fig. 15.5 arises. This leads to much more
complex crystallisation, even for a binary mixture. Naturally, edible oils and fats
are composed of many more than two TAGs with a corresponding increase in the
complexity of the phase behaviour!
Ingredient preparation: the science of tempering
A
321
B
Liquid
Liquid
+
Solid A containing B
Temperature
Liquid
+
Solid B
containing A
Solid A
containing B
Solid B
containing A
Solid A containing B + Solid B containing A
0
20
40
60
80
100
B (%)
Fig. 15.5
Example of a complex, two-component phase diagram showing eutectic
behaviour and limited solubility in the solid phase.
Once nucleation has occurred, the composition of the crystallising solid will
vary as crystallisation progresses. Thus, the composition will vary continuously
from the centre of each crystal to the outside, that is, the composition of the centre
will differ from the outer layer. Of course, the crystals or crystallites that form will
begin crystallising at different times, will be of varying sizes and each crystal will
have a different average composition. Those crystals that nucleate earlier will have
more opportunity to grow larger than will those nucleating later.
The TAGs present in cocoa butter have a range of melting points. These relate
to differences in saturation and chain length. When liquid cocoa butter is cooled,
each of these TAGs will perceive a different degree of supercooling. It seems
obvious that the ‘higher melting’ TAG will crystallise first, but the phase diagram
must be considered. The first solid will, of course, be rich in the higher melting
TAGs but will also include some of the softer TAGs. A group of molecules will
come together to form an embryo (a nucleus too small to survive). Most embryos
will dissolve quickly again, but some will grow. Around the kernel of this embryo,
different TAGs may join. In such a process, a nucleus and later a crystallite will
grow with an individual composition. Numerous crystallites will develop, differing slightly in composition owing to microfluctuations in the composition and
temperature in the liquid and due to formation at slightly different times. Eventually,
322
Enrobed and filled chocolate, confectionery and bakery products
each crystallite will have a unique composition, melting point and polymorphic
structure related to that particular composition. The perceived melting range and
polymorphic form of the solidified cocoa butter will be the average of all those
individual crystallites.
15.4 Cocoa butter polymorphism
Cocoa butter is predominantly composed of three TAGs: POP, POSt and StOSt.
These vary from more than 60% to about 85%, depending on the origin of the
cocoa butter, warmer climates giving rise to higher levels. The remainder of the fat
is principally StOO and POO. The relative simplicity of the cocoa butter TAG
composition lies behind its sharp melting behaviour: it is nicely solid at a
temperature of 20 °C (room temperature) yet melts cleanly away at 35–36 °C, in the
mouth. The three main TAGs dominate the polymorphism of cocoa butter.
Depending on the process conditions used, cocoa butter can be crystallised into
several different polymorphs. Since the 1950s, there has been much debate in the
literature about the number of polymorphic forms of cocoa butter owing to their
great influence on the physical and sensory properties of chocolate. Vaeck (Vaeck,
1951) suggested the presence of four different crystal forms of cocoa butter in
chocolate, with different melting points and confirmed this opinion almost 30
years later (Merken and Vaeck, 1980). Subsequent studies, however, seemed to
indicate the existence of up to six crystal forms in cocoa butter (Loisel et al., 1998a;
Dimick and Davis, 1986; Lovegren et al., 1976; Chapman, 1971; Wille and Lutton,
1966). Until recently, general agreement settled on six forms, using the nomenclature of Wille and Lutton (1966), that is, the Roman numerals I through VI, with
form VI being the most stable and having the highest melting point. Following
Chapman’s notation for fat polymorphs (Chapman, 1971), form I is identified as
being sub-α, form II as α, forms III and IV as β' and forms V and VI as β. However,
cocoa butter polymorphs have been designated in a great variety of ways. Table
15.2 lists some of the nomenclatures used.
The sub-α and α forms of cocoa butter (CB) have a double chain length spacing,
as do the β' forms, but both of the β forms are triple chain length spacing.
Some authors have proposed that form III is a mixture of forms II and IV (Wille
and Lutton, 1966; Merken and Vaeck, 1980; Schlichter-Aronhime et al., 1988a;
Schlichter-Aronhime et al., 1988b), and some that form I is also a mixture of
phases (Wille and Lutton, 1966). Similarly, some consider that form VI may be the
result of a phase separation within the solid phase (Merken and Vaeck, 1980;
Schlichter-Aronhime et al., 1988b; Becker, 1957). Recently, others confirm six
polymorphs (Loisel et al., 1998a) and report on the crystallisation and transformations between forms I to V (Loisel et al., 1998b; Sato and Koyano, 2001).
Almost simultaneously, however, other papers proposed that earlier work may
have been mistaken in terms of the number of forms and their melting points (Van
Malssen et al., 1999; Schenk and Peschar, 2004). They identified only five
polymorphs, γ (or sub-α), α, a continuous range of β' (incorporating those
Ingredient preparation: the science of tempering
323
Table 15.2 Nomenclature of cocoa butter polymorphic forms
Wille and Vaeck, Vaeck, Duck, Larsson, Witzel and Lovegren Hernqvist, Van Malssen
Lutton,
1951 1960 1964 1966
Becker,
et al.,
1988
et al.,
1966
1969
1976
1999
I
II
III
IV
V
VI
γ
α
γ
α
γ
α
β"
β
β'
β
β"
β'
β
β'2
α
mixed
β'1
β2
β1
α
β'1
β'2
pre-β
β
VI
V
IV
III
II
I
sub-α
α
β'2
β'1
β
β
γ
α
β' range
β-V
β-VI
previously identified as forms III and IV) and two β forms. In addition, they
propose that the melting point of the sub-α or γ form has rarely been measured
correctly owing to the extremely rapid transformation of this polymorph into the α
form. They also propose that the melting point usually attributed to the α polymorph (form II) is likely to be due to β' that was formed during the preparation for
the measurement or during the measurement itself. As noted in the previous
section, each crystal can have its own composition and polymorphism; the
observed properties being an average of all the separate crystals. This is proposed
as the justification for the apparent continuous β' phase range, encompassing forms
III and IV (Van Malssen et al., 1999). Nevertheless, even more recent studies
appear to establish the existence of the six polymorphic forms, using differential
scanning calorimetry (DSC) and mathematical deconvolution of the peaks (Fessas
et al., 2005).
Table 15.3 compares the melting points determined for cocoa butter polymorphs.
Here, the polymorphs are referred to as forms I to VI. Whatever the true situation,
it is fair to say that cocoa butter polymorphism is complex!
Chocolate that is composed of unstable (or mixtures of) polymorphs, has a
tendency to undergo physical changes associated with the transitions of the
unstable forms into more stable forms. These physical changes are likely to affect
adversely the appearance and/or texture of the chocolate. Thus, it is necessary to
obtain cocoa butter in a stable β form for maximum stability and shelf life. Indeed,
early on, Duck (1964) verified that better quality chocolates showed crystallisation
in the β form, that is, the most stable, in the face of small temperature fluctuations.
The sub-α, least stable and with the lowest melting point, is the first crystal form
that is formed when the fat is submitted to a fast cooling to very low temperatures.
After slow reheating, it rapidly changes into βV, via α and β' forms (Chapman,
1971). If chocolate is poorly tempered, before solidifying, it will generally
crystallise in the β' form, either alone or in combination with some amount of βV.
The βVI polymorph is not usually formed by solidifying chocolate after tempering,
but arises after long-term storage.
βV and βVI are the most stable polymorphs of the cocoa butter. βV is produced in
a well tempered chocolate. During storage it can very slowly change into βVI.
According to Wille and Lutton (1966), the complete transition of βV into βVI can
324
Enrobed and filled chocolate, confectionery and bakery products
Table 15.3 Melting points of cocoa butter polymorphs
I
II
III
IV
V
VI
sub-α
α
β'
β'
βV
βVI
Wille and
Lutton, 1966
Riiner,
1970
Huyghebaert and
Hendrickx, 1971
Dimick and
Davis, 1986
Van Malssen
et al., 1999
17.3
23.3
25.5
27.5
33.8
36.3
2
16
25
14.9–16.1
17.0–23.2
22.8–27.1
25.1–27.4
31.3–33.2
33.8–36.0
13.1
17.7
22.4
26.4
30.7
33.8
–5 to +5
17–22
20–27
32
29–34
take up to four months, but the transformation is accelerated by elevated temperatures and temperature fluctuations. The βV form is the polymorph preferred by
consumers, not only for its melting characteristics, but also its hardness. The
hardness of a chocolate, and indeed, of any fat, depends on the amount of solid fat
present, the shape (morphology) of the fat crystals and the links (network,
sintering) between the crystals. Both the amount of solid fat present and the crystal
morphology depend on the polymorphic form and the way in which it is crystallised (Marangoni and McGauley, 2003; Brunello et al., 2003). The βVI form, in
bloomed chocolate, yields a coarse structure and a dry mouthfeel (owing to the
higher melting point compared to the βV form; it does not give rise to the ‘cool
melting’ sensation in the mouth).
Although very slow to appear from cocoa butter melted at 50 °C or above, the
βV form can be crystallised from cocoa butter that has been melted at just 1 or 2 °C
above the melting point – the so-called memory effect (Van Malssen et al., 1996;
Van Langevelde et al., 2001).
The structure of the βV form of CB has recently been determined by Peschar et
al. (2004) using high powered powdered X-ray diffraction by comparison with that
determined for the β2 form of StOSt. The precise βVI structure has yet to be
determined, but the powder X-ray diffraction pattern is very similar to that of the
single β form of POSt.
15.5 Changes during tempering
The purpose of tempering is to form stable β seed crystals in a controlled manner
such that the whole of the chocolate mass subsequently crystallises into the stable
crystalline form (Cook, 1984). Properly tempered chocolate allows fast solidification of the chocolate in the mould and is important for qualities such as mould
release (good contraction), hardness, snap, mouthfeel, flavour release, gloss and
resistance to fat bloom. The chocolate tempering process is essentially a controlled
crystallisation where, by means of thermal and mechanical treatment, a specific
percentage of stable cocoa butter crystal is formed. Seguine (1991) defined temper
as ‘the largest number of the smallest possible crystals of the right crystalline form
(polymorphic form)’.
Ingredient preparation: the science of tempering
325
Fat bloom is a physical defect that appears during the storage of the chocolate,
resulting in the formation of large fat crystals at the surface of the product, giving
a pale appearance (Loisel et al., 1997a). Its mechanism of formation is not clearly
understood, but is related to the crystal forms of cocoa butter (Lonchampt and
Hartel, 2006). Fat bloom is considered to be the migration of the liquid fraction of
the fat inside the chocolate matrix and its gradual uncontrolled recrystallisation at
the surface. This recrystallisation is characterised or accompanied by a polymorphic transition from a less stable phase to a more stable one. This can be from α or
β' into βV, if the chocolate is undertempered or experiences temperatures above its
melting point during storage, or can be from βV to βVI in tempered chocolate during
long-term storage.
If molten chocolate is cooled to 34 °C (or, at least, above the melting point of the
β' form but below that of the βV form), crystallisation will start to occur into the βV
polymorph. However, this will take a very long time, perhaps even many days
(Beckett, 2000). Since this is impractical, tempering processes have been established to generate β seed crystals more rapidly.
Tempering starts with completely molten chocolate, at temperatures around
50 °C. Controlled cooling is carried out, under constant stirring or shearing of the
chocolate, to the crystallisation temperature necessary to induce crystal growth of
both β' and βV. Note that at this point, unstable, or metastable crystals are also
formed as well as stable ones. MacMillan et al. (2003) have shown that, at least
above 14 °C, the β' forms crystallise initially, before transforming into the βV form.
Finally, the chocolate is heated to a temperature at which only the unstable crystal
forms are melted. This heating also reduces the viscosity of the chocolate,
facilitating subsequent stages of moulding or enrobing. The final reheating temperature depends on the type of chocolate that is used.
Chocolate can be tempered manually, on a small scale, or via tempering
equipment, which may operate in a batch or continuous process. Whichever
route is taken, the chocolate must be fully molten at the start. This means
heating the chocolate to at least 50 °C, to remove any residual solid crystals or
seeds.
A very traditional tempering method involves removing about one-half to
three-quarters of a batch of molten chocolate on to a cool marble slab. The
chocolate is spread and stirred on the slab until an increase in viscosity indicates
that a significant amount of crystallisation has occurred. The partly crystalline
chocolate (which will contain both unstable and stable polymorphs) is returned to
and mixed into the remaining molten chocolate. Since the molten chocolate is still
at a higher temperature than the partially crystallised mass, unstable polymorphs
will either melt or be transformed into stable ones, leaving stable seed crystals in
the chocolate.
In the simplest seeded batch operation, molten chocolate is cooled to a temperature above that of the unstable polymorphs (e.g. 29–30 °C for a dark chocolate). A
small amount of powdered, flaked or grated chocolate (or even fat itself), which is
already in the stable β form, is added and the mixture is stirred while holding at this
temperature until proper temper has been achieved.
326
Enrobed and filled chocolate, confectionery and bakery products
40–50 °C
Temperature
Zone 1
Zone 2
Zone 3
27–33 °C
27–32 °C
22–28 °C
Little crystallisation;
specific heat
removed.
Crystallisation of both
stable & unstable
polymorphs; latent
heat removed
Unstable polymorphs
melted or transformed
into stable forms;
viscosity reduced.
Time
Fig. 15.6
Stages of tempering via a continuous process.
In an unseeded batch operation, molten chocolate is cooled, while stirring, to a
temperature below the melting point of the β' forms. This induces crystallisation to
occur into both the β' and β forms. Once a sufficient amount of solid has formed
(which may represent less than 10% of the fat phase), the temperature is increased
above (or near to) the β' melting point. It is held isothermally for a time so that the
unstable forms will melt or transform and so that further crystallisation may take
place into the stable polymorph, until temper is achieved. This type of process can
be automated but can also take a significant amount of time compared to continuous processes.
Many types of continuous tempering equipment exist. Although there are
differences in the precise mode of operation, they follow a common regime.
Molten chocolate is passed through a series of scraped surface heat exchangers.
There are generally at least three heat exchangers but equipment with seven or
more exchangers exist. As a general rule, the chocolate is cooled in the initial heat
exchanger(s), cooled a little further in the intermediate exchangers during which
crystallisation occurs into a mixture of polymorphs and finally is reheated in the
last stage(s) to transform the unstable polymorphs into the stable β seed crystals.
This process is illustrated in Fig. 15.6.
Ingredient preparation: the science of tempering
327
In zone 1, the sensible heat is removed from the chocolate, thus lowering the
temperature. Little or no crystallisation occurs in this zone. In zone 2, a little more
sensible heat and a lot of latent heat of crystallisation is removed. In this zone, the
bulk of the crystallisation occurs. Since the walls of the temperer are cold,
crystallisation begins here, principally into unstable α and β' forms, since the
energy barrier to their formation is less than that of the stable β forms. As the walls
are scraped, these unstable crystals are mixed back into the warmer chocolate and
some, particularly the α crystals, transform into more stable forms. During the final
zone, 3, the temperature of the chocolate is raised to melt and transform the
unstable crystals leaving only stable, βV, seed crystals. The rise in temperature also
leads to a reduction in the viscosity of the chocolate, which helps in the later
enrobing or moulding processes. The specific temperatures involved are very
dependent on the composition of the chocolate. Milk and white chocolates will
require lower temperatures than dark chocolate.
Some tempering equipment has a final ‘maturing’ zone where the stable seed
crystals can mature. Shear also aids the formation of stable solid by increasing
nucleation rate (Ziegleder, 1985), breaking up crystals to generate further seeds,
ensuring a good heat and mass transfer, encouraging the transformation of
unstable crystals, and uniformly distributing the seeds through the mass. However, the shear must be carefully applied. Shear imparts energy to the system
and will add heat. If the shear rate is too high, this heat can melt the seeds
crystals as they form.
Attempts have been made to model the tempering process and these can give
useful indications of the important parameters needed to control during the
process. The aim in tempering is to obtain a chocolate that will crystallise into
the stable form, but that will maintain this condition for as long as possible
following tempering. As already noted, this is achieved in tempering machines
by cooling in two zones and reheating in the third. However, there is no single
way to set up a tempering machine that will lead to a tempered chocolate.
Rather, there is a collection of such conditions. Although the chocolate may
yield a well tempered curve by the temper meter, the conditions are not all
equally desirable.
Cebula et al. (1991) studied tempering using a model tempering machine (Fig.
15.7) comprising three cylindrical heat exchangers through which the chocolate
was pumped. A screw or auger, which also helped in conveying the chocolate
through the machine was used to stir the chocolate. The temperature of the water
flowing through the jackets of the heat exchangers was independently controlled
and the temperature of the chocolate was adjusted by altering the temperature of
the water. (Note that this differs from many commercial tempering machines in
which the flow rate of the water is controlled, rather than the temperature.) The
temperature of the chocolate could be measured at each stage.
The machine was operated in a continuous recycling mode where the tempered
chocolate was directed through a fourth heat exchanger to melt the chocolate fully
before returning it to the feeding tank. Samples of tempered chocolate could be
removed at the exit of the third stage. In a series of experiments using this
328
Enrobed and filled chocolate, confectionery and bakery products
Heat
exchanger
Temperature
sensor
1st stage
Water
Fig. 15.7
Pump
Hold/feed
tank
Recycle
2nd stage
Heat
exchanger
3rd stage
Tempered
chocolate
Schematic diagram of a three-stage continuous tempering unit.
equipment, the second stage temperature was set to be a constant 1.5 °C lower than
the first stage temperature, simply to remove one variable. This left two independent variables: the first stage temperature and the throughput (flow rate). These
parameters were varied and the third stage temperature that produced a well
tempered curve from a temper meter was sought.
There was no unique set of temperatures and throughput that produced a well
tempered chocolate. Rather, there was a set of conditions that would do so. Figure
15.8 shows plots of the third stage temperature against the first stage temperature
and the throughput for two milk chocolates containing 5% and 25% milk fat. The
surface shown represents all conditions that resulted in a well tempered chocolate.
Any point on the surface has an associated flow rate and stage temperatures that
yield a well tempered chocolate at the exit of the unit. Any point in space above the
surface represents undertempered chocolate, while points below the surface
represent overtempered chocolate.
It is apparent from Fig. 15.8 that decreasing temperatures in the first and second
stages requires an increase in temperature of the third stage in order to maintain
well tempered chocolate. This occurs because a greater amount of solid is formed
in the initial stages and a higher temperature is required to melt or transform this
into stable crystals in the final stage. Similarly, if the throughput is decreased, the
longer time in the first stages permits greater amounts of crystallisation to take
place, requiring higher temperatures in the final stage.
If the temperatures in the first two stages are increased, a point is reached where
Ingredient preparation: the science of tempering
3rd stage
temperature (°C)
36
329
5% milk fat
32
28
24
20
19
21
tem 1s
23
pe t st
ra ag
tur e
e(
°C
)
3rd stage
temperature (°C)
36
25
27
10
18
14
ut
p
h
g
u
ro
Th
–1 )
h
(kg
10
14
25% milk fat
32
28
24
20
19
21
tem 1s
pe t st 23
ra ag
tur e
e(
°C
)
25
27
18
put
Through
–1 )
h
g
(k
Fig. 15.8 Charts showing the dependence of final stage temperature (third stage) on the
initial stage temperatures (first stage) and flow rate for a low (top) and high (bottom)
milk fat chocolate.
insufficient crystals can form and the final stage temperature must be drastically
reduced. Ultimately, it is not possible to produce a tempered chocolate at all. This
is where the plateau drops off. Clearly, operating near the edge of the plateau
would not be desirable. Thus, normal operational conditions should be away from
this edge.
Figure 15.8 also shows that higher milk fat levels require lower tempering
temperatures, as previously mentioned. The plateau temperature (third stage) is
lower for the higher milk fat chocolate and the position of the plateau edge (first
and second stages) is also lower. Cebula et al. (1991) also found that higher
POP levels necessitated lower tempering temperatures but that diacylglycerols
did not greatly influence the temper surface and that trisaturated triacylglycerols
330
Enrobed and filled chocolate, confectionery and bakery products
similarly had little effect, although they markedly increased the viscosity at
temper.
A similar surface probably exists for each tempering machine and chocolate
formulation and an understanding of the extent and shape of this surface would
enable the optimum settings for the machine to be selected (e.g. to avoid operating
on the edge of the plateau).
15.6 Factors affecting tempering
In tempering, the crystallisation of about 0.1–5% (or more) of the fat present in the
mixture occurs (Loisel et al., 1997b; Nelson, 1988; Jewell, 1988; Beckett, 2000),
resulting in an increase in the viscosity of the chocolate. The crystallisation
continues during the cooling of the chocolate reaching, at the exit of the cooling
tunnel, approximately 75% of solid (ITAL, 1998). The composition of the solid
that forms initially has been the subject of investigation (Davis and Dimick,
1989a,b), but although it is composed of a similar TAG to the cocoa butter itself,
it is enriched in StOSt. Davis and Dimick (1989a,b) also found that certain minor
lipid components (e.g. glycolipids, phospholipids) and trisaturated TAGs were
present in the initial crystals at much higher concentrations than in the original
cocoa butter. However, in other studies, the trisaturated TAGs were not found to
increase the ease of tempering (Cebula et al., 1991).
There are three process parameters that must be controlled simultaneously to
get good tempering: temperature (sometimes linked to cooling rate), crystallisation
time and agitation speed (Johnson, 1998; Hartel, 1991).
The crystallisation temperature selected depends on the fat phase present in
the chocolate. The presence of milk fat slows the crystallisation and lowers the
melting point of the polymorphic forms of cocoa butter. Thus, chocolates with
high concentrations of milk fat require lower temperatures and longer tempering
times (Chapman, 1971; Jeffrey, 1991; Hartel, 1991; Barna et al., 1992; Lohman
and Hartel, 1994; Weyland, 1998). Initial crystallisation begins on the cooling
surfaces of the tempering machine. Thus, if the temperature at this point is less
than about 5 °C, the sub-α polymorph will be able to crystallise but will rapidly
transform into the α form, or beyond. At slightly higher temperatures (less than
15 °C), the α polymorph will form. This polymorph could survive for some time
at temperatures below 20 °C, but as it is moved into the warmer chocolate away
from the cooling surfaces, and as it experiences the shear produced by the
stirring (or movement) of the chocolate, it will quickly transform into the β'
form.
The crystallisation time must be long enough to allow the nucleation and growth
of stable crystal forms, as well as allowing the crystals to mature. The crystallisation time depends on the type of equipment used, but is also a function of the
formulation of the product. According to Nelson (1988), when the chocolate is
tempered over a longer period, greater numbers of stable crystals form and these
have a higher melting point. Thus, there is greater flexibility to increase the final
Ingredient preparation: the science of tempering
331
temperature, improving the viscosity characteristics of the chocolate. However,
special care must be taken not to melt the stable forms already present when finally
heating. Tempering for longer times has other advantages, including shorter
solidification time in the cooling tunnel, better contraction and demoulding and
greater heat resistance.
The stirring speed or shear rate of the chocolate, affects the efficiency of
mixing and also the rate of heat and mass transfer within the tempering equipment. However, too much shear will produce heat, which could melt the stable
crystals already formed. Conversely, too little shear will cause an insufficient
heat and mass transfer in the chocolate. Thus, an optimum shear rate exists
between these extremes. The shear rate is a function of the stirrer blade design
and varies between tempering equipment (Nelson, 1988). Studies on pure cocoa
butter established that shear would induce crystallisation as well as facilitate
polymorphic transformation into stable forms (Sonwai and Mackley, 2006),
although this study was limited to a crystallisation temperature of 20 °C. Other
studies also demonstrate this effect of shear (Ziegleder, 1985; Toro-Vazquez et
al., 2004; Dhonsi and Stapley, 2006), with some suggesting that shear is almost
essential for βV formation (MacMillan et al., 2002) and others proposing that, as
a general rule, monotropic polymorphic phase transitions are promoted by shear
(Mazzanti et al., 2003).
Nucleation, as opposed to the crystal growth, is encouraged by fast cooling.
This leads to a more homogeneous distribution of small crystals in the chocolate,
resulting in a final product with a denser structure, better snap and better gloss
characteristics. If the cooling is too fast, however, nucleation is inhibited. The best
cooling rate depends on the type of chocolate desired and the formulation used
(Hartel, 1991).
The final crystal size distribution itself is important, as can be seen in Fig. 15.9.
The left chart shows how a broad crystal size distribution shifts towards larger
crystal sizes over time, as Ostwald ripening takes place. In this process, larger
crystals grow at the expense of smaller crystals. In the right chart, a narrower, more
uniform, size distribution at the start leads to less Ostwald ripening, since the
smaller difference in size leads to a smaller driving force for ripening; crystals
remain small. To inhibit recrystallisation and ripening in the final chocolate
product, it is desirable to produce many small crystals of uniform size during
tempering.
Different chocolate formulations can significantly influence the tempering
process. Milk and white chocolates require a different tempering regime to that
of dark chocolate, owing to the interactions between the milk fat and the cocoa
butter. The precise effect of these interactions in the crystallisation processes is
not clearly understood in its complexities (Hartel, 1991), but milk fat inhibits the
crystallisation of cocoa butter TAGs as well as reducing the melting point of the
fat.
The milk fat contributes to the flavour and texture of the milk and white
chocolates, as well as assisting in the prevention of the occurrence of fat bloom
(Chapman, 1971). Because of its different TAG composition, milk fat itself
332
Enrobed and filled chocolate, confectionery and bakery products
Wide size range
Size
Narrow size range
Size
Fig. 15.9 Illustration of the effect of storage (solid line = before storage; dotted line = after
storage) on crystal size distribution for samples starting with a wide distribution (left) or a
narrow distribution (right).
crystallises more slowly and has a lower melting point than cocoa butter. When
added to cocoa butter, milk fat retards crystallisation and lowers the melting point
of all polymorphs (Hogenbirk, 1990).
According to Timms (1980), the maximum concentration of milk fat in chocolate must be 30–35% of the total fat phase, above which eutectic effects occur. The
eutectic effect is characterised by a lowering of the melting point of the fat phase
owing to chemical incompatibility between molecules of the TAGs present in the
fats (see Fig. 15.5 for an illustration of a eutectic).
Yella Reddy et al. (1996) adjusted the optimum tempering conditions for milk
chocolates to account for different percentages of anhydrous milk fat and its
fractions. These authors observed that the degree of tempering of the chocolates
depended on the time and the temperature of crystallisation and that it could be
measured by differential scanning calorimetry, which proved to be a fast and
efficient analytical tool. The authors concluded that, from the formulation and
composition of the fats, it was possible to adjust the process conditions in order to
get a well tempered product and managed to produce chocolates with up to 40%
milk fat. Thus, chocolates that contain higher concentrations of milk fat require
lower temperatures and longer times in tempering. Therefore, defining the best
conditions for a given formulation requires a more in-depth study, in the form of
adjusting the process parameters.
Other ingredients commonly used in the chocolate industry are the emulsifiers
lecithin and polyglycerolpolyricinoleate (PGPR). These are used (separately or
together) to reduce the viscosity of the chocolate. The viscosity of chocolate
increases during tempering, owing to formation of crystals (Schremmer, 1980;
ITAL, 1998; Minifie, 1989) and the consequent reduction in the amount of liquid
phase. The control of viscosity during the tempering process is very important for
production of a consistent final product. The thickness of the layer of chocolate in
shell moulds, the demoulding time, the removal of air bubbles in the chocolate and
the proper flow in an enrober curtain all depend directly on the viscosity of the
Ingredient preparation: the science of tempering
333
chocolate. It is essential to control this parameter in order to maintain a high quality
final product. As well as influencing the viscosity, emulsifiers may also influence
the crystallisation of cocoa butter, as can the presence of other surfaces, such as
sugar and cocoa powder (Bowser, 2006; Talbot et al., 2007). Sugar apparently
reduces the amount of solid fat measured at temper, while cocoa powder has little
effect. Lecithin slightly lowers the amount of solid fat at temper but skimmed milk
powder increases it.
Dimick and his team have explored the role of very minor lipid components on
cocoa butter crystallisation, since they found these to be at proportionately higher
levels in the initial seed crystals (Savage and Dimick, 1995; Chaiseri and Dimick,
1995).
One TAG type, present at low levels in cocoa butter, is trisaturated TAGs. Some
cocoa butter equivalents (CBEs) have even higher levels of these types of TAG
than those found in cocoa butter. It has been found that elevated levels of these
TAGs do not contribute to the tempering of chocolate (i.e. they do not seed the
subsequent crystallisation into the stable form). However, they do contribute
greatly to the viscosity of the chocolate at temper. This is a very important factor
to consider in the downstream processing.
15.7 Measurement of temper
Tempering is a key step in the manufacture of chocolate. Consequently, it is
necessary to quantify the state of temper (amount of seed crystals) in the chocolate
after the tempering process. Before the introduction of temper meters, trained and
experienced confectioners were responsible for checking the state of temper of a
chocolate mass. They may have used a variety of techniques including taking a
sample through the cooling stage and inspecting the result, rubbing a sample of the
chocolate across their lips or between their tongue and the roof of their mouth (to
feel for the formation of sufficient seed crystals) or simply to assess the viscosity
and gloss of the chocolate, by dipping a finger in the mass and letting the chocolate
run off.
Aside from the experienced eye (or mouth, or finger!), researchers have
attempted to describe more objective methods to measure the degree of temper
(Motz, 1957; Vos, 1965; Vaeck, 1973). Some have described the use of DSC (see,
for example,Yella Reddy et al., 1996) or differential thermal analysis (DTA)
(Adenier et al., 1984) to quantify the state of temper but, commonly, a temper
meter is used (see, for example, Nelson, 1988). More recently, the temper meter
method has been compared with sophisticated instrumental methods (near infrared
and fluorescence spectroscopies) and chemometrics (Svenstrup et al., 2005),
while Loisel et al. (1997b) have investigated the link between degree of temper and
viscosity. In addition, semi-continuous in-line measurement systems have been
devised (Sollich, 1989; Sollich, 2005). However, the temper meter cooling curve
remains the cheapest and simplest objective quantifier of temper degree. It should
be noted that all methods applied in this area give an indirect indication of the
334
Enrobed and filled chocolate, confectionery and bakery products
Fig. 15.10 Arrangement of a typical temper meter.
number, size and polymorphism of the seed crystals. This being the case, it is up to
each chocolate manufacturer to decide what level of which measurement equates
with well tempered material.
The JW Greer Company was one of the first to introduce a temper meter.
There are a number of varieties of such instruments, including automatic systems (Allen, 1995), but they all operate in a similar way, cooling the chocolate
(e.g. by ice water or Peltier system) and measuring the cooling curve. Figure
15.10 shows a schematic of typical temper meter components. A sample of the
chocolate is placed into the upper part of a metal (e.g. copper) tube whose base
is cooled by an ice water bath. The temperature is recorded via a thermocouple
as a function of time and the resulting curve is diagnostic of the degree of
temper in the chocolate.
When a material crystallises, heat is generally given out. This causes a deviation
from the cooling profile expected in a non-crystallising system. The particular
deviation manifested is indicative of the progress towards proper temper. Figure
15.11 shows examples of temper curves. All the cooling curves begin in a similar
manner as heat is removed from the chocolate and it cools. Likewise, the latter part
of the curves are similar, where the final cooling takes place. However, the curves
differ significantly in their middle portions. A well tempered chocolate is often
assumed when the cooling curve shows a plateau. Numbers can be extracted from
the curves to aid in the quantification of the temper degree. Some take the
minimum temperature attained prior to the rise in temperature when undertempered. Some extrapolate lines, as shown by arrows in the left-hand chart in Fig.
15.11 for the undertempered curve and take the temperature at the intersection
(Bolliger et al., 1998); this may have an arbitrary temperature subtracted to yield
Ingredient preparation: the science of tempering
Temperature
Temperature
Time
Overtempered
Temperature
Well tempered
Undertempered
335
Time
Time
Fig. 15.11 Examples of temper curves. Note that lines may be extrapolated (as indicated
by the arrows) to yield a temperature at the intersection that some use as a measure of temper
quality.
the ‘Greer temper unit’ or GTU (Allen, 1995). Others measure the slope at the point
of inflection, often referred to as tan(α), which becomes zero when a plateau is
present. Although it has been proposed that more information is readily available
by plotting the temperature on a logarithmic scale (Reade, 1980a; Reade, 1980b),
most methods use a linear scale.
A number of factors combine to give the observed cooling curves. The ice water
removes heat from the chocolate at a rate that depends on the difference in temperature between the chocolate and the ice water. Thus, the greater the temperature of
the chocolate, the faster will be the cooling rate. This is why the chocolate cools more
rapidly at the start, but slows as it gets closer to 0 °C. This can be seen in the chart in
Fig. 15.12(a). This is the simplest situation, where no crystallisation occurs. The
upper part of the chart shows the temperature of the chocolate (the cooling curve),
while the bottom half shows that the ice water removes heat at a slower and slower
rate as time progresses and the chocolate temperature falls.
Where few seed crystals have been formed (i.e. the chocolate is undertempered), crystallisation does not begin until a relatively low temperature is reached
(Fig. 15.12(b)). However, once crystallisation is initiated, it proceeds quickly,
owing to the low temperature and high degree of undercooling (cooling below the
melting point). The crystallisation generates heat, the rate of generation dependent
on the rate of solid formation. Figure 15.12(b) shows how the heat is generated
(bottom half of the chart) as the solid phase increases (top half of the chart). In
addition, the temperature differential between the chocolate and the ice bath is
relatively low, resulting in lower degrees of cooling than at higher temperatures.
The result is that the considerable amount of latent heat released cannot be
removed sufficiently rapidly (note that the removal of heat by the ice is not now a
simple curve) and the temperature rises. The resultant cooling curve shows a
significant rise in temperature before finally cooling further. Chocolate in this state
of temper risks crystallising in an unstable β' form after moulding/enrobing and
cooling. This can give rise to problems such as difficulty in demoulding. Additionally, recrystallisation or transformation of this unstable form into the β form will
lead quickly to bloom and/or a coarsening of the texture of the chocolate.
336
Enrobed and filled chocolate, confectionery and bakery products
No crystallisation
(a)
Undertempered
(b)
Temperature
Solid
Temperature
Temperature
Solid
Heat flow
Heat flow
Crystallisation heat
Ice cooling
Time
Time
Temperature
Solid
Temperature
Heat flow
Heat flow
Time
Fig. 15.12
Overtempered
(d)
Solid
Well tempered
(c)
Time
Illustration of the factors that lead to the observed temper curve, showing
the reason for the differences observed between states of temper.
Ingredient preparation: the science of tempering
337
If there are sufficient seed crystals present (i.e. the chocolate is well tempered),
crystallisation starts earlier than in the previous case and at a higher temperature.
However, the temperature at which the crystallisation is occurring is also higher
and consequently the crystallisation rate is a little lower than before and the latent
heat is released more slowly. In addition, the temperature differential between the
ice bath and the chocolate is greater, leading to greater cooling. Together, these
factors prevent the temperature from rising since the heat generated by crystallisation is exactly balanced by the heat removed by the ice; the temperature simply
reaches a plateau for a period of time before continuing to fall (Fig. 15.12(c)).
There exists, however, a series of curves in which the temperature achieves a
plateau. While all of these might be considered well tempered, the optimally
tempered sample is generally thought of as the one with the highest plateau.
Properly tempered chocolate will crystallise in fine crystals of the stable βV form,
and will thus readily demould. Such a chocolate will have the best shelf life.
In the situation where an excess of seed crystals has formed (i.e. the chocolate
is overtempered), crystallisation begins even earlier, at yet higher temperature.
Since the temperature is higher, the crystallisation rate (at least initially) is much
lower. The temperature differential between the ice and the chocolate is even
greater, thus the cooling rate is higher. In this situation, no temperature rise is seen
and, indeed, the fall in temperature is not arrested at all (lFig. 15.12(d)). Rather, the
cooling profile deviates to some degree from that observed when no crystallisation
occurs, that is it cools more slowly. This chocolate is more viscous than properly
tempered material and can give rise to difficulties in filling the moulds, removal of
air bubbles or enrobing. In addition, the structure of the final chocolate can be
coarser than in the best case.
Having stated that the curves in Fig. 15.11 represent states of undertempered,
well tempered and overtempered chocolate, respectively, and having noted the
potential problems with chocolate that is not well tempered, it should be said that
the precise desired shape of the temper curve can be a matter of preference. The
definition of the best temper curve is somewhat empirical. There are no step
changes between undertempered, well tempered and overtempered. Rather, there
is a smooth evolution between such states. Thus, the temper curve provides a
simple means by which to indirectly measure the quantity and quality of stable β
seed crystals. Nevertheless, the number and quality of seeds required will differ for
different products and different downstream processes. This being the case, it is up
to the manufacturer to determine the preferred point of inflection and temperature
rise (if any) in the temper cooling curve that gives rise to the best quality of
chocolate in their particular product and process.
15.8 Future trends
In the past, developments in tempering have mostly focussed on optimising
cooling, shearing and reheating in continuous tempering machines. Where batch
tempering is carried out, seeding with powdered or flake chocolate has also been
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Enrobed and filled chocolate, confectionery and bakery products
used. However, there are a few technologies which may yet be developed to a
practical scale in tempering.
Since the late 1990s, work has been carried out to produce a continuous method
in which the chocolate is seeded. Using seeding material means that the chocolate
need not be cooled to temperatures where the formation of unstable polymorphs is
unavoidable. The seeds may be a fluidised powder (Hachiya et al., 1989; Willcocks
et al., 1998), a slurry of fat crystals or a partly crystalline fat (Cain et al., 1995,
Windhab and Zeng, 2000; Zeng et al., 2002), or even tempered chocolate that has
been treated in separate streams or recirculated (Van Malssen et al., 2004). One
particular instance of this concept has already been realised in a commercial
machine (Braun, 2002) but its use is still not widespread. Micronisation can be
applied to generate powdered fat crystals for use as seed (Letourneau et al., 2005).
In this technique, supercritical CO2 is introduced into an autoclave with solid cocoa
butter. At high pressure, two liquid phases result, both of which can be sent to a
depressurisation nozzle, where a fine powder results. The particles are in the βV
polymorph and can be used to seed chocolate during tempering.
Having noted previously the importance of shear or pressure, this latter may, of
itself, be useful for tempering. It has been shown that applying and releasing high
pressure (300 MPa) can produce cocoa butter in the βV polymorph (Oh and
Swanson, 2006). Whether this is something that could be applied in a commercial
tempering process has yet to be established.
Ultrasound has been shown to influence the crystallisation of many materials,
including fats. The mechanism is not well understood, but some believe that the
formation and collapse of bubbles of gas (from dissolved air) in the fat have a part
to play. Thus, a tempering process utilising ultrasound to induce crystallisation at
higher temperatures, producing more stable seed crystals in the chocolate has been
proposed (Baxter et al., 2001).
Finally, it has been shown that strong magnetic fields can promote the crystallisation of certain TAGs into more stable polymorphs (Miura et al., 2004). Indeed,
the use of a magnetic field has been patented as a process for obtaining chocolate
in the βV or βVI form (Beckett, 2002). Nevertheless, the practicality of its use in a
commercial tempering process must be questionable since the reported effect was
to reduce the solidification time from over 20 hours to less than 15 hours when
cycled between 26 °C and 28 °C every 4 hours. Most of the processes described
above have yet to be fully, or even partly, utilised in a commercial setting but it is
certain that developments in the tempering process will continue, even if only
along conventional lines of temperature and shear optimisation.
15.9 Sources of further information and advice
There are many publications relating to the tempering of chocolate, as will be seen
from the list of references at the end of the chapter. However, there are a few
resources that should be explored for further information.
For a detailed description of TAG polymorphism and interactions, Garti and
Ingredient preparation: the science of tempering
339
Sato’s books Crystallization and Polymorphism of Fats and Fatty Acids and
Crystallization Processes in Fats and Fatty Acids (Garti and Sato, 1988; Garti and
Sato, 2001) are a good starting point. Although quite technical, they extend the
descriptions given earlier in this chapter. Timms (1984) gives a clear description of
the phase behaviour of fats in his paper ‘Phase behaviour of fats and their
mixtures’.
To look more into cocoa butter polymorphism, the reviews in the papers of Van
Malssen et al. (1999) and of Loisel et al. (1998a) are very helpful, although they
disagree on the precise nature of cocoa butter polymorphism, demonstrating that
the debate on this topic continues. The former concludes that forms III and IV
represent two examples of a β′ phase range, while the latter considers that they are
clearly separate polymorphs.
Talbot’s book, Application of Fats in Confectionery covers many of the topics
included here, including polymorphism and tempering (Talbot, 2006), as does
Timms’ Confectionery Fats Handbook (Timms, 2003). Both of these compile a
wealth of useful information.
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Scherge Falles’, Int Z f Lebensmittel-Technol u -Verfahrenstech, 36, 412–8.
UENO S, MINATO A, SETO H, AMEMIYA Y AND SATO K
16
Tempering process technology
Karsten Richter, Sollich KG, Germany
Abstract: The art of tempering is to form a stable crystal structure within the cocoa
butter in the chocolate. This chapter describes the process, specifies different philosophies of how to temper chocolate, introduces ways to measure the degree of temper and
how to process the chocolate further by coating, moulding and aerating.
Key words: coating with chocolate, chocolate aeration, chocolate moulding, degree of
temper, stable crystal structure within the cocoa butter, tempering of chocolate.
16.1 Introduction
This chapter describes the tempering process by which means chocolate is converted from the liquid form into a partially crystallised state suitable for further use
in moulding or enrobing. This means generating a particular crystal structure
within the cocoa butter in the chocolate. The basic physical chemistry of fats such
as cocoa butter is described in Chapter 4; the science of tempering is detailed in
Chapter 15. Tempering, coating, moulding, flavouring, aerating and ingredient
addition require special equipment. These are pictured together with flow schemes
and explanations of the various processes.
16.2 Characteristics of cocoa butter
As has been described in Chapter 15, cocoa butter can solidify in different crystal
forms, of which only the higher melting forms βV and βVI are stable. The βVI form
is the most stable crystal structure which is formed only after a lengthy period of
storage. A tempering machine can only produce crystals in form βV. This crystal
Tempering process technology
345
Melting range of the β crystal form
uid
Liq
uid
Me
ltin
g
Supercooling
Time
Liq
So
lid
ify
lid
So
in
g
lid
So
Temperature
Self-heating due to
solidification heat given off
Fig. 16.1
Supercooling and reheating of chocolate caused by latent heat of
crystallisation.
form provides good gloss, long shelf life and good mouldability. There is still
controversy over exactly how many crystal forms cocoa butter has – the traditional
view is that there are six but more recent work suggests there may only be five, one
of which is actually a spectrum of many β' forms. The melting points and ranges of
these different crystal forms are shown in Tables 4.2 and 4.3 of Chapter 4.
Because of these characteristics, chocolate must be cooled down below the
melting range of the βV form of cocoa butter when tempering (precrystallisation).
As unstable β' crystals may also be formed during this stage, highly developed
tempering units are provided with so-called reheating zones where the temperature
of the chocolate can be increased to the extent that the unstable nuclei melt out. The
precrystallisation level which can be achieved, that is, the percentage of solidified
fat as compared with the total amount, depends on the time, temperature and
intensity of mixing. Solidification and melting curves do not coincide. Figure 16.1
shows graphically the phenomenon of supercooling, in which a material (in this
case cocoa butter) can be cooled to a temperature well below its melting point and
yet still remain in the liquid form. Because it supercools, when it does begin to
346
Enrobed and filled chocolate, confectionery and bakery products
crystallise it generates latent heat of crystallisation and the temperature rises before
falling again as the product cools and crystallises further. When the material is
melted, however, solid material is still found at temperatures at which, during
supercooling, the material was still liquid, resulting in a type of hysteresis.
Cocoa butter is monotropic meaning that the different crystal forms are converted automatically from low melting to higher melting crystal forms. When this
happens in a finished chocolate product, heat energy is released which may result
in fat bloom forming at the surface of the product. To eliminate this as a source of
fat bloom, only stable crystals should be present at the end of the tempering
process.
Cocoa butter is a mixture of different triglycerides (mainly 1,3-dipalmitoyl-2oleoylglycerol (POP), 1-palmitoyl-2-oleoyl-3-stearoylglycerol (POSt) and
1,3-distearoyl-2-oleoylglycerol (StOSt)). The relative levels of these triglycerides
can vary depending on the origin of the cocoa butter. As these different triglycerides
also have different physical properties, chocolates may have different melting and
solidification behaviour even if the same recipe is used if, for example, cocoa
butter from another country of origin or a different production process is used. In
milk chocolate, the hardness, melting and solidification behaviour is also influenced because the softer milk fat has a lower melting range.
16.2.1 Seed crystals
Cocoa butter has the tendency to solidify in the bulk in the form of whatever seed
crystals are present during the final cooling stage. However, the rate of growth
needs to be taken into consideration here, that is cooling should not be so ‘deep’
that unstable crystals are also formed.
16.3 Chocolate tempering
Tempering in its conventional form relies on a tempering unit producing seeds of
both the correct crystal form and in the correct quantity to ensure that the bulk of
the chocolate crystallises in the same form during subsequent cooling. Such a
tempering machine is a highly developed heat exchanger which nowadays is
provided with computer-aided control equipment and a touch screen operating
environment. In the past, screw-type tempering machines were preferred which
could be installed in both horizontal and vertical positions. All enrobers with
inboard tempering units were operated with the tempering unit in a horizontal
configuration. Because of increased output requirements, wear at the tempering
screws and – last but not least – limited space conditions, the disk-type tempering
machine has particularly established its position among the types of machine now
on the market. This is because of its flexibility and excellent heat transfer which
means it can be used to give outputs ranging from 200 to 18,000 kg h–1.
However, there is another method of tempering chocolate which should be
mentioned – tempering by seeding. This process uses a stable crystal suspension
Tempering process technology
347
Chocolate outlet
Mixing disk
Drive shaft
Re-heating stage
Tempering
column
Cooling stage
Chocolate inlet
Fig. 16.2 Disc-type tempering machine.
and mixes it with precooled chocolate at a temperature at which it has not yet begun
to crystallise.
There are a number of reasons why tempering or precrystallisation is required:
•
•
•
•
•
•
•
to accelerate solidification of the chocolate in the cooling tunnel
to enable solidification in the stable βV crystal form
to give a good gloss on the surface of the chocolate
to give sufficient heat resistance and hardness to allow the chocolate to be
‘handled’ in later processes (e.g. packing)
to avoid fat bloom
to give good contraction and mouldability
to give a fine fracture when the chocolate is broken.
However, it is important to remember that tempering does not just mean cooling
348
Enrobed and filled chocolate, confectionery and bakery products
down to a certain chocolate temperature but generating a certain stable crystal
structure within the cocoa butter.
16.3.1 Disc-type tempering machines
These machines consist of heat exchanger discs arranged one on top of the other to
form the tempering column (Fig. 16.2). Each heat exchanger disc consists of a
water chamber and a chocolate chamber. A mixing disc, driven by a central shaft,
operates in each chocolate chamber. This machine is used to temper and/or
precrystallise liquid chocolate prior to processing in an enrober and/or moulding
line. In it, the chocolate is cooled down in a controlled physical process while, at
the same time, being intensively mixed in the cooling stage such that the seed
crystals are formed. In the reheating stage, the chocolate is then heated up again so
that unstable crystals melt out. The art of tempering is to form a homogenous
crystal structure of predominantly stable βV crystals within the cocoa butter.
The tempering process is a circulation process. On the one hand, the chocolate
is tempered. On the other, the chocolate which is not required has to be melted
again before being passed back into the tempering machine. The minimum
temperature for a crystal-free chocolate is 45 °C. Tubular heat exchangers are
preferably used as decrystallisation units and are filled with warm water at a
temperature between 55 °C and 60 °C.
Only about 1 % of the cocoa butter is crystallised during one pass. This
seems to be a very low percentage, but these crystals are the important seeds for
further crystallisation. The tempering machine is responsible both for a consistent degree of temper, consistent viscosity and for the gloss and shelf life of the
finished product. It should always be chosen on the basis of its robustness and
availability.
16.3.2 Typical chocolate process flow schemes
Feeding an enrober according to the recirculation tempering process
The chocolate storage tank is supplied with fresh warm chocolate from the tank
farm. A variable speed pump, located underneath the tank, feeds the tempering
machine and discharges the tempered chocolate to the enrober. A control keeps the
level inside the enrober constant and returns unused chocolate to the storage tank,
passing through a tubular heat exchanger to decrystallise the chocolate on its way
back. Please note that process water at 55–60 °C is required to feed the heat
exchanger (Fig. 16.3).
Feeding a bar or shell moulding line
Instead of the enrober, a moulding line can be fed, with the following differences.
The moulding head is supplied with tempered chocolate via a level sensor operated
valve on the ring main. Unused chocolate returns to the storage tank if the valve is
closed and has to be decrystallised in the same way as described above.
Process water supply
(55–60 °C)
Process water return
(50–55 °C)
Fresh chocolate supply
from tank farm
Chocolate return
Tubular heat exchanger
Chocolate discharge
Protective
sieve
Enrober
Tempering machine
TURBOTEMPER
Double jacketed
water heated tank
Chocolate circulation
pump
Feeding an enrober according to the recirculation tempering process.
Chocolate
return pump
349
Fig. 16.3
Chocolate feed pump
M5-CIP
Tempering process technology
ENROMAT
Process water return
(50–55 °C)
Chocolate return
Tubular heat exchanger
Automatic valve
controlled by
level sensor
Protective
sieve
Tempering machine
TURBOTEMPER
Double jacketed
water heated tank
Chocolate feed pump
Fig. 16.4
Feeding a bar or shell moulding line.
Moulding
head
Enrobed and filled chocolate, confectionery and bakery products
Fresh chocolate supply
from tank farm
350
Process water supply
(55–60 °C)
Tempering process technology
351
Discharge
to user
Decrystalliser
Cocoa butter
supply
3/2 way
valve
Cocoa butter
holding tank
Cocoa butter
feed pump
Cocoa butter
dosing pump
Static
mixer
Shear
crystalliser
Plate heat
exchanger
Chocolate
holding tank
Chocolate
return
Chocolate
dosing pump
Fig. 16.5 Schematic of tempering by seeding.
16.3.3 Tempering by seeding
This process is based on a two-stream system shown in Fig. 16.5. In contrast to the
conventional chocolate tempering method, this process produces both super stable
βVI and stable βV crystals in a cocoa butter suspension in a ratio of 2:1. They are
generated in a small-sized circulation process (grey-shaded in Fig. 16.5). Cocoa
butter from the holding tank is circulated by means of a feed pump and tempered
while passing a high speed driven shear crystalliser. The subsequent dosing pump
now injects the suspension, containing about 12–15% crystal seeds, into precooled
but untempered chocolate in the required proportion. Unused cocoa butter is
returned to the holding tank via a heat exchanger. In the static mixer, the
suspension is blended and homogenised with chocolate provided at a constant flow
rate, cooled down by a plate type heat exchanger to a temperature at which it has
not yet begun to crystallise (31–33 °C) but also a temperature at which the crystal
seeds will remain in a solid form. The final crystal seed concentration in the
chocolate mix is then around 1% of the predominantly βV crystals.
352
Enrobed and filled chocolate, confectionery and bakery products
16.3.4 Degree of temper
The degree of temper and/or the amount of solidified fat crystals is critical for
evaluating the quality of the chocolate to be processed. Too low a percentage
(undertemper) will result in solidification times that are too long during final
cooling and the consequences may be poor gloss and a short shelf life. Too high a
percentage of crystals (overtemper) will result in an increased viscosity of the
chocolate and the consequences may be poor contraction during final cooling and
poor gloss.
16.3.5 Measuring the degree of temper
Different methods of measuring are known. Most of them measure the temperature
curve of the chocolate while cooling it down and analyse the inflection point.
Others go in the opposite direction. For example, the differential scanning calorimeter (DSC) method heats up a chocolate sample at a constant heating rate and
measures the melting curve. This gives information on the quality of the crystals in
the cooled chocolate. It is, however, an expensive and complicated method. Below
is a description of two popular instruments: the manual and the automatic
tempermeter.
Manual tempermeter
The manual tempermeter is a simple method that can be used to determine the
degree of temper within about 10 minutes. A sample cup is filled with a small
amount of tempered chocolate. The sample is then cooled down under standardised conditions and, at the same time, the temperature curve is recorded, allowing
a cooling curve to be printed. The degree of tempering is determined automatically
by the instrument from the slope of the temperature curve at the inflection point.
Crystallisation starts at this point. Heat of solidification (which is a measure of the
degree of temper) is released. The degree of temper is printed as a numerical value
under the designation ‘tempering index’. The temperature at which the chocolate
starts to solidify in the sample cup (i.e. the inflection point) is called the crystallisation temperature. It indicates the type of crystals that are formed (high or low
melting) and thus the quality of temper. The manual tempermeter requires only a
mains connection and works using thermo-electric cooling installed in the instrument. Thus the process runs under the same cooling conditions at all times.
If a deviation from ideal temper is found when measuring the degree of temper,
correction is possible by a simple change of setting at the tempering machine. This
allows a nearly constant degree of temper to be achieved during the whole period
of production. Keeping temper constant will also ensure consistent viscosity in the
tempered chocolate. Consistent viscosity will result in a constant coating thickness, consistent product weights, consistent cooling times, constant shell thickness,
and so on. The visual appearance of the product can be improved and the level of
reject can be reduced by monitoring the tempering level, allowing enormous
chocolate savings to be achieved by means of close production tolerances.
For a more detailed explanation of the tempermeter curves, see Chapter 15. The
Tempering process technology
TEMPERMETER E4
TEMPERMETER E4
Unit No: 1
Unit No: 1
TEMPERMETER E4
Unit No: 1
minute
minute
minute
1
1
1
2
2
2
3
¤
¤
3
Date 17/04/06
Start temp.
26.0 °C
Date 17/04/06
Start temp.
Time 08:29:21
Crystallisation 21.5 °C
Time 08:29:21
Cool 8.0 °C
Elapsed time
2.3 min
Temper index 3.5
Fig. 16.6 Undertempered
chocolate.
¤
3
23 °C 24 °C 25 °C
23 °C 24 °C 25 °C
353
26.0 °C
23 °C 24 °C 25 °C
Date 17/04/06
Start temp.
Crystallisation 22 °C
Time 08:29:21
Crystallisation 22.8 °C
Cool 8.0 °C
Elapsed time
Cool 8.0 °C
Elapsed time
0
Temper index 5.0
–0.65
Temper index 7.2
2.6 min
Fig. 16.7 Well-tempered
chocolate.
26.0 °C
2.3 min
Fig. 16.8 Overtempered
chocolate.
manufacturer should always determine the optimum degree of tempering required
by the process and the product. The measuring instrument is a help in ensuring
reproducibility. But even then, the gloss and shelf life of the finished product
should be checked.
Figures 16.6, 16.7 and 16.8 show different temper curves for chocolate with
normal fat content which would be typical of undertempered, correctly tempered
and overtempered chocolate, respectively.
Undertempered chocolate would have a temper curve similar to that shown in Fig.
16.6. This is typical of a chocolate in which insufficient precrystallisation has
occurred and means that the tempering machine is too warm. Typically, the degree
of temper as defined by the tempering index is 3.5 with a crystallisation temperature of 21.5 °C (depending on the type of chocolate). The low percentage of nuclei
initially allows a deep drop in the temperature before solidification starts. Because
a relatively high percentage of fat is still present in the liquid phase in the
undertempered chocolate, a relatively high amount of heat is released during
solidification, which causes the chocolate to self heat.
Correctly tempered chocolate would have a temper curve similar to that shown in
Fig. 16.7. An ideally tempered chocolate results in this typical tempering curve
with the vertical course of curve during the solidification phase. Here, the released
heat of solidification and the heat dissipated by the cooling unit are temporarily in
balance. In this case the degree of temper as defined by the tempering index is 5.0.
This is the value that, using this type of machine to test temper, a chocolate
manufacturer should be aiming for. The crystallization temperature is also higher
at 22.0 °C, depending again on chocolate type.
Overtempered chocolate would have a temper curve similar to that shown in Fig.
16.8 This curve is obtained if the chocolate contains a high level of crystal nuclei.
354
Enrobed and filled chocolate, confectionery and bakery products
The consequence is that solidification starts relatively early, that is at a relatively
high temperature. Because less crystallisation occurs in the sample cup because of
the higher degree of precrystallisation, the heat of solidification that is released is
relatively low for this chocolate. This becomes evident from the flat shape of the
cooling curve in the area of solidification.
Overtempered chocolate suggests that the tempering machine has been set to
too cold a temperature. A typical tempering index for an overtempered chocolate
would be 7.2, with a crystallisation temperature of about 22.8 °C (even higher than
that for a correctly tempered chocolate). More details of the thermodynamics
relating to the shapes of each of these temper curves is given in Chapter 15.
The tempermeter curve can be used to define the state of temper. The experienced user of the instrument will recognise the degree of temper at first glance
simply by the shape of the curve. In modern tempermeters, the degree of temper is
also given as a numerical value with the designation ‘tempering index’. Essentially, a tempering index of 1 to 3 would indicate an undertempered chocolate; 4 to
6 would indicate a well-tempered chocolate; 7 to 9 would indicate an overtempered
chocolate. Within these ranges it is possible to define further sub-divisions:
1=
2=
3=
4=
5=
6=
7=
8=
9=
very highly undertempered
highly undertempered
undertempered
slightly undertempered
ideally tempered
slightly overtempered
overtempered
highly overtempered
very highly overtempered
Depending on the requirements, it is possible to change the degree of temper at the
tempering machine by making changes to the temperature settings in 0.2–0.3 °C
increments. A good degree of temper at a high crystallisation temperature requires
a constant chocolate inlet temperature of at least 45 °C.
Automatic tempermeter
The automatic tempermeter is a measuring instrument which determines in-line the
degree of temper of a precrystallised chocolate. This instrument is installed in the
discharge pipe of a tempering machine.
The sampler takes a chocolate sample from the chocolate pipe at regular
intervals. This sample is cooled thermoelectrically and caused to solidify. At the
same time, the installed sensor measures the temperature curve. At the end of
measuring, the solidified sample is placed in the heating cylinder, melted and then
added to the chocolate flow.
A touch screen PC controls the sampler, regulates the cooling and heating
temperatures, checks all functions and prepares and saves the measuring values.
The measurements are started and the results are saved for evaluation at regular
intervals. After determining the degree of temper and the temperature of
Tempering process technology
355
Fig. 16.9 Automatic tempermeter.
crystallisation, the solidification curve is displayed graphically on the screen. All
curves and evaluations are saved continuously and can be recalled at any time. A
USB port is used to transfer the data to an external data carrier. The automatic
tempermeter is shown in Fig. 16.9
The parts indicated are as follows:
1.
2.
3.
4.
5.
6.
7.
Piston with temperature sensor
Motor for longitudinal sensor movement
Cooling chamber
Cooling device
Adapter piece
Melting chamber
Chocolate discharge piping.
16.4 Chocolate coating
The basic requirements of a chocolate coating machine or enrober have not
changed for decades. Products such as bars, chocolate centres or cookies are
coated fully or partially with chocolate. It is important to ensure that the amount of
chocolate applied to the product is consistent and that it also has a uniform bubblefree appearance. After cooling, a shiny product which is resistant to handling
should be available for packaging.
Processing real chocolate always requires a tempering unit. The type, or more
correctly, the position of the tempering unit differentiates between enrober types,
that is outboard (without an internally installed tempering unit) and inboard
enrobers (with an internally installed tempering unit). Despite these differences
Process water return
(50–55 °C)
356
Process water supply
(55–60 °C)
Chocolate discharge
Enrober
Tempering machine
TURBOTEMPER
ENROMAT
M5-CIP
Vibratory
sieve
Collecting
vessel
Return pump
Double jacketed
water heated tank
Chocolate feed pump
Fig. 16.10 Enrober with outboard tempering unit.
Chocolate circulation
pump
Chocolate
return pump
Enrobed and filled chocolate, confectionery and bakery products
Chocolate return
Tubular heat exchange
Tempering process technology
357
they all use the circulation process. The retention time of the tempered chocolate
is constant irrespective of the chocolate consumption. This ensures a constant
chocolate viscosity and allows continuous operation of such a machine if a suitable
decrystallisation unit and a three-shift heating package are available. Enrobing and
enrobers are described in much more detail in Chapter 17.
If only one product is processed on an enrober line at normal rate (3–6 m min–1),
the use of an enrober with an inboard chocolate tempering unit and a temperature
controlled decrystallisation unit is recommended because of the low purchase
price and low space requirements. However, the choice between an enrober with
inboard tempering or outboard tempering unit mainly depends on the type of
application. If low purchase costs and low installation and space requirements are
important considerations, the inboard tempering unit will always be the first
choice. Its installation is simple because neither a return pump nor a return pipeline
is necessary. The purchase costs for such a system are lower than those of machines
with outboard tempering. However applications are restricted by the consumption
of chocolate and the speed of operation.
16.4.1 Outboard enrober
This enrober is not provided with an installed tempering unit. An example of such
a layout is shown in Fig. 16.10. An outboard enrober requires about 1 kg h–1 of
freshly tempered chocolate per 1 mm width of the wire-mesh belt and this must be
supplied from a separate tempering machine. The size of the tempering machine is
not, though, determined by the expected chocolate consumption! The worst case
scenario is always the basis for the design of the unit, taking into account events
such as accident or failure!
If no chocolate is consumed, all the tempered chocolate supplied by the
tempering machine must be melted and pumped back to the intermediate tank. If
the decrystallisation unit is too small, the temperature in the intermediate tank
slowly decreases, resulting in a worse degree of temper and enrobing quality.
Lower chocolate supply temperatures to the tempering unit require lower working
settings, resulting in thickening of the chocolate as well as deposits inside the
enrober, which considerably limit the availability of the machine. An additional
circulation pump operates in the enrober which supplies a sufficient amount of
chocolate to the curtain trough. Depending on the design, the curtain trough can
require up to six times more chocolate circulating compared with the output of the
tempering machine. Higher viscosities in the enrobing chocolate can result in a
high percentage of friction heat being produced which, of course, must be
compensated for by suitable temperature settings.
An outboard tempering unit is preferred if:
• there are frequent changes to the chocolate (for example, chocolates of different
types and colours, changes between chocolate and compound);
• optimum tempering quality is particularly important;
• a separate easily accessible tempering unit is desired;
• the chocolate consumption is extremely high.
358
Enrobed and filled chocolate, confectionery and bakery products
6
7
40–50 °C
30–32 °C
1
2
3
4
5
8
Fig. 16.11
Enrober with inboard tempering unit.
In comparison to Fig. 16.3 this system is equipped with a vibratory sieve.
Certain products like cereal bars may contaminate the chocolate inside the enrober
and here it is functionally essential to separate this debris from the returning
chocolate. However, before entering the sieve the chocolate has to be decrystallised. Debris cannot be removed from tempered chocolate!
16.4.2 Inboard enrober
The inboard machine is essentially more compact than an outboard machine.
However, it is more complicated in its design and thus produces a much higher
amount of friction heat. Figure 16.11 shows a schematic arrangement of such an
enrober. A level switch controls the automatic refeeding of freshly melted chocolate in the warm tank (1). A mixer homogenises the fresh chocolate with that
Tempering process technology
359
overflowing from the tempering trough (2). When passing the heating cylinder (3),
the chocolate is melted completely (decrystallised) and then passes through the
tempering cylinder (4) where the chocolate is cooled down and the first seed
crystals are formed. The reheating stage (5) ensures that any unstable crystals in the
cocoa butter are melted out again and thus only chocolate with a stable seed crystal
structure is fed to the circulation process. In order to cover the chocolate demand
for the curtain (6) and bottoming pan (7), two different flows of chocolate are
combined directly upstream from the curtain pump (8). Full coating requires
approximately six times as much chocolate to circulate compared with the tempering output of the machine. The curtain pump takes in the missing amount of
chocolate from the tempering trough. It is important to note at this point that the
pump must be capable of feeding gently, because too high an absorption of friction
heat will reduce the stability of the tempered chocolate. Part of the chocolate leaves
the enrober on the enrobed product; the rest flows off the product and must be
returned to the tempering trough. A balance can be achieved only if the amount
coated on the product is less than 50% of the tempering output. Surplus chocolate
in the tempering tank flows back into the warm tank and a new circulation process
is started
16.5 Chocolate moulding
Instead of an enrober, it is also possible to supply a moulding line with tempered
chocolate (Fig. 16.12). The pipeline circuit is identical and can be provided, if
necessary, with branches for direct supply to the moulding unit, filling a mixer to
allow the addition of ingredients or for adding flavours. All these additional units
allow additions to be made to the chocolate without contaminating the chocolate in
the main circuit.
16.6 Aerated chocolate
To obtain an alternative texture and taste, it is also possible to aerate the chocolate.
Gas injection is used and has an enormous influence on the specific weight. Both
micro- and macro-aeration can be achieved depending on the size of the air
bubbles. In both cases, aeration takes place inside the tempering machine which,
therefore, has to be equipped with a special mixing head. Chocolate macroaeration is used to produce bars and fillings with a coarse highly visible bubble
structure, as in aerated chocolate with bubble diameters of 0.5–2 mm. Aeration can
be carried out simultaneously with the tempering process in one operation.
Suitable gases for this process include nitrous oxide (N2O) or carbon dioxide
(CO2).The minimum specific weight which can be achieved is approximately 0.4–
0.5 kg dm–³. Chocolate micro-aeration is used for coating chocolate or moulding
chocolate and gives a fine structure with bubble sizes below 50 µm, too small to be
Chocolate return
Tubular heat exchanger
Chocolate discharge
Automatic valve
controlled by
level sensor
Dosing
unit
Protective
sieve
Mixer
Tempering machine
TURBOTEMPER
Double jacketed
water heated tank
Chocolate feed pump
Fig. 16.12 Feeding of a moulding line with ingredient addition.
Moulding
head
Enrobed and filled chocolate, confectionery and bakery products
Fresh chocolate supply
from tank farm
Process water return
(50–55 °C)
360
Process water supply
(55–60 °C)
Tempering process technology
361
perceived by the consumer. Suitable gases for this process include purified air and
nitrogen (N2). The specific gravities which can be achieved are very different here.
Moulding chocolate can be reduced by approximately 10–30% and coating
chocolate by approximately 6–18% of the original specific gravity.
16.7 Future trends
Tempering is a complex physical process which can be carried out more easily and
more reliably thanks to continuously evolving tempering and cooling systems. The
state of temper can be monitored continuously using an automatic tempermeter
(supplied as an option) and – in the near future – controlled by means of an
automatic evaluation of the data provided. Together with highly developed control
systems, the availability and operation of the tempering machine is capable of
further optimisation. This will enable the quality of the end product – whether
coated or moulded – to profit. No single machine is critical in the overall process
scheme but the interactions of the individual components have to be precisely
adapted and balanced with each other.
As has always been the case, the knowledge and familiarity of the operator with
the machinery are important and so will also determine how efficiently the system
operates.
16.8 References
(2002). ‘Tempering and aerating of chocolate for enrobing and moulding’,
Lecture at ZDS Schoko-Technik Conference, Cologne, 11 December 2002.
BECKETT ST (1990). Moderne Schokoladentechnologie, B. Behr’s Verlag, Hamburg.
BUNDESVERBAND DER DEUTSCHEN SÜßWARENINDUSTRIE E.V., BONN (1991). Schokolade
und Kakao. Über die Natur eines Genusses, Lebensmittel Praxis Verlag GmbH, Neuwied,
Germany.
RICHTER K (2006). Chocolate Processing. Physical basics: Measuring the degree of temper,
Tempering, coating, cooling, fat bloom. Lecture and Training course, 3rd issue, Sollich
KG, 32105 Bad-Salzuflen, Germany.
SCHUHMACHER K, FORSTHOFER L AND RIZZI S (1995). Das große Buch der Schokolade.
Teubner, Stuttgart, Germany.
WINDHAB E AND ZENG Y (2000). Method of Producing Seed Crystal Suspensions Based on
Melted Fat, WO Patent 0072695.
BÄUMER V
17
Manufacturing processes: enrobing
M. J. Bean, Baker Perkins Ltd, UK
Abstract: The enrobing process comprises the application of chocolate or compound
coatings to cover centres, such as confectionery units, confectionery bars, plain biscuits,
biscuit sandwiches, granola bars, or other baked items such as cakes or croissants. This
chapter aims to illustrate the various techniques that are used in enrobing machines to
ensure good operation and a high quality end product. Aspects to be covered include
different types of enrobing machine, including full and half coating, and pre-bottoming;
centre preparation prior to the enrober, including conditioning and presentation at infeed; chocolate application systems; chocolate removal methodology; chocolate and
compound handling systems including inboard and outboard tempering options; environmental control and hygiene aspects; ancillary equipment such as ‘decorating’ devices;
typical operating parameters; faults and remedies; and new developments and trends for
the future.
Key words: biscuit, chocolate, confectionery, enrober, tempering.
17.1 Introduction
The enrobing process comprises the application of chocolate or compound coatings to cover centres, such as confectionery units, confectionery bars, plain
biscuits, biscuit sandwiches, granola bars, or other baked items such as cakes or
croissants. The ‘coating’ can be applied to cover the complete centre (full coating)
or on the bottom only (half-coating) or on the bottom and the lower sides (shoulder
dipping).
Whatever the requirement, the enrober should first apply the chocolate to the
selected area to ensure that full coverage is obtained. Excess chocolate must then
be removed to achieve a specified chocolate ‘pick-up’ weight, without exposing
pin holes or leakage paths that will allow the centre to leak out or air to leak in after
Manufacturing processes: enrobing
363
solidification. Finally, the enrober must transfer the product to the in-feed of the
chocolate cooler without creating a chocolate tail or damaging the bottom coverage.
The chocolate handling system within the enrober also plays a major part in
providing a consistent coating which exhibits a good gloss with no bloom after
cooling and subsequent storage. The chocolate application methodology, the
handling of excess chocolate in the application process, the treatment of excess
chocolate which is removed from the centre after application, and the feeding of
the freshly tempered chocolate into the system are all critical to the effectiveness
of the enrober and the final consistency of production output.
Enrobing processes can be implemented at band speeds up to 25 m min–1 and
with belt widths up to 2.6 m. As running speeds increase and machines become
wider, then particular challenges are presented to the machine designer in that full
coverage, consistent pick-up weights to avoid giveaway and final coating quality
must still be maintained across the width over long running periods.
This chapter aims to illustrate the various techniques that are used in enrobing
machines to ensure good operation and a high quality end product. Aspects to be
covered include:
• different types of enrobing machine – full and half-coating, pre-bottoming, etc;
• centre preparation prior to the enrober – conditioning and presentation at infeed;
• chocolate application systems;
• chocolate removal methodology;
• chocolate and compound handling systems within the enrober including in•
•
•
•
•
board and out-board tempering options;
environmental control and hygiene aspects within the enrober;
ancillary equipment such as ‘decorating’ devices;
typical operating parameters;
faults and remedies;
new developments and trends for the future.
17.2 Types of enrobing machines
With all enrobers, the centres are transported through the machine on a wire belt.
This allows chocolate to be applied to the bottom and the top of the centre and
allows excess chocolate to drain from the centre and the belt after application. The
specification of the wire belt and the design of the wire belt circuit, including belt
drive and tension arrangement, are critical to operational effectiveness and will be
discussed later in the chapter.
17.2.1 Full coating enrobers
These machines are designed to cover the centre completely with a precise coating
of chocolate. Whilst the enrober will be configured to suit the particular type of
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Enrobed and filled chocolate, confectionery and bakery products
Direction of flow
Chocolate surge
Wire belt
Surge plate
Bottoming
Surge
removal
Bottoming bath
Fig. 17.1
Bottoming of enrobed centres.
product required, there are several discrete and consecutive operations, which are
common to most applications, and these will be described here.
Bottoming:
Chocolate is applied to the base of the centre by creating a bed of chocolate across
the full width of the wire belt, applied from below, via a roller. The roller picks up
a chocolate film from a reservoir below the belt and passes the chocolate onto the
moving wire belt. A plate, sitting below and across the full width of the wire belt,
strips the chocolate from the roller on its leading edge and then supports the bed as
the chocolate is driven forward on the belt. At the trailing edge of the plate the
chocolate bed is often pulled away from the wire belt by a forward running,
rotating roller below the wire belt and the bed disappears. This bed is generally
known as a ‘surge’ of chocolate, the roller is called a ‘surge roll’ or a ‘bottoming
roll’, the plate is called a ‘surge plate’ and the reservoir is called a ‘bottoming bath’.
This process is illustrated in Fig. 17.1.
Design considerations with bottoming arrangements can include:
• Prevention of chocolate build-up: Agitation and scraping is often incorporated
into the bottoming bath arrangement to maintain a consistent chocolate surge
across the machine. The bath can be directly jacketed where long running times
are required.
• Chocolate feed: Ensuring there is an even distribution of chocolate across the
width of the bottoming bath is critical. The bottoming bath is generally fed,
symmetrically, with tempered chocolate from the top flow pan overflows on
each side of the wire belt. The chocolate level in the bath is then set by adjustable
overflows fabricated into the bath assembly. The positions of the overflows are
again determined with symmetry in mind. In some situations the bottoming bath
is fed directly from the main chocolate feed pump. In this situation, on wide
Manufacturing processes: enrobing
•
•
•
365
machines, the feed manifold in the bottoming bath is designed with multi outlet
points across the width.
Surge roll rotation: Either forward running (with the belt) or reverse running
(against the belt) surge rolls can be specified. Rotation direction is fixed for a
particular enrober configuration. Machine manufacturers will claim advantages
for either arrangement, depending on their preference. Reverse running rolls
enable smaller bath volumes to be used, which can be less prone to chocolate
build up. Forward running rolls give less product disturbance on the belt where
the centre is light and the chocolate is viscous. If centre pitching on the wire belt
is tight this can be critical.
Length of surge: The length of the surge and the contact time needs to be
sufficient to give good coverage and adhesion of chocolate to the centre. For
difficult products with cavities in their bottoms, such as bars with a cereal skin
for example, an extended surge plate length may be required. Where coating
characteristics cannot be predicted, a surge plate with adjustable length can be
included. In some extreme cases two or even three complete surge roll assemblies can be specified on a single enrober to ensure good bottom coverage at
high speeds.
Control of the chocolate film picked up on the surge roll: This is usually
controlled via a simple gap adjustment between the surge roll and an adjustable
scraper. In addition, for greater flexibility, the surge roll can be made to function
at variable speeds to allow faster or slower speeds relative to the wire belt to
drive up more or less chocolate to the surge.
Top coating
Chocolate is applied to the top and sides of the centre by single or multiple
chocolate curtains through which the centres pass on the wire belt. The quantity of
chocolate adhering to the centre is a function of the centre surface consistency and
the rheological properties of the chocolate at the curtain. It is particularly important
in this operation to ensure that the curtains are continuous across the machine at all
times. In addition, bare uncoated sides will be seen if there is insufficient gap
between centres through the curtain, such that pulling and bridging of the chocolate curtain across the gap occurs. There are many methods that can be used to
create a chocolate curtain. The most common are as follows:
• Gravity flow pan (Fig. 17.2): A trough, sitting across the wire belt, contains a
•
reservoir of chocolate. The reservoir or flow pan is continuously fed from the
main tempered chocolate holding tank in the base of the enrober. An adjustable
slot along the bottom of the flow pan allows chocolate to flow by gravity
generally onto a splitter plate which splits the flow pan chocolate ‘curtain’ into
two, such that the centres pass through two curtains per flow pan. For viscous
chocolates, the incorporation of agitation and scraping in the flow pan reservoir
can be beneficial in maintaining an even chocolate curtain across the wire belt.
Roller flow pan (Fig. 17.3): The adjustable slot is replaced by a rotating roller,
which picks up a film of chocolate from the flow pan which is then scraped off
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 17.2
Gravity flow pan for top coating.
Fig. 17.3
Roller flow pan for top coating.
the roll and drops to the splitter plate. The quantity of chocolate metered from
the roll is set by the speed of the roll and the roller clearance where it exits the
flow pan. Roll peripheral speed is generally several times faster than the wire
belt speed. A roller flow pan is used where viscous chocolates are applied at
high speeds and outputs across the wider enrobing lines. Spreading the chocolate as a thin film over the roller also helps to break out any bubbles in the
chocolate prior to application. With high line speeds, a double roller can be
Manufacturing processes: enrobing
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367
specified where two rollers sit, back to back, in the same flow pan. With splitter
plates this arrangement gives four curtains.
Manifold flow pan: The chocolate is pumped directly from the main holding
tank through to a pressure manifold with multiple outlets across the width of the
wire belt. These outlets can generally be adjusted to fine tune chocolate
distribution across the width. The chocolate can drop onto a splitter plate, or the
manifold arrangement can be used in conjunction with a gravity flow pan to
improve chocolate spread across the width without resorting to a more expensive roller flow pan arrangement.
When designing a flow pan arrangement, the elimination of chocolate build-up
is a priority. This is minimised by ensuring that high flow rates of chocolate are
circulated from the main holding tank to the flow pan using the circulation pump.
The pipe from the pump to the flow pan is called the ‘riser’ pipe and this is typically
jacketed to maintain chocolate temper. It is usual to recirculate chocolate at rates
of between 10 and 18 times the ‘takeaway’, this being the final chocolate weight on
the end product after enrobing. The excess chocolate helps to form a complete
curtain and fill the bottoming bath via overflows at each side of the flow pan. The
excess from the bottoming bath then overflows to the sides of the wire belt circuit
and returns by gravity to the main holding tank.
The position of the flow pan along the wire belt within the enrober should be
adjustable within the limits of the riser pipe drop point and the chocolate overflow
geometry. With some products and configurations it may be beneficial, for best
performance, to position the chocolate curtains at a particular point on the surge.
The height of curtain is also generally adjustable. The centres must clear the flow
pans as they pass beneath on the wire belt. However, excessive drop and associated
curtain acceleration, can cause the chocolate in the curtain to thin and break-up,
creating gaps which will give variable coverage. The longer curtain will also have
a tendency to fold over and ripple which will create air bubbles.
Blowing
Following the chocolate application processes of bottoming and top coating
comes the chocolate removal process, where excess chocolate is methodically
removed from the centre to achieve the target pick-up weight without exposing
the centre. The first step in this process is blowing where the product passes
under an air curtain which is applied across the machine by a fabricated blower,
supplied with temperature conditioned air from a centrifugal fan mounted above
the product zone, as illustrated in Fig. 17.4. The curtain velocity, blower height
above product and blower angle are all adjusted to give the optimum chocolate
thickness on the top surface of the centre. The excess chocolate from the top
surface runs down the sides of the centre. In addition, the blower can give that
characteristic ripple on the top surface of many enrobed products. In fact, as we
will see later in the chapter, some enrobers have multiple blower systems, with
the first blower controlling chocolate removal and the second blower creating
the ripple if required.
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Enrobed and filled chocolate, confectionery and bakery products
Blower
Sha
ker
Fig. 17.4 Enrober blower unit.
Design considerations for blowers include:
• Maintenance of a consistent air velocity and air temperature across the width of
•
•
•
the wire band with pressure equalisation across the blower provided by ‘airflow’ baffles, twin or treble air feed ports from the fan, or perforated air
distribution plates; manufacturers aim to maintain a tolerance for blower jet
velocity across the width of ± 1%.
Some fragile products are better suited to a low velocity broader air jet.
Alternatively, some viscous chocolates can only be removed by using a high
velocity, narrow jet of air. The precise adjustment of the air slot or gap at the
bottom of the blower is therefore critical to achieving a satisfactory product.
The overall adjustment of air flow rate or quantity through the blower is best
effected through inverter speed regulation of the fan.
When high air velocities are used chocolate can be splashed upwards from the
top of the product or from the wire belt. These splashes of chocolate tend to
build up on the product zone access covers and become unsightly and unhygienic. They can also lead to poor performance due to lack of visibility when the
operator checks the machine. In this situation horizontal skirts are fitted to the
blower, on each side across the width, and just above the air outlet to prevent
splash. These should be easily removable for regular cleaning.
Shaking
The blower has removed excess chocolate from the top of the centre. The excess
chocolate from the sides of the centre now needs to be removed. This operation is
Manufacturing processes: enrobing
369
actioned by vibrating or shaking the product on the wire belt using a vertically
vibrating frame or shaker in contact with the underside of the belt. A shaker is
illustrated in Figs 17.4 and 17.8.
The shaker frame can be pivoted at one end and oscillated at the other end by a
mechanical cam or ratchet arrangement. By varying the cam drive motor speed, the
shaking frequency can be changed and the amplitude of shake can be set by a
simple mechanical stroke adjustment. Another technique is to mount the shaker
frame on flexible rubber mountings and attach an oscillating air motor to the frame.
Frequency and amplitude can be adjusted by varying supply air pressure and flow
and changing counter weights on the motor.
On the basis that tempered chocolate tends to be thixotropic and will only flow
when agitated, the more severe the oscillation of the shaker, the more the chocolate
will flow to the bottom of the product. The time allowed for shaking, as the centres
pass above the shaker frame, is critical for efficient chocolate removal.
Licking
Having blown excess chocolate from the top of the product and shaken down the
sides, we need to remove the excess from the bottom. This is achieved by one or
more ‘licking’ rollers, which can rotate in contact with the underside of the wire
belt either with or against the direction of travel. The rolls remove or strip excess
chocolate from the base of the centre by chocolate adhesion to the roll as it rotates
and the thickness of the bottom coverage can approximately correspond to the wire
diameter. The rollers are scraped such that they are kept clean for each revolution
and the chocolate removed then drops to the return system in the base of the
enrober.
Design considerations for licking rolls include:
• Number of rolls: One, two, or three rolls are generally used. An arrangement
•
•
•
with three licking rolls is illustrated in Fig. 17.5. Often the middle roll is running
against the belt direction and the outer two rolls are running with the belt. This
helps to smooth out imperfections by filling any cavities in the base of the centre
and removing any air bubbles, which could create leak paths to the centre. To
aid smoothing, a licking roll scraper can be backed off to leave a film of
chocolate permanently on one roll.
Roll speed: By increasing roll speed, more chocolate is removed. In many
enrobers all licking rolls have a common drive such that all roll speeds are
changed together. In a small number of cases, where bottom pick-up is critical,
individual licking rolls can be fitted with independent drives for individual
speed adjustment.
Heated scrapers: As chocolate is stripped off the licking rolls, build up can occur
on the scrapers and this can inhibit chocolate removal and create coating
inconsistencies, lane to lane, across the width. Scrapers are therefore heated to
overcome this problem.
Grooved and plain licking rolls: For maximum chocolate removal, the licking
rolls can be grooved such that the lateral joints or ‘knuckles’ of the wire belt sit
370
Enrobed and filled chocolate, confectionery and bakery products
Fig. 17.5 Licking rolls.
•
in the grooving to enable the cross wires of the belt to sit directly on the licking
roll. This reduces the gap between the product bottom and the roll circumference to the thickness of the wire. This is illustrated in Fig. 17.6. With plain
licking rolls the knuckles lift the cross wires off the roll circumference, thereby
reducing the ability to strip the chocolate. It is very common to see combinations
of grooved and plain rolls in simultaneous use on enrobing machines.
Wire band lifters: For greater flexibility, the wire belt can be lifted away from
the licking rolls to reduce the stripping effect if heavy bottoms are required for
certain centres. With this option, which is carefully calibrated, the enrober can
be made sufficiently flexible to handle a wide range of centres.
Anti-tailing
The centre, which is now fully coated with the correct weight of chocolate on the
top, sides and bottom, and with no bare patches or pin-holes, is now ready for
discharge to the conveyor band of the cooling tunnel where the chocolate will be
solidified prior to final packaging. This operation must be completed without
damaging the bottom coating and without leaving a ‘tail’ of chocolate trailing
behind the product on the cooler band. The tail is unsightly and increases giveaway. It can also break off in subsequent handling, potentially creating build up
and malfunction in the wrapping area and spoiling the wrapped product. Tail
formation is prevented by the ‘anti-tailer’ device, which comprises a high speed
rotating rod, generally between 3 mm and 8 mm diameter, which is positioned
between the wire belt discharge terminal roll and the in-feed nose piece of the
chocolate cooling tunnel. This arrangement is illustrated in Figs 17.7 and 17.8.
The rod, which generally runs in the reverse direction, flicks the trailing edge of
the bottom coating as it leaves the wire belt. This operation removes the tail and
gives a clean back edge for the coating on the centre as it completes the transfer to
Manufacturing processes: enrobing
2d
2d Belt height at knuckles
1d Belt height on cross wires
d
Wire belt
lateral joints
Plain roll – minimum
distance between
roll surface and
product = 2 wire
thicknesses
Groove roll – joint
in groove – lateral
wires in contact
with roll; one wire
thickness from
roll surface to
product
Fig. 17.6
Plain and grooved licking rolls.
371
372
Enrobed and filled chocolate, confectionery and bakery products
Enrober wire belt
Anti-tailer
Cooler belt
Driven terminal
roll
Heated supports
Fig. 17.7 Enrober anti-tailer.
Fig. 17.8
Enrober belt showing shaker, licking rolls and anti-tailer.
the band of the chocolate cooler. The direction of the rod can be reversed on most
enrobing machines if this is beneficial to performance. The rod is mounted in a
heated ‘V’ shaped block, which supports the rod, preventing deflection and
breakage, and provides a scraping action to keep the rod clean. Clips prevent the
rod from whipping and hold the rod in the ‘V’. The heating of the block maintains
chocolate liquidity and prevents build up and fouling of the anti-tailer operation.
Design considerations for licking rolls include:
Manufacturing processes: enrobing
373
• Transfer geometry: Generally speaking, for most products, best results are
•
•
obtained when the wire belt, the top diameter of the anti-tailer rod and the belt
surface at cooler in-feed are all at the same level. This alignment is critical and
fine adjustments for anti-tailer height and cooler in-feed nose-piece height
should be incorporated. These adjustments must allow for the fact that some
products for best performance may require a slightly different height configuration. It is very important, in set-up, to ensure that the rod does not make full
contact with the bottom of the coated centre as the centre passes over the rod.
Otherwise it will damage the bottom coverage. The gap between enrober
terminal roll, anti-tailer rod and in-feed nose is also critical for good transfer.
With small centres, the correct selection of radii for these three elements ensures
that the product transfers with minimum disturbance and misalignment to the
cooling tunnel. Again fine horizontal adjustment should be incorporated on
both anti-tailer and cooler nose piece. On some enrobers, where bottom transfer
is absolutely critical, the cooler nose, with all its adjustments, can be directly
attached to the enrober such that any small misalignment of the tunnel with the
enrober during installation will not affect the relationship between the key
components at enrober discharge.
Rod breakage: The rod can be vulnerable to breakage in the event of hardened
chocolate or centre debris getting caught up in the device. Modern enrobing
machines incorporate a quick change facility where the anti-tailer assembly and
its plug in drive motor can be quickly removed as a cartridge by the operator and
replaced with a spare, without a major line stoppage.
Clip design and breakage: The clips can also be damaged. They tend to wear
and, for the best results, should be positioned between product lanes to minimise
any product contact. Some manufacturers have utilised a magnetic mounting
block to eliminate the need for clips.
This concludes the summary of the consecutive operations performed on a coated
centre in a typical full coating enrober. We will now review other types of enrobing
machine.
17.2.2 Half-coating enrobers
These machines only coat the bottom of the product and are very common in the
biscuit industry. They therefore generally run at high speeds above 10 m min–1. The
operations performed are as follows:
• Bottoming: Chocolate flow rates through the bottoming bath are generally
much higher compared to a full coating enrober as chocolate take away from the
bath is high. The tempered chocolate feed to the bath can be more than double
the rate of the chocolate take away on the product to maintain stable temper
across the width of the surge. As this is the only chocolate applicator in the
enrober, the issues highlighted in the earlier section ‘Bottoming’ become more
critical. The chocolate surge length is longer compared to a full coating machine
as band speeds are faster.
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 17.9
Turn-over of half-coated (bottomed) biscuits.
• There is no chocolate curtain as top coverage is not required.
• There are therefore no blowers and, usually, no shakers, as sides are normally
short.
• Licking rolls: At least three licking rolls are normally provided which are
•
•
usually grooved. Many of the adjustments and features as described in the
section ‘Licking’ are incorporated, as these are the only means of controlling
chocolate pick-up weight. As pick-up weight consistency is key in this style of
machine, the feed pitch of biscuits across the band is fixed such that one biscuit
lane fits between the knuckles of the wire belt. No biscuit will therefore sit on
a knuckle and the best licking and best appearance will be maintained across the
bottom of all biscuits.
Transfer to cooling tunnel: With half-coated biscuits the style is often to turn the
biscuit over at the enrober exit such that the chocolate is face up when entering
the cooling tunnel. Alternatively, the product can be transferred, chocolate
down, into the cooling tunnel utilising an anti-tailer arrangement as described in
the section ‘Anti-tailing’. These two techniques give radically different appearances to the final product.
Biscuit turnover: This technique utilises the adhesive effects of the liquid
chocolate. It is illustrated in Fig. 17.9. A fast running, grooved ‘turnover roll’ is
positioned after the discharge terminal roll of the enrober, which picks up the
biscuit via its chocolate bottom. The chocolate basically sticks the biscuit to the
turnover roll as it rotates and ‘knock off’ bars break the joint once the biscuit is
inverted. The biscuit then drops below to a fast moving ‘take away’ conveyor,
which delivers the biscuits to the cooling tunnel in-feed. The high yield value of
the chocolate gives this product its characteristic, highly reflective, ‘chequer
Manufacturing processes: enrobing
•
375
board’ pattern with the cross line markings being created by the cross wires as
the product leaves the wire belt and with the longitudinal line markings forming
on the grooved turnover roll and during knock off. We should also remember
that the biscuit does not sit on the knuckles of the wire band, so preventing the
knuckle impression from spoiling the finished chocolate appearance.
For larger biscuits, a smaller supporting grooved roll may be incorporated
between the terminal roll and the turnover roll to ensure that the pattern is
maintained across the trailing edge of the biscuit.
Vertical adjustment of the supporting roll, the turnover roll and the take away
conveyor should be included for best operation. Roll scraper mounts should
also be heated to prevent chocolate build up. It is also advisable to include a
variable speed facility on the turnover roll drive to fine tune turnover efficiency.
In extreme cases, for very tight control, the supporting roll can also be
independently driven.
Chocolate down transfer: The chocolate finish now takes on the appearance of
the band surface in contact with the product. If the band is highly polished and
embossed with the brand name for example, an attractive product can be made.
17.2.3 Pre-bottoming enrobers
These machines again only coat the bottom of the product, but pre-bottomers
always precede a full coating enrober in the production line. The pre-bottomer
applies a first bottom coating to the centre, which is then cooled and set before the
full coating enrober. There are several reasons why this may be beneficial to the
end product:
• When a centre, such as a bar, is very heavy, it can sink through the chocolate to
•
•
•
the wire belt, leaving wire marks on the chocolate bottom of the finished
product.
With confectionery centres, such as fondant cremes, which are light in colour,
a single bottom coating of a fluid plain chocolate for example will be transparent
and will be prone to breakage after setting and in packaging. To provide a
visually appealing, robust, product with no transparency, two bottom coatings
will be required.
When centres have uneven bottoms with severe cavities, an initial bottoming
operation will help fill the cavities, and after bottom cooling, will provide a
flatter base for a more efficient bottom coating operation in the full coating
enrober.
When a centre has pressure points on its bottom, such as peanuts or crispies in
a confectionery bar, or the ring of a meniscus in an inverted moulded fondant
creme piece, after a single bottom coating and through the in-feed to the cooling
tunnel, while the chocolate base is still liquid, the centre can sink under its own
weight. The pressure points may then penetrate through the chocolate base
towards the band surface creating a potential leak path or a visual flaw. Prebottoming will ensure that the pressure points are removed before the second
bottoming operation in the full coating enrober.
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Enrobed and filled chocolate, confectionery and bakery products
• Very fragile centres can partially or totally collapse as they pass through the
curtains of a full coating enrober. By pre-bottoming the centre, the solidified
chocolate base can then hold the centre together through the subsequent full
coating operation.
Pre-bottomers comprise a bottoming bath, licking rolls and anti-tailing arrangement, but as the main coating operation is still to come, the range of features and
adjustments does not generally compare with full or half-coating enrobers unless
the machine is designed to handle a particularly difficult product.
In some operations, the specification of the chocolate applied at the prebottomer can be to a lower standard and cost compared to that applied in full
coating, as the first bottom will be totally covered in the final product. The
manufacturer must ensure that, in this situation, fat bloom, for example, does not
transfer from the first coating to the top coating. It should also be noted that a full
coating enrober can be converted to a pre-bottomer by simply removing the top
flow pans and diverting chocolate feed to the bottoming bath. This could be
appropriate, for example, in a flexible confectionery centre coating operation
where half coating or shoulder dipping is required on products such as toffee
centres.
We have now covered, in outline, the functionality of three of the most common
types of enrobing machine and we have described the basic operations that are
performed on the centres as they pass through the enrobing process. With this
understanding we will now discuss how we can optimise the preparation and
presentation of the centres to the enrober to achieve best coating efficiencies and
quality.
17.3 Centre preparation and presentation to the enrober
The layout of centres on the wire belt is critical to successful operation. There must
be sufficient gap between the lanes of product down the belt to ensure that the
chocolate curtain is able to wash down the sides of the centre without bridging. The
centres can also move as they pass over transfers and through the surge of
chocolate. If centres touch, bare patches can be created where no chocolate has
penetrated, or if touching occurs after coating then the centres can stick together on
solidification, creating doubles.
As a guide, confectionery units generally require between 10 and 13 mm
between products across the belt for good efficiencies. Bars with vertical walls, for
example, may require 15–17 mm. The gap between rows of product along the belt
is adjusted by varying the belt speed, according to the number of rows per minute
and the length of product. A typical longitudinal gap might be between 15 and
25 mm. Depending on the feed equipment before the enrober, some products may
not be presented to the depositor in regular rows across, but all products should be
in defined lanes along the plant. It is always good practice to fill the wire belt and
maximise chocolate take away rather than run the plant with large gaps on the belt.
Centre temperature before the enrober must be maintained below a preset level
Manufacturing processes: enrobing
377
to ensure that chocolate will not be detempered on contact and that the correct
cooling of the chocolate coating and the centre can take place in the final chocolate
cooler. A typical working centre temperature for good operation is 24 °C. Depending on chocolate specification, centres can be introduced at temperatures up to
27 °C but this will not apply to all products. Conversely if the centre temperature
is too cold, not only will unstable cocoa butter crystals be formed on contact, but
chocolate will also adhere more readily to the centre and target weights may be
exceeded. In extreme cases as the centre temperature climbs to ambient, during
chocolate cooling or in packaging, the centre could still be expanding after the
chocolate has set. The chocolate coating may then crack, or the centre may extrude
from a weak point in the coating such as an air bubble or a wire marked bottom.
With some centres, such as fragile foams, a low surface temperature can be a
requirement such that skinning can take place and the product can withstand the
applied heat and flow of the chocolate curtain without deformation. When centres
are overcooled for process reasons, we need to ensure that the surface temperature
of the centre is not below the dew point of the surrounding ambient conditions
between centre cooler exit and enrober entry. Condensation on the centre surface
will not only spoil those particular products but, in excess, can contaminate the
enrober circulation chocolate with a small quantity of water, so thickening and
spoiling the chocolate in retention.
Many centres, before coating, have loose ‘attachments’ which can give problems in the enrober if they drop away into the chocolate handling system or sit on
the wire belt. Severe enrober malfunction often results and bare patches or
deformed product can be created. These ‘attachments’ can include biscuit or cake
crumb, wafer dust, loose nuts or crispies or granules, tailings from a previous
depositing process, or even release agent from a previous process. It is best to
attempt to remove this debris prior to the enrober and this is usually done with a
wire belt in-feed conveyor with single or multi air blowers mounted above.
17.4
Chocolate application case study
The basic building blocks for an enrobing operation have been described in
Section 17.2. However, the range of products that can be enrobed in chocolate is
vast and many products require specific enrobing configurations for best results.
By illustrating the techniques used in a specific case study, where we focus on a
coated biscuit sandwich product, much can be learned.
• A typical arrangement for biscuit sandwiches is shown in Fig. 17.10. The biscuit
passes onto the surge and under what is called an ‘overhead wire belt’ which
pushes the biscuit into the chocolate in the surge and holds it in position as it
travels through the surge. A deep surge is required for a sandwich biscuit such
that, as the sandwich is pushed down, chocolate travels up the sides of the
sandwich and the air that is trapped in the indent or groove between the two
biscuit layers at the edge of the cream, shown in Fig. 17.11, is pushed upwards
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Enrobed and filled chocolate, confectionery and bakery products
Double roller flowpan
Double roller flowpan
Twin blower
Overhead wire belt
Direction of travel
Double surge roll
Blower
Shaker
Wire belt circuit
Fig. 17.10
Three licking rolls
and secondary wire
belt circuit
Arrangement for enrobing biscuit sandwiches.
Biscuit
Air bubbles
Cream layer
Chocolate coating
Fig. 17.11 Biscuit sandwiches showing where air can be trapped.
as the chocolate enters the groove. If the sandwich is allowed to float on the
surge and through the curtain, the curtain chocolate seals the air into the groove
temporarily and, during subsequent blowing, shaking and cooling, the air
breaks through to the outside as bubbles which create unsightly leak paths. The
overhead wire belt also provides the added advantage of maintaining centre
alignment through the surge.
As this type of product is particularly difficult to coat, following the first
curtains after the overhead wire belt, a blower is fitted to expose any flaws in the
coverage before the application process is repeated through a second flow pan
arrangement to ensure full coating. This is followed by a twin blower system to
maximise removal of chocolate from the top surface.
As these machines are generally heavily loaded with product, the wire
diameter of the belt is increased for load bearing purposes. Under normal
circumstances this would limit the effectiveness of the licking rolls as bottom
coverage cannot be less than the wire diameter. To overcome this issue, the
centres are transferred to a second, shorter, wire belt circuit with a smaller wire
diameter within the enrober such that efficient licking using a three-roll system
can take place.
Manufacturing processes: enrobing
379
17.5 Chocolate handling systems within the enrober
Up to now we have concentrated on the various coating operations that can be
performed directly on the centres as they pass through the enrober. In this section
we turn our attention to the methodology used in the movement of chocolate
through the enrobing system. This is a key area and the correct application of basic
principles is important if best quality is to be achieved. We should first note that the
chocolate tempering unit can be either ‘built in’ to the enrober system or can be
positioned externally. The ‘in-board’ arrangement, where the tempering unit,
generally in the form of a horizontal swept surface heat exchanger, is positioned
below the wire belt circuit, as shown in Fig 17.12, is generally specified for low
output lines. As output increases, the external arrangement is specified with
tempered chocolate being fed from a remote, or ‘out-board conventional tempering unit as shown in Fig. 17.13.
The theory and practice of tempering is covered elsewhere in this volume but
we should remember some basic points:
• Tempered chocolate is potentially in a dynamic state in the enrober, where, with
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time or with small temperature changes, the quantity of crystal nuclei present in
the liquid chocolate can increase or decrease, so affecting the rheological
properties of the mass in terms of liquid viscosity and yield value.
As these changes develop, the chocolate can become ‘overtempered or
‘undertempered’. ‘Overtempered’ chocolate will exhibit a higher viscosity and
yield value and precise control of pick-up weight by controlled chocolate
removal becomes more difficult. Potential for chocolate build up in the enrober
also increases, so reducing efficiency. ‘Undertempered’ chocolate will be more
fluid but final quality will be at risk, with potential for bloom, less gloss and a
softer set.
If the tempering unit, in-board or out-board, delivers chocolate with the correct
temper to the enrober tank system, a poor enrober design can destroy the temper
and deliver a poor quality end product.
Conversely, if the tempering unit delivers a poorly tempered chocolate to the
enrober tanks, then even the best of enrober designs cannot correct this
situation.
If correctly tempered chocolate is contaminated with poorly tempered chocolate within the enrober in varying amounts, then a stable coating condition will
never be achieved.
The enrober and its tempering unit must be capable of achieving and stabilising
the correct tempered chocolate condition at the flow pans and surge for normal
production or ‘day running’, starting from a detempered state or ‘night running’. This must be done with no chocolate take away on the product but, most
importantly, the condition must not be disturbed when production running
commences or when there are subsequent short stoppages in centre feed to the
enrober.
Good enrobing systems are designed with the above in mind.
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Enrobed and filled chocolate, confectionery and bakery products
Fig. 17.12
Fig. 17.13
‘In-board’ chocolate tempering unit.
Enrober with ‘out-board’ chocolate tempering unit.
Chocolate handling systems are built into the base of the enrober below the wire
belt. A typical arrangement with out-board tempering is shown in Fig. 17.14 and
a typical arrangement with in-board tempering is shown in Fig. 17.15. These
arrangements can vary, depending on the preferences of the machine supplier but
most manufacturers apply the same basic process.
Manufacturing processes: enrobing
381
17.5.1 Out-board tempering
This arrangement gives most flexibility and is used on high output lines where 24hour running is a requirement. The main tank, sometimes called the chocolate
holding tank, acts as a reservoir of tempered chocolate. This chocolate is pumped
to the flow pans and bottoming baths at a rate well in excess of the chocolate take
away of the product. The excess then returns to the main tank from the flow pan and
bottoming bath overflows. Chocolate is usually pumped around at a rate of
between 10 and 18 times maximum take away, subject to application. This ensures
there is sufficient chocolate to provide full curtains and an even surge across the
machine. The chocolate pump, as previously noted, is called the main circulation
pump or the riser pump and the pipe to the flow pans is called the riser pipe.
Tempered chocolate from the remote tempering unit is fed directly into the main
tank at a rate equivalent to the maximum take away of the product plus a 20–25%
coverage.
The main tank has a sweeping agitator, which not only keeps the bottom and
sides of the tank clear of chocolate build up but also ensures that the chocolate mass
is well mixed and homogeneous at all times. The tank is also jacketed with
temperature controlled water to maintain the chocolate temperature at the required
level. In an ideal situation, the chocolate temperature in the tank should be above
the melting point of unstable crystals but not so high that stable crystals will begin
to melt. However, as stable crystals will continue to develop with time in this
situation and to avoid overtempering, it can be beneficial in certain situations to
deliver a slightly reduced temper in the chocolate from the tempering unit to the
enrober to compensate. If, for any reason, the chocolate retention time is excessive,
then overtempering will result and the chocolate will become viscous, leading to
poor coverage and overweight. Retention time in the main tank is therefore a
critical parameter and this should be adjusted with the other parameters to give
optimum temper at the point of application to the product.
Clearly, at all times, there is an excess of chocolate flowing into the tank, which
must be returned to detempering outside the enrober. On the schematic shown in
Fig. 17.14, this is achieved with an adjustable overflow leading to a chocolate
return pump. The overflow can be positioned to give a longer or shorter residence
time in the main tank. Longer residence times are generally used with milk
chocolate to stabilise temper with the milk fats. Alternatively, the level of chocolate in the main tank can be controlled by a level probe system. The return pump
speed is then modulated to maintain a preset level.
This return system, together with the overfeed of freshly tempered chocolate,
stabilises temper conditions and the rheological properties of the tempered chocolate in the main tank. This provides what is often called a ‘state of equilibrium’,
which is a constant whether product is passing through the enrober or not.
Chocolate is always flowing through the tank at a fixed rate. As freshly tempered
chocolate enters the tank, an equivalent amount of chocolate is removed by a
combination of take away on the product, and excess pumped away by the return
pump, therefore maintaining the level. At full take away, 20–25% of the tempering unit feed rate still overflows to the return pump to ensure that the state of
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Enrobed and filled chocolate, confectionery and bakery products
Detempering
heat exchanger
Top up
of fresh
chocolate
Untempered
chocolate
storage tank
Adjustable
overflow
Tempering
unit pump
Out-board
tempering
unit
Drain
tray
Chocolate Main tank
Main circulation pump
return pump
Fig. 17.14 Enrober with out-board tempering unit.
equilibrium is maintained. This overflow also ensures that the return system is
continuously flushed. With no product take away, the full rate of tempered
chocolate will overflow and be passed through the return pump. The detempering
heat exchanger, which follows the return pump, must have sufficient capacity to
deseed this full rate. This ensures that the output from the out-board tempering unit
remains at a constant temper irrespective of enrober usage, which in turn stabilises
the temper in the enrober chocolate handling system before centres are passed
through on the wire belt. In addition, stability is also maintained in the event of a
short interruption to the feed of centres to the enrober when there is again no take
away.
17.5.2 Inboard tempering
There are many ways in which a tempering unit can be configured into the enrober.
The simplest arrangement, and the easiest to understand, is shown in Fig. 17.15.
The main tank of the enrober still functions as described above but the excess
chocolate passes from the overflow to a fully jacketed and stirred buffer tank,
fabricated with the main tank, but with jackets fed permanently with hot water to
maintain a detempered condition. Fresh untempered chocolate from storage is
pumped on demand into the buffer tank from a level probe signal to top up. The
tempering unit is positioned adjacent to the buffer tank and pumps chocolate from
the tank, again at a rate 20–25% in excess of maximum take away, through the
tempering unit heat exchanger and delivers tempered chocolate into the main tank
in the same way as with an out-board system. The tempering unit normally
comprises a ‘built in’ chocolate pump and a swept surface heat exchanger for
Manufacturing processes: enrobing
383
Adjustable
overflow
Drain tray
Top up of
fresh chocolate
Chocolate buffer
tank (detempered)
In-board
tempering unit
Main tank
(tempered)
Fig. 17.15
Main circulation
pump
Enrober with in-board tempering unit.
tempering. Good practice in tempering unit design should be followed, with
provision for good heat transfer via a screw transporting system with small
clearances to sweep the chocolate continually off the heat exchange surfaces.
Good mixing, together with a high shear rate, are incorporated to enable rapid
precrystallisation with stable crystals at the highest practical temperatures. On
some in-board units, a reheat zone is included prior to exit, to fine tune chocolate
temperature and viscosity. However, owing to space constraints, there is less
flexibility in terms of cooling profiles and shear application within an in-board
tempering unit compared with an out-board unit with a similar capacity.
As previously noted it is important that all the chocolate is detempered or
deseeded of crystals prior to the tempering process, otherwise the chocolate temper
at the outlet will be variable. This is often achieved by raising the return chocolate
temperature in the buffer tank. However the heat input needed to increase chocolate temperatures to between 40 °C and 45 °C prior to the tempering unit, particularly
when there is low take away and minimum warm, untempered, chocolate top up,
can lead to an overall increase in atmospheric temperatures within the enrober,
which can destabilise the chocolate conditions in the product zone. Some manufacturers, therefore, include an initial detempering section in the in-board tempering
unit to deseed before the tempering section. The heat required to deseed can then
be contained and reduced, the heat exchange in the detempering section being far
more efficient compared to the buffer tank.
17.5.3 The drain tray
This is a very important element in the chocolate handling system. It is shown in
both Figs 17.14 and 17.15. Before discussing the drain tray, we should quickly
384
Enrobed and filled chocolate, confectionery and bakery products
summarise the chocolate return paths from the wire belt area after coating and
chocolate removal. The excess chocolate routings from coating are generally as
follows:
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•
•
•
top flow pan overflow to the bottoming bath
bottoming bath overflow to the main tank
curtains to the surge and to the main tank
surge to roll removal to main tank.
These return paths usually end at the main tank, as the chocolate is maintained
at the correct state of temper through the application process and will not contaminate freshly tempered chocolate in the main tank. The volumes of chocolate
returning are also very high and this helps maintain consistent conditions.
The excess chocolate routings from the chocolate removal area are generally as
follows:
• wire belt in blower area to the drain tray
• wire belt in shaker area to the drain tray
• licking roll scrapers to the drain tray.
The volumes of chocolate returning from these areas are generally much lower
and with heated scrapers on the licking rolls, for example, the chocolate can be in
a partially detempered condition. In addition, the chocolate removal area can be
very long, necessitating a long drain tray, which may need to be heated to detemper
the chocolate partially and encourage flow down the tray.
Machine manufacturers have their own views on the geometry of the drain tray
and and its position in the system. From a theoretical perspective there is no doubt
that, for best running and optimum set up, the drain tray should pass chocolate
directly to the return pump, as illustrated in both Figs 17.14 and 17.15. This allows
all heating options to be used to prevent build up, without risking contamination of
main tank chocolate with untempered or lightly tempered chocolate.
Machines where drain tray chocolate is passed to the main tank need to be
carefully assessed for contamination issues or, conversely, for the approach taken
to eliminate build up if chocolate is not partially detempered in draining. In this
situation some manufacturers may use a secondary ‘drag chain’ system, with
scrapers or roller bars across the width of the tray. This system runs continuously
to free any chocolate build up and to drag the chocolate down the tray to the tank.
17.5.4 Compounds not requiring tempering
When enrobers are dedicated to compounds that do not require tempering, the
handling system can be much simpler. For the best results, the compound is cooled
to a predetermined temperature above the crystallisation temperature before being
transferred to the enrober. Only the main tank is included in the enrober and the
jackets are preset to the required compound temperature as above. All compound
not taken away on the product drains back to the main tank for recirculation. Fresh
compound is fed to the main tank on demand.
Manufacturing processes: enrobing
Fig. 17.16
385
Enrober hood.
17.6 Environmental and hygiene issues
17.6.1 Air conditions in the hood area
The enclosure or ‘hood’ covering the wire belt circuit protects the enrobing
process from outside contamination and provides a suitable air temperature
which is sufficiently warm to maintain chocolate fluidity, thereby preventing
premature set and build up, but not so warm that the chocolate begins to
detemper as it recirculates. Fig. 17.16 shows a typical hood system. The hood
design should provide good access and good visibility. Hinged clear plastic
access windows are the norm. The hood designs on some enrobing machines are
configured in very creative ways to meet these requirements and to give an
attractive visual appearance. Good hood illumination is important such that all
aspects of the enrobing operation can be clearly seen and monitored. The area
above the hood can be used for controls and normally houses the blower fans
and the hood ‘air heating’ unit based around a small recirculating air system
with electric heating.
17.6.2 Air conditions in the enrober room
For the best operation, temperatures between 24 °C and 27 °C are considered to be
the optimum for a general purpose enrobing area. This is sufficiently high to
prevent rapid cooling of chocolate at the peripheries of the hood zone but not so
high that chocolate detempering can occur with air ingress into the hood area. Care
should also be taken to ensure that no cold air draughts enter the enrober from
cooling tunnels in the line before or after the enrober.
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Enrobed and filled chocolate, confectionery and bakery products
17.6.3 Hygiene
Despite a wire band in-feed arrangement as described above, debris from centres,
such as nuts, crispies, and so on can be washed off the centre by the chocolate and
contaminate the chocolate handling system, particularly in the main tank. If
attention is not paid to this issue, the enrober operation can be rapidly impaired by
some products. In addition, now that cross contamination, with nuts for example,
has become such a major issue for end users, designers have paid particular
attention to the ease of cleanability of modern enrobing systems.
Mesh filters can be employed at one or more points in the chocolate system if
severe running problems caused by debris are likely:
• a static or vibrating mesh filter frame below the wire belt to catch all or some of
the chocolate prior to return to the main tank
• an enclosed duplex or scraped filter system in the riser pipe to protect the flow
pans from debris
• a similar enclosed filter system, after the return pump, to protect the outboard
tempering unit and isolate debris to the enrober.
• a simple open vibrating filter frame above the external chocolate storage tank,
which receives returned chocolate after passing through the deseeder.
Clearly the out-board tempering option provides the best opportunity for
removing debris from the enrober with the chocolate overfeed flushing particles
through on a continuous basis to clear tanks and pipes before being pumped out of
the system. With in-board tempering and no external chocolate return, the debris
remains trapped in the enrober.
Good access for cleaning is also required in the bottom tank area. A sump in the
main tank with easy side access is beneficial for collection and manual removal of
solid debris. Where downtime is to be kept to a minimum, enrobers can be designed
such that the complete bottom tank arrangement below the wire belt can be
removed on wheels after a predetermined running period and a second arrangement quickly installed for a rapid return to production while cleaning takes place
off line. This ‘removable tank’ enrober is illustrated in Fig. 17.17.
Finally some manufacturers produce enrobers which can be water washed. This
technology was originally developed for enrobing systems coating ice cream
centres where dairy hygiene standards are required. These are special machines
where great care must be taken in selection of the materials of construction to avoid
corrosion on water contact. Tanks are generally filled with hot water to cover the
wire belt and riser and return pumps are used for recirculation of water. Water
consumption is therefore kept to a minimum. A full drying system is also required
to ensure that all the water is evaporated prior to chocolate feed and there is no risk
of contamination. This drying system can utilise hood and blower air heating and
circulation systems, with jacket water set to high temperatures for the drying mode.
With some designs, removal of some parts, assemblies or internal pipe work may
still be required to ensure that cleaning and drying is efficiently implemented. The
duration of the clean down cycle would, typically, be between 90 minutes and 150
minutes with current designs, subject to machine size and complexity.
Manufacturing processes: enrobing
Fig. 17.17
387
Removable tank enrober.
17.6.4 Metal contamination
This is a particular issue with enrobing machines. Small metal pieces can pass into
the system from previous equipment in the line and the wire belt can be vulnerable
to damage and wire breakage. A magnetic metal trap is normally inserted in the
riser to protect the chocolate application system.
17.6.5 Wire belt life
Manufacturers of enrobing machines offer particular design features, which will
prolong wire belt life and keep the belt flat across the width through the
enrober.These include:
• driven terminal rollers rather than static nose pieces
• the largest diameter terminals commensurate with product size and good
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transfer; for small confectionery units these could be 6 mm diameter. For bars
or biscuits at faster speeds, roller diameters would generally be between 12 and
16 mm in diameter
grooved terminal rollers to support the cross wires around the turning point with
the larger diameter terminals
high build quality with no roller misalignment
air tensioning arrangements with tensioning roller mechanisms to facilitate
accurate and even tension settings side to side, and with belt breakage detection
wire band drive interlocks with chocolate and hood temperature to prevent a
cold start
specifying a wire belt with an edge design or ‘selvedge’ of the appropriate
strength and rigidity to suit the application, generally with either a single loop
or double loop.
388
Enrobed and filled chocolate, confectionery and bakery products
17.6.6 Chocolate changeover
When, for example white, milk and dark chocolate-coated products are to be
produced on a line, the enrobing system needs to be cleared, as much as is possible,
of the previous chocolate before recharging. There are many ways in which this
can be carried out depending on the design of the enrober:
• The simplest technique is to start the production cycle with white and, at the
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change, drain out the excess via the return pump and appropriate drain valves
before recharging with milk. The process is repeated in changing from milk to
dark. Finally the residual dark is cleared by flushing through with either a small
charge of white or cocoa butter which, when contaminated with dark, is then
used elsewhere.
Design features can be incorporated into an enrober to reduce cross contamination at change over. The drives to the in-board tempering unit screw agitators
can be made reversible to clear chocolate from the tube and circulation pump
drives can be made reversible to clear riser pipes. Hot air application devices can
be incorporated rapidly to heat and melt out areas where chocolate build up is
prevalent. Jacket water set points are raised to assist in melting.
Chocolate contamination can also be reduced by the specification of an enrober
with a removable tank. Additional tank assemblies can then be dedicated to each
chocolate colour.
As noted above, a water washing option might be considered where any
contamination is unacceptable. This would be necessary, for example, if a
compound were to replace a chocolate in a production sequence.
In certain situations it may be beneficial to consider a dual enrobing system, where
products can be enrobed with two chocolates simultaneously, each chocolate
being processed on one half width of the machine. Chocolate handling systems
are totally separate for each chocolate and two wire belt circuits are used.
17.7 Ancillary equipment
17.7.1 Decorating devices
These are generally ‘stand alone’ systems positioned above the licking roll area, or
between licking and detailing, or in some cases, on a dedicated unit following the
enrober, above the chocolate cooler in-feed for example. They take many forms:
• Simple static marking devices, which contact and ‘smear’ or ‘scrape’ the top
•
•
coating of the product as it passes underneath on the wire belt, creating a
chocolate pattern on the top surface. A chocolate with a medium to high yield
value is required such that the chocolate stands up after marking.
Rotary mesh cages, discs, or grooved rollers, which rotate in contact with the top
of the product to create unique patterns.
Moving nozzle decorators where separately tempered chocolate is pumped to a
series of nozzles mounted on moveable bars positioned across the top of the
products as they pass below. The nozzle bar movement can be profiled to give
Manufacturing processes: enrobing
Fig. 17.18
389
Bypass conveyor.
an assortment of different patterns on the chocolate surface, such as single loop,
double loop, on the top and the sides of the centre. The decorating chocolate can
be a different colour from the full coating chocolate for contrast. Moving nozzle
decorators can also be used to apply decoration to uncoated top surfaces on halfcoated or shoulder-dipped products.
17.7.2 Bypass conveyors
On flexible lines, not all products are enrobed. In fact from an enrobing perspective
it is often detrimental to use the wire belt to transport uncoated product. The belt
becomes dry and debris can interfere with the wire band circuit and enter the
chocolate handling system below. Most manufacturers offer a bypass conveyor
option, which can be extended either through the hood, as illustrated in Fig. 17.18,
following removal of flow pans and blowers, or routed over the top of the hood
where space permits. Some enrobing systems are portable and can be removed
from the line and replaced with a standard transport conveyor. This can be a
manual operation or the repositioning can be mechanised with a rail or hover pad
system and with articulated chocolate pipework connections.
17.7.3 Shoulder dipping attachment
This addition is required when chocolate needs to be applied to the bottom of the
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Enrobed and filled chocolate, confectionery and bakery products
centre and to all or part of the sides only. A plain roller or ‘depressing roll’ is
positioned above the surge and the clearance above the chocolate is set precisely
to depress the piece to a given depth in the surge to cover the required area. The
attachment can be fitted to a full coating enrober where top flow pans are disabled
or to a prebottomer. The depressing roll is driven at the same peripheral speed as
the wire belt and is usually scraped.
17.8 Typical operating parameters
These are intended as a rough guide only to give the reader some idea of
quantitative data so that performance can be compared. In practice, parameters will
vary depending on the chocolate used, the enrober configuration and the end
product:
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Typical chocolate temperature at enrober entry: milk, 28 °C
Typical chocolate temperature at enrober entry: plain, 29 °C
Chocolate temperature in main tank: milk, 29.5 °C
Chocolate temperature in main tank: plain, 30.5 °C
Main tank retention time: milk, 15–25 min
Main tank retention time: plain: 8–15 min
Typical wire belt speed range, units, 2–5 m min–1
Typical wire belt speed range, biscuits, 5–26 m min–1
Typical wire belt speed range, bars, 2–15 m min–1
Standard nominal wire belt widths: 600, 800, 1000, 1200, 1400, 1500 and
1800 mm.
Typical chocolate surge depths: 6–15 mm
Typical maximum chocolate take away: 1.6 kg m–2 of belt for full coating; 0.8
kg m–2 of belt for half coating
Chocolate recirculation to take away ratio: 10:1 up to 18:1
Tempered chocolate feed to take away ratio: 1.25:1.00 full coat; 1.60:1.00 half
coat
Wire diameters: 1.0 mm and 1.2 mm
Blower air temperatures: 24–27 °C
Blower air humidity: 35–40% relative humidity
Overhead wire belt depression time: 4 s
Minimum time required for chocolate removal: 10 s.
17.9 Faults and remedies
17.9.1 Chocolate has lost temper and is dull or soft on the coated product
after cooling
• Remove coated samples at enrober discharge and slowly cool samples in
wrapping room ambient until set. If the chocolate sets with good, stable gloss
Manufacturing processes: enrobing
•
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391
then focus trouble shooting efforts on the cooling tunnel. If temper is still poor,
focus on the enrober and tempering unit.
Take temper or solidification curves with tempered chocolate samples from the
in-feed to the enrober main tank from the tempering unit, and from the chocolate
in the main tank, the curtains and the surge.
If chocolate is not correctly tempered at the enrober in-feed then we must
investigate the tempering unit and the chocolate condition at its in-feed. A
sample taken at the tempering unit in-feed should show no temper on the curve.
If the chocolate is being partially detempered in the chocolate handling system
of the enrober, we must check the following:
• Main tank and riser water jacket temperatures. Are they too high? Best
results are achieved with jacket temperatures just under chocolate temperature.
• Main tank retention time. Is this too low to maintain stable crystals? Level
setting is too low or solid chocolate build up is reducing retention time.
Increase level and/or check for build up.
• Shear heat, from an overheating circulation pump for example. Is the
tempered chocolate being warmed as it passes through the system?
• High hood or blower air temperatures. These can raise ambient temperatures
in the enrober and warm the tempered chocolate. These can be caused by
incorrect settings or, for enrobers with in-board tempering and a detempering
tank below, heat from the detempered chocolate and the tank jackets can
raise surrounding air temperatures.
If the chocolate is well tempered in the application system but loses temper on
the centre through the chocolate removal then check the following:
• Centre temperature. If this is too warm then heat will dissipate into the
chocolate.
• Blower air and hood air temperatures. See above.
17.9.2 Chocolate pick-up is overweight
• Identify if this variation is a constant across the width and over time, or is pickup variable, lane by lane, or minute by minute?
• Methodically measure centre weight and size to ensure that overweights are not
•
•
caused by centre variations. We should note that as the centre surface area
increases then, inherently, we have more chocolate pick-up.
If variation is a constant, first check for overtempering on curtains and surge or
for any decrease in chocolate temperature. Has retention time in the main tank
increased for some reason? If the temper is constant, then inspect the cooled
chocolate thickness around the centre and increase the blower air velocity,
shaker speed or licking roll speeds to suit.
If pick-up weight is variable across the width, we should carefully check widthdependent variables such as distribution of chocolate at the curtain and on the
surge, blower velocity variation across the width, uniformity of shaking, licking
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roll and scraper alignment, and the flatness of the wire belt as it sits on shaker,
licking rolls and band support and terminal rolls.
If pick-up weight is varying with time, check for similar variations in temper,
hood temperature or centre weight/dimensions.
17.9.3 Centres float in the enrober is causing touching and doubles
• Reduce quantity of chocolate in the surge.
• Reduce quantity of chocolate in the curtain.
• Move the curtain position downstream from the surge. Agitation from the
falling curtain when applied to centres floating through on the surge can
misalign centres.
17.9.4 Chocolate feet on the cooled product
• These can occur when chocolate flows down the sides of the product after
•
•
enrobing. It is common with compounds, which can be more fluid compared to
chocolate. The problem is generally overcome by increasing shaker agitation to
clear the sides of excess before the enrober exit.
Feet can also occur with heavy centres and fluid chocolates, where the bottom
coating after licking is thick. On cooler entry, before the chocolate sets, the
centre sinks through the bottom coating, squeezing some chocolate to the sides
and so creating feet. This problem can be magnified if centre movement at the
cooler in-feed is created by cooler band vibration, for example. Increasing the
licking roll speed to remove excess bottom chocolate generally clears this
problem.
Slippage of coated centre on the surface of the chocolate cooler conveyor belt
at transfer across the anti-tailer will cause the bottom to smear onto the
conveyor, creating thin chocolate webs which, when set, will disfigure the
product or chip off, creating waste, underweights and wrapping problems. The
line speeds, enrober wire belt and cooler belt should be exactly matched and
generally, for the best results, the top of the wire belt, the top diameter of the
licking roll and the top surface of the cooler belt should be at the same level.
17.9.5 Poor quality bottom coverage after transfer to the cooler belt
• This usually takes the form of cross-wire marking on the bottom of the coated
product with, in some instances, bare patches.
• These can be caused by the polygonal effect of the wire belt as it passes around
the discharge terminal if the terminal is not grooved and the wire belt is a ‘U’
section as opposed to a ‘W’ section. This is illustrated in Fig. 17.19. The cross
wires rise up and penetrate the bottom coating as the belt passes around the
terminal.
Manufacturing processes: enrobing
393
Right
Wrong
Fig. 17.19
Correct and incorrect wire belt designs to minimise cross-wire marking on
product bases.
• Check that the anti-tailer is not distorted or rotating eccentrically and that clips
are not broken.
• If the centre is very soft and, as it passes through the enrober, begins to deform
•
or sag through the wire belt, then the bottom pick-up will be heavier in the
grooves created by the wire and will be lighter on the high points, which become
the pressure points on the cooler belt. The chocolate is squeezed out from the
pressure points, creating a striping effect on the chocolate bottom. Can the
centre be further cooled to firm up before enrobing or can the chocolate be
thickened to reduce flow on the cooler belt?
If the chocolate is overtempered and yield value is increased, the licking rolls
can partially strip off a portion of the bottom coating, particularly if the centre
has a loose coating of dust or if a release agent has been applied to the centre in
a previous process. Again, check for increase in chocolate temper, decrease in
chocolate temperatures and any increase in main tank retention time.
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17.10 Future trends
17.10.1 Longer running times
End users expect modern enrobing machines to run consistently for long periods
without the need for melt down and restart. The techniques used in the enrober to
reduce chocolate build up have been reviewed above and we can expect further
improvements in heating, agitation and control of temper as designs are improved.
We will also see improvements in wire belt materials and wire belt circuit design
for longer life.
17.10.2 Hygiene
Manufacturers of enrobing machines are continually improving both the internal
and external hygiene aspects of their designs. We saw in Section 17.6 how
chocolate changeover and cleaning can be improved with washdown, for example.
We should expect to see this aspect of operation receiving even more attention
from end users in the future, particularly with the focus on avoiding cross
contamination with nuts, for example.
17.10.3 Automation and flexibility
When products are changed on a regular basis, or when a high level of adjustment accuracy is required for best product performance, end users require
repeatability in the various aspects of enrober set up: retention time, speeds,
temperatures, and so on. These adjustments can be automated and directly
controlled for particular products from ‘recipes’ which can be set up and then
selected on demand for particular products by the operator on the control panel.
This can speed up changeover and eliminate some of the human error involved
in set up.
The actual operation or sequence of chocolate changeover can be automated
within the enrober, in combination with the chocolate feed and chocolate tempering equipment. With automated valving and pump actuation and with operator
prompts, the sequence can be programmed to minimise changeover time and cross
contamination. As controls continue to become more extensive, we will continue
to see the operator interface on most of the larger enrobing machines mounted on
a remote control panel or on a pod, rather than in the hood.
17.10.4 Energy saving
As with all processes, this aspect is now being given serious attention by end users.
It is important to ensure that hot water jackets, for example, are designed with
minimum volume, commensurate with functionality. High efficiency motors
should be used if possible. Hood designs should minimise air loss to ambient
atmosphere.
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395
17.10.5 Scrap monitoring and giveaway
Web cams are being increasingly used at the enrober to enable remote, visual
monitoring of performance. On line check weighing of centres in, and coated
centres out, to determine average pick-up weight is now a realistic option on the
higher output lines. Improvements in precision and consistency in operational
adjustments will be seen which will lead to greater accuracy.
17.10.6 Microaeration
Several manufacturers now offer the option of enrobing with microaerated chocolate that is, chocolate with occluded small air bubbles. If chocolate is aerated to a
level of, say 10%, then for the same volume coverage of chocolate, a 10% saving
can be achieved in chocolate usage. The aeration is achieved by injecting a gas
such as nitrogen into the chocolate and passing the mass through an aerating head,
which provides a high level of shear and mixing without loss of chocolate temper.
Injection and head back pressures are maintained up to the application point to
minimise deaeration on pressure release.
17.10.7 ‘In-line’ temper measurement
To be able to measure, inline chocolate temper in the riser pipe, just prior to
chocolate application, would deliver great benefits to the end user. Major steps
have been taken in recent years in designing a viable and reliable sampling
arrangement, eliminating the human input in sample collection and preparation. To
relate temper reading, over a period of time, to the other enrober recipe parameters
such as chocolate temperature, band speed, hood temperature, and so on, in a
graphical format can be a significant trouble shooting/quality control aid.
17.10.8 Machine size
Enrobing machines will continue to grow wider and longer as economies of scale
dictate that production is rationalised onto a smaller number of higher output lines.
As end users reduce fat content for better economics, more time, and therefore
length, is required to remove the more viscous chocolates to maintain pick-up
weight. Enrobers in excess of 2.0 m wide can now be seen on many sites and length
has increased beyond 4.0 m for the large sophisticated high speed enrobing
systems. These requirements present the enrober designer with real challenges in
terms of performance and product consistency at higher outputs.
I hope that, having read this chapter, the reader now has some insight into the
various issues that must be considered when designing and operating a successful
enrobing operation.
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17.11 Sources of further information and advice
There are many books and articles which touch on enrobing technologies. A very
good introduction in English to chocolate enrobing, dated now in detail, but
fundamentally sound, wide ranging and still a favourite, is provided in four papers
given in the Pennsylvania Manufacturing Confectioners Association (PMCA)
proceedings and presented at the 42nd production conference in 1988 in Hershey,
Pennsylvania.
• ‘Coating machines and bottomers’ by Heinz Schremmer, Sollich, Germany.
• ‘Tempering systems, inboard/outboard’ by Dr Phil Niccolls, Baker Perkins,
UK.
• ‘Center preparation’ by Tom Myers, See’s Candies, USA.
• ‘Enrobing Technology’ by Maurice Jeffery, Jeffery Associates, USA.
General reference books giving good background to general chocolate manufacture and its application, including enrobing are:
• Industrial Chocolate Manufacture and Use, 4th edition, edited by Stephen T.
Beckett and published by Wiley–Blackwell, Oxford, 2009.
• Making Chocolates in the Factory, by Robert Whitefield and published by
Kennedy Publications Ltd, Essex, UK, 2005.
17.12 Acknowledgements
I am indebted to my own company, Baker Perkins Ltd, for their permission to use
photographs and diagrams from our range of chocolate enrobing equipment both
past and present.
18
Manufacturing processes: chocolate
panning and inclusions
G. Geschwindner and H. Drouven, Drouven & Fabry GmbH,
Germany
Abstract: This chapter provides information about chocolate and compound panning of
different centre types as well as descriptions of traditional and modern panning processes. Besides providing details of all the necessary process steps, the focus is on the
process conditions that should be kept to in order to obtain a high-quality product. Here,
the processes of ‘engumming’ or ‘precoating’ play a decisive role. Other important
aspects are the coating techniques and the polishing agents, both of which can help to
save time if the appropriate ones are chosen. Future trends will be to develop time and
cost saving alternatives for both.
Key words: belt coater, centres, chocolate panning, chocolate spraying system, coating
pan, coating techniques, compound panning, drying powder, engumming, future trends,
polishing, precoating, saving time and costs, sealing, stabilization, weight increase.
18.1 Introduction
Dragees or panned goods are becoming more and more important in the confectionery and chocolate industry. The reasons for this are, among others, that the
consumer always wants new product ideas and, above all, a combination of
different textures and flavours. A large variety of chocolate panned goods is on the
market and they might be polished, dusted with cocoa powder or icing sugar or
have an additional sugar coating layer. Chocolate panned goods are also used as
inclusions by the ice cream or bakery industry. This chapter deals with a description of the working process for chocolate panned goods, beginning with the
different centre types, up to the finished product, which can either be polished or
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enrobed. Furthermore, the different coating techniques are explained and advice is
given on how to update existing plants.
18.2 Centres and raw materials
18.2.1 Centres
Basically, all kinds of centres (kernels) can be panned. The only limiting factor
may be the form and stability of the kernels. The kernels must not have a flat or
shrunken side and they should have a certain stability in order to avoid deformation
or cracking in the coating pan. The following is a more detailed description of the
different centre types.
Confectionery centres
In reality, there is no restriction on the usage of confectionery centres as long as
they can be technologically processed. Nowadays, there is a large variety of
chocolate panned confectionery centres in the market:
•
•
•
•
•
•
•
•
•
•
soft caramels, toffees, fudge
gums and jellies
marshmallows, crystallized and non-crystallized
fondant
sugar crust liqueurs
extruded liquorice
chocolates
nougat
croquant
marzipan.
The production techniques of these confectionery centres are based, for example, on mogul technology, stamping, lamination, extrusion, giving the advantage
that the kernels are very homogeneous in view of dimension, size and form. This
is important for the subsequent coating process and simplifies production. Attention must be paid to ensure that the kernel has a texture that is as solid as possible,
that is, that it cannot break or deform during coating and that there are no flat sides,
as otherwise the products might stick to one another. Another important parameter
is the recipe of the centre.
Centres with a high residual moisture content such as gums and jellies or toffees
might have the tendency to release humidity leading to sugar bloom after some
time. Furthermore, for centres based on lauric fatty acids there is the tendency for
these fatty acids to migrate into the chocolate panning layer. Incompatibility with
the cocoa butter can result in fat bloom and a softening of the chocolate coating.
The final products lose their gloss, soften and get a grey veil of fat bloom. This can
also happen if nut oils are released from panned nut centres.
Manufacturing processes: chocolate panning and inclusions
399
Natural centres
Most of the coated products that can be found in the market are made with natural
centres. The main advantage is that there is no additional machinery necessary for
their production. The following types can be used:
• dry nuts like hazelnuts, almonds, peanuts, pistachios, macadamia nuts, pecan
nuts, cashew nuts, pumpkin kernels
• roasted coffee or cocoa beans
• dried fruits like raisins, orange peel, cranberries
• candied fruits.
Unlike confectionery centres, these natural products are subject to fluctuations in size, oil or fat content, residual humidity and surface condition.
However, it is important that the size used is as uniform as possible. Therefore,
a calibration unit and an additional cleaning unit are recommended. The kernel’s
form is important as well because very flat shaped kernels might lead to cohesions. For dried fruits the biggest problems are the oil and water content which
might lead to problems during panning, either because the chocolate adheres
badly to the kernel or because the oil mixes with the chocolate and the latter
does not solidify sufficiently during the subsequent chocolate coating process.
This increases the danger of stickiness or, later on, the danger of oil or moisture
migration. Furthermore, the chocolate’s solidity is decreased, which might lead
to problems in the polishing process.
Cereal centres and bakery products
An area which is of growing interest are chocolate-coated cereals and bakery
goods. This area is interesting as it is about snack products which are light and have
a high volume with low weight. Examples of cereal centres are:
• puffed cereals
• flakes, such as cornflakes
• biscuits
Extruded products are especially suitable for panning as they can be produced
in a round or oval form and in different sizes which are relatively easy to coat.
Products such as cornflakes which are flat and have an uneven surface can be
chocolate coated but then a spraying system is recommended. This system sprays
the chocolate onto the products without cohesion and guarantees a closed surface.
Biscuits always have a flat side owing to the production process. In this case also,
chocolate application by spraying is necessary in order to avoid as many cohesions
as possible.
For biscuits or bakery goods, a pretreatment or even engumming (see section
below) with an aqueous solution is impossible as the humidity of this will soften
the characteristic crunchy structure. Attention must also be paid to ensure that the
chocolate coating is applied as evenly as possible and without holes in order to
avoid subsequent softening of the cereals by moisture migration.
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18.3 Preparation of the centres: precoating
18.3.1 Means of precoating, stabilization, isolation of centres
Precoating means the application of a separate coating layer between the centre
and the panning layers. Precoating is also called engumming, isolation and
stabilization of the centre and serves to prepare the kernels for the real panning
process. Precoating can have different functions, depending on the type and
formulation of the centre, the technical equipment and the raw materials at the
manufacturer’s disposal. During precoating the centre is humidified with an
aqueous hydrocolloidal solution and, after distribution of the solution, it is dusted
with a drying powder so that a homogeneous and stable layer is built up, fulfilling
the corresponding requirements and functions. Besides quality improvement, the
amount of rework and the total panning process time can be reduced.
Engumming
Engumming means the application of a solution forming a film between the centre
and panning layer by means of a hydrocolloid. Thus, the adhesion between kernel
and chocolate panning layer is increased as the engumming layer forms a homogeneous film on the centre’s surface. The surface is smoothed and the application of
a homogeneous dispersion of chocolate is guaranteed. Edges or cones, such as in
an almond, are coated and the adhesion of chocolate to almond is increased.
Stabilization
Stabilization is of great importance for flexible and fragile centres such as gums
and jellies or sugar crust liqueurs. For these centre types, the precoating’s main aim
is to avoid deformation or breaking. Besides the hydrocolloid, a high proportion of
sugar is added so that the sugar crystallizes and forms a solid and stable surface. In
general, the quantity of solution applied and the quantity of dusting powder is
higher (by at least 10%) for normal engumming.
Isolation of centres
Isolation of centres means the formation of a migration barrier in order to avoid an
exchange of oil and moisture from the kernel to the panning layer and vice versa.
The phenomena of sugar or fat bloom can be observed in chocolate panned goods.
In the case of nuts, a good engumming delays the formation of bloom and increases
the product’s shelf life by delaying the nuts’ rancidity and the softening of
chocolate caused by the incompatibility of the fat in the kernel with the fat in the
coating layer.
Weight increase
Another economic advantage is that, by precoating, the final product weight is
increased. There is greater interest in finding potential ways to save costs,
particularly in times of increasing prices of raw materials such as dry fruits and
chocolate and, in this respect, precoating helps with quality improvement and
product protection. By adapting the engumming solution and dusting powder, the
Manufacturing processes: chocolate panning and inclusions
401
product weight can be increased by 10–20%. This percentage can then be saved on
kernel or chocolate without a reduction in final weight or volume. On the other
hand, attention must be paid to the sensory properties of the final product.
18.3.2 Precoating solution
The precoating solution should have the following characteristics:
•
•
•
•
film-forming property
adhesion power
both lipophilic and hydrophilic properties
variable viscosity depending on temperature and total solids.
Therefore, the following hydrocolloids are suitable:
•
•
•
•
gum arabic
gelatine
modified starches
maltodextrin.
Gum arabic is the hydrocolloid that is mostly used for this application. It forms
a thin, stable and, at the same time, flexible film, has good adhesion properties and
thus increases protection against breaking product edges or cones. Gum arabic also
has the function of an emulsifier with lipophilic and hydrophilic properties. The
solution’s viscosities can be varied and gum arabic can both be used for sugarbased and sugar-free applications.
Gelatine forms flexible and reversible films and has a high adhesion power. It
provides the highest protection against exudation of moisture. However, gelatine
is of animal origin and there is a general tendency is to avoid products of animal
origin in confectionery products. The solution must be kept warm and also be
applied in a warm condition, otherwise it gels prematurely and might increase
viscosity.
Modified starches and maltodextrin: There are different techniques for the
modification of starches. Among these are starches that are suitable for precoating
as they can be modified to give film-forming properties with high adhesion power.
Another advantage of these hydrocolloids is that maltodextrin and, partly also,
modified starch are cheaper than gum arabic and gelatine. On the other hand, in
choosing the starch you must ensure that it fulfills the same functions and provides
the same properties. For most of the starches it must be checked whether they are
also suitable for sugar-free application.
Besides the choice of the hydrocolloid, the total solids of the solution are
important. Depending on the hydrocolloid type, a certain water quantity must be
added in order to dissolve the hydrocolloid. The gelatine level used is, for example,
0.5–2% in water. This means that the solution contains too much water which then
has a negative influence on the kernel (absorption of moisture). Furthermore, you
would have to apply a very high quantity of dusting powder which would eventually
not adhere completely after the drying phase. Thus, the total solids of nearly all
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hydrocolloidal solutions are increased by the addition of sugar and/or glucose syrup.
The total solids of the engumming solution should be between 40 and 60%.
To adjust the total solids the centre’s absorption speed is decisive, that is,
whether the centre has the tendency to take up moisture from the solution or not.
Other factors are the nature of the centre’s surface, particularly whether it has an
irregular surface. In this case, the total solids must be adapted for this so that these
irregularities are also filled up. The centre’s form determines the solution’s
adhesion properties. The higher the total solids, the higher is the danger of
cohesions. Finally, the mechanical and heat stability of the centres determine the
solution’s temperature. Specific surface and required weight increase determine
the quantity of solution to be applied. In general the quantity is between 3 and
15 cm3 kg–1 of centres.
For the engumming process it is important that centres and precoating solution
are at the same temperature and that the solution always has the same total solids.
The centres can be precoated either in cold or in warm conditions, however, the
precoating solution’s temperature must always be adapted accordingly. In the case
of warm or hot nuts, for instance after roasting, there is a high amount of humidity
released. The solution must spread homogeneously over the centre over a period of
approximately 1–2 minutes. Subsequently, the surface is dusted with drying
powder before the products become too sticky.
18.3.3 Drying powder for precoating
After dispersion of the precoating solution, it is important to bind its humidity and
therefore icing sugar is mostly used as the dusting powder. However, sucrose
might also be used in different particle sizes. The important point is that the
precoating solution must have spread well before the dusting powder is evenly
dispersed, allowing the binding of moisture. The quantity of drying powder used
depends on the quantity of solution, its composition and the specific surface of the
kernel. As soon as the surface is dry, the precoated centres must be stored
intermediately so that they can dry further. The intermediate storage time should be
between 6 and 24 hours depending on room conditions (temperature and relative
humidity). The optimal conditions are 20–25 °C and < 45% relative humidity.
For dusting, mixtures of gum arabic and sucrose or starches with sucrose can
also be used. These both dry faster and bind moisture. Here, however, attention
must be paid to ensure that the powder mixture is mixed homogeneously and has
an uniform particle size in order to avoid a demixing and thus achieve a homogeneous coating layer.
Nowadays, some of the engumming agents in the market allow direct chocolate
panning after precoating. Thus, intermediate storage is saved and continuous
processing is possible.
18.3.4 Advantages and disadvantages of precoating
Precoating is a process that improves the product quality because it extends the
Manufacturing processes: chocolate panning and inclusions
403
product’s shelf life by retardation of migration phenomena such as fat bloom and
sugar bloom. It protects and stabilizes the centre during the panning process and
reduces the process time, cracking and rework. Furthermore, for some products,
development work becomes possible by precoating only. Precoating protects
cones and edges against abrasion and can make the panning process easier.
Despite all these advantages, many companies are working without the
precoating process. The reason is that it is a discontinous process, so there is a
higher demand for storage and expenditure of labour. Many automatic plants were
not equipped with corresponding dosing devices. Furthermore, handling of extra
raw materials and solutions is necessary engendering additional costs. This is the
reason for some companies to accept a reduced quality and save this process step.
18.4 Panning process
In general, panning consists of following process steps:
• pretreatment of the centre
• chocolate/compound panning
• polishing and sealing.
The pretreatment of the centres has already been described and this process step
is not obligatory.
The second process step is coating with chocolate or compound and it is in
general a molten fat-based mass that is applied to the centres either manually,
automatically or by spraying system. The molten mass solidifies under cold air and
forms a closed and homogeneous layer on the centre’s surface.
18.4.1 Chocolate panning
For chocolate panning, all chocolate types can be used: bitter, milk and white
chocolate. The chocolate should have a total fat content between 28 and 35%.
Here, milk solids and fat content play a decisive role. The quantity of milk
components influences the viscosity and the proportion of cocoa butter to milk fat
influences the hardness of the final product and consequently the polishing process
as well. The characteristics of a chocolate panned product can be described as
follows.
The residual humidity of the chocolate in the panning layer should be below
1%. A higher residual humidity increases the chocolate’s viscosity and causes
problems for its dispersion which can consequently lead to the products sticking
together. The chocolate is applied in between 15 and 25 layers and the total
processing time is between 60 and 120 minutes depending on the centre and
chocolate type as well as the applied quantity and available machinery. This means
that 3–4 minutes per layer are needed.
For each layer, the chocolate quantity must be sufficient to fill up the surface. If
too much chocolate is applied, the products stick to one another and can only be
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Enrobed and filled chocolate, confectionery and bakery products
separated either with difficulty or not at all. The temperature of the air supply is
important and should range between 14 and 16 °C with a relative humidity of
maximum 45%. After every application the chocolate must disperse well on the
surface. Subsequently cold air is used so that the chocolate solidifies. Air speed and
quantity must be sufficient and depend on the centre quantity. In general, the air
quantity is about 10 m3 kg–1 at the centre and the air speed is 10 m s–1.
During the panning process, heat is produced by friction. Depending on the
centres’ tare weight, friction heat is produced which must be removed by the cold
air supply. As soon as the entire quantity of chocolate has been applied to the
centres, the smoothing process follows. In this last step the quantity of cold air is
reduced so much that the product’s surface softens again by friction and disperses
to a smooth surface under the influence of this friction. Attention must be paid to
ensure that too long a smoothing time or too warm temperatures do not allow the
products to stick together. There might also be a higher danger of fat bloom during
subsequent storage.
After smoothing, the products must crystallize again under the cold air supply
and the surface must be completely solidified before polishing. If the surface is not
solid enough, the chocolate might mix with the polishing agent causing the latter
to lose its function.
In the confectionery industry there is not complete agreement about whether the
chocolate should be tempered or not. Nowadays, nearly all companies are working
with non-tempered chocolate. The chocolate is mostly delivered in liquid form
already or is molten before usage at around 38–42 °C and applied or sprayed on.
Here, the advantage is that the chocolate’s viscosity is lower and thus there is less
danger of stickiness. Another advantage is a more homogeneous surface allowing
the smoothing time to be reduced. Another aspect is that a tempering machine is not
necessary, removing the need for a high investment.
The application of tempered chocolate, on the other hand, has the advantage
that the cooling time between the single layers is reduced. Furthermore, the
quantity of chocolate sticking to the coating pan’s walls can be reduced.
18.4.2 Compound panning
The process of compound panning is similar to chocolate panning. However, it is
important to distinguish between the different types of compound that can be used.
A compound based on CBE (cocoa butter equivalent) needs to be treated as
chocolate with cocoa butter. Compounds made of CBR (cocoa butter replacer) and
CBS (cocoa butter substitute) require a stronger cooling and higher air quantities.
The residual humidity of the compound should be lower than 1% for the same
reason as for chocolate, that is to have the correct viscosity, and also to prevent
hydrolytic breakdown of the fat. The number of layers is also between 15 and 25,
depending on centre and compound type, applied quantity and available machinery. Owing to the longer crystallization time, a longer panning time must be
calculated (approximately 10–15% longer) compared to chocolate panning. However, this also depends on the process conditions, the fat type and fat content of the
Manufacturing processes: chocolate panning and inclusions
405
compound. In general, for CBR and CBS compound the air temperature must be
reduced to 8–12 °C with a maximum air humidity of 45% and, in general, a higher
air speed and quantity than for chocolate. The compound temperature is adapted to
the viscosity and can range between 30 and 40 °C. After smoothing and before
polishing it might be necessary to let the products crystallize for 6–24 hours.
18.5 Finishing
After the smoothing process, chocolate or compound panned goods are subject to
subsequent treatments, such as a polishing layer, or dusting the surface with icing
sugar, cocoa powder, rasped coconut or other powders. When dusting with powder
after smoothing, the outer layer is not completely crystallized but the icing sugar or
another powder is dusted onto the soft surface so that the powder sticks to the
surface.
Similarly, hard or soft coating can be applied to the chocolate panned centres in
order to give the product a crunchy effect. In order to guarantee optimal adhesion
of the sugar layer to the chocolate, an engumming layer is recommended. The
sugar coating layers are mostly very thin and thus must adhere optimally to the
chocolate layer in order to keep the smoothing process as short as possible.
Usually, 30–50 layers of hard panning are applied onto the chocolate-coated
products, providing a pleasant crunchy effect during consumption.
Polishing is the third possibility for finishing the chocolate panning process.
Therefore, certain polishing and glazing agents are used to treat the surface. After
chocolate panning, smoothing and crystallization, the dragee’s surface is dull and
is comparable to the base of a chocolate tablet. The base of a chocolate tablet is not
in contact with the chocolate mould and thus the growth of cocoa butter crystals is
not limited compared to the chocolate tablet side that is in contact with the
chocolate mould.
Refraction at the chocolate mould’s surface is homogeneous owing to an even
dispersion and a smooth surface. Consequently, the surface is glossy. The base of
the chocolate tablet is irregular not smooth, deriving from air and mould movement
in the cooling tunnel. Therefore, refraction is irregular and the surface appears dull.
It is possible to make chocolate dragees glossy without application of a
polishing agent by a combination of temperature control, sufficient friction and
much time. Normally, hydrocolloidal solutions are used which the company either
produces itself or are available in the market ready for use as polishing solutions.
Polishing agents consist of different raw materials aimed at providing a most
glossy surface and a stable product brilliance. In choosing the polishing agent you
must consider whether chocolate or compound has been used and which fats have
been applied that might influence the surface’s hardness. The polishing agent
should build up a protecting film, reduce stickiness and achieve the highest
possible gloss. The polishing agent itself should have a good shelf life, achieve the
gloss in a relatively short time and be easy to handle. It should also correspond to
the legal requirements.
406
Enrobed and filled chocolate, confectionery and bakery products
Irrespective of the polishing agent, the surface of the chocolate dragees must be
very smooth and have sufficient hardness before application of the polishing
solution. Otherwise, the polishing agent might mix with the chocolate or compound and lose its function. The surface should be dry, must not have condensed
water that may be derived, for example, from high temperature differences and
must be free from dust or particles, as the latter could be seen through the polishing
layer. The conditions of the air supply (e.g. temperature, air quantity and relative
humidity) should be chosen such that condensation is avoided, that the polishing
agent can disperse sufficiently and the surface does not soften.
As already mentioned for compound panning, there are special requirements
that need to be fulfilled which also need to be considered for the polishing process:
for the extremely low temperatures of 8–12 °C, a good air supply system must be
available as the danger of condensation is high.
In comparison to hard or soft coated dragees for which waxes are mostly used,
the polishing agent for chocolate panned goods is mostly gum arabic solutions.
Gum arabic forms a film with emulsifying and polishing properties. The thin film
also serves as a protective film. It is of importance that the solution disperses well
by sufficient friction, but without producing too much heat. The air supply must
not be too humid or too dry as otherwise this film cannot develop.
Another important point for a good polishing agent is that it is easy to handle.
Therefore, glucose syrup is added as it protects the gum arabic layer against
cracking and increases the polishing agent’s total solids for a better shelf life. Some
polishing agents additionally contain oils or fats to reduce stickiness or preservatives for a longer shelf life. As an alternative to gum arabic, nowadays modified
starches are applied, also in combination with gum arabic.
In general, chocolate or compound dragees are not only polished but also
sealed. Shellac dissolved in alcohol is used for sealing. As soon as the alcohol
evaporates, shellac forms a hard and transparent layer and protects the polished
dragee against moisture absorption. Products that are not treated with shellac easily
take up moisture and, in the case of bad packaging, begin to stick to one another and
finally lose gloss relatively quickly, especially under humid air conditions. At
present, shellac is the only sealing agent known that protects panned goods against
outer influences and provides a good shelf life.
18.6 Equipment
The term ‘dragees’ derives from the Greek word tragemata (meaning goodies,
sweets, dessert) and means ‘sugar coated almond’ in French.
The panning process itself has been known since the 9th century, coming from
Greek–Arabian culture and applied to the coating of medicine. Later on in
mediaeval France, developments advanced, first with honey, then with sugar. The
first panning processes were nothing but stirring and movements in normal pots.
This processing was steadily improved so as to to sweeten bitter medicine or to
ennoble products with gold and silver coatings.
Manufacturing processes: chocolate panning and inclusions
407
The first modern coating processes were developed in the 18th and 19th
centuries in the confectionery industry. In the 19th century the first moving copper
vessels were developed. Coating techniques for the confectionery and pharmaceutical industries remained the same up to the 1940s. In the mid-1950s automatic
coating plants were developed and mostly used in the pharmaceutical industry for
film coating. In the 1970s, the first semi- and fully automatic coaters were used.
Confectionery producers specializing in chocolate panned goods are mostly
small- and medium-sized companies which need a high degree of flexibility. The
more flexible that a company must be in view of frequent product changes and
different chocolate types, the more manual is the production. The higher the
quantity produced per product, the more automatic the process can be, for example
automatic coaters of up to 2,500 litres capacity.
18.6.1 Equipment for precoating
Earlier in this chapter the advantages of precoating and its necessary components
were mentioned. Precoating is mostly done directly after a separation or cleaning
process in a classical coating pan. The pan is filled with a defined quantity of the
centre. Then the solution is applied into the rotating vessel and after dispersion of
the precoating solution, the products are dusted with powder until they are dry.
Then the products are taken out of the vessel, stored intermediately for drying
before being chocolate panned in another vessel or coating plant. This discontinuous process requires a lot of expenditure of labour and time.
For this reason, a new processing technique was developed which combines the
advantages of precoating with continuous processing. The continuous system was
developed in order to automate the time and labour intensive batchwise process.
The system used for a continuous precoating process with a special precoating
powder consists of a feeding station for the centres, a transport channel with a
spiral conveyor equipped with dosing stations to apply precoating syrup and
powder and the final drying drum. Inside the conveyor a brush spiral distributes
first the precoating syrup, then the powder and transports the products towards the
exit. In the drying drum the adhesion to the centre is increased before, in a last step,
the residual moisture is bound by application of additional powder.
Whereas with traditional precoating solutions the distribution of 10–20 cm3
–1
kg of centres needs up to 3 min, depending on the centre type, and the drying time
is 10–20 min, Fig. 18.1 shows the precoating in a fast continuous process with a
precoating agent.
Precoating increases the product’s weight by up to 15% according to product
type and application mode. With the protecting film that now covers the products,
the time for the main coating process can be reduced by approximately one-third.
18.6.2 Equipment for chocolate panning
Classical coating pan
In nearly every dragee producing company, even nowadays, you still find classical
408
Enrobed and filled chocolate, confectionery and bakery products
2
1
5
4
6
3
7
8
9
Legend
1. Feeding of base product
2. Dosing of gum solution
3. Dispersion of the gum solution
4. Dosing of sugar mix
5. Dosing of Quick Coat
6. Dosing of Quick Coat
7. Tumbling of coated product
8. Recovery of fines
9. Discharge of coated product
Fig. 18.1
Continuous engumming line by VFS Systems.
coating pans which are often made of copper. New coating pans, however, are
made of stainless steel. Conventional coating pans can be used for precoating,
chocolate coating, smoothing and polishing. The capacities vary from laboratory
coating pans of 3 litres capacity up to a production vessel of 500 litres nominal
capacity. Conventional coating pans are installed with a specific angle of inclination, depending on the product type being processed and can have lentil, onion or
pear shape. Good mixing is achieved by the inclination of the vessel’s axes and the
steeper the vessel the smaller are the dead zones in which the centres rotate less and
friction is lower. However, mechanical stress is very high which might lead to a
breaking of edges and cones or to an abrasion of the chocolate by too high friction.
The movements in the vessel are influenced by the amount of kernel, the vessel’s
speed, form and surface condition of the kernel and the chocolate’s viscosity.
After chocolate application it is essential that the chocolate spreads evenly on
the surface and then crystallizes under cold and dry air. The specific surface that
the cold air hits is low in a conventional coating pan so that the products must be
cooled for quite a long time and with a relatively great quantity of air. Furthermore,
Manufacturing processes: chocolate panning and inclusions
Fig. 18.2
409
Belt coater, from Schröter Maschinenbau GmbH.
the corresponding dead zones are quite large so that the quantities applied might be
irregular.
Chocolate is often still applied manually. In more modern systems chocolate is
applied via a nozzle at certain time intervals. For light and flat products a chocolate
spraying system is used which can be installed additionally to existing pans
without problems.
Belt coater
In general, belt coaters are only used for chocolate coating. Since the end of the
1960s belt coaters have been on the market and are a further development of
conventional coating pans for chocolate dragees. In contrast to a conventional
coating pan, the centres run on an endless, revolving belt which can either be a
stainless steel grid or made of synthetic material. This belt is limited at the sides and
it is driven by two disk wheels. The products run evenly in a panning cavity over
the entire breadth of the belt at low product height. Generally, the number of
revolutions of the belt is infinitely variable.
The advantages of this system are an evenly dispersed product bed and no dead
zones. Owing to the higher specific surface, the retention and dryings time are
shorter.
Chocolate feeding is done over a guide rail with heatable depositing nozzles
installed above the panning cavity. The nozzles are mostly equipped with a
pneumatic cleaning mechanism. The chocolate is applied continuously in defined
time intervals. For flat and light centres it is often recommended to use a chocolate
spraying system. This spraying system is usually supplied as standard or, if not, can
be installed additionally (see Figs 18.2 and 18.3).
410
Enrobed and filled chocolate, confectionery and bakery products
Cold air
Chocolate
Dropping system
Side wheel
Stainless
steel belt
Air outlet
Fig. 18.3
Belt coater scheme, machinery from Schröter Maschinenbau GmbH
(www.chocolatecoating.com).
Automatic pan
Fully automatic coating pans are nowadays used for large-scale production of the
same product. These plants are equipped such that feeding is done automatically
and that it manages, fully automatically, the processes of engumming, chocolate
panning, polishing and intermediate storage in big bags.
These large-scale plants consist of up to 4.5 m-long horizontal drums with
capacities of up to 2,500 litres. The drum is not perforated as it would be for sugar
coating but equipped with mixing blades that allow for a good mixing throughout
the entire product bed. Chocolate is applied via spraying nozzles which are
distributed all over the product bed. At the drum’s outer side infrared heating is
installed in order to melt the chocolate and clean the drum after production and to
avoid chocolate accumulation at the drum’s walls.
Manufacturing processes: chocolate panning and inclusions
411
18.6.3 Chocolate spraying systems
The classical method for chocolate application is manually by means of a ladle.
Besides the fact that this manual method is very labour-intensive there is the
problem that too much chocolate might drop onto one spot. There is a great danger
of products sticking together, especially for light and flat products (flakes, raisins)
as well as for small products.
Chocolate spraying systems can be additionally installed to classical coating
pans and belt coaters, helping to automate the chocolate panning process and thus
reducing labour. Panning time is decreased, especially for products that are likely
to stick together such as cornflakes or coffee beans. Owing to the faster application
of chocolate, processing time might be decreased by 50%. In spraying, the
chocolate at the nozzle’s outlet is dispersed by compressed air and a fine spraying
film is created which is spread over a relatively large surface.
There are also mobile systems on the market. These mobile systems are
suitable as additional equipment for existing machinery with low expenditure.
They consist of a tank in which the liquid chocolate is put under pressure. This
tank is connected to a flexible pipeline that disperses the chocolate on the
product surface via a spraying nozzle working under compressed air. The whole
system is heated by a water-filled double jacket. The tank is under pressure and
the more pressure is applied the more chocolate is sprayed. This mobile equipment can be used especially for the engrossing phase which requires application
of the desired chocolate quantity within the shortest time. Afterwards, the mobile equipment is taken to the next vessel so that during smoothing and polishing
of the first batch, the next batch of chocolate coating can be carried out in the
next vessel.
Cleaning can be done in only minutes and the equipment can be changed for
another chocolate type. Apart from this mobile equipment, this spraying system
can also be fixed to a coating pan. Here, the chocolate tank is connected to a
chocolate panning pipeline and in this way is filled up regularly. A third possibility
is to pressurize the entire chocolate pipeline, however, this would mean that all the
pressure would have to be adapted to 6 bar and that this pressure would have to be
maintained as spraying is done in several vessels at the same time.
18.6.4 Equipment for polishing
Nowadays, chocolate panning can be carried out with various systems such as the
classical coating pan, belt coater or automatic pan. In practice today, the entire
process from chocolate coating, smoothing and polishing, up to sealing is done in
a classical pan or an automatic pan in one sequence. In some cases, after smoothing, the chocolate panned product is stored intermediately so that it solidifies.
However, owing to the high costs of labour and time this is no longer desirable. For
modern polishing agents, an intermediate storage is no longer necessary for
optimal handling.
Belt coaters are used for chocolate panning in order to increase productivity,
whereas smoothing and polishing is done in conventional coating pans. Classical
412
Enrobed and filled chocolate, confectionery and bakery products
coating pans are especially suitable for polishing because higher friction is
achieved which leads to a faster and better gloss.
As already described in Section 18.5 polishing is done with solutions based on
hydrocolloids, such as gum arabic or modified starches. The quantity of polishing
agent varies between 0.5 and 1% depending on the product type and they are
usually applied manually. For automatic plants, there are special spraying systems
available which disperse the solution on the products’ surface. An important aspect
is a good distribution in the coating pan with high friction and pressure as well as
appropriate air conditions (14–16 °C, < 55% relative humidity) to avoid softening
of the product surface.
18.7 Future trends
Panning is a time-consuming and labour-intensive process. The future trend will
be for processes that are more automated and for production to be rationalized
further.
As raw materials become more expensive special attention will be paid to
engumming and to stabilization of the centres in order to decrease rework and
prolong shelf life. Engumming will become more important for small and mediumsized production quantities and continuous engumming for large product quantities.
Owing to rationalization and automation, conventional coating pans will increasingly disappear or only be used for polishing. Belt coaters will be used more
often. Copper vessels will disappear for conventional coating pans, mainly for
reasons of hygiene, and will be replaced by belt coaters.
There might be tendencies for the development of polishing agents that allow
direct polishing in the belt coater, however, the polishing agent must achieve the
gloss by less friction and pressure within the shortest time. At present, it is
necessary for the gloss on chocolate panned goods to be made resistant and longlasting by means of a sealing agent. There should be some interest in developing a
polishing agent that provides the same properties without shellac solution.
The large variety of dragees also make this product type very attractive for
confectionery producers. Panning can be done on nearly every centre type and be
combined with chocolate panning and soft and hard coating. This allows endless
combinations of texture and flavouring. All current tendencies and trends such as
functional food, addition of vitamins, high fibre content or light snacks can be
combined with one another and so panning is and remains an exciting subject
which has a stake in the future.
18.8 Sources of further information and advice
BENECH, A
(2004), ‘Confectionery process and progress’, Food Marketing & Technology,
06, 14–15.
BENECH, A (2007),‘Allround Schutz – Glanz und Schutz für Drageewaren’, Food Design, 04,
35–6.
Manufacturing processes: chocolate panning and inclusions
413
BOUTIN, R (2004), ‘Polishing and finishing of panned goods’, Manufacturing Confectioner,
06, 57–64.
(1996), Silesia Confiserie Manual No. 4: Reference book for the manufacture of
Panned Goods and the Surface Treatment of Snack Products (including pharmaceutical
dragees), Silesia Gerhard Hanke KG, Abt. Fachbücherei, Neuss.
MÜNCHOW, F (1959), Bonbon und Drageeherstellung, Fachbuchverlag, Leipzig.
STEENKEN, G (2000), ‘Schokoladendragées sind en vogue, Technik zum Dragieren mit
Schokolade’, ZSW (Zucker und Süßwarenwirtschaft), 10, 301–3.
MERL, S
19
Manufacturing processes: production of
chocolate shells
J. Meyer, Bühler Bindler GmbH, Germany
Abstract: Chocolate shells have traditionally been produced by filling moulds with
tempered chocolate, inverting and oscillating to allow much of the chocolate to drain
away and then crystallizing the resulting thin shell of chocolate remaining in the
mould. In the late 1980s the first trials on a new chocolate shell production concept,
called ‘cold stamping’, began. The idea was to have a very fast way of forming a
chocolate shell. Very precise tools could be manufactured to form a variety of geometrically abstract shells, which could not be produced by the traditional forming
process. There is no greater challenge than that of producing thin chocolate shells that
are subsequently filled with quick melting or even liquid centres. Cold stamping
technology is the best way of producing uniformly thin chocolate shells with accurate
weights and complex geometries. This method involves plunging a cooled stamping
tool into a mould filled with chocolate, so simultaneously shaping and stabilizing the
chocolate shell. However, it is important for the atmosphere to be dry, because
otherwise ice crystals form on the stamp and the chocolate shell sticks to the stamping
tool. The modern eye and palate yearn for variety, encouraging producers constantly to
create new types of chocolates. This is a challenge for the cold stamping process, since
every time a production changeover to a new product format is needed, the stamping
plate has to be changed and the dry air atmosphere has to be re-established, using
considerable amounts of time and energy. The innovative FlexiStamp™ multiple
stamping head produced by Bühler Bindler consists of up to four different stamping
plates, arranged with their backs around a rotatable shaft, each having its own individual cooling medium supply, thus overcoming this problem. To produce a new shell
shape, the stamping head can simply be turned to the corresponding product format,
either manually or automatically. Stamping plates are only cooled when they are in
use. Not only that, but a dry atmosphere is maintained and does not have to be reestablished again with each new chocolate format. These features save energy and time
and so significantly cut production costs.
Key words: chocolate shells, cold forming, cold stamping, shell moulding.
Manufacturing processes: production of chocolate shells
415
19.1 Fundamentals of chocolate shell production methods
Centres and inserts in confectionery and bakery products can be coated by
enrobing or by panning. These are the subjects of other chapters. This chapter deals
with the production of empty shells that can then be filled with a suitable centre.
There are a number of ways of producing such shells. As well as the traditional
procedure, newer methods of cold stamping have been developed for shell
production and will be described. More recently there have been further innovations in this area which have the same target of producing a chocolate shell but
which, nevertheless, give possibilities for new products. There are many facets to
chocolate shells particularly when the numerous options with regard to different
filling types are considered: from firm, through soft to liquid fillings.
19.1.1 Traditional shell forming
Conventional shell forming uses an oscillating process. Traditional shell production is mainly of two kinds: wet shell production and dry shell production. The
differences between these procedures lie in the different chilling stages and
production stages and with the different structure or consistency of the chocolate
mass used to produce the shells. In both methods, the shell mould is filled with
chocolate and inverted to drain off excess chocolate, thus forming a shell. In the
wet shell method, the shell is re-inverted while the chocolate is still mobile. Any
excess chocolate remaining at the lip of the shell is removed by means of a licking
roller and only then does the product go through a cooling stage. In the dry shell
method, the shell is cooled directly after the first inversion until a leathery structure
has formed from the initial crystallisation of the chocolate. This can then be
trimmed by means of heated knives. The two procedures result in different shell
edges and strengths. The wet shell method forms a fine, sharp-edged shell, while
the dry or cut shell method gives a wide, cut-off shell edge together with a fairly
strong shell structure.
By producing two shells and by warming up the edges, connected hollow
bodies can be formed. However, a rotation procedure is used to produce fully
three-dimensional hollow figures and products. In this, two half-shell moulds are
filled with enough chocolate to coat all the internal surfaces with a sufficiently
thick coating of chocolate. The two half-moulds are brought together and inserted
into a rotating machine which rotates the moulds and, in doing so, coats all the
inner surfaces with chocolate. This method is used for the production of hollow
products such as Easter eggs and figures. With the new cold stamping methods,
although shells can be connected by warming the edges as described above, it
would be necessary to use folding form technology to produce hollow figures and
three-dimensional products.
19.1.2 Cold stamping
As an alternative to the conventional oscillating process, cold stamping technology
offers completely new possibilities for the formation of chocolate shells in terms of
416
Enrobed and filled chocolate, confectionery and bakery products
weights and of producing even, thin shapes with uniform wall thickness. Speed is
one of the success factors with this method. Shell forming is performed by a short,
rapid immersion of a specially cooled stamping tool into an amount of chocolate
already deposited into the shell mould. The process is so fast that crystallization of
the chocolate mass only occurs initially on the contact surface in order to stabilize
the shell shape. Final, full crystallization only takes place during the subsequent
cooling stage.
19.2 Cold stamping technology
Although there are a number of different cold stamping methods available,
commercially they are all based on the same physical principles. A deeply cooled
stamp or former is plunged into the chocolate in the mould and forms a thin shell
by forcing the chocolate into the gap between the mould and the stamp. The
stamping tool (temperature, shape, etc), with crystallization and time all interact
together to produce a good product. Table 19.1 gives a list of currently available
cold stamping methods together with the manufacturers and trade marks of these.
The FrozenShell® differs from the other methods in that it is a patented process
for producing thin chocolate shells without the need for a mould. These shells can
then be filled and enrobed. A wide variety of shapes can be achieved by a simple
and quick exchange of the forming plate. Shells are produced by plunging a frozen
stamp into a bath of chocolate and then immediately removing it. The products
(shells) formed in this way have an extremely thin shell thickness (approx. 0.7
mm). They are loosened from the stamps by gentle air pressure and can then be
lowered onto a belt for further processing. This method of stamping a shell differs
the most from all the others as no moulds are used for this process. Shell forming
by the use of a stamping tool and suitable product moulds (cavities) represents the
basic principle of all the other methods.
A strongly cooled stamping tool is plunged into a mould cavity filled with
chocolate. The predefined gap between the mould cavity and the stamp is filled
with chocolate by the pressure from this action, forming a shell in the mould which
can then be treated like a conventionally manufactured shell in any further
processing.
Table 19.1 Cold stamping suppliers
Producer
Trade mark
Bühler Bindler GmbH
Knobel
Carle & Montanari
Winkler und Dünnebier Süßwarenmaschinen GmbH
Aasted Mikroverk
Chocotech
Cool CoreTM
Cold Press®
Fast Shell®
Flash Shell Cooling® (FSC)
Frozen Cone®
Frozen Shell®
Manufacturing processes: production of chocolate shells
417
19.2.1 Stamping tool design
Naturally, there are differences between the stamping tools that are used. It is
possible to use either fixed stamps, manufactured from one piece of metal, or to use
plates with flexible stamps. The Aasted Company holds a patent for flexible
stamps. These involve placing a rim plate onto the mould prior to the actual
stamping process. The stamp is then plunged through openings (template) within
the plate into the mould cavity.
The Knobel and Bühler Bindler Company share a patent for a plate design with
fixed stamping tools, which however, features an enclosed stamping area with
dried cooled air circulation to avoid freezing of condensate on the stamps. The
dried air reduces the dew point and eliminates the risk of freezing. The materials
used for the stamps can vary and can be composed of different metals, with the
objective of achieving a good transfer of cooling energy and conductivity. This
will considerably shorten the process steps, allowing fast recooling of the tool after
immersion into the warm chocolate mass. Copper, silver and aluminium are, for
example, known as metals with a good conductivity. Moulds and stamping tools
should always be manufactured by the same supplier to keep the tolerances
between mould and stamp to a minimum. Accurate centering of moulds underneath the stamp is important to avoid mould crashes and to produce exactly formed
shells.
Guiding and centering bolts on the stamping plate has proved to be of value for
the CoolCoreTM stamping process. This system is of a space-saving design that
does not require any additional drive technology as movement is effected by the
lifting table, stamping head or both devices. Thus movement of stamps is flexible,
allowing an individual design for each moulding line. In addition, the plate design
permits a quicker, safer and easier changeover of the stamping patterns. One
stamping plate may include uniform as well as different mould geometries. In this
connection it is to be noted that chocolate deposition and shell volume should be
kept constant to avoid over- or underdosing of some cavities upon immersion of
the stamp. The same rules that are valid for conventionally manufactured shells
will apply to the moulds used for this process. It is important to maintain an angle
of more than 7 ° for good demoulding of the products. Experience has shown that
a smaller angle negatively affects product demoulding. If two half-shells are to be
glued together, shell rims can be excellently matched by application of the
stamping technology as geometry can be ultimately predefined by the gap between
mould cavity and plunging tool. In a manner of speaking the chocolate mass will
be squeezed in its mould.
19.2.2 Cold stamping procedures with moulds
The CoolCoreTM stamping process (see Fig. 19.1) is characterized by the use of a
metal stamping plate with inserted fixed stamping patterns cooled by a refrigerant
from the inside to a temperature of –20 ° C. The stamp is designed with nozzles and
milled channels to allow circulation of the cooling medium on the inside. This ensures faster recooling after immersion into the warm chocolate mass at 28–30 °C.
418
Enrobed and filled chocolate, confectionery and bakery products
Slight surplus of mass
Depositing
Cold shell forming
Shell rim shaving
Fig. 19.1 CoolCore stamping movements.
The actual stamping temperature on the surface roughly ranges between –16 and
–18 ° C. Approximately a time of 1–3 s are required for plunging during which the
tool heats up to about –14 to –16 ° C.
19.2.3 Cold forming without moulds
The Frozen Shell® method for cold forming without the use of moulds was
referred to earlier. It is described as follows in the Chocotech GmbH patent (2004):
Method and apparatus for producing shell-like hollow bodies from a
confectionery mass …
Machine for producing chocolate shells (16) for making filled sweets
comprises plungers (1) which are immersed in a bath of melted chocolate
so that it hardens on their outer surfaces. They are then raised and residual
liquid or pasty chocolate removed by passing them across a roller (12)
which revolves in the same or the opposite direction.
The numbers in parentheses refer to the diagram in Fig. 19.2.
19.3 Depositing, vibrating, cooling and demoulding
The various production stages of the traditional oscillating process and the more
modern cold stamping (as exemplified by the CoolCore™ process) are compared
in Table 19.2.
A further point to bear in mind is that the cold stamping method needs less space
and can be fitted into a smaller line (see Fig. 19.3 for a comparison of the space
requirements of the two types of process).
The first action to make a chocolate shell is to deposit a mass of chocolate into
a cavity (mould). For a consistent stamping result it is necessary to dose the mass
very evenly into the mould cavities. The various methods of depositing include
point shot (i.e. deposited through a nozzle to one point in a mould without any
movement apart from that of a lifting table) and ribbon deposit (i.e. deposited with
Manufacturing processes: production of chocolate shells
1
419
1
16
12
Fig. 19.2
Frozen Shell® patent (Chocotech GmbH, 2004).
Table 19.2 Comparison of production steps
Oscillating process
CoolCore™
Mould heating
Depositing
Extraction of air
Mould turnover
Oscillating
Vibration
Scraping
Precooling
Shell rim cutting
Mould turnover
Shell cooling
Mould heating
Depositing
Extraction of air
Stamping
Shaving/cutting
Shell cooling
movement of the depositor along the cavity to produce, for example, bars or tablets)
with or without the use of a shutter knife to stop the chocolate flow. To get an even
film of chocolate mass after vibrating, it is necessary to place the nozzles in the
correct positions. Smaller products are not very difficult to dose and they are mainly
made using one nozzle for one product. Flat and larger products, like tablets or bars,
often need more nozzles per product or use a ribbon way of dosing. The aim for all
products should be to get an airless film of chocolate mass inside the mould design.
If the mass includes too much air (air bubbles) either before or as a result of
420
Enrobed and filled chocolate, confectionery and bakery products
Fig. 19.3
Comparison of space requirements for oscillating (lower) and cold stamping (upper) processes.
Manufacturing processes: production of chocolate shells
421
depositing, subsequent vibration is often insufficient to remove this air. Too many
air bubbles are a result of either sieving the mass above the mass hopper or dosing
through too many nozzles with very fine diameters. In that case the adjustment of
the depositor is very important and should be adapted to the masses which are
being dosed.
After depositing there can still be a large amount of air enclosed in the mass. In
order to avoid faulty products, a vibrating section should be installed after the
depositor as in the conventional shell-forming process.
As evenly and well shaped chocolate shells are required, it is advantageous if
the mass deposited forms a thin closed film within the cavity. As the mass of
chocolate deposited is only slightly more than the shell weight required, the
moulds are always filled at a relatively low rate. In conventional shell moulding,
about 5% extra chocolate is initially deposited. In cold stamping, about 0.1–0.2 g
of chocolate, in addition to the required shell weight, is used.
Besides degassing the mass, vibration is provided to distribute the chocolate
evenly within the cavities. Criteria such as the chocolate mass spilling over rims
can be disregarded owing to the low filling rate of the cavities. Vibration can be
effective in both the horizontal or/and vertical directions. A vibrating time of 8–
10 s is usually applied on most moulding lines. The longer the vibration (depending
on product, design, line configuration) the more air can be released. Mould
preheating is another important issue. Mould temperatures for conventionally
manufactured shells are usually about 2 °C below the depositing temperature of
the chocolate mass. Normally, mould temperatures between approximately 24 and
28 °C are used for the CoolCoreTM stamping process. However, these temperatures
strongly depend on the chocolate masses used. Whereas compound masses involving higher production temperatures allow the moulds to be used at lower
temperatures, too fast a crystallization resulting in faulty products can be observed
when using chocolate in moulds that are too cold. Attention should also be paid to
further factors such as the rheological and crystallization behaviour, manufacturing temperature and tempering of the mass. Highly viscous masses tend to quickly
crystallize during the stamping process and are rather slow to move which leads to
faults in shaping (e.g. shell rim not fully formed). Adjustments to tempering can
help to avoid this problem.
The latest tempering methods (e.g. SeedMaster®) where precrystallized cocoa
butter is injected into the chocolate in small quantities offer a larger temperature
range for chocolate processing in comparison to conventional tempering. With the
SeedMaster® method, a range of 3 °C is possible while still maintaining a fully
stable state of temper of the chocolate, compared to only 0.1–0.2 °C range in
conventional tempering. The use of a higher chocolate temperature can positively
influence the rheology of the chocolate mass if required.
After stamping precise and well-shaped shells, there are almost no limits to the
variety of products that can be made. If a small amount of mass spills over the
cavities, the surplus will be cut off by licking rollers or knives in order to achieve
an even surface for product backing and to maintain clean moulds. Depending on
the shape and thickness of the shell, the cold stamped shell will only require a short
422
Enrobed and filled chocolate, confectionery and bakery products
a
b
m
b
a
b
m
m
a
b
12
a
8
m
m
4
b
0
Fig. 19.4
Distribution of oil concentration (source: AIF-Project, TU Dresden; Dr. B.
Böhme/Dr. G. Ziegleder; Ziegleder and Hornik, 2003).
residence time of approximately 5 minutes in the adjacent shell cooler at a
temperature of 12–16 °C, as the shell has already attained a partially crystalline,
leathery structure before entry into the cooler. After cooling, the shells are ready
for the further manufacturing processes of filling, backing off and demoulding,
and so on in a similar way to the conventionally formed chocolate shells.
19.4 Process conditions and product quality
In the last few years the number of cold stamping methods has grown. At the
Technische Universität, Dresden (Bohme et al., 2003), the various process parameters and product properties have been evaluated. The main results of these studies
are that the stamping time should be short (e.g. 3 s) and the stamping tool temperature
should be very cold (e.g. –20 °C). This is so that, for example, the Cool Core® system
does not begin or end the crystallization of chocolate in the shell too quickly. In the
subsequent cooling unit, the shell is crystallized in the same way as in conventionally
produced shells. Using the stamping procedure, however, helps the fat crystals to
form in a homogeneous configuration so that the density of the shell helps to combat
the effects of oil migration. The hardness of shell and the evenness of the shell
structure together have a beneficial effect in minimizing fat bloom.
In Fig. 19.4 oil migration in a conventionally formed shell (left) and a cold
stamped shell (right) are compared. Higher levels of migration occur at the thin
parts of the shell (labelled ‘a’ in the left hand diagram) compared with the thicker
parts of the shell (labelled ‘b’ in the left hand diagram). In a shell produced by cold
stamping where the shell thickness (m) is much more consistent, the degree of oil
migration observed is also much more consistent across the shell as a whole. While
it is not possible to stop fat bloom, the good combination of crystal structure with
an even shell thickness can help to extend shelf life.
Manufacturing processes: production of chocolate shells
Fig. 19.5
423
Bühler Bindler FlexiStampTM
19.5 Faults, causes and solutions
Table 19.3 lists the main faults that can occur during shell production, together
with the actual causes of these faults and possible solutions to them.
19.6 Future trends
In most chocolate production factories there are moulding lines running a great
variety of products. Changing from one product to another with only one stamping
tool, takes a lot of time. The cold stamping system has to be heated up, the moulds
need to be changed and after changing the stamping tool, it has to be cooled again
before starting the next production with the new design. This means a lot of
production time is lost. The FlexiStampTM system of Bühler Bindler (Fig. 19.5)
makes the changeover faster and less complicated.
There are three or four different stamping plates placed on a multiple stamping
head. With this head, changing the product assortment is more efficient and easier.
After producing one product, the moulds are changed and, in the meantime, the
multiple head is moved around to the correct stamping tool. After the moulds have
been changed, production of the new product can run directly.
424
Faults
Causes
Solutions
The stamping tool is frozen by water
crystals
The dew point is too high in the ambient air.
Too much chocolate is squeezed out of
some designs.
• Too much chocolate deposited
• Tolerances of the depositor per shot are
too big
• Different volumes in the cavities
Bad demoulding situation:
• Product does not come out of the mould
• Shells are broken by demoulding
•
•
•
•
•
The Bindler/Knobel patent includes an air dryer
and cooler with internal circulation streaming of
dried air into covering cap.
There are some points to check:
• Depositor system
• Flow rate and yield value of shell chocolate
• Volume of the mould cavities should be the same
• Tolerances of stamping tools and moulds
should be checked
• Shorten up the stamping time
• Gentle mould temperatures in the preheating zone
• Check up the tempering of chocolate
• Chocolate shell should be in the range of 1.0–2.0 mm.
• Adjust the depositor and vibrating section
Air bubbles in the formed shell
Stamping time too long
Mould temperatures too warm
Untempered chocolate
Very thin chocolate shells
Depositing and vibrating could have an
influence
• Stamping tool does not work in the geometry • Adapt the stamping tool
• Mould temperatures too cold
• Heat up the preheating zone
• Big and flat product with thin shell
• Use a bigger shell constellation, e.g. 1.5–2.0 mm
(e.g. 100 g tablet and 1 mm shell)
shell thickness
Enrobed and filled chocolate, confectionery and bakery products
Table 19.3 Faults, causes and solutions
Manufacturing processes: production of chocolate shells
425
Coolcore™ station with four triple heads
Vibration
Depositor
Licking rollers
Fig. 19.6
Bühler Bindler FlexiStampTM layout with four triple heads.
Every stamping plate is provided individually with a dedicated cooling media
supply without loss of energy. Both the triple and the quadruple heads include
interchangeable stamping plates (three or four places for the tools). If there is one
position not in use, dummies can be installed for later extension of the product
range. The advantages of this type of cold stamping system are that products can
be frequently changed and smaller batches can be manufactured.
The speed of the line (see Fig. 19.6) is also a point of consideration. With more
stamping plates following one after another, it is possible to stamp more moulds in
one step. During the stamping process the tools move simultaneously in the
production direction. Refreshing the stamping tool (i.e. recooling the tool to the
correct stamping temperature) is carried out as the plates move back to the start
position. For example the four triple heads of the FlexiStampTM can stamp four
moulds at one time continuously. The mould speed underneath the plates is
calculated to be eight moulds per minute, making the effective output 32 moulds
per minute with evenly formed chocolate shells.
19.7 Sources of further information and advice
BECKETT ST (1990). Moderne Schokoladentechnologie. Behr’s Verlag, Hamburg.
BINDLER (1994). Verfahren und Vorrichtung zur Herstellung von Schokoladenartikeln,
Insbesondere Hülsen für Schokoladenhohlkörper. European Patent EP 0715813.
(1998). Süsswarentechnologie II: Füllmassen und
Pralinen. Drouven & Fabry GMBH, D-52224 Stolberg-Vicht.
EGLOFF F (1998). ‘Praktische erfahrungen mit frozen cone, tagungsmaterialien’. Lecture
given at ZDS Schoko-technik Conference, Köln.
KNIEL K (1997). ‘Frozen cone und cold stamp; eine vorläufige bilanz. Neue verfahren der
hülsenbildung’. ZSW., 6, 228–30.
KNOBEL (1997). Verfahren und Vorrichtung zur Herstellung von Verzehrgütern Durch
Fließpressen. German Patent DE19720844 C1.
MINIFIE BW (1989). Chocolate, Cocoa and Confectionery: Science and Technology, 3rd
edition, AVI, Chapman & Hall, New York.
SCHUSTER-SALAS C (1998). ‘DSC – messungen bei schokoladenmassen – überprüfung der
vorkristallisation dient dem endprodukt’. ZSW, 4, 152–4.
TSCHEUSCHNER H-D AND MARKOV E (1986). ‘Laborverfahren zum temperieren von
schokoladenmassen’. ZFL.-Heidelberg, 5, 315–16, 318–20.
ZIEGLEDER G (1988). ‘Kristallisation von schokoladenmassen. Teil I: Kristallkeimbildung’.
ZSW, 5, 165–8.
DROUVEN H, FABRY I AND GÖPEL G
426
Enrobed and filled chocolate, confectionery and bakery products
ZIEGLEDER G AND KEGEL M (1989). ‘Kristallisation von schokoladenmassen. Teil III: DSC-
messung der kühlungskristallisation’. ZSW, 10, 338–42.
ZIEGLEDER G, BECKER K, BAUMANN M AND ROSSKOPF O
(1988). ‘Kristallisation von
schokoladenmassen. Teil II: Vorkristallisation und temperiergrad’. ZSW, 7/8, 238–43.
19.8 References
BOHME B, LINKE L AND ZIEGLEDER G
(2003). ‘Optimale Bedingungen beim Kaltformen’.
Süsswaren, 11, 22–4.
CHOCOTECH GMBH (2004). Verfahren und Vorrichtung zur Herstelling schalenartiger
Hohlkörper aus Süsswarenmasse, European Patent EP 1,444,901.
ZIEGLEDER G AND HORNIK H (2003). ‘Fettreif im Visier’. Süsswaren Technik und Wirtschaft,
6, 22–4.
20
Manufacturing processes: deposition of
fillings
J. Meyer, Bühler Bindler GmbH, Germany
Abstract: The manufacture of a filled chocolate product, like a praline, requires a
large production line, including up to three depositors, a number of vibrating and
oscillating units, pipelines and tanks for the masses, cooling energy and so on. The
idea of depositing the whole filled chocolate product in one operation (One-Shot) was
considered as early as 1930, but it is only in the last few years approx. since 1998 that
the technology has been developed to give an efficient manufacturing process. Through
a special combined inner and outer nozzle, the chocolate shell mass and the filling
mass can be deposited into a mould cavity in one step or in ‘one-shot’. After depositing in this way, a gentle shaking unit, the final cooling unit and the demoulding station
follow as production steps. This means a shorter production line for a whole filled
chocolate product which saves energy, time and significantly reduces the production
costs. However, it needs a good balance between the chocolate mass and the filling
mass to get stable products. The one-shot technology requires almost identical shell
and filling masses, particularly in terms of yield value, flow rate and density, to
optimise the filling ratio and the shelf life of the products. Development of the oneshot process is continuing with the latest production applications being the triple- and
the quadro-shot processes in which three or four phases are codeposited. These two
new manufacturing technologies are based on the one-shot technology but they can
create a new range of products. Either two or more fillings can be placed in the
chocolate shell, or a two-coloured shell can be dosed with one or more different
fillings in one step. Another variation is the One-Shot depositing of bars using the
ribbon way of dosing. These are all examples of a process which many consider to be
a flexible and efficient alternative to traditionally formed sweet chocolate products.
Key words: filling masses, fill shot®, One-Shot, One-Shot product, quadro shot, triple
shot, single shot.
428
Enrobed and filled chocolate, confectionery and bakery products
20.1 Modern processes for depositing fillings into premade
shells: One-Shot technology
The one-shot injection moulding technology is a very quick way of manufacturing
filled chocolate products. The aim is to create a whole product in a very short time
and in one step. To achieve this, the shell mass and the filling mass are injected
through specially designed nozzles simultaneously into the mould cavities. There
are many applications of products, such as filled chocolate pralines, on the market
that can be produced in this way. They can, for example, be filled with caramel,
fondant, fat-based creams, truffle masses and so on. It is very important that the
masses to be dosed by the One-Shot system have similar densities and rheological
behaviour, that is viscosity and yield value. These aspects have a direct effect on
the coating: filling ratio. The shape or the design of the product also has a major
influence on the flow of the masses during dosing into the cavity of the mould.
However, to deposit a One-Shot product, very well-designed technology inside
both the depositor and main control panel is needed. With the latest technology it
is possible to dose a One-Shot product with one, two (triple shot) or three fillings
(quadro shot). This has given rapid growth in the ranges of products that can be
made. If three masses are deposited at the same time it is possible to have a twocolour shell with one filling inside, a double shell of coating with one filling or one
shell with two fillings inside. It is also possible to manufacture a whole bar by
ribbon movement using One-Shot technology. In addition, the production line is
shorter than a traditional shell-forming moulding line. These facts have a big
influence on saving energy, manufacturing time and mass handling equipment.
20.2 One-Shot process conditions and product quality
One-Shot technology uses similar equipment as other chocolate production methods, but with the difference that the depositor has a special movement and control
and that the whole moulding line is very short. Fig. 20.1 shows the difference in
space needed for the traditional shell moulding process (lower line) and the OneShot process (upper line). In this, the One-Shot line has a length of 11.5 m, while
the traditional moulding line is much longer needing approximately 28.5 m, for
example. This is a saving of space of approximately 17.0 m (i.e. about 60%),
compared with a traditional moulding line. This is very important for those
manufacturers of sweet chocolate products who do not have much space for the
installation of a conventional line.
Table 20.1 gives an overview of the unit processes and equipment needed for
traditional shell manufacture (left) and the One-Shot process (right). These differences in unit processes also give an idea of how the electrical requirements are
reduced in a One-Shot application.
20.2.1 Depositor
As with a conventional manufacturing process, the masses have to be dosed into a
Comparison of required space: One-Shot application and oscillating shell (from Bühler Bindler GmbH).
429
Fig. 20.1
Manufacturing processes: deposition of fillings
8
430
Enrobed and filled chocolate, confectionery and bakery products
Table 20.1 Moulding line equipment overview: conventional shell
forming and One-Shot (from Bühler Bindler GmbH)
Conventional manufacturing process
One-Shot
Shell deposit
Vibration
Shell forming
Shell cooling
Centres deposit
Vibration
Centres cooling
Preheating
Backing deposit
Vibration
Backing scraping
Vibration
Final cooling
Shell and centres deposit
‘Gentle’ vibration
Final cooling
mould cavity. The depositor for a One-Shot application has two different mass
hoppers (or three with the triple-shot and four with the quadro-shot processes) with
separate piston lines for each mass hopper. The dosing process is controlled by the
piston stroke and rotary valve which dispense defined volumes of mass. Each mass
hopper needs its own pistons with a separate piston movement. Usually there is one
piston to one nozzle, with the aim of giving accurate dosing weights with closely
defined tolerances. If, for example, one piston stroke were to control two nozzles,
there would be a greater chance of differences between the weights being deposited in the two nozzles. This is because of the lengths of the channels between the
rotary valve and the nozzles. There are differences in pressure and volumetric flow
of mass inside the longer channels compared to the shorter ones. This can be seen
in Fig. 20.2 which shows an example of a One-Shot dosing system. Different
lengths of channel configuration are shown between the left side (shell mass) and
the right side (filling mass).
Most modern depositors are capable of One-Shot application. An example of a
dosing system similar to that shown in Fig. 20.2 with horizontal pistons on both
sides (left and right) is the PowerShot® depositor from Bühler Bindler GmbH. The
pistons can also be placed in a vertical configuration as in the PreciShot® system
from Bühler Bindler GmbH. A combination of horizontally and vertically placed
piston blocks or simply of vertical piston blocks is used by the triple- or quadroshot applications. These combinations need more space in the depositor system
compared with a One-Shot application. During the last few years, big improvements have been made to the servo technology and the control systems, with
computers becoming smaller.
One area of great importance is the communication between the servo drives
and the control system. With the revolution in process optimisation, there is now
the possibility of having exact, direct movements and time control in each of the
process steps. One-Shot means that the product masses will be dosed in one step,
Manufacturing processes: deposition of fillings
Fig. 20.2
431
Example of One-Shot dosing system (from Bühler Bindler GmbH).
but the movements of pistons, rotary valves or slide valves need special timing
and do not have the same start and end times as each other. This is important in
terms of setting the different depositing parameters. The operator only needs to
set the parameters once and these can then be saved for future manufacture of
that product on the One-Shot moulding line. Different parts of the equipment
need to move either simultaneously or in different ways and at different times.
Such movements are, for example, the piston movement and the motion of the
lifting table.
By means of motion curves, which are calculated in the background by the PLC
(programmable logic controller), it is very easy to see what the movement or
motion for every part of the equipment should be. As well as the dosing steps,
another important aspect is the position of the nozzle in relation to the mould cavity
and the movement of the lifting table. At the start, the nozzle should be placed
deeper into the cavity than in conventional dosing (to approximately 2 mm from
the inside of the rim). The position of the inner nozzle depends on the product
dimensions and the type of mass to be used and will be set by the manufacturers of
the depositor equipment. The mass flow starts with the shell mass. Usually when
the filling action starts, the lifting table moves a little lower down. This movement
is necessary in order to have a good homogenous mass flow in the two masses
during the dosing process into the cavity. The speed of this movement should be
similar to the speed of deposition of the mass, so that no mixing occurs inside the
product between the shell and filling mass. When dosing is complete, the last
movement is set to give a good tailing effect. Finally these different movements
can be saved by the operator via the touch panel. The PLC can calculate the motion
drives for each servo drive accurately in the newer generation of machines with
their improved precision.
All the movements can be set by motion curves as shown in Fig. 20.3, so that the
operator has the chance to see where the position of the filling is and how the
432
Enrobed and filled chocolate, confectionery and bakery products
Filling
Shell
Lifting table
Fig. 20.3
One-Shot motion curves (from Bühler Bindler GmbH).
movements relate to each other in terms of speed (y-axis) and time (x-axis) of the
piston, for example. All these parameters will be defined by a good combination of
equipment and a good control of the mechanical and electrical parts inside the
system. As computers continue to develop, the calculation time will decrease so
that, in the near future, the reaction times of the movement will be very exact.
20.2.2 Vibrating and shaking zone
After deposition, the moulds move to the shaking area. In the same way as in the
conventional manufacturing process, this is placed after the depositor. But there is
a difference from the traditional motion of shaking. A smooth, gentle shaking is
used in order to have a really even surface on the back and no mixing effects inside
or too great a release of air bubbles. This motion operates on the horizontal, so as
not to give too much movement to the whole product, but just to make the bottom
very even. The shaking time depends on the product, but should be not too long.
Usually it takes between 5 and 15 s. The frequency is set very low and the
amplitude is usually set quite high. Therefore there is no significant input of
shaking energy to the product, in order to smooth the bottom surface.
20.2.3 Cooling
The filled chocolates need to be cooled to solidify them and to contract them
sufficiently to be demoulded. One-shot products need only one cooler in the
moulding line, the final cooler. The cooler should cool down both the shell mass
and the filling mass. Normally, different coolers have to cool down different parts
of a traditionally formed product. For example, the filling or centre cooler has to
cool down the filling/centre and only stabilises the shell, which has already been
cooled by the shell cooler at an earlier stage. It is possible to have different zones
in the final cooler, so that the temperature profile can be adjusted to different
temperatures. The whole product needs to be cooled slowly, but this also depends
Manufacturing processes: deposition of fillings
433
on the different masses used. Too much cooling energy during the process will
reduce the processing time, but will also have a very poor effect on the product. For
example, cracks can sometimes appear on the surface of the shell. These look as
though they are caused by an air bubble bursting, but they are formed by the
different degrees of contraction in shell and filling during cooling. So, the cooling
profile has to be set very accurately and the throughput controlled to avoid this
crack formation. This means that it is often better to have more cooling zones in the
final cooler to provide the control that is needed.
20.2.4 Shell and filling masses
The types of mass used for the shell and the filling are also important in terms of
how they influence the manufacturing process of a One-Shot product. Many
different types of chocolate and compound can be used for the shell. There is also
a wide variety of masses used for the filling, for example fondant fillings, caramel
or caramel cream, chocolate masses, fat-based fillings, truffle, nougat, and so on.
Normal filling ratios are mostly in the range of 30–65% (i.e. 30–65% of the final
product will be filling, the remainder being the chocolate shell). This also depends
on how well the filling and shell masses ‘harmonise’ with each other and on the
product dimensions and product design. For example, some products with fatbased masses can have a higher filling ratio of up to 70% or 80%. The aim or the
advantage of having these higher filling levels is the reduction in product costs
achieved by using a cheaper filling mass compared with an expensive shell
chocolate mass.
There are, however, some major disadvantages in having very high filling
ratios. First, the shell will not be as well-stabilised, resulting in leakages or breaks.
Second, the more filling fat present, the more prone the product is to fat migration
from the filling to the shell, which has a direct influence on fat bloom and the shelf
life of the product. The third disadvantage is that there is less chocolate taste
coming from the shell and the overall taste of the product will be more representative of the filling. Caramel or fondant filling masses are also very difficult to dose.
This is because of the tailing effect which can happen after dosing these special
filling masses. Because of these issues, the normal filling ratio is set between 30
and 40%.
Shell and filling masses should have the same temperature when dosed and a
comparable ambient temperature should also be used inside the depositing system.
Round and geometrically shaped products are easier to deposit with a higher filling
content than are small and non-geometrical designs. The next important point is the
temperature of each mass. The mass temperature will be determined by the exit
temperature from the tempering unit. Having said this, the two separate mass
hoppers can also be installed with different water heating systems, to set different
temperatures.
The main influence on the chocolate mass viscosity does not result from the
mass hopper temperature but from the tempering conditions in the tempering unit.
For example, tempering by a seeding process such as the SeedMaster® Twin
434
Enrobed and filled chocolate, confectionery and bakery products
System could temper two different chocolate or fat-based masses at the same time.
This makes it easier to handle two different input viscosities, with the aim of having
nearly the same output viscosity. Caramel and fondant masses also need to be
given special consideration in this regard. It is important that the temperature of the
caramel filling, for instance, should not be too high, otherwise there will be a
detempering effect on the chocolate shell mass.
A major issue is how to dose a filling with inclusions. Depending on the
dimensions of the inner nozzle, inclusions are normally limited to 1–2 mm
diameter. As a quick guide, the diameter of the inner nozzle should be double the
inclusion size. A very simple product to make is the two-coloured drop or chip or
a marbled chocolate tablet. Here two different shell masses are dosed at the same
time. Although these products are considered to be One-Shot products, they are
made using a special nozzle construction. It looks very simple to deposit these
products, but here also a good balance between the characteristics of the two
masses is needed to get a stable, attractive product. The movement of the pistons
is slightly different to a normally filled One-Shot article and has the same starting
time and the same end time. This means a shorter dosing time and a higher output
compared with a normal One-Shot process. However, the flexibility of a One-Shot
product depends on the ability to quickly change the masses (e.g. fat-based filling
masses with different flavours), so that a large variety of articles can be manufactured on one small production line.
20.2.5 Product quality
To bite into a well-filled chocolate praline is a delicious thing. The soft melt and the
combination of chocolate and flavoured filling gives a special sensation to the
consumer. Therefore it is important to consider the quality points of such a OneShot product. Various universities and trade organisations have carried out research
in this area. For instance, Ziegleder (2002–2004) compared the fat content and
shell hardness in an oscillated, traditional product and a One-Shot product. Both
products were made on the production lines of well-known German chocolate
manufacturers and filled with the same nougat filling. The nut filling was chosen
to show quickly fat bloom and effects on the shell hardness. The effects on the solid
fat contents on the shell and the centre were very interesting. The oscillated
(traditional) product had, at the beginning, a higher solid fat content than the OneShot product, but during storage of about 200 days at 23 °C the solid fat content of
the oscillated product reduced significantly. The One-Shot product was more
stable and showed a slower reduction in solid fat content with time. Fat migration
started earlier in the traditionally formed product. Fat bloom, which is often caused
by fat migration, was seen after only 50 days. Figure 20.4 shows these measurements graphically.
Fat bloom formation is a major parameter in determining the quality of a
product. Filled chocolate produced by both the conventional and One-Shot processes were stored at 20 °C and 23 °C and evaulated for bloom formation. The
results are shown in Table 20.2.
Manufacturing processes: deposition of fillings
435
75
Solid fat content (20%)
70
65
Conventional
ü One-Shot
üü ü
ü ü
ü
ü
60
ü
ü
üü
55
ü
ü
ü
ü
ü
ü
ü
üü
Begin fat bloom
50
0
50
100
150
200
250
Storage time (days)
Fig. 20.4 Comparison of solid fat content (stability) of chocolate shells for oscillated
(conventional) and One-Shot pralines with a nougat filling, stored at 23 °C (from G.
Ziegleder, Fraunhofer IVV).
Table 20.2 Comparison of fat bloom for One-Shot and conventional processes
Storage temperature
23 °C
20 °C
Storage time (week)
Convent.
One-Shot
Convent.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
21
23
25
28
30
32
0
0
0
1
2
2
2
3
3.5
3.5
3.5
4
4
4
4
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
0
0
0
0
1
2
2
2
2
2.5
2.5
3
3
3.5
3.5
3.5
3.5
3.5
4
4.5
4.5
4.5
4.5
4
0
0
0
0
0
0
0
0
1
1
1
1
1.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
3
3
3
0 = no fat bloom, 1 = loss of gloss, 2 = slight, 3 = middle, 4 = strong, 5 = extreme.
Extract of final report March 10th, 2005 from G. Ziegleder, Fraunhofer IVV.
One-Shot
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1.5
2
2
2
2
2.5
2.5
2.5
2.5
2.5
436
Enrobed and filled chocolate, confectionery and bakery products
Table 20.3 Viscosity differences
Fault
Cause
Solution
The chocolate mass has a
• Temper the shell chocolate at
lower viscosity than the
a lower temperature or filling
filling mass. The shell is not
mass at a higher temperature,
very stable, because the filling
to get the same viscosity in
mass has pushed away the
both phases. This is possible,
shell mass to the top of the
for example, by using the
product (bottom of the mould).
SeedMaster® System
• Change the adjustment by
depositing the filling a little
bit later (does not work every
time).
• Reduce the filling ratio and
starting time of deposition of
filling.
• Optimise the recipes of the
filling mass, e.g. add some
more fat.
The chocolate mass has a
higher viscosity than the
filling mass.The shell is not
very stable on the bottom,
because the filling mass was
pressed away from the shell
mass to the top of the product
(bottom of the mould).
• Temper the shell chocolate at
a higher temperature or the
filling mass at a lower temperature to get the same viscosity in both phases. Again,
this is possible by using the
SeedMaster® System
• Reduce the filling ratio and
adjust the depositing
parameters.
• Optimise the shell mass
recipes, e.g. add some more
emulsifier or cocoa butter.
It is important to note how quickly fat bloom occurs on the traditionally
manufactured product compared with the One-Shot product which has a much
lower rate of fat bloom formation. Although fat bloom cannot be stopped by using
a One-Shot process and even though the onset of bloom will be depend on the
product, the shell thickness and the centre filling, it can be said, in summary, that
the One-Shot process is a very good alternative way of producing these filled
products.
20.3 Faults, causes and solutions
The most important way to obtain a well-manufactured One-Shot product is to
harmonise the two (or more) masses which are dosed into the cavities. A good
example of this is the type of product that is deposited directly on to a belt and not
into the mould cavities, for example chocolate drops or chips made with different
Manufacturing processes: deposition of fillings
437
types of chocolate. If there are some differences in the viscosity ranges, one
coloured mass will flow differently from the other mass. The distribution of the
two phases in products like this, formed without the use of a mould, will not be as
even as they would be with a better match of viscosities. Table 20.3 shows what
happens if the viscosities are different in a filled One-Shot product.
Another point to bear in mind is the adjustment of the equipment. The shape of
the droplet at the nozzle after injection is an indicator of whether the subsequently
moulded One-Shot article will have an air bubble at the bottom or not. There are
three different droplet sizes to consider (see Table 20.4). Normally the drawback
or restroke (i.e. retraction of the piston after the depositing stroke) of both masses
should happen at the same time. The shell chocolate mass will be sucked into the
inner nozzle, so that no dripping is started. These adjustments require the operator
to have a good feel for the movements of the depositor during production and
operators should be trained in these aspects.
Another important operation is the cooling of the product. If the air temperature
Table 20.4 Indicator for air bubbles
Number Droplet at nozzle
1
Without a droplet =>
The masses will suck
back into the nozzle
after dosing. The nozzle
will look very clean.
2
A very small droplet=>
The masses (especially
the shell mass) will look
like a small tailing at the
nozzle with a length of
approximately 1–2 mm.
3
A too large droplet=>
The masses (especially
the shell mass) will look
like a large tailing at the
nozzle with a length of
approximately 9–10 mm.
Cause
Solution
• A large air bubble will • Reduce the restroke
be built into the first
length.
dosing step of the
• Raise the restroke
product deposit.
speed.
• It will be shown by
• A higher restroke is
cutting the product
needed for the filling
into two halves.
mass and the restroke
• Too much air was sucked of the shell should be
into the nozzle by the
smaller, this depends
restroke operation.
on two different nozzle
outlet free spaces and
piston diameters.
• An air bubble will be
• Nearly the same effect
found in the shell
as before, a little bit of
formation on top of the
air was sucked in by
product after demoulding. the restroke operation.
• The air bubble is mostly • The same handling for
seen without cutting the the restroke as at
product.
Number 1.
• In the last step of
• The restroke is too
deposition a small drop
low.
will fall into the finished • A larger restroke and a
dosed product. A little bit lower restroke speed
of air will be included in could help.
this dripping.
• The air bubble will be
placed directly under
the bottom shell inside
the filling.
438
Enrobed and filled chocolate, confectionery and bakery products
in the final cooler is too low, for example, in order to have a faster output, a crack
could appear in the product. Because the shell and centre may be contracting at
different rates, this could result in the shell breaking. Usually the crack will be seen
on the bottom of the product after cooling. It looks like an open air bubble, but
when the product is cut, it is more obvious that it is a crack. In such a case the
cooling temperature was too low and should be adjusted.
20.4 Future trends
If a One-Shot product is cut into two halves, the shell should look good. But, in this
day and age, ‘good’ is often not good enough. A shell produced by cold stamping,
for instance, has a greater precision than even a very good One-Shot shell.
However, the necessity to back off a traditional or Cool Core® formed shell needs
a lot of equipment such as rim-heaters, another depositor, a backing off station
(scraper) and various vibrating systems. This requires a lot of space. However, the
One-Shot process essentially backs off in one step, without any special equipment.
At Bühler Bindler GmbH, the idea of a patented FillShot® application was borne
and realised. The FillShot® process allows a traditionally formed or a Cool Core©
formed shell to be filled and closed to a base in One-Shot. This needs a special
depositing programme setting. Of course, a shell rim heating station will be
needed, to provide a better sealing effect between the bottom and the shell mass.
But the space needed is not so much as for a complete backing-off line for a filled
praline with a precise shell.
Apart from this development the One-Shot process is very popular and ideas for
creating more special and better-looking products are growing. Recently, the
triple- and quadro-shot systems have become more and more popular. The product
variety of one depositor for a triple shot is enormous and examples have already
been outlined in Section 20.1.
The use of the ribbon depositor in a One-Shot process gives another extension
to the variety of products that can be made. For example, a bar with two different
fillings can be deposited in One-Shot. One disadvantage of this is the reduction in
dosing speed needed to make these complex products in one step but a big
advantage is the shorter production line with a more flexible and wider variety of
products.
20.5 Sources of further information and advice
BECKETT ST (2009). Industrial Chocolate Manufacture And Use, Blackwell, 4th edition.
HARTMANN L (2006). Verfestigungseigenschaften unterschiedlicher vorkristallisierter
Milchschokolade bei Verarbeitungstemperatur. Bachelor Thesis, ETH Zurich.
KNIEL K (2001). ‘Produzieren mit one-shot’, Zucker- und Süßwaren Wirtschaft, 07–08.
WEBER S (2008). Investigation on the Operational Range of the One-Shot Injection Moulding
Process for Confectionery Systems, Master Thesis, ETH Zurich.
Manufacturing processes: deposition of fillings
439
20.6 References
(2002–2004). Manufacture and Imperishability of Filled Chocolate Articles
with One Shot Deposit, 01.11.2002 – 31.12.2004, Fraunhofer IVV. FEI-AIF Projekt no.
13435 GB. In conjunction with Bühler Bindler GmbH, Kölner Straße 102–108, D-51702
Bergneustadt, Germany.
ZIEGLEDER G
INDEX
Index Terms
Links
A
accelerated shelf-life testing
for confectionery
250
252
acetoglycerides
222
aeration
116
fat content effect on density
117
agitation speed
330
alcohol (ethanol) migration
211
minimisation
229
types of liqueur
229
ammonium phosphatide E442
226
229
40
anhydrous milk fat see milk fat
Arrhenius equation
270
ASTM E 2454-05
234
atomic force microscopy
193
automatic tempermeter
354
271
203
B
barriers
carbohydrate barriers
227
dual-layer barriers
228
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navigation.
Index Terms
Links
barriers (Cont.)
effect of fat type in barrier on moisture
uptake of biscuits
219
fat barriers
217
fat-based, effect of non-fat solids
221
layer thickness from enrober
223
protein barriers
227
reduction permeability by adding
vegetable waxes
wax-based barriers
batch systems
Macintyre refiner conches
227
224
20
21
Beer’s law
200
beeswax
222
biscuits and bakery products
152
biscuits
247
chocolate formulation
153
emulsifiers in chocolate
155
filling for bakery products
161
22
225
future trends in chocolate
enrobing
162
moisture barriers for caramel- and jamcontaining biscuits
155
non-hydrogenated coatings
156
processing
157
biscuit and cake crumb-causing
problems
158
cooling the coating
159
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navigation.
Index Terms
Links
biscuits and bakery products
processing (Cont.)
full coated products
157
half coated products
158
quality issues
159
bloom, thermal cracking and
moisture migration
legislative
160
159
that cause consumer
dissatisfaction
160
Borneo tallow see illipé butter
bottoming bath
364
bottoming roll
364
bromelain
127
brushing
223
butterscotch
142
bypass conveyors
389
C
candelilla wax
CAOBISCO
capillary action
225
5
187
197
caramels
and crème viscosity change with
moisture and temperature
276
formulations
274
recipe
142
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navigation.
Index Terms
Links
caramels (Cont.)
soft, flow curves
275
and toffees
142
carnauba wax
225
Casson equation
262
264
Casson method
260
262
Casson viscosity
171
172
174
176
Casson yield value
171
173
174
176
262
CBE see cocoa butter equivalent
centres and fillings
caramels, fondants and jellies
123
cereal centres and bakery
products
399
confectionery centres
398
controlling the rheology
255
deposition
427
enrobed Turkish Delight
149
future
149
low calorie products
150
sugar free
150
gelled products
147
agar jelly recipe
147
gelatin jelly recipe
147
pectin fruit jelly recipe
148
Turkish Delight recipe
148
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navigation.
Index Terms
Links
centres and fillings (Cont.)
ingredients
127
colours
134
dairy
129
emulsifiers
131
flavours
134
gums and gelling agents
135
sugars
127
natural centres
399
precoating
400
advantages and disadvantages
402
drying powder
402
138
means of precoating, stabilisation
isolation
precoating solution
400
401
processing
138
confectioners’ boiling pan
139
depositing
141
drop roller
140
rheology
140
shaping
140
vacuum plant high boilings
139
products
142
caramels and toffees
142
chocolate enrobed bar containing
nougat with expanded cereal pieces
fudge pieces
146
145
grained products
143
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navigation.
Index Terms
Links
centres and fillings
products (Cont.)
high boiled products
142
toffees
143
and raw materials
398
stability
124
biological stability
124
crystallisation
125
fat stability
125
gelling
126
chemometrics
chocolate
333
1
aerated
359
aeration
177
stabilised by encasement in ice
cream
coating
179
355
inboard enrober
358
outboard enrober
357
co-extruded ice cream and chocolate
product
controlling the rheology
178
255
and couvertures
applications in ice cream
163
effect of chocolate emulsifiers on
viscosity at low shear rate
269
emulsifiers permitted within the
EC
268
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navigation.
Index Terms
Links
Chocolate (Cont.)
enrobed and filled products
definitions
3
4
EU production and consumption of
chocolate confectionery
market trends
6
5
factors affecting rheology
264
and fat-based fillings measurement
259
features
166
flow curve vs universal flow
curves
264
flow curves
263
formulations for industrial
applications
29
future trends
51
health aspects
49
ingredients
34
legislation
30
product formulation
40
specialty products
45
36
and ice cream spraying for layered
products
176
microstructure by scanning electron
microscope
167
and moisture
271
moulding
359
range of possible flow curves
265
scope
6
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navigation.
Index Terms
Links
chocolate (Cont.)
supercooling and reheating
345
surface cold stamping
180
typical flow curves
263
variation of fat content and type
168
vs caramel viscosity change with
temperature
263
vs couverture as ice cream
coatings
chocolate manufacture
169
11
basic recipes
dark chocolate
16
milk chocolate
16
white chocolate
16
conching
21
conche
25
flavour changes
21
liquefying
23
future trends
27
grinding
16
batch systems
20
dry grinding
19
five-roll refiner
17
five-roll refiner diagram
19
parallel operation of five-roll
refiners
18
particle size
16
two- and five-roll refining
17
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navigation.
Index Terms
Links
chocolate manufacture (Cont.)
quality
26
flow properties
26
sensory properties
26
raw materials
12
cocoa based
12
emulsifiers
15
milk
15
sugar
14
chocolate shells
4
chocolate-flavoured coatings
4
cis mono-unsaturated fatty acids
55
cis poly-unsaturated fatty acids
55
coating
61
coatings and fillings
fats
53
coating and filling range
61
crystal structure and fat
polymorphism
57
effect on quality and processing,
69
future trends
76
selection for application type
71
Coberine
69
206
cocoa
12
34
36
chocolate formulations with different
cocoa solids
cocoa butter
36
14
drying
13
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navigation.
Index Terms
Links
cocoa (Cont.)
fermentation
13
grinding
14
growing areas and conditions
12
harvesting
12
beans in pods
roasting and winnowing
13
14
cocoa bean
1
cocoa butter
14
fatty acid composition
62
triglyceride composition
62
cocoa butter alternatives
formulation constraints
61
82
84
cocoa butter and lauric CBR isosolids
86
cocoa butter and non-lauric CBR
iso-solids
85
lauric cocoa butter replacers
84
non-lauric cocoa butter replacers
82
supercoatings
82
cocoa butter equivalent
63
153
301
404
advantages over cocoa butter
153
typical fatty acid composition
63
typical triglyceride composition
63
component fats and fractions
cocoa butter improver
66
230
301
cocoa butter replacer
301
404
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navigation.
333
Index Terms
cocoa butter substitute
Code of Federal Regulations
Codex Alimentarius Commission
Links
404
33
4
34
composition summary to meet
standards
35
milk chocolate standards
comparison
CODEX STAN 87-1981
5
34
co-extrusion
177
cold flow
130
cold stamping
415
Bühler Bindler FlexiStamp
layout with four triple heads
CoolCore stamping movements
68
423
425
418
depositing, vibrating, cooling and
demoulding
418
distribution of oil concentration
422
faults, causes and solutions
423
Frozen Shell patent
419
future trends
423
424
425
oscillating process vs CoolCore
production steps
419
process conditions and product
quality
422
suppliers
416
technology
416
cold forming without moulds
418
procedure with moulds
417
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navigation.
Index Terms
Links
cold stamping
technology (Cont.)
stamping tool design
417
vs oscillating process space
requirements
colour
420
134
list of synthetic colours
135
measurement
242
natural
135
248
natural colours in sugar and
confectionery chemistry
136
synthetic
134
compound coatings
80
cocoa butter alternatives
82
formulation constraints
84
lauric cocoa butter replacers
84
non-lauric cocoa butter
replacers
82
supercoatings
82
cocoa commodity prices
81
fat choice effect on manufacturing
process
93
coating production
93
cooling
94
enrobing
94
future trends
98
non-lauric coating gloss
96
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navigation.
Index Terms
Links
compound coatings
fat choice effect on manufacturing (Cont.)
non-lauric cocoa butter replacement
and lauric cocoa butter substitute
fats crystallisation
95
packaging and storage
96
specific problem associated with
lauric cocoa butter substitute
coatings
tempering
flavourings and colourings
96
93
89
formulation on sensory and functional
properties
90
melting profile and meltdown in the
mouth
90
melting profile of coating fats
91
shelf life and fat bloom risk
92
solid fat contents of compound
coating fats
91
future trends
98
recipes
87
lauric CBE coatings
89
non-lauric CBR coatings
88
supercoatings
87
conche
25
Elk conche mixing element
25
typical three-shafted conche
24
conching
21
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navigation.
Index Terms
Links
confectionery products, microscopy for
understanding the properties
285
confocal scanning laser microscopy,
291
CoolCore
417
Copernica Cerifera
225
corn syrup
129
Couette rotational viscometer
259
418
421
couvertures
and chocolate application in ice
cream
vs