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INDUSTRIAL CHOCOLATE MANUFACTURE AND USE INDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USEINDUSTRIAL CHOCOLATE MANUFACTURE AND USE
INDUSTRIAL CHOCOLATE MANUFACTURE AND USE Industrial Chocolate Manufacture and Use: Fourth Edition Edited by Stephen T Beckett © 2009 Blackwell Publishing Ltd ISBN: 978-1-405-13949-6 SBeckett_FM.indd i 10/1/2008 10:00:43 AM INDUSTRIAL CHOCOLATE MANUFACTURE AND USE Fourth Edition Edited by Stephen T Beckett Formerly Nestlé PTC York, UK SBeckett_FM.indd iii 10/1/2008 10:00:44 AM This edition first published 2009 Third edition published 1999 Second edition published 1994 by Chapman and Hall First edition published 1988 by Chapman and Hall © 1999, 2009 by Blackwell Publishing Ltd Blackwell Publishing was acquired by John Wiley & Sons in February 2007 Blackwell’s publishing programme has been merged with Wiley’s global Scientific, Technical, and Medical business to form Wiley-Blackwell Registered office John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom Editorial offices 9600 Garsington Road, Oxford, OX4 2DQ, United Kingdom 2121 State Avenue, Ames, Iowa 50014-8300, USA For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic books Designations used by companies to distinguish their products are often claimed as trademarks All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners The publisher is not associated with any product or vendor mentioned in this book This publication is designed to provide accurate and authoritative information in regard to the subject matter covered It is sold on the understanding that the publisher is not engaged in rendering professional services If professional advice or other expert assistance is required, the services of a competent professional should be sought Library of Congress Cataloging-in-Publication Data Industrial chocolate manufacture and use / edited by Steve Beckett – 4th ed p cm Includes bibliographical references and index ISBN-13: 978-1-4051-3949-6 (hardback : alk paper) ISBN-10: 1-4051-3949-8 (hardback : alk paper) Chocolate Cocoa I Beckett, S.T TP640.I53 2008 664.5—dc22 2008006200 A catalogue record for this book is available from the British Library Set in 10/12 pt Palatino by Newgen Imaging Systems Pvt Ltd, Chennai, India Printed in Singapore by Fabulous Printers Pte Ltd SBeckett_FM.indd iv 2009 10/1/2008 10:00:44 AM CONTENTS Preface Contributors xxii xxv Traditional Chocolate Making S.T Beckett 1.1 History 1.2 Outline of process 1.2.1 Preparation of cocoa nib – flavour development 1.2.2 Grinding – particle size reduction 1.2.3 Conching – flavour and texture development 1.3 Concept of the book References Cocoa Beans: from Tree to Factory M.S Fowler 2.1 Introduction 2.2 Growing cocoa 2.2.1 Where cocoa is grown 2.2.2 Varieties of cocoa: Criollo, Forastero, Trinitario and Nacional 2.2.3 Climatic and environmental requirements 2.2.4 Propagation of the planting material 2.2.5 Establishment and development of the plants in the field 2.2.6 Major pests and diseases 2.2.7 Flowering and pod development 2.2.8 Harvesting, pod opening and yields 2.2.9 Environmental aspects of cocoa cultivation 2.2.10 Labour practices on farms 2.3 Fermentation and drying 2.3.1 Fermentation 2.3.2 Microbiological aspects of fermentation 2.3.3 Development of cocoa flavour precursors 2.3.4 Drying 10 4 10 10 10 12 13 14 14 15 15 17 19 19 20 20 21 21 23 v SBeckett_FM.indd v 10/3/2008 3:49:44 PM vi SBeckett_FM.indd vi Contents 2.4 The cocoa supply chain 2.4.1 Internal market 2.4.2 International cocoa markets 2.4.3 Fairtrade 2.4.4 Shipment of cocoa 2.4.5 Moisture movement during shipment 2.4.6 Storage of cocoa 2.4.7 Infestation of cocoa 2.5 Quality assessment of cocoa 2.5.1 Composition of cocoa beans 2.5.2 Cocoa beans: quality aspects and contracts 2.5.3 Cocoa beans: sampling and the ‘cut test’ 2.5.4 Contaminants and residues 2.5.5 Cocoa butter hardness 2.5.6 Sensory evaluation 2.6 Types and origins of cocoa beans used in chocolate 2.6.1 Sources of bulk cocoas 2.6.2 Côte d’Ivoire (Ivory Coast) 2.6.3 Ghana 2.6.4 Indonesia 2.6.5 Nigeria 2.6.6 Cameroon 2.6.7 Brazil 2.6.8 Ecuador 2.6.9 Speciality, origin and ‘fine’ or ‘flavour’ cocoas Conclusions References and Further reading Abbreviations/Acronyms/Websites 24 25 25 28 29 29 31 32 33 33 33 37 39 39 40 40 40 41 41 42 43 43 43 43 44 45 46 47 Sugar and Bulk Sweeteners Ch Krüger 3.1 Introduction 3.2 The production of sugar 3.3 Sugar qualities 3.4 The storage of sugar 3.5 Sugar grinding and the prevention of sugar dust explosions 3.6 Amorphous sugar 3.7 Other sugars and bulk sweeteners 3.7.1 Invert sugar 3.7.2 Glucose 3.7.3 Fructose 3.7.4 Tagatose 3.7.5 Lactose 48 48 48 50 51 53 56 57 57 58 58 59 60 10/3/2008 3:49:44 PM Contents 3.7.6 Isomaltulose 3.7.7 Trehalose 3.7.8 Polydextrose 3.7.9 Inulin 3.7.10 Sorbitol 3.7.11 Mannitol 3.7.12 Xylitol 3.7.13 Erythritol 3.7.14 Maltitol 3.7.15 Maltitol syrup 3.7.16 Isomalt 3.7.17 Lactitol 3.8 Physiological characteristics of sugars and bulk sweeteners 3.9 The sweetening power of sugars and bulk sweeteners 3.10 Other sensory properties of sugars and bulk sweeteners 3.11 Solubilities and melting points of sugars and bulk sweeteners 3.12 Maximum conching temperatures of chocolate masses with different bulk sweeteners Conclusions References Further reading SBeckett_FM.indd vii Ingredients from Milk S.J Haylock and T.M Dodds 4.1 Introduction 4.2 Milk fat 4.2.1 Anhydrous milk fat 4.2.2 Flavour of milk fat 4.2.3 Interactions of milk fat and cocoa butter 4.2.4 Milk fat fractions 4.2.5 ‘Free’ and ‘bound’ milk fat 4.2.6 Bloom 4.3 Milk powder 4.3.1 Skim milk powder: non-fat dried milk 4.3.2 Whole milk powder 4.3.3 High-fat powders 4.3.4 Buttermilk powder 4.3.5 Formulated milk powders 4.3.6 Whey powders 4.4 Milk crumb 4.5 Lactose 4.6 New consumer requirements vii 60 60 60 61 61 62 62 63 63 64 64 64 65 67 69 70 71 72 73 75 76 76 79 80 82 83 85 87 89 90 90 92 94 94 95 96 96 97 98 10/3/2008 3:49:44 PM viii Contents Summary Acknowledgements References SBeckett_FM.indd viii Chocolate Crumb M.A Wells 5.1 Introduction and history 5.2 Benefits of milk crumb 5.3 Typical crumb recipes 5.4 Flavour development in chocolate crumb 5.5 Sugar crystallization during crumb manufacture 5.6 The structure of chocolate crumb 5.6.1 Crystallinity 5.6.2 Fat availability 5.6.3 Fat droplet size 5.6.4 Aeration 5.6.5 Overall particle size distribution 5.7 Typical crumb processes and equipment 5.7.1 Batch oven process 5.7.2 Continuous processes 5.8 Effect of the crumb process upon the crumb properties 5.9 Changes to crumb during storage Conclusions References Production and Quality Standards of Cocoa Mass, Cocoa Butter and Cocoa Powder H.J Kamphuis 6.1 Introduction 6.2 Cleaning of cocoa beans 6.3 Removal of shell 6.4 Breaking and winnowing 6.5 Alkalization 6.6 Bean and nib roasting 6.7 Cocoa mass (cocoa liquor) 6.7.1 Grinding cocoa nibs 6.7.2 Quality of cocoa mass for the chocolate industry 6.7.3 Quality of cocoa mass for the production of cocoa powder and butter 6.8 Cocoa butter 6.9 Cocoa powder 6.9.1 Types of cocoa powder 6.9.2 Quality of cocoa powder Summary 98 99 99 101 101 102 103 103 107 109 109 110 110 111 111 112 112 113 117 117 119 119 121 121 121 122 124 126 127 130 130 131 132 133 135 136 137 139 10/3/2008 3:49:44 PM Contents SBeckett_FM.indd ix ix Acknowledgements References Further reading 139 139 140 Particle Size Reduction G.R Ziegler and R Hogg 7.1 Introduction 7.2 Principles of fine grinding 7.2.1 Breakage mechanisms 7.2.2 Grinding processes 7.3 Grinding equipment 7.3.1 Crushers 7.3.2 Media mills 7.3.3 Impact mills 7.3.4 Fluid energy mills 7.3.5 Guidelines for equipment selection 7.4 Cocoa nib grinding 7.5 Chocolate refining 7.5.1 The five-roll refiner 7.5.2 Crumb chocolate 7.5.3 Sugar substitutes 7.5.4 The refiner-conche 7.5.5 Refining in the presence of water 7.5.6 Milling cocoa powder 7.6 Particle size reduction and chocolate flow properties 7.7 Particle size and sensory properties Conclusions References 142 Flavour Development in Cocoa and Chocolate G Ziegleder 8.1 Introduction 8.2 Fermentation 8.2.1 The fermentation process 8.2.2 Chemical changes and development of flavour precursors 8.2.3 Over-fermentation 8.3 Drying 8.4 Roasting 8.4.1 Roasting process and the further development of flavour precursors 8.4.2 Roast flavour 8.5 Conching 8.5.1 Thin-film-treatment of roasted cocoa liquor 8.5.2 Effect of conching on aroma development 142 143 143 144 146 146 146 147 148 148 149 152 154 158 158 159 159 160 160 165 166 166 169 169 170 170 171 173 174 176 176 179 184 184 184 10/3/2008 3:49:44 PM x 10 SBeckett_FM.indd x Contents 8.6 Plain chocolate and milk chocolate Conclusions References 187 188 188 Conching S.T Beckett 9.1 Introduction: The reason for conching 9.1.1 Flavour development 9.1.2 Flow property optimization 9.2 The principles of conching 9.2.1 Removal of volatiles and temperature control 9.2.2 Fat and emulsifier additions 9.2.3 The degree of mixing 9.3 The three phases of conching 9.3.1 Dry phase conching 9.3.2 Pasty phase conching 9.3.3 Liquid phase conching 9.4 Conching machines 9.4.1 History 9.4.2 Batch conches 9.4.3 Continuous conches 9.4.4 Cocoa mass (liquor) treatment devices 9.4.5 Liquefiers 9.4.6 Combined grinding/conching machines Summary References 192 Chocolate Flow Properties S.T Beckett 10.1 Introduction 10.2 Non-Newtonian flow 10.3 Presentation of viscosity measurements 10.4 Single point flow measurement 10.4.1 Flow-cup viscometer 10.4.2 Falling-ball viscometer 10.4.3 Gardner mobilometer 10.4.4 Torsion viscometer (Gallenkamp or Fison) 10.4.5 MacMichael viscometer 10.5 Rotational viscometers 10.6 Sample preparation and measurement procedures 10.6.1 Sample preparation 10.6.2 Checking the viscometer 10.6.3 Preconditioning 10.6.4 Shear rate range 192 192 193 193 193 195 196 198 199 200 201 202 202 204 210 214 217 219 221 222 224 224 225 228 229 230 230 231 232 233 233 235 235 236 236 237 10/3/2008 3:49:44 PM Chocolate Flow Properties Casson yield value (Pa) Casson plastic viscosity (Pa s) 240 2 10 20 30 % >20 microns 40 60 40 20 10 20 30 % >20 microns 40 Figure 10.15 The influence of particle fineness on the Casson viscosity parameters in two milk chocolates with 0.25% lecithin: (1) 30% fat; (2) 32% fat devices such as the Malvern (Chapter 22) This type of instrument is able to show the distribution from sub-micron to above a millimetre The percentage of larger particles is required to determine the textural roughness of the chocolate Another parameter that the instrument calculates is the specific surface area, which relates to the surface area of solid particles which must be coated with fat As the chocolate is ground finer, there are more particles to interact so the yield value is increased In practice, the effect upon the yield value is much greater than for the plastic viscosity (Figure 10.15, Chevalley, 1999) The yield value normally correlates with the measured specific surface area This is not the case for the Casson plastic viscosity, however, where at very large particle sizes the plastic viscosity can indeed increase again This may be due to increasing amounts of bound fat or to how the solid particles pack themselves together If spherical particles all of a similar size are packed together a lot of space remains between them, which must be filled with fat or smaller particles (Figure 10.16 and Chapter 7, Section 7.6) In the extreme of having a lot of larger particles or chocolates with very few very fine ones, further grinding will reduce the viscosity This is however very unusual Where an industrial chocolate is found to have a very high yield value, but the plastic viscosity is correct or only slightly high, then the particle size should be investigated as it is possible that the grinding procedure is producing an excessive proportion of fine particles A high yield value can be counteracted by the use of a surface-active agent 10.7.3 Surface-active agents (emulsifiers) Although it is necessary to coat sugar particles with fat, this is not always easy as the sugar surface is lipophobic, i.e it tries to repel the fat The flow SBeckett_C010.indd 240 9/26/2008 3:15:25 PM Chapter 10 Monomodal Bi-Modal 65% 86% 241 Figure 10.16 Illustration of the packing of spheres that are: (1) all the same size; (2) two different sizes Figure 10.17 Schematic diagram of lecithin molecules around a sugar particle can be aided however by placing a surface-active agent, normally known as an emulsifier between the two (see Figure 10.17) The most common emulsifier is lecithin, which has been used in chocolate since 1930 It is naturally occurring, often produced from soya and is said to have positive health benefits One end of the molecule is lipophilic so remains in the fat, whereas the other end lipophobic end attaches itself to the sugar surface (it will affect the other solid particles, but the predominant effect is with the sugar) This aids the flow properties to such an extent that for additions of up to about SBeckett_C010.indd 241 9/26/2008 3:15:26 PM 242 80 70 Casson yield value (Pa s) Casson plastic viscosity (Pa s) Chocolate Flow Properties 60 50 40 30 20 10 0.2 0.4 0.6 Lecithin (%) 0.8 0.2 0.4 0.6 Lecithin (%) 0.8 Figure 10.18 The influence of soya lecithin addition on the Casson viscosity parameters in two dark chocolates: (1) 33.5% fat, 1.1% moisture; (2) 39.5% fat, 0.8% moisture (Finke, 1965) 0.3% it has an effect equivalent to ten times this weight of cocoa butter As with cocoa butter editions, the higher the viscosity, the more effective is the addition of the emulsifier, see Figure 10.18 Unlike cocoa butter however, further additions of lecithin can cause the yield value to increase This may be due to lecithin particles attaching themselves to each other forming new particles called micelles, or due to the lipophilic ends attaching themselves to the lipophilic ends of a second layer of lecithin and reducing its effectiveness The point at which this occurs depends upon the surface area of the solid particles being coated A fine chocolate with a high sugar content can therefore tolerate a higher lecithin level than a coarse one or one with a lower sugar content In addition it will depend upon the type of lecithin used Lecithin can vary and some manufacturers have tried to optimize those components which are beneficial to chocolate flow (Preston, 1989) and fractionated lecithins are available The phosphatidylcholine part of lecithin has been shown to be particularly effective in reducing the plastic viscosity of some dark chocolates (van Nieuwenhuyzen, 1995), whereas other fractions are less effective than standard lecithin in reducing the yield value Because the ratio of the different phospholipids vary within standard lecithins, its effectiveness in reducing chocolate viscosity can change from batch to batch For this reason, some suppliers provide a standardized product (Schmitt, 1995) SBeckett_C010.indd 242 9/26/2008 3:15:27 PM Chapter 10 243 Table 10.1 Flow characteristics of plain chocolate with added emulsifiers at 50C (Harris, 1968) Addition 0.3% soya lecithin 0.3% YN 0.3% sucrose dipalmitate 0.3% PGPR 0.8% PGPR Casson plastic viscosity (Pa s) Casson yield value (Pa) 0.6 1.03 0.9 3.25 2.0 9.2 3.0 16.6 2.5 In addition to lecithin, other new surface-active agents have been developed for chocolate One of the most widely used is the synthetic lecithin, YN (obtained from partially hardened rapeseed oil after glycerolysis, phosphorylation and neutralization) YN is more constant in composition than soya lecithin: its flavour is bland and neutral; its efficiency is said to be greater than that of soya lecithin, and at levels above 0.3%, no thickening occurs When compared with soya lecithin, YN can sometimes have a stronger effect on CA than on CA (see Table 10.1) Concern about genetically modified soya has led to increased interest in YN and lecithin produced from other crops such as sunflower Another widely used emulsifier is polyglyceryl polyricinoleate (PGPR), sometimes known as Admul-WOL PGPR has the ability to strongly reduce or even cancel the yield value of chocolate (Table 10.1) This useful property is exploited by the confectioner in such applications as the moulding of Easter egg shells and also for correcting the viscosity of a chocolate that has too many fine particles, or indeed if too much lecithin has been added A combination of lecithin and PGPR can in fact produce good flow properties, especially in low fat chocolates It is possible to purchase this combination as a mixture Other emulsifiers include citrem, soritan tristearate, sucrose esters and calcium-stearoyl lactoyl lactate Citrem (citric acid ester) has the properties of the lecithin/PGPR combination, whereas sorbitan tristearate is an emulsifier which is used to reduce bloom formation rather than control viscosity Emulsifiers sometimes affect the tempering of chocolate, which in turn affect the flow properties of the tempered chocolate The effect of the emulsifier on chocolate flow is normally evaluated on untempered chocolate as in Figure 10.18 It is however useful to check the results on tempered chocolate (Weyland, 1994) It should also be noted that over tempering thickens chocolate and can cause a low viscosity chocolate to become unuseable The stage in the process at which the emulsifier is added is a very important factor for example lecithin added towards the end of conching reduces viscosity by a greater amount than when exactly the same amount is added SBeckett_C010.indd 243 9/26/2008 3:15:27 PM 244 Chocolate Flow Properties at the start The reason for this is that, as the action of lecithin is a surface effect, if it is added to the masse too early, some of it may (by prolonged mixing and grinding) be absorbed into the cocoa particle, thus reducing its efficiency (Minifie, 1980) It is also known that exposure to relatively high temperatures for long time reduces lecithin performance In addition it can reduce the work input provided by the conche 10.7.4 Conching Besides the time of addition of the fat and emulsifier, the time and intensity of the conching have a big effect upon the final chocolate viscosity The longer a chocolate is conched normally the thinner a chocolate becomes However with increased time, the lowering of viscosity becomes less significant or economic The intensity governs the rate at which the solid particles are coated with fat This is normally governed by the conche design, but can be helped by changing the amount of material in a conche and the time and order in which the fats and emulsifiers are added A low intensity conche will never produce as thin a chocolate as a high intensity one however long it is operated As was noted earlier (Section 10.6), poor conching results in big differences between the up and down measurements in a viscosity Further details concerning the effect of conching parameters on chocolate viscosity are given in Chapter In addition to coating particles, conching also removes moisture from the chocolate masse, which also has a big effect upon viscosity 10.7.5 Moisture If some per cent of moisture is added to chocolate it will become very thick Indeed if as little as 0.3% extra moisture is left within the chocolate it will be necessary to add another 1% of cocoa butter to restore the viscosity to what it should have been This is probably in part due to water on the surface of the sugar particles sticking them together and impeding the flow Where lecithin is also present this is less likely to happen and indeed chocolates containing this emulsifier can have more water present and yet retain their correct flow properties Lecithin can have a negative effect during conching however when its hydrophilic properties will reduce the amount of water evaporating from the masse Below the 1% level, however, most of the moisture is bound into the ingredients for example as water of crystallization in lactose, and so has little effect upon the flow properties 10.7.6 Vibration This is important for removal of air bubbles or the weight control of enrobed sweets (Chapter 14) Bartusch (1961) showed that apparent viscosity (at a slow SBeckett_C010.indd 244 9/26/2008 3:15:28 PM Chapter 10 245 shear rate of s1) decreased with increasing amplitude of vibration and he postulated that the yield value had disappeared This was confirmed by Barigou et al (1998) on both milk and dark chocolate Here the effect of frequency was found to be more important than amplitude It was possible to obtain chocolate with a Newtonian flow by vibrating it at 50 Hz and an amplitude of 0.1 mm (0.004 in.) The effect was reversible however and the chocolate regained its previous viscosity as soon as the vibration stopped Conclusions The flow properties of chocolate are very complex However, an understanding of both flow property measurement and factors affecting the flow can greatly help trouble-shooting and plant optimization It is always important to measure the flow properties of chocolate under conditions that are as close as possible to those under which it is being processed Where faults occur, it is necessary that corrective action should be taken according to the flow parameter that is incorrect for example add PGPR for a high apparent viscosity at a low shear rate (Casson yield value), or cocoa butter for a high reading at a high shear rate (Casson plastic viscosity) References Aeschlimann, J.-M and Beckett, S.T (2000) Journal of Texture Studies, 31, 541–576 Barigou, M., Morey, M and Beckett, S.T (1998) Chocolate – the shaking truth International Food Ingredients, 4, 16–18 Bartusch, W (1961) First Fette and Seifen, 63, 721–729 Beckett, S.T (2000) The Science of Chocolate RSC, Cambridge, UK Beckett, S.T (2001) Casson model for chocolate, friend or foe? Manufacturing Confectioner, 81, 61–66 Chevalley, J (1999) Chocolate flow properties In: Industrial Chocolate Manufacture and Use (ed S.T Beckett), Blackwell Science, Oxford, UK Chevalley, J (1991) Journal of Texture Studies, 22, 219–229 Fincke, A (1965) Handbuch der Kakaoerzeugnisse Springer Verlag, Berlin, p 357 Harris, T.L (1968) SCI Monograph, 32, 108–122 Hogenbirk, G (1986) Manufacturing Confectioner, 66 (Jan), 56–59 Koch, J (1959) Manufacturing Confectioner, 39 (Oct.), 23–27; Rev Int Choc, 330–335 Martin, R.A and Smullen, J.F (1981) Manufacturing Confectioner, 61 (May), 49–54 Minifie, B.W (1980) Manufacturing Confectioner, 60 (April), 47–50 Office International du Cacao et du Chocolat (E/1973) Analytical Methods 10; Rev Int Choc (1973) (Sept.) 216–218 O.I.C.C.C (2000) International Office of Cocoa, Chocolate and Sugar Confectionery, Viscosity of Cocoa and Chocolate Products Analytical Method 46 Cabisco, Bruxelles, Belguim Preston, M (1989) Food Flavourings, (Feb.) 25–29 Riedel, H.R (1980) Conference Production, 46 (Dec.), 518–519 SBeckett_C010.indd 245 9/26/2008 3:15:28 PM 246 Chocolate Flow Properties Schmitt, H (1995) Zucker und Süsswarenwirtschaft, 7/8, 300–312 Stumpf, D (1986) Manufacturing Confectioner, 66 (Jan.), 60–63 Seguine, E.S (1986) Manufacturing Confectioner, 66 (Jan.), 49–55 Seguine, E.S (1988) Factors influencing the taste, selection and specification of chocolate 42nd PMCA Confernce, pp 56–61 Van Nieuwenhuyzen, W (1995) Food Technology International Europe, 47–50 Weyland, M (1994) Manufacturing Confectioner, 77 (May), 111–117 Windhab, E.J (1995) Rheology in food processing In: Physico-Chemical Aspects of Food Processing (ed S.T Beckett) Blackie Academic and Professional, Glasgow SBeckett_C010.indd 246 9/26/2008 3:15:28 PM Chapter 11 BULK CHOCOLATE HANDLING J.H Walker 11.1 Introduction The output from chocolate manufacturing plants has continued to increase and this, coupled with a demand for higher rates of productivity, has resulted in the transport of the ingredients and the finished masse becoming more important Wheeled tanks and the transport of solid blocks of material have often been replaced by the use of pumps and heated pipe work Within large confectionery factories, the flow rate of chocolate in the pipelines can be as high as 10 tonnes/h and the distance to which it is transported is often as far as 200 m (600 ft) or even more It is important, therefore, that the pump and pipe system is designed to meet the expected duty Liquid chocolate is a non-Newtonian fluid and this means that both the yield value and the plastic viscosity and operating temperature (see Chapter 10) must be considered when specifying the chocolate delivery system There are many different types of pump that can be used to transport chocolate, each with its own advantages and disadvantages In addition, there are numerous applications for pumps, ranging from the metering cocoa liquor to pumping tempered chocolate, which means that many different types of pumps are employed in a single manufacturing plant The purchase cost of the pump may also influence the choice, however it should be remembered that the incorrect choice could lead to considerable problems 11.2 Viscosity and viscometry 11.2.1 What is viscosity? It is easy to tell the difference between a thin and thick chocolate, but difficult to quantify viscosity in a meaningful way except by using specialized instruments It is important to understand the influence of the chocolate viscosity since a high viscosity chocolate requires more power to pump than a low viscosity one Knowing its rheological behaviour therefore, is essential when designing pumping and piping systems When specifying pump Industrial Chocolate Manufacture and Use: Fourth Edition Edited by Stephen T Beckett © 2009 Blackwell Publishing Ltd ISBN: 978-1-405-13949-6 SBeckett_C011.indd 247 247 9/26/2008 3:15:49 PM 248 Bulk Chocolate Handling requirements to a supplier, it is always necessary to quote the expected viscosity and temperature variations, together with the flow rate and pressure limitations for sensitive ingredients or vulnerable equipment such as tempering machines Viscosity is the measure of the internal friction of a chocolate This friction becomes apparent when a layer of chocolate is made to move in relation to another layer The greater the friction, the greater the amount of force required causing this movement, which is called ‘shear’ Shearing occurs whenever the chocolate is physically moved or distributed, as in mixing, pumping, stirring, depositing, etc Highly viscous chocolate therefore requires more force to move than less viscous chocolate Isaac Newton defined viscosity by considering the model shown in Figure 11.1 Two parallel planes of fluid of equal area ‘A’ are separated by a distance ‘dx’ and are moving in the same direction at different velocities ‘V1’ and ‘V2’ Newton assumed that the force (F) required to maintain this difference in speed was proportional to the difference in speed through the liquid, or the velocity gradient at the part of liquid under consideration A F dx V2 V1 dv Figure 11.1 Diagram illustrating shear The velocity gradient (V2 – V1)/dx, is a measure of the change in speed at which the intermediate layers move with respect to each other It describes the shearing the liquid experiences and is thus called the ‘shear rate’ and is often symbolized as ‘D’ Its unit of measure is the reciprocal second (cm per second/cm or s1) The term F/A indicates the force per unit area required to produce the shearing action and is known as the shear stress () Newton stated that the coefficient of viscosity remained the same at varying flow rates, but this only applies to Newtonian fluids at a fixed temperature Using these simplified terms, viscosity (h) may then be defined mathematically by this formulae: Viscosity h /D shear stress/ shear rate SBeckett_C011.indd 248 9/26/2008 3:15:49 PM Chapter 11 249 For confectionery products, the units of viscosity are usually centipoise, poise or Pascal seconds If the viscosity is a constant and does not vary with changing values of D, then the fluid is Newtonian A Newtonian liquid is therefore one for which the graph of shear stress plotted against the rate of shear is a straight line for example glucose syrup (see Figure 10.3) For such materials, the pump supplier only needs one viscosity figure at the temperature of use N.B Viscosity can vary a lot with temperature, so it may be necessary to carry out several measurements A non-Newtonian fluid is defined as one in which the relationship of shear stress/rate of shear is not a constant, as is shown in Figure 11.2 In other words when the shear rate is varied, the shear stress does not vary in the same proportion The viscosity of such fluids will therefore change as the shear (flow) rate is varied The measured viscosity at any particular shear rate is known as the ‘apparent viscosity’ at that shear rate The value of the shear rate should always be quoted When providing the viscosity specification to a plant designer, measurements should be obtained at both a high and a low shear rate The type of viscometer that is used can also affect the measurement obtained (see Chapter 10) Viscosity Non-Newtonian fluid Shear rate Figure 11.2 Diagram illustrating non-Newtonian flow 11.2.2 Laminar and turbulent flow The flow of a fluid down a pipe may be either laminar or turbulent In laminar (streamline) flow, the molecules within the fluid follow well-defined paths, which may converge or diverge, but their motion is in the general direction of the bulk flow The viscosity is dependent upon temperature but largely independent of pressure and surface roughness If the shear rate becomes very high however, the movement of the molecules within the fluid becomes more random and some molecules can SBeckett_C011.indd 249 9/26/2008 3:15:49 PM 250 Bulk Chocolate Handling even move in the opposite direction to that in which they are being pumped and the flow becomes turbulent This should never be allowed to happen within a chocolate pipeline as it can cause damage to the system The shear stress down a pipe is proportional to its diameter, so larger pipes should be installed if any turbulence occurs In addition, since many of the chocolate pumps and pipeline fittings available are only suitable for working pressures of 10 bar maximum, it is advisable to size the pipeline to be big enough to operate below this limit 11.3 Pump sizes 11.3.1 Power The power requirement for the pump has to take into account all frictional inefficiencies, such as those arising from gearboxes, belt drives and the internal friction of the pump bearings and seals These vary greatly between the different types of pumps that are used Never size a pump using the viscosity of chocolate measured for standard operating conditions Allowances must be made for start-up conditions, particularly after shutdown periods such as weekends and holidays If the chocolate is not constantly moved in the pipeline or storage tank, sedimentation of the solid particles within the chocolate may occur This can result in an increase in the system pressure or even blocking of the pump 11.3.2 Speed The speed at which the pump operates should be as low as possible without causing the pump to slip excessively Some chocolates are shear sensitive and can have their viscosity changed by over shearing by the pump Excessive speeds can also produce heat which may result in caramelization of the chocolate, which in turn may eventually lead to the pump seizing The life of the pump and the seal can also be extended by operating the pump at low speed Many chocolate pumps are built to a special configuration using large internal clearances between the fixed and rotating parts within the pump and are designed to minimize the damage caused by frictional heat to the chocolate whilst at the same time maintaining operational efficiency 11.4 General criteria for choosing a pump All pumps must have a means of keeping the chocolate warm when they are not in operation This is usually achieved by the means of a hot water jacket or saddle built in to the pump SBeckett_C011.indd 250 9/26/2008 3:15:50 PM Chapter 11 251 When choosing a pump for the transport of chocolate or chocolate ingredients the following criteria should be considered: • The quantity of chocolate the pump is required to deliver • The pressure the pump will need to overcome (pressure drop in pipeline) • The accuracy to which the pump will need to operate, for example • • • • • metering cocoa mass The type of seal arrangement for example gland packing, lip seal The operating control and shear action of the pump Heating caused by excessive shear may cause caramelization or de-tempering of the chocolate The length of time the pump will be required to operate without stopping, for example a ring main where the pump operates 24 h per days per week Or intermittent batch operation such as discharging a conche If inclusions are to be included in the chocolate, the pump will be required to accommodate this The material in contact with the chocolate Cast iron and steel pumps are normally satisfactory, but stainless steel may also be used 11.5 Types of pumps There any many different types of pumps used in the manufacture of chocolate, but most fall into the following categories: • • • • • • • Gear pumps Sliding vane pumps Lobe and rotary piston pumps Screw pumps Progressive cavity (mono) pumps Pawl pumps Positive displacement piston and diaphragm pumps 11.5.1 Gear pumps Internal gear pumps are suitable for use with high viscosity chocolates In addition they provide a non-pulsating flow and are self-priming Because they have only two moving parts they are reliable, simple to operate and easy to maintain (Figure 11.3) By reversing the drive motor, the pump can operate in either direction This facility is particularly useful to drain a tempering machine prior to a change of chocolate There are several types of gear pumps, but the most common types found in the confectionery industry are the simple spur gear pump and the internal gear pump The spur gear pump has two meshing gears that revolve in opposite directions and has a very small clearance between the gear and the body of the pump The chocolate that fills the cavity between SBeckett_C011.indd 251 9/26/2008 3:15:50 PM 252 Bulk Chocolate Handling Drive shaft Inlet Outlet Idler ger Figure 11.3 Internal gear pump two successive gear teeth must follow the rotation of the gear When the gear teeth mesh together, the space between the teeth is closed and the entrapped chocolate is pushed out As the gears revolve and the teeth disengage, the space on the low-pressure side of the pump is created, trapping new quantities of chocolate 11.5.2 Sliding vane pumps In a sliding vane pump the eccentric (off-centre) rotor incorporates sets of sliding vanes, which mechanically displace the fluid (Figure 11.4) Internal clearances although small, are required in this type of pump and therefore they cannot be truly classified as positive displacement pumps By design this system of displacement creates a pulsation in the discharge flow from the pump However these pumps can handle solids entrained in the chocolate These pumps are less suitable for applications that involve very high throughputs, high viscosity, or large pressure drops for example pumping over long distances Figure 11.4 Mode of operation of a vane pump SBeckett_C011.indd 252 9/26/2008 3:15:50 PM Chapter 11 Inlet 253 Outlet Figure 11.5 Mode of operation of a lobe pump 11.5.3 Lobe and rotary piston pumps Lobe pumps are similar to external gear pumps in operation in that fluid flows around the interior of the pump body (Figure 11.5) However in this case the lobes are prevented from making contact with each other by timing gears located in the external gearbox Rotary lobe pumps can handle large inclusions with minimal damage and a gentle pumping action minimizes product degradation They are usually made from stainless steel and therefore can be cleaned with water When the rotors have a covering of chocolate then the air gaps around them become ‘sealed’ This improves the efficiency of the pump to self-prime A lobe pump should not normally be used to move white chocolate, since severe caramelization of the chocolate can occur in the area of the lobe lock nut housing (The front plate of the pump is recessed to fit around the locknut, and it is in this recess where chocolate can become heat damaged.) 11.5.4 Screw pumps Screw pumps have been used for many years in the conveyance of bulk chocolate They normally have two or three rotors A twin-screw system is illustrated in Figure 11.6 As the twin screw systems is driven by a set of gears, situated in the gearbox, there is no contact between the two pumping screws These pumps can operate equally well when driven in reverse and at low speed offer a gentle pumping action, together with a uniform flow with little pulsation or turbulence They are available either manufactured from cast iron or stainless steel Some designs can cope with inclusions in the product of up to mm (0.2 in.) The three rotor design comprises of a central rotor, which is connected to the drive motor and two idling satellite rotors which are driven by this central rotor The rotors are encased in a closely fitting steel housing The rotors are free to mesh together (there are no external timing gears) This therefore SBeckett_C011.indd 253 9/26/2008 3:15:51 PM Outlet Bulk Chocolate Handling Inlet 254 Figure 11.6 Illustration of twin screw pump consists of a sealed chamber through which the chocolate is conveyed When the centre rotor is turned by the drive shaft these sealed chambers receive the chocolate to be pumped at the suction side of the pump and convey the medium in a uniform (non-pulsating) flow to the discharge port 11.5.5 Pawl pumps This type of pump is frequently used as a circulation pump in chocolate enrobers or to pump tempered chocolate A gentle action is achieved by having a high conveying volume within the pump but operating at a very low speed The central rotor is shaped so that two swept volumes of material are present within the pump As the rotor turns, the material is pushed round the pump until it comes up against a scraper blade (Figure 11.7) This is forced against the rotor by a spring, which diverts the flow to the outlet and prevents the chocolate from re-circulating back into the suction area These pumps are suitable for medium pressure applications with or without inclusions such as nuts and raisins 11.5.6 Progressive cavity mono pumps The progressive cavity pump has a single helical rotor rolling eccentrically in a double thread helix of twice the pitch length When the rotor turns it forms a series of sealed cavities, 180 apart, these progress from suction to discharge as the single helix rotates As one cavity diminishes, the opposing cavity is increasing at exactly the same rate: so the sum of the two is constant This results in a pulsation free flow which may contain particulate matter The rotor is usually manufactured from hardened stainless steel and the stator from natural or synthetic rubber SBeckett_C011.indd 254 9/26/2008 3:15:52 PM ... 24.2.1 Moulded chocolate tablets and bars 24.2.2 Chocolate countlines 24.2.3 Bulk chocolate 24.2.4 Boxed chocolates 24.2.5 Twist wrapping 24.2.6 Easter eggs and others seasonal chocolate novelties... introduced a chocolate drink to Spain Chocolate drinking spread to Italy Chocolate drinking reaches France First chocolate house established in London Nicholas Sanders invents a milk chocolate drink... suspension coating 16.3 The process of chocolate panning 16.3.1 Centre selection 16.3.2 Centre preparation 16.3.3 Selection of chocolate and compound coatings 16.3.4 Chocolate and compound engrossing