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The Science of Chocolate2nd Edition
The Science of Chocolate2nd EditionStephen T BeckettFormerly Nestle Product Technology Center, York, UK
ISBN: 978-0-85404-970-7A catalogue record for this book is available from the British Libraryr Stephen T Beckett 2008All rights reservedApart from fair dealing for the purposes of research for non-commercial purposes orfor private study, criticism or review, as permitted under the Copyright, Designs andPatents Act 1988 and the Copyright and Related Rights Regulations 2003, thispublication may not be reproduced, stored or transmitted, in any form or by anymeans, without the prior permission in writing of The Royal Society of Chemistry, orin the case of reproduction in accordance with the terms of licences issued by theCopyright Licensing Agency in the UK, or in accordance with the terms of thelicences issued by the appropriate Reproduction Rights Organization outside the UK.Enquiries concerning reproduction outside the terms stated here should be sent toThe Royal Society of Chemistry at the address printed on this page.Published by The Royal Society of Chemistry,Thomas Graham House, Science Park, Milton Road,Cambridge CB4 0WF, UKRegistered Charity Number 207890For further information see our web site at www.rsc.org
PrefaceIn 1988 I wrote a paper for School Science Review, in which Idescribed some of the science involved in chocolate making andfollowed this by two experiments that could be tried in the classroom. As a result of this I received letters from both pupils andteachers requesting more information or new experiments to try.Subsequently I was contacted by Chris Butlin, who was thendeveloping a food option for the Salters’ Physics Advanced Levelcourse. This resulted in some of the science of chocolate beingincluded in this option. The numerous talks given by my colleaguesand myself to junior schools, societies and universities also convinced me that there was a genuine interest in this topic and thatpeople were not just coming for the free samples.When, therefore, the Royal Society of Chemistry asked me if Iwould write a full book on this topic, aimed at schools anduniversities, I agreed to do so, without realising the amount ofwork involved. It was very gratifying, however, to learn in 2006that the sales were such that a second edition of the book wasrequired. Several people had commented that they wished to knowmore about the health and nutrition aspects of chocolate and, as alot of research has recently been carried out in the area, this seemedthe ideal subject for a new chapter. In addition, in 2005 NewScientist published a book entitled Does Anything Eat Wasps? inwhich the question was asked about how are bubbles put intoAeros. Possible solutions are given here as part of a second newchapter.Having graduated in physics, the book is naturally biased in thisdirection, although I have tried to include a substantial amount ofchemistry and even some mathematics in the project work. Severalv
viPrefaceof the chemical terms used in industry are different from thosetaught in schools. I have attempted to use the current terminologyand have included a glossary in the hope that it will be useful, ifsomeone is not familiar with the term in the text. This glossary alsoexplains some of the industry’s own technical names.This book should be especially useful for someone studying foodscience at university or who is about to join the confectioneryindustry. Although a scientific background is required to understand the more difficult sections, such as fat chemistry or theMaillard reaction, most of the rest of the book should be readableby 16–18 year olds. Here I have attempted to show how conceptssuch as latent heat, relative humidity etc. play an important part inthe making of something as apparently simple as chocolate. I hopethat this in fact might prove to be a ‘‘painless’’ way of learningabout them.Several sections are relatively simple and can be adapted byteachers of GCSE science or even younger pupils. This is especiallytrue of the projects described in Chapter 12. These are meant to bejust basic ideas that can be adapted according to age. All useapparatus or ingredients that should be easy to make or obtain.The appropriate safety precautions must, of course, be takenespecially for those involving glass, heat or chemicals.Finally I would like to thank my wife Dorothy for her helpwith the book and our sons Christopher and Richard for their helpwith the diagrams, together with John Birkett, Patrick Couzens,Peter Geary, Duane Mellor and Lynda O’Neill for correcting thescript, or testing the projects to ensure that they worked. I am alsograteful to Awema, Blackwell Science, Loders Croklaan andPalsgaard Industri A/S for their permission to reproduce picture,diagrams and tables. In particular, Figures 1.2, 2.3, 3.5, 3.6, 3.10,3.13, 3.14, 4.9, 4.11, 4.12, 5.2, 5.3, 5.8, 5.10, 5.13, 6.8, 7.1, 7.5 and9.8 are all reproduced from Industrial Chocolate Manufacture andUse with the permission of Blackwell Science and Figures 1.3 and1.4 with the permission of the Nestlé Archives, Vevey, Switzerland.Stephen BeckettYork, UK
ContentsChapter 1The History of Chocolate1.11.2Chocolate as a DrinkEating Chocolate1.2.1 Chocolate Crumb1.2.2 White Chocolate1.3 Chocolate Marketing in the UK1.4 Chocolate is Good for YouReferencesChapter 213789910Chocolate .6Sugar2.2.12.2.22.2.32.2.42.2.5BeansCocoa TreesCommercial Cocoa-Producing CountriesCocoa PodsFermentation2.1.4.1 Fermentation Procedure2.1.4.2 Microbial and ChemicalChangesDryingStorage and Transportand Sugar SubstitutesSugar and its ProductionCrystalline and Amorphous SugarLactoseGlucose and FructoseSugar Alcoholsvii111112141515182022232324262828
viiiContents2.2.6 PolydextroseMilk and Other Dairy Components2.3.1 Milk Fat2.3.2 Milk Proteins2.3.3 Milk Powders2.3.4 Whey and Lactose Powders2.4 Chocolate CrumbReferencesAdditional Reading2.3Chapter 3Cocoa Bean Processing3.13.2Bean CleaningRoasting and Winnowing3.2.1 The Problem of Bean Size Variation3.2.2 Winnowing3.2.3 Bean Roasting3.2.4 Nib and Liquor Roasting3.2.5 Roasters3.2.6 Chemical Changes during Roasting3.2.7 Maillard Reaction3.3 Grinding Cocoa Nib3.3.1 Cocoa Mills3.3.1.1 Impact Mills3.3.1.2 Disc Mills3.3.1.3 Ball Mills3.4 Cocoa Butter and Cocoa Powder Production3.4.1 Alkalising (Dutching)3.4.2 Cocoa Butter3.4.3 Cocoa PowderReferencesChapter 4555757Liquid Chocolate Making4.14.2Chocolate Milling4.1.1 Separate Ingredient Grinding Mills4.1.2 Combined MillingChocolate Conching4.2.1 Chemical Changes6162646869
ixContents4.2.24.2.34.2.44.2.5ReferencesChapter 5Physical ChangesViscosity ReductionConching Machines4.2.4.1 The Long Conche4.2.4.2 Rotary Conches4.2.4.3 Continuous Low VolumeMachinesThe Three Stages of Conching767879Controlling the Flow Properties of Liquid Chocolate5.15.2ViscosityParticle Size5.2.1 Particle Size Distribution Data5.2.2 Effect of Particle Size on Viscosity5.3 Effect of Fat Additions on Viscosity5.4 Moisture and Chocolate Flow5.5 Emulsifiers and Chocolate Viscosity5.5.1 Lecithin5.5.2 Polyglycerol Polyricinoleate5.5.3 Other Emulsifiers5.6 Degree of MixingReferencesChapter 670717373748184848690929394989999101Crystallising the Fat in Chocolate6.16.26.36.46.56.6Structure of Cocoa ButterDifferent Crystalline FormsPre-Crystallisation or TemperingMixing Different Fats (Fat Eutectics)Chocolate Fat BloomSome Types of Non-Cocoa Vegetable Fat6.6.1 Cocoa Butter Equivalents6.6.2 Enzyme Interesterification6.6.3 Lauric Fat Cocoa Butter Replacers6.6.4 Non-Lauric Fat CocoaButter Replacers6.6.5 Low Calorie FatsReferences104107110112116118119120121122124124
xChapter 7ContentsManufacturing Chocolate Products7.1Tempering7.1.1 Liquid Chocolate Storage7.1.2 Tempering Machines7.1.3 Hand Tempering7.1.4 Temper Measurement7.2 Moulding7.2.1 Solid Tablets7.2.2 Chocolate Shells7.3 Enrobers7.3.1 Maintaining Tempered Chocolate7.4 Solidifying the Chocolate7.4.1 Coolers7.5 Panning7.5.1 Chocolate Coating7.5.2 Sugar PanningReferencesChapter 8Analytical Techniques8.18.28.38.4Particle Size MeasurementMoisture DeterminationFat Content MeasurementViscosity Determination8.4.1 Simple Factory Techniques8.4.2 The Standard Method8.5 Flavour8.6 Texture Monitoring8.7 Crystallisation Amount and Type8.7.1 Nuclear Magnetic Resonance8.7.2 Differential Scanning CalorimetryReferencesChapter 53156158159159161163165167167169170Different Chocolate Products9.19.2Special Recipes9.1.1 Ice-cream coatingsShape-Retaining Chocolate171172173
xiContents9.2.19.2.29.2.39.2.49.39.49.5Modifying the Fat PhaseTransparent CoatingsWaterBuilding a Frameworkof Solid ParticlesAir Bubbles in Chocolate9.3.1 Factors Affecting Bubble Size9.3.2 Water Evaporation BubblesCream Eggs and Other FilledChocolate ShapesMultiple Chocolates and Centres173174174175176178179180183Chapter 10 Legislation, Shelf Life and Packaging10.110.210.3LegislationShelf LifePackaging10.3.1 Foil and Paper Wrap10.3.2 Flow Wrap10.3.3 Biopolymers10.3.4 Robotic PackingReferences184186187189190193194195Chapter 11 Nutrition and Health11.1Nutrition11.1.1 Fats11.1.2 Carbohydrates11.1.3 Proteins11.2 Obesity11.3 Tooth Decay11.3.1 Anti-Caries Factor in Cocoa11.3.2 Tooth-Friendly Milk Proteins11.3.3 Oxalic Acid11.3.4 Oral Clearance11.4 Other Alleged Negative Reactions11.4.1 Migraine and Headaches11.4.2 Acne11.4.3 4
xiiContents11.5 Positive Health Effects11.6 Psychoactive CompoundsReferences204206208Chapter 12 Experiments with Chocolate and Chocolate rojectProjectProjectProjectProject1: Amorphous and Crystalline Sugar2: Particle Separation3: Fat Migration4: Cocoa Butter Separation5: Chocolate Viscosity6: Particle Size of Chocolate7: Effect of Lecithin8: Changing the Continuous Phase9: Chocolate Temper10: Hardness Measurement11: Chocolate Composition and ProductWeight Control12: Distributions and Probabilities13: Chromatography of Colours14: Effectiveness of Different PackagingMaterials15: Viscosity and Flavour16: Heat-Resistance Testing17: Coefficient of Expansion18: The Maillard 227228229231Glossary232Subject Index234
CHAPTER 1The History of ChocolateChocolate is almost unique as a food in that it is solid at normalroom temperatures yet melts easily within the mouth. This is becausethe main fat in it, which is called cocoa butter, is essentially solid attemperatures below 25 1C when it holds all the solid sugar and cocoaparticles together. This fat is, however, almost entirely liquid at bodytemperature, enabling the particles to flow past one another, so thechocolate becomes a smooth liquid when it is heated in the mouth.Chocolate also has a sweet taste that is attractive to most people.Strangely chocolate began as a rather astringent, fatty andunpleasant tasting drink and the fact that it was developed at all,is one of the mysteries of history.1.1 CHOCOLATE AS A DRINKThe first known cocoa plantations were established by the Maya inthe lowlands of south Yucatan about 600 AD. Cocoa trees werebeing grown by the Aztecs of Mexico and the Incas of Peru whenthe Europeans discovered central America. The beans were highlyprized and used as money as well as to produce a drink known aschocolatl. The beans were roasted in earthenware pots and crushedbetween stones, sometimes using decorated heated tables and millstones, similar to those illustrated in Figure 1.1. They could then bekneaded into cakes, which could be added to cold water to make adrink. Vanilla, spices or honey were often added and the drinkwhipped to make it frothy.1 The Aztec Emperor Montezeuma wassaid to have drunk 50 jars of this beverage per day.Christopher Columbus bought back some cocoa beans toEurope as a curiosity, but it was only after the Spaniards conquered1
2Figure 1.1Chapter 1Ancient decorated mill stone with a hand grinder from the Yucatan.Mexico that Don Cortez introduced the drink to Spain in the 1520s.Here sugar was added to overcome some of the bitter, astringentflavours, but the drink remained virtually unknown in the rest ofEurope for almost a hundred years, coming to Italy in 1606 andFrance in 1657. It was very expensive and, being a drink for thearistocracy, its spread was often through connections betweenpowerful families. For example, the Spanish princess Anna ofAustria introduced it to her husband King Louis XIII of Franceand the French court in about 1615. Here Cardinal Richelieuenjoyed it both as a drink and to aid his digestion. Its flavour wasnot liked by everyone and one Pope in fact declared that it could bedrunk during a fast, because its taste was so bad.The first chocolate drinking was established in London in 1657and it was mentioned in Pepys’ Diary of 1664 where he wrote that‘‘jocolatte’’ was ‘‘very good’’. In 1727 milk was being added to thedrink. This invention is generally attributed to Nicholas Sanders.2During the eighteenth century, White’s Chocolate House becamethe fashionable place for young Londoners, while politicians of theday went to the Cocoa Tree Chocolate House. These were muchless rowdy than the taverns of the period. It remained however,very much a drink for the wealthy.One problem with the chocolate drink was that it was very fatty.Over half of the cocoa bean is made up of cocoa butter. This willmelt in hot water making the cocoa particles hard to disperse aswell as looking unpleasant, because of fat coming to the surface.The Dutch, however, found a way of improving the drink by
The History of Chocolate3removing part of this fat. In 1828 Van Houten developed the cocoapress. This was quite remarkable, as his entire factory was manually operated at the time. The cocoa bean cotyledons (known ascocoa nibs) were pressed to produce a hard ‘‘cake’’ with about halfthe fat removed. This was milled into a powder, which could beused to produce a much less fatty drink. In order to make thispowder disperse better in the hot water or milk, the Dutch treatedthe cocoa beans during the roasting process with an alkali liquid.This has subsequently become known as the Dutching process.By changing the type of alkalising agent, it also became possible toadjust the colour of the cocoa powder.1.2 EATING CHOCOLATEHaving used the presses to remove some of the cocoa butter, thecocoa powder producers were left trying to find a market for thisfat. This was solved by confectioners finding that ‘‘eating’’ chocolate could be produced by adding it to a milled mixture of sugarand cocoa nibs. (The ingredients used to make dark chocolate areshown in Figure 1.2.) If only the sugar and cocoa nibs were milledand mixed together they would produce a hard crumbly material.Adding the extra fat enabled all the solid particles to be coated withFigure 1.2Unmilled ingredients used to make dark chocolate: A, sugar; B,cocoa butter; C, cocoa nibs.3
4Chapter 1fat and thus form the hard uniform bar that we know today, whichwill melt smoothly in the mouth.Almost twenty years after the invention of the press in 1847,the first British factory to produce a plain eating chocolate wasestablished in Bristol in the UK by Joseph Fry.Unlike Van Houten, Fry used the recently developed steamengines to power his factory. It is interesting to note that manyof the early chocolate companies, including Cadbury, Rowntreeand Hershey (in the USA) were founded by Quakers or people ofsimilar religious beliefs. This may have been because their pacifistand teetotal beliefs prevented them from working in many industries. The chocolate industry was, however, regarded as beingbeneficial to people. Both Cadbury and Rowntree moved to theoutside of their cities at the end of the 1990s, where they built‘‘garden’’ villages for some of their workers. Fry remained mainlyin the middle of Bristol and did not expand as quickly as the othertwo companies. It eventually became part of Cadbury.With the development of eating chocolate the demand for cocoagreatly increased. Initially much of the cocoa came from theAmericas, with the first cocoa plantation in Bahia in Brazil beingestablished in 1746. Even earlier, however, the Spaniards tookcocoa trees to Fernando Po (Biyogo), off the coast of Africa, andthis soon became an important growing area. In 1879 a WestAfrican blacksmith took some plants home to the Gold Coast(now Ghana). The British governor realised its potential andencouraged the planting of trees, with the result that Ghana hasbecome a major source of quality cocoa. Other European powersalso encouraged the growing of cocoa in their tropical colonies,e.g. France in the Ivory Coast (Côte d’Ivoire), which is now theworld’s largest producer of cocoa.The chocolate made by Fry was initially a plain block and it wasonly in 1875 that the first milk chocolate was made by Daniel Peterin Switzerland. Chocolate cannot contain much moisture, becausewater reacts with the sugar and turns melted chocolate into a pasterather than a smoothly flowing liquid (see Project 5 in Chapter 12).As little as 2% moisture can give a product a poor shelf life as wellas an inferior texture. This meant that Daniel Peter had to findsome way of drying the plentiful supply of liquid milk that hefound in his own country. He was helped in this by the recentdevelopment of a condensed milk formula by Henri Nestlé. This
The History of Chocolate5meant that he had much less water to evaporate, and he was ableto remove the remaining amount using relatively cheap waterpowered machines. In most countries milk chocolate productsare now much more popular than plain chocolate ones. In theearly 1900s Daniel Peter was challenged to prove that he did in factinvent milk chocolate, so he took his original notebook to thelawyer to get it stamped. The original page together with thelawyer’s mark is reproduced in Figure 1.3.Figure 1.3Page from Daniel Peter’s notebook (permission of Nestlé Archives,Vevey, Switzerland).
6Figure 1.4Chapter 1Advertisement for Peter’s chocolate (permission of Nestlé Archives,Vevey, Switzerland).At this time most of the milk chocolate-like bars were still usedto make drinks. Figure 1.4 shows an early 1900s’ advertisement forPeter’s company. At the foot of it is a triangular bar which wasknown as Peter’s Delta chocolate. It was made so that it couldeasily be broken into smaller triangular pieces, each of whichwould dissolve in a cup full of hot water.In order for the chocolate to feel smooth on the tongue when itmelts in the mouth, the solid non-fat particles must be smaller than30 microns (1000 microns ¼ 1 mm). The chocolates made by Fryand Peter were ground using granite rollers, but still had a grittytexture. This was because of the presence of some large particlesand some groups of particles joined together to form agglomerates,also because the fat was not coating the particles very well.In addition, the chocolate tended to taste bitter because of thepresence of some acidic chemicals (see Chapter 4).In 1880 Rodolphe Lindt, in his factory in Berne in Switzerland,invented a machine which produced a smoother, better tasting
The History of ChocolateFigure 1.57Chocolate being processed in a long conche.chocolate. This machine was known as a conche, because its shapewas similar to the shell with that name (Figure 1.5). It consisted ofa granite trough, with a roller, normally constructed of the samematerial, which pushed the warm liquid chocolate backwards andforwards for several days. This broke up the agglomerates andsome of the larger particles and coated them all with fat. At thesame time moisture and some acidic chemicals were evaporatedinto the air, producing a smoother, less astringent tasting chocolate. A schematic diagram of the chocolate making processes isshown in Figure 1.6.1.2.1 Chocol
5.4 Moisture and Chocolate Flow 92 5.5 Emulsifiers and Chocolate Viscosity 93 5.5.1 Lecithin 94 5.5.2 Polyglycerol Polyricinoleate 98 5.5.3 Other Emulsifiers 99 5.6 Degree of Mixing 99 References 101 Chapter 6 Crystallising the Fat in Chocolate 6.1 Structure of Cocoa Butter 104 6.2 Different Crystalline Forms 107 6.3 Pre-Crystallisation or .
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