Baked-Products-Science-Technology-and-Practice.pdf

Baked Products: Science, Technology and Practice Stanley P. Cauvain and Linda S. Young BakeTran, High Wycombe, Bucks, UK Baked Products Baked Products: Science, Technology and Practice Stanley P. Cauvain and Linda S. Young BakeTran, High Wycombe, Bucks, UK © 2006 by Stanley P. Cauvain and Linda S. Young Blackwell Publishing editorial ofﬁces: Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK Tel: +44 (0)1865 776868 Blackwell Publishing Professional, 2121 State Avenue, Ames, Iowa 50014-8300, USA Tel: +1 515 292 0140 Blackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053, Australia Tel: +61 (0)3 8359 1011 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. First published 2006 by Blackwell Publishing Ltd ISBN-10: 1-4051-2702-3 ISBN-13: 978-1-4051-2702-8 Library of Congress Cataloging-in-Publication Data Cauvain, Stanley P. Baked products : science, technology and practice / Stanley P. Cauvain and Linda S. Young. P. cm. Includes bibliographical references and index. ISBN-13: 978-1-4051-2702-8 (hardback : alk. paper) ISBN-10: 1-4051-2702-3 (hardback : alk. paper) 1. Baked products. I. Young, Linda S. II. Title. TX552.15.C375 2006 664′.752–dc22 2006004707 A catalogue record for this title is available from the British Library Set in 10/13 pt Palatino by SNP Best-set Typesetter Ltd., Hong Kong Printed and bound in India by Replika Press Pvt Ltd The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. For further information on Blackwell Publishing, visit our website: www.blackwellpublishing.com We dedicate this book to the memory of our parents Stanley W. and Theresa P. Cauvain and John H. and Doris L. Hughes and in doing so recognise the importance of their support and encouragement during our formative years. Contents Preface xi 1 Current Approaches to the Classiﬁcation of Bakery Products 1 Introduction 1 Historical background to the production of baked products 2 Traditional basis for classifying bread and fermented goods, cakes, pastries and biscuits 5 The concept of recipe balance in the development of baked products 8 Reconsidering the basis for baked-product classiﬁcation 11 2 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 14 What makes baked products different from other processed foods? 14 An introduction to the methods used to characterise baked products 15 Methods for evaluating the character of baked products 18 Subjective scoring sheets 18 Measurement of size 18 Measurement of volume and density 21 Measurement of colour 23 Texture properties 23 Measurement of cellular structure 27 Measurement of moisture content 27 Water activity and its relevance 27 Key physical characteristics of bread and fermented goods 28 Key physical characteristics of sponges and cakes 31 Key physical characteristics of biscuits, crackers and cookies 32 Key physical characteristics of pastry 34 viii Contents 3 Characterisation of Bakery Products by Formulation and the Key Functional Roles of the Main Ingredients Used In Baking 35 Introduction 35 Key functional roles of individual ingredients 36 How baked-product formulations are expressed 38 Baker’s percent 41 Total weight percent 42 Ingredient weight 44 Other methods 44 Conversion factors 44 Typical recipes used in the manufacture of baked products 44 Relationships between product groups 44 Flour types 46 Sample recipes 46 4 Ingredients and Their Inﬂuences 72 Wheat ﬂour 72 Fibre 78 Soya ﬂour 79 Cocoa powder 79 Sugars and sweeteners 80 Sucrose 80 Dextrose/glucose syrups 82 Invert sugar/honey 82 Glycerol and sorbitol 82 Fats 83 Butter 87 Margarines 88 Emulsiﬁers 88 Egg products 90 Baking powders and their components 91 Dried and candied fruits 93 Chocolate chips 94 Salt 94 Yeast 94 Ascorbic acid and other improvers 94 Enzymes 95 Water 97 Milk products 98 5 The Nature of Baked Product Structure 99 Introduction 99 Techniques used to evaluate baked-product structure 101 Contents ix The formation of cellular structures 104 The formation and properties of gluten 105 The role of fat in the formation of baked product structures 109 Mechanisms of structure formation and expansion in baked products 111 Bread and fermented goods 111 Cakes and sponges 113 Biscuits and cookies 114 Short and sweetened pastry 115 Savoury pastry 116 Laminated products and crackers 116 Flat breads 117 Doughnuts 117 Bagels and steam breads 118 Hot-plate products 118 6 Interactions between Formulation and Process Methodologies 120 Introduction 120 The main processing methodologies 121 Mixing 121 Dividing/scaling/depositing 134 Forming/moulding/shaping 134 Expansion and relaxation 140 Baking 141 Frying 141 Boiling and steaming 142 Using re-work 142 The contribution of ingredients and formulation to the evolution of current processing methodologies 143 7 Heat Transfer and Product Interactions 148 Introduction 148 Heat transfer processes 149 Refrigeration and retarding 150 Proving 151 Baking cake batters 152 Baking bread doughs 155 Baking biscuit and cookie doughs 158 Baking pastry products 159 Baking laminated products 160 Microwave baking 161 Frying doughnuts and other products 163 Baking on a hot-plate 164 Cooling 165 Deep freezing 167 x Contents Foam-to-sponge conversion and the collapse of bakery products 167 Ingredient, recipe and product interactions 170 8 Understanding and Manipulating the End-Product Requirements 174 The importance of records 174 Optimising baked-product quality through test baking 176 Control of baked-product characteristics by manipulation of ingredients, formulation and processing methods 182 Optimising baked-product quality through the application of knowledge-based systems 185 Knowledge-based systems for bread products 186 Using the Bread Advisor 186 Fault diagnosis or quality enhancement 188 Processing details 190 Other useful software tools for fermented products 190 Knowledge-based systems for cake products 194 Determining raising or leavening agents in cake and biscuit/cookie products 194 Advice and help in using knowledge-based software 195 9 Opportunities for New Product Development 197 Processes involved in the development of baked products 197 The start 197 The product-development brief 197 The product-development process 198 Characterising the product 199 Potential for new product development using IT methodologies 202 Cake product development using IT systems 203 Software for determining process settings 207 Ensuring product safety using software 207 HACCP software 211 Company-speciﬁc knowledge 211 Using structure assessment in innovation 212 Matching patterns in baking for innovation 214 Visualising the world of baked products 216 Conclusions 217 References 219 Further reading 223 Index 226 Preface From the start, we recognised that writing one book to cover the world of baked products was an impossible task; there are so many types of products and variants that to cover all the necessary details would require the production of an encyclopaedia. There are many books and papers that cover the details of the various groups of baked products so why produce another one? Between us we have spent over 65 years working in and with the baking industry on its technology and production processes. During that time our research experiences alerted us to the value for individ- ual companies and the baking industry as a whole of having the body of baking knowledge assembled in appropriate forms. In some cases the most appropriate form is the written word while in others computer-based solutions can be more relevant. Whatever the ﬁnal form, gathering and systemising the available knowledge is the ﬁrst and most critical step in the process. When studying baking technology, one is immediately struck by the complexity and detail that separate the various sub-groups that com- prise the world of bakery products; inevitably ‘knowledge products’ have to address that level of complexity and detail. In all cases, a knowledge of ingredients, recipes, processing methods and equipment is essential to the successful manufacture of products. While appreciat- ing the complexity that characterises bakery products, it is also the case that there are scientiﬁc and technical issues which cross the boundaries between the sub-groups. The need for detailed scientiﬁc and technical information in the development of new bakery products is obvious. However, the rules that are used by the developer tend to be product-based rather than technology-based and it was such observations that provided the impetus for this book. One objective was to deal with the common themes that link the various sub-groups of bakery products, as a means of identifying ways of developing new products and processes. This requires thinking ‘outside of the boxes’ in which we classically put bakery products. In doing so, some of the low-level detail for many individual products is not discussed in this work; to get that detail we xii Preface recommend that readers access some of the texts suggested in the Further Reading section. In attempting this work, we have tried to challenge some of the conventional approaches used in discussing the manufacture of baked products. In doing so we do not wish to denigrate the approaches and work of many individuals who have attempted to discuss this complex subject; we do so more in the spirit of research, to see if, by taking an alternative approach, we can add to the knowledge base that can be applied to the manufacture of baked products. We hope that we have done so and that the approach we have used sparks the creative talents of those working in the baking industry and so bring future beneﬁts to manufacturers and consumers. Chapter 1 Current Approaches to the Classiﬁcation of Bakery Products Introduction The term ‘baked products’ is applied to a wide range of food products, including breads, cakes, pastries, cookies and crackers and many other products, and it can be difﬁcult to identify a common thread linking the members of such a diverse group. The most commonly-identiﬁed link is that they all use recipes that are based on wheat ﬂour. This deﬁnition, though, would need to be expanded to include baked goods such as gluten-free products, used by people with coeliac digestive disorders, or rye bread, which are still considered to be baked products even though they are based on cereals other than wheat. However, the same leniency of deﬁnition could hardly be extended to include meringues, which contain no cereal-based material at all, let alone wheat ﬂour, their main components being sugar and egg white. It may be more appropriate to consider that baked products are those prod- ucts which are manufactured in a bakery, that is the place of manufac- ture deﬁnes the product rather than some ingredient, recipe or process feature. One view is that baked products should be deﬁned as having under- gone heat processing – baking – which causes changes in both form and structure. This is certainly true for the many different base prod- ucts manufactured in bakeries. Some exceptions to this deﬁnition might include Chinese steamed breads, some steamed puddings and doughnuts, which are fried, though all of these products do undergo a heat-conversion process. By using the presence of a heat-processing step to characterise bakery goods we can capture some composite products, such as fruit and meat pies, since the ﬁllings in such products do undergo physical and chemical changes as the result of the input of heat. Not captured in the heat-processed deﬁnition of those products made in bakeries would be the ﬁllings and toppings that are applied or used after baking. In this category will fall creams and icings, even 2 Current Approaches to the Classiﬁcation of Bakery Products though they will become part of the product offered in the shop or store. The weakness of deﬁning baked products as being those which have undergone a heat-processing step is that the same deﬁnition could be applied to any form of cooked product. Physical and chemical struc- tures in all food are changed through heating, albeit in many cases adversely. In many people’s minds there is no distinction between the ‘baking’ of bread and the ‘cooking’ of bread, though bakers would be loath to accept that bread is ‘cooked’. If we are to characterise or deﬁne baked products then it will have to be using a composite deﬁnition, perhaps something like: Baked products are foods manufactured from recipes largely based on or containing signiﬁcant quantities of wheat or other cereal ﬂours which are blended with other ingredients, are formed into distinctive shapes and undergo a heat-processing step which involves the removal of moisture in an oven located in a bakery. These thoughts illustrate the problems of deﬁning baked products and also show the arbitrariness of the deﬁnitions that are commonly applied to the concepts of both a bakery and baked products. They also suggest that, to some extent, deﬁnitions of baked products are of limited value since they all involve arbitrary judgments and so will be subject to individual interpretation. The arbitrary nature of these judgements also affects published works on bakery products, and this book will be no exception. However, our aim is to offer alternative ways of deﬁn- ing bakery products and to suggest new rulesets for controlling par- ticular product characteristics. In doing so, we hope to encourage new ways of looking at baking, which will provide a basis for innovation, new product development, quality optimisation and problem solving. We do not propose that we have all of the answers to the questions which may be posed by the reader; we can only provide you with the stimulus and some of the means to improve existing products and develop new ones. Historical background to the manufacture of baked products Baked products have a long history of production, though the moment in time when humans ﬁrst learnt how to bake with cereal grains to improve their palatability and digestibility is not known. A ﬂat, unleav- ened bread is most likely to have been the ﬁrst baked product devel- oped in the ancient Middle East, the accepted home of domesticated cereal-grain production. It is likely that the ﬂat breads of antiquity were Current Approaches to the Classiﬁcation of Bakery Products 3 similar to those made by traditional means in the Middle East to this day. Baking would have been a craft practised in most, if not all, house- holds following its discovery. No doubt not all early bread production was based on wheat, with barley being a common ingredient, even in the peasant breads of the Middle Ages in Europe. It is said that the Babylonians passed on the art of baking to the ancient Egyptians who in turn developed the ﬁrst organised bakeries, that is, they made baking a specialist occupation. A painted panel of Rameses III at Thebes, dated c. 1200–1175 BC, depicts the court bakery making breads of different types (Pomeranz and Shellenberger, 1971). It also shows the manufacture of cakes in different forms, including some baked in moulds or pans and others which were fried in hot oil. In many cases the moulds or pans used to manufacture the breads and cakes took the shape of animals (some sacred to the Egyptians) and this suggests that the products were used in religious ceremonies or ritual feasting. No doubt the consumption of elaborate forms of breads, and certainly the more expensive cakes, was mainly restricted to the higher social classes, with bread consumption in the lower classes being conﬁned to coarse, ﬂat breads. The ceremonial functions of bread are recorded in many ancient texts. Fermentation and its role in bread aeration were known about at this time. The ancient Hebrews distinguished between the leavened and unleavened forms of bread. Even today the unleavened bread is reserved for certain ceremonial occasions. Bread quickly took its place in the psyche of humankind in the ancient world, and the technology spread rapidly wherever wheat and other cereal grains could be grown. Later, as wheat and other grains began to be imported and exported around the ancient world, the art of baking either spread with the grain or was discovered in different locations. No doubt three thousand years ago bakers were developing their own distinctive style of bread based on their cultural beliefs or just for the simple reason of wanting to be different from their competitors. References to bread and baking begin to appear in Greek literature from the seventh century bc. Wheat became so important that at one time its export from Greece was prohibited, and bread was such a staple and important food that its weight and price were ﬁxed in law. The place of wheat and bread in religion remained pivotal and the Greeks built temples to the goddess Demeter, who has remained asso- ciated with agriculture since those ancient times. The importance of bread was not lost on successive Roman emperors either, and the goddess Ceres was high on the list of important gods. So important was the provision of bread to the Romans, that it is con- sidered that much of the expansion of their empire was driven by the need to acquire control of more wheat-growing areas to feed her armies 4 Current Approaches to the Classiﬁcation of Bakery Products and growing homeland population. Indeed, it is claimed by some that the Roman invasion of the British Isles was mostly about acquiring control of the large wheat and barley growing areas that existed at that time. The status of the baker began to change during the years of the Roman Empire. It became a profession for men, and baking acquired a respectable and signiﬁcant status as a trade. During this period the ﬁrst guilds, or trade unions, of bakers began to form, reﬂecting the respectable nature of the trade. Government interference with the trade of baking was never far away. This was because of the political impor- tance of bread and its use to manipulate popular opinion (popularised in the saying ‘bread and circuses’ when applied to pleasing the masses). Control was ever present, with the weights of bread and its price being ﬁxed on many occasions. Free bread was the Roman form of alms and if the Emperor could not provide everyone with bread he soon lost the Imperial Crown, if not his life! While the manufacture of bread may largely have disappeared from the historical records of the so-called Dark Ages it certainly still per- sisted. There are occasional references to baking activities. For example, in England a legend has it that an Anglo-Saxon king, Alfred, burnt the cakes while thinking about the forthcoming struggle with the Vikings for control of England. Whether true or not such stories continue to reinforce the crucial position that bread and baking had in people’s minds. Control of the baking industry was ever present throughout history. In the UK, the Assize of Bread was introduced in 1226 to control weight and price, and remained in force for 450 years. In the Middle Ages baking was well established as a profession throughout Europe and many of today’s bread forms were developed. The basis of some of the change and development was the use of sifting to remove branny materials from the ground meal. White ﬂour was used to make products for the richer elements of society with whole- meal and coarse, mixed grain breads being reserved for the lower orders. The diversiﬁcation of baked products which accelerated in the medieval period in Europe gave us the basis of our modern cakes and pastries. The association with whiteness, purity and status, was a sig- niﬁcant theme throughout history and persists today, even though health gurus would now encourage people to eat the ‘peasant’ breads of history. The availability, weight and price of bread remain important politi- cal issues right up to the present day, and bread remains ﬁrmly in place in our psyche. We refer to bread as the ‘staff of life’, bread as a staple food, the ‘breadwinner’ of the household and, in common parlance, the term ‘bread’ is equated with money. Bread still retains its religious signiﬁcance today with expressions such as ‘breaking bread together’ Current Approaches to the Classiﬁcation of Bakery Products 5 and the ceremonies of the Christian religion – for example, ‘Give us this day our daily bread’. Traditional basis for classifying bread and fermented goods, cakes, pastries and biscuits Given that baking has such a long history and so many traditions associated with it, how have the various groups of baked products come to be deﬁned? Unlike botany or zoology there has never been an attempt to develop a speciﬁc taxonomy of baked products. In part this may be because of the long, local traditions associated with the manu- facture of baked products and therefore the difﬁculties associated with translation from one tongue to another of the terms and descriptors used for the products and their associated baking processes. To some extent, this nomenclature problem has persisted to the present day. For example, in English the term ‘biscuit’ is commonly used for describing a low moisture, hard-eating, sweetened, thin product with a long shelf-life, that is eaten as a snack. In the USA, however, it commonly refers to a sweetened product of intermediate moisture, commonly eaten at breakfast along with savoury foods. The UK biscuit is closer to the US cookie while the US biscuit is closer to a UK scone. To increase the confusion, the French biskuit refers to a low- moisture, dry-eating, long-shelf-life, sponge-type cake with an aerated structure. The closest UK product to the French biskuit is indeed a sponge cake, though with higher moisture content. We cannot blame differences in language and culture entirely, though, for the lack of a baking taxonomy – after all the same problems must have arisen (and probably still exist today) in botany and zoology. However, scientists involved in such subjects did eventually agree a common taxonomy (largely) and a common descriptive language (Latin). One wonders whether the long traditions and more emotive nature of baking have prevented such a development. After all, get a handful of bakers together in a room and they seldom agree on any- thing to do with baked products. Despite (or because of) its long history, baking still has strong and deep roots in the craft and still struggles to develop its scientiﬁc credibility. Until it truly graduates to being a science a common taxonomy remains impossible. Common English dictionary deﬁnitions for groups of baked products include: Bread – n. food made of ﬂour or meal (and) baked Cake – n. baked, sweetened bread Biscuit – n. dry, small, thin variety of cake Pastry – n. article of food made chieﬂy of ﬂour, fat and water 6 Current Approaches to the Classiﬁcation of Bakery Products All of the above deﬁnitions illustrate the difﬁculties associated with deﬁning the various groups of baked products. These difﬁculties are further compounded by other imprecise deﬁnitions, such as the phrase ‘ﬁne bakery wares’, which was applied to the display of cakes and pastries illustrated in Figure 1.1. This term has become more univer- sally accepted and used in recent years but remains a relatively unchar- acterised grouping. Why should we be so concerned with baked product groupings and deﬁnitions? In one sense we do not need to be concerned at all. We can simply continue to live with the current amorphous lists and texts that exist. Redeﬁning baked-product groupings will not change their exist- ing character and, if a new baked product is developed, does it really matter what it is called or into which category it is placed? The practical answer for many people is clearly ‘No!’ While baked-product nomenclature or groupings in themselves do not matter, we cannot take the same laissez-faire attitude towards product deﬁnitions or groupings when it comes to understanding and using the underpinning science itself. This is because product deﬁni- tions and groupings become more important in the development of the rulesets which determine the ﬁnal quality of a baked product and, in turn, its acceptance by consumers. The same rulesets are needed in order to ensure that consistent product quality is achieved and to provide the basis for correcting product deﬁciencies. Thus, develop- ing the appropriate underpinning scientiﬁc knowledge of the raw Figure 1.1 Display of ‘ﬁne bakery wares’. Current Approaches to the Classiﬁcation of Bakery Products 7 materials used, the recipe construction and the processing technology applied are all crucial activities in the manufacture of baked products. This requires a systematic approach to knowledge gathering, the struc- tures used to store the information and the methods by which it is applied to the different aspects of baked-product manufacture. A key factor in the purchase of a particular baked product by con- sumers is the consistency of the product. Since all baked products are based on natural raw materials, however, there will be variations which inevitably occur in the raw-material inputs. This is especially true for the most common raw material – wheat ﬂour – since environmental and agronomic conditions can have a profound impact on the quality of the grain. This in turn will lead to some quality variation in the ﬂour, despite the best efforts of the ﬂour miller to blend wheat varieties to give a uniform and consistent product quality. Part of the challenge that faces millers and bakers is that no ﬂour speciﬁcation or analytical technique captures all of the essential end- performance information that is required. This is not because we do not have suitable testing methods, but because even after much study we simply do not completely understand what determines ﬂour per- formance in baking. The development of quality rulesets is thus very important for ensuring product consistency and troubleshooting when things go wrong. The traditional baked products with which we are all familiar have a long history of development through trial and error rather than sys- tematic study. The origins of many baked products can be assigned to the error category. Indeed, the discovery of leavened bread has been ascribed to the error of leaving dough overnight before baking, and the discovery of laminated pastry to the apprentice who forgot to add fat to the bread dough and tried to recover the situation by folding the missing ingredient into the dough after mixing (though there can be no absolute proof of either story). More recently, systematic studies have been applied to the development of new baked products but most commonly the rulesets applied have tended to be limited and conﬁned by the traditional deﬁnition of baked products. The constraining nature of baked-product groupings can best be illustrated by asking the question: ‘In UK terminology, what is the dif- ference between a cake and a sponge?’ There will be many answers based on: Size (weight and speciﬁc volume) Shape (sponges tend to be round while cakes assume many shapes – but what about the Swiss roll?) Recipe (sponges tend to have lower fat levels – but what about a Victoria sponge?) 8 Current Approaches to the Classiﬁcation of Bakery Products Processing methods (sponges tend to be aerated by whisking and cakes tend to be beaten with a paddle – but with continuous mixing is there a difference?) Cell structure (sponges tend to be more open and cellular in struc- ture while cakes have less obvious cellular structure and a denser character) Eating qualities (sponges tend to be drier-eating while many cakes are considered moist-eating) Organoleptic shelf-life However, one could argue that popular differences are based purely on the artiﬁcial constraints that we have imposed on them using tra- ditional terms and deﬁnitions. Further one could argue that by con- straining our thinking with traditional rulesets we have created barriers to innovation and the development of new baked products. The concept of recipe balance in the development of baked products An illustration of how conventional thinking may constrain baked- product development can be given based on the development of a knowledge-based computer program known as BALANCE (Young et al., 1998). The program was part of a suite of programs comprising a Cake Expert System (Campden & Chorleywood Food Research Association [CCFRA], undated). The development of the BALANCE module in the Cake Expert System was based on the premise that it was possible to identify a series of technological rules which could be used to deﬁne particular types of cakes and sponges and to identify the limits which might be applicable to the ratios of ingredients used in the recipe. The rules that were available, though derived from the sys- tematic study of the effects of changing ingredient ratios by a number of workers (e.g. Devlin, 1954), were largely empirical in nature and based on traditional forms of a limited range of cake types. The most common cakes studied were the round sponge cake, the round Madeira- type cake and the loaf-shaped, unit cake commonly baked in a bread pan. In the 1950s and 1960s the quality of ingredients available for the manufacture of cake products changed, so that along with chlorine treatment of ﬂours intended for cake making it became possible to manufacture what have become known as ‘high-ratio’ cakes, that is cakes in which the weights of sugar and liquid (largely the sum of water, egg and milk) individually exceed the weight of the ﬂour used in the recipe. If the levels of sugar and liquids are lower than that of Current Approaches to the Classiﬁcation of Bakery Products 9 the ﬂour then the products are commonly considered as low ratio and the use of treated ﬂour was not essential. A comparison of the same form of high- and low-ratio cakes is illustrated in Figure 1.2. There are two important points to be made here. First, it is common to express baker’s recipes on the basis of the ﬂour weight used in the recipe. Further, it has become common practice to develop bakery- product recipes based on 100 parts of ﬂour, expressed in various units, such as kilograms, grams, pounds or ounces. This method was devel- oped by bakers so that the functional effects of ingredients in a given recipe could be readily identiﬁed. For example, for a given high-ratio cake the sugar level should be between 105 and 135 parts of ﬂour because, if lower, the cake volume will be restricted and, if higher, col- lapse of the structure may occur. Such a ‘rule’ is developed based on the fact that the level of sugar in the recipe (or the sucrose concentra- tion) has a direct impact on the temperature at which starch will gelatinise and thus, in turn, the setting of the structure of the cake. Second, chlorine treatment of ﬂour is no longer permitted in the UK and many other countries of the world. It has been replaced by the treatment of ﬂour with heat. The heat-treatment process largely confers the same technological beneﬁts as chlorine treatment, but without the (a) (b) Figure 1.2 Comparison of (a) high- and (b) low-ratio slab cakes. 10 Current Approaches to the Classiﬁcation of Bakery Products bleaching effect (though this was never a signiﬁcant reason for chlorine treatment). Following the development in the USA of the high-ratio cake, and its subsequent introduction into the UK in the 1950s, new rules for cake-recipe balance were evolved. This evolution can be followed in a number of (sadly now unavailable) ingredient-company publications (Thomas Headley & Co. Ltd., undated) and relevant textbooks (Street, 1991). Similar, though perhaps less elaborate, rules have been devel- oped for other baked products. In the development of the BALANCE program, the acceptable ranges for a number of different cake ingredients, with respect to ﬂour weight, could be deﬁned. The initial approach taken had been to break the recipes down according to whether they were cakes and sponges and to deﬁne the recipes as high- or low-ratio. A further sub-division, based on a shape and/or size criterion, was proposed. This represented a conventional way to deﬁne the world of cakes. However, closer scru- tiny suggested that a division based on high- or low-ratio was not required since the rules which would be applied would differentiate between the product types and deﬁne the type of ﬂour required without having to be speciﬁed by the user. The subsequent approach suggested deﬁning rulesets on the basis of whether products were: A cake or a sponge Plain (based on whole egg), white (using egg white only), chocolate (containing cocoa solids) and fruited (containing fruit or particulate materials) Baked as a unit (loaf-shaped), slab, layer, cup, Swiss roll, sandwich (round) or drop (small ﬂat shape, often baked directly on the oven sole) The above classiﬁcations allowed for a theoretical 2 × 4 × 7 = 56 recipe combinations. However, when it came to deﬁning the individual rule- sets that would be required for each of the 56 combinations it was clear that quite a number did not exist in a completeness that would be required with the knowledge-based system. In some cases there was doubt as to whether it was possible to make particular combinations. To some extent this view was formed because of the traditional classiﬁcation of products. For example, sponge cakes were commonly associated with the shape/size classiﬁcations Swiss roll, sandwich and drop yet there appeared to be no practical reason why some sponge recipes could not be baked in other shapes, for example loaf-shaped or large slab. A few simple experiments showed that a number of combinations initially thought not to be possible in Current Approaches to the Classiﬁcation of Bakery Products 11 fact were possible. This led to the realisation that new rulesets could be deﬁned by populating them with information derived from the more conventional views of sponge and cake making. In the development of the Cake Expert System, some 1200 experiments were performed to study the quality impacts of changing the levels of the major ingredients used in the manufacture of sponges and cakes. The changes in external and internal features were recorded. These photographic records were then combined with the rulesets which had been evolved so that in BALANCE it was possible to show the user the likely consequences of increasing or decreasing a range of ingredients in a given recipe by comparison with a standard or control product. The combination of image and knowledge base presented new opportunities for product development, since it was possible to visu- alise changes in key physical properties of individual products and to link those features with a particular recipe structure. The use of the BALANCE module did not restrict recipe formulation to a limited range of products; rather it allowed users to concentrate on developing particular features in new products without having to worry about remembering all of the rules by which recipes were structured. And, most importantly, it provided a rapid and inexpensive way to try out ideas before undertaking the more expensive and time-consuming test baking for new product development. Reconsidering the basis for baked-product classiﬁcation As stated earlier, one of the purposes of the approaches that will be taken to considering the family of baked products is to provide the opportunity for greater innovation using underpinning knowledge of how baked products are characterised. In Chapter 2 we will consider in more detail the inﬂuence of ingredients and recipe variation on the ﬁnal quality of baked products, along with the factors that link and separate the various categories of baked goods. However, at this time we would like to introduce brieﬂy a concept of characterising baked products which has been around for some time but has yet to be fully exploited for innovation. In Figure 1.3 the positions of examples of baked products are plotted using a 2-dimensional diagram in which the two axes are based on the ratio of sugar to ﬂour in the recipe (X axis) and the ratio of fat to ﬂour in the recipe (Y axis). The world of bakery products does not consist of discretely-deﬁned groups clearly separated from one another by rigid rules. In fact many successful new products are successful because they break the conven- tional rulesets that have evolved to deﬁne particular product areas. In 12 Current Approaches to the Classiﬁcation of Bakery Products LR cake HR cake 80 Puff pastry 60 Short pastry 100 × ratio fat : flour HR cake (fruit) Shortbread Cookie Butter 40 puffs LR cake (fruit) Short sweet and shortcake Sponge 20 Cream Ginger snaps crackers Semi-sweet Buns Bread 0 20 40 60 80 100 120 100 × ratio sugar: flour Figure 1.3 A two-dimensional representation of bakery products based on ratios of sugar and fat to ﬂour in the recipe. view of the lack of clearly-deﬁned boundaries between groups of bakery products there is a strong argument for viewing the world of bakery products as one continuous spectrum, with one product merging into another. This view invokes comparison with the world of colour, where the boundaries between particular colours with deﬁned wavelengths are most certainly blurred by the intermediate wavelengths. Two- dimensional colour models based on wavelength and three- dimensional models exist to deﬁne the colour space. In the case of the three-dimensional model, the shifts from one deﬁned colour segment to the next are very small. An analogy for the bakery world is to consider each of the colour segments as representing a particular bakery product and in doing so the close relationship between prod- ucts may be observed (the coloured segments are illustrated as shades of grey in Figure 1.4). However, three dimensions are inadequate to represent the differences and similarities between bakery products, and so better means of visualising how bakery products are related or differ are required. One possible way is through the use of the spider diagram, so often used in sensory science (Jones, 1994). An example is given for selected parameters based on a subjective scoring system for each of the ﬁve identiﬁed parameters (Fig. 1.5). The proper- ties used could readily be augmented or replaced with objectively measured data. Current Approaches to the Classiﬁcation of Bakery Products 13 Puff pastry Cakes Short pastry Bread Cookies Figure 1.4 Diagrammatic representation of the relationship between bakery products based on the colour solid. Softness 8 6 4 Gumminess Friability 2 Bread 0 Cake Chewiness Springiness Figure 1.5 A visual representation of key characteristics for bread and cake based on spider or radar plots. These few examples illustrate that by being able more readily to visualise relationships between bakery products and groups of bakery products it may be possible to identify new product and process oppor- tunities. A further beneﬁt of this approach will be the improved capa- bility to optimise the quality of existing and new products. In order to gain best value from such visualisations it is important that a sound and extensive knowledge base is available on which to base innovation. In the next few chapters this knowledge base will be explored and provided. Chapter 2 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups What makes baked products different from other processed foods? Those involved in the manufacture of any processed food will always make the same claim: namely that their particular food is unique and that special rules, which make their own food sector different from all other food sectors, apply. It is true that in deﬁning any processed food there will be factors that are unique to that particular sector and are not shared to any signiﬁcant degree by other manufactured foods. However, there may be one factor which characterises all processed food: the raw materials used undergo some changes in physical and/or chemical form as they make the transition to a processed food. Usually, the key step in the process is some form of heat process – boiling, frying, roasting, steaming or baking. The fundamental nature of the heat-induced changes can be appreci- ated by considering the processing of potatoes. As a raw material, potatoes can be eaten raw, though their palatability is considerably improved by some form of heat processing. In this respect baking, boiling or roasting potatoes may be compared to the conversion of raw dough to a baked product. The dough could be eaten raw, though its lack of palatability would be evident and would contrast greatly with the vastly improved palatability of the baked product. A similar dis- cussion could be applied to the preparation of baked products such as biscuit dough, sweet and savoury pastes and batters, all of which undergo major changes in palatability during baking. Clearly, the presence of a heat-setting process is not unique to baked products but applies to many other raw materials that are included in processed foods. The difference between baked products and other processed foods may then lie with the deﬁnition of the ‘raw material’. In the example of potatoes discussed above, the raw and processed Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 15 forms can remain very similar. The same cannot be said for the manu- facture of bread and other baked products. This is because the basic raw material in these cases is wheat or wheat ﬂour. In the case of wheat, the ﬂour-milling process is required to provide wheat ﬂour, which is the starting point of most bakery processes, and the wheat ﬂour itself needs further conversion to a dough/paste/batter before it becomes a ‘raw material’ for the heat-setting process – baking. With baked products, again unlike the potato, wheat ﬂour has to have another raw material added to it before baking. The other ingre- dients combined with wheat ﬂour in the baked products recipe impart considerable changes to the functionality of wheat ﬂour. For example, while the addition of sugar to bread, cake and biscuit recipes provides sweetness, the functionality that the sugar imparts to structure forma- tion is an equally important aspect of its use in baking. The multi- functional properties of sugar include the restriction of available water and therefore the reduction in the gluten-forming potential of wheat proteins and the modiﬁcation of the gelatinisation properties of wheat starch, both during and after baking. While there may be interactions between ingredients used in other processed foods, few tend to be as complex or comprehensive as the ingredient interactions which char- acterise bakery products. An introduction to the methods used to characterise baked products Take any baked product and you will observe that it has a number of different textural and sensory attributes. Even the matrix of a loaf of bread is not as homogenous as it ﬁrst appears. Starting from the outside, we would see a light- to dark-brown surface which, when fresh, is hard to the touch and has a dry and crisp eating character. The inside of the loaf, however, has a sharply-contrasting appearance. It is white or light brown (depending on whether white, brown or wholemeal ﬂour has been used in its preparation) and has an expanded and cellular structure. By comparison with the crust, the crumb is soft to the touch and may well spring back after compressive forces are removed. The sensory properties in the mouth will be dominated by softness and chewiness. The degree of variation depends very much on the bread recipe and the process employed, especially in the dough making, but there will almost always be a contrast between the surface and interior properties of the loaf. A range of texture and sensory variations is also experienced when base cakes, pastries and bis- cuits are examined. When the base product is combined with other foods, for example as in a jam- and cream-ﬁlled sponge cake with a 16 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups sugar-icing topping, the contrast of textures and sensory sensations is greatly enlarged. The assessment of the characteristics of all baked products (and indeed most food) starts with the visual observation of physical appear- ance, then aroma/odour, texture, mouth-feel and ﬂavour. In making any subjective assessment of baked-product character, individuals are primarily affected by their cultural background, which is then modi- ﬁed in the light of their personal experiences and preferences. None of the inﬂuences on product quality remain unchanging, so that overall assessment of product quality by an individual will change with time. The impact of aging of the product on the assessment of product quality has been discussed in detail elsewhere (Man and Jones, 1994). It is inevitable that the subjective judgment of product quality begins with its exterior – after all we see the product, touch and smell it before it ﬁnally reaches our mouths. As the saying goes ‘The ﬁrst bite of a baked product is with the eyes.’ This has become very important to baked products and has contributed considerably to the variation that one sees with products that are nominally the same. For example, changing the size, shape or surface cutting on breads can distinguish a particular baker’s product from that of the competition, and if associ- ated with particular pleasurable sensory experiences will considerably enhance the prospect of repeat purchases by consumers. While the ultimate assessment of baked-product quality lies with the consumer, in the manufacture and optimisation of existing baked products and the development of new ones, objective assessment of particular product characters is important. This is not to say that sub- jective sensory evaluations should not be carried out, but one of the problems of relying on sensory characterisation lies with the difﬁcul- ties of calibrating the individual assessment or panel. There have been numerous attempts to make sensory assessment of foods more objec- tive and readers are referred elsewhere for detailed discussions of this topic (Kilcast, 2004). Assessing baked-product quality starts with a consideration of the external features and moves to the internal features. The main features that are likely to be considered are listed in Table 2.1. As will be discussed in later chapters, there are many factors con- tributing to variation in baked-product qualities. Some of the main ones may be summarised as follows: Size 䊊 Dough or batter piece weight 䊊 Product volume Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 17 Table 2.1 Main features considered in making an evaluation of baked-product qualities. External Internal Size Y N Shape Y N Crust character Y N Colour Y Y Crumb cellular structure N Y Softness N Y Mouth-feel Y Y Taste Y Y Aroma Y Y Shape 䊊 Moulding, shaping, forming or depositing 䊊 Using pans, trays or processing as a free-standing item External colour 䊊 Ingredients and their qualities 䊊 Formulation, ingredient ratios 䊊 Baking and other processing technologies Crust character 䊊 Baking temperatures, times and control of oven atmosphere, e.g. the use of steam or oven damper Crumb cellular structure 䊊 Ingredient qualities 䊊 Formulation, ingredient ratios 䊊 Mixing and other processing technologies 䊊 Heat transfer during baking Internal colour 䊊 Ingredient qualities 䊊 Formulation, ingredient ratios 䊊 Crumb cellular structure Crumb softness 䊊 Final product moisture content 䊊 Ingredient qualities 䊊 Formulation, ingredient ratios 䊊 Crumb cellular structure 䊊 Baking temperatures, times and control of oven atmosphere 䊊 Post-baking treatment, for example packaging and staling Mouth-feel 䊊 Moisture 䊊 Crumb cellular structure 18 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 䊊Formulation, ingredient ratios 䊊Post-baking treatment Taste 䊊 Specialist processing, such as prolonged fermentation of bread dough 䊊 Ingredient qualities 䊊 Formulation, ingredient ratios 䊊 Crumb cellular structure 䊊 Baking temperatures, times and control of oven atmosphere 䊊 Post-baking treatment Aroma 䊊 Specialist processing 䊊 Ingredient qualities 䊊 Formulation, ingredient ratios 䊊 Crumb cellular structure 䊊 Baking temperatures and times 䊊 Post-baking treatment Methods for evaluating the character of baked products Brief descriptions of methods that might be used in the evaluation of baked products, with some appropriate references, are given below. Subjective scoring sheets This approach goes beyond the simple recording of product attributes and tries to provide a framework for making more objective compari- sons of baked-product qualities. Among the main problems with sub- jective evaluations are the inevitable variations in scoring between individuals and drift with time for any given individual. Thus, in order to make effective use of scoring sheets it is necessary to have trained individuals making the assessment. It is also helpful to have some ﬁxed reference points that any assessor may use. These usually com- prise templates of size or shape, photographs (especially for inter- nal appearance), colour prints or ‘chips’ and standard descriptors. Examples of scoring sheets for bread, cake and pastry are given in Figures 2.1 to 2.3. Measurement of size In many cases it is possible to carry out a simple measurement of product dimensions with an appropriately graduated rule. The most useful measure for fermented products and cakes baked in pans tends Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 19 External Score Quality descriptors Number Descriptor Volume score (10) A. Small B. Large Average volume, cc Specific volume, cc/g Uniformity of shape (10) A. Lack of boldness B. Uneven top C. Shrunken sides D. Low side E. Low middle F. Flat top G. Small end Crust characteristic (10) A. Light B. Dark C. Uneven D. Dull E. Thick F. Tough G. Brittle Break and shred (10) A. Wild B. None C. Shelled D. Insufficient Subtotal 40 Internal Cell structure (20) A. Open coarse B. Thick cell walls C. Holes D. Non-uniform Crumb colour (10) A. Dull grey B. Creamy Crumb strength (10) A. Tough B. Weak Texture (10) A. Rough B. Core C. Crumbly D. Firm E. Gummy Flavour and aroma (10) A. Satisfactory B. Unsatisfactory Subtotal 60 Total score 100 Numbers in brackets refer to proportion of score for the characteristic being assessed Figure 2.1 Bread quality score sheet. to be height. This follows because of the physical constraining effect of the pan. The pan has ﬁxed dimensions and so any variation of dough or batter expansion mostly occurs upwards (provided the baking dough or batter does not overﬂow the sides of the pans before they are set in the oven). Thus, variations in dough gas retention and batter expansion, which are both directly related to product volume, can be assessed quickly in terms of height. 20 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups External Score Quality descriptors Number Descriptor Volume score (20) A. Small B. Large Average volume, cc Specific volume, cc/g Uniformity of shape (10) A. Uneven top B. Shrunken sides C. Low side D. Low middle F. Sunken top Crust characteristic (10) A. Light B. Dark C. Uneven D. Dull E. Thick Subtotal 40 Internal Cell structure (20) A. Open coarse B. Thick cell walls C. Holes D. Non-uniform Crumb colour (10) A. Dull grey B. Dark C. Streaks/cores Crumb strength (10) A. Tough B. Weak Texture (10) A. Rough B. Streaks/cores C. Crumbly D. Firm E. Gummy Flavour and aroma (10) A. Satisfactory B. Unsatisfactory Subtotal 60 Total score 100 Numbers in brackets refer to proportion of score for the characteristic being assessed Figure 2.2 Cake quality score sheet. Many pan breads and cakes have a domed shape after baking, that is the highest point is in the approximate middle of the product and the ends of the product are lower. It is usually desirable that the overall shape should be uniform. A more realistic assessment of product height would therefore be to take the measurement at selected points along the (usually longitudinal) product cross-section – typically 2–4 mea- surements would be used. If the product dome is not uniform then multiple height measurements become more valuable as they can provide useful ingredient- and process-related information. Dimensional data can be obtained from individual slices, using image-analysis systems such as C-Cell (Calibre Control International, Warrington, UK). Measurements include slice height, width and area. Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 21 External Score Quality descriptors Number Descriptor Volume/lift score (10) A. Low B. High Height/thickness (mm) Uniformity of shape/lift A. Irregular B. Sunken (10) Crust characteristic (10) A. Pale B. Dark C. Uneven Surface appearance (10) A. Blistered Subtotal 40 Internal Cell structure (20) A. Open coarse B. Thick cell (laminated pastry) walls C. Non-uniform Texture (20) A. Fragile B. Pasty C. Gummy Flavour and aroma (20) A. Satisfactory B. Unsatisfactory Subtotal 60 Total score 100 Numbers in brackets refer to proportion of score for the characteristic being assessed Figure 2.3 Pastry quality score sheet. Estimates of the degree of concavity associated with a slice may also be obtained (Whitworth et al., 2005). C-Cell may be used for measuring the external dimensions of bread, fermented products and cake slices. Its use for the assessment of crumb structure is discussed below. In the case of pastries, biscuits, cookies and other free-standing products, height data may be supplemented using length and width data. Product eccentricity may be calculated by comparing product dimensions with those of the cutter which may have been used in the product preparation. Measurement of volume and density The measurement of product volume provides valuable information about product quality and is an invaluable tool with which to make comparisons of ingredient and process effects. Unfortunately, baked 22 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups products cannot be measured by the basic method of liquid displace- ment so we have to use other modiﬁcations on the displacement prin- ciple. The most commonly encountered method for measuring product volume is using seed displacement (Street, 1991). In this case seeds, usually rape or canola seeds or pearled barley, take the place of a liquid. The process is quite straightforward. A box of known volume will be ﬁlled with seed and the weight of seed required to just ﬁll the box is noted. The sample is introduced and the seed poured back into the box. The volume of seed displaced is equal to the volume of the product. The more seed that is displaced the larger the product volume. More recently, an instrument has come onto the market which uses a laser sensor to measure product volume (TexVol instruments, BVM-L series, www.Texvol.com) (Fig. 2.4). This technique has speciﬁc advan- tages over the traditional seed-displacement techniques, such as no compression of the sample, but provides the same information on product volume. Figure 2.4 TexVol instrument for volume measurement. Reproduced with per- mission of TexVol Instruments AB, Viken, Sweden. Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 23 After volume data have been obtained it is common practice to con- sider product density. This is simply described as the mass of the product divided by its volume, d = m/v. An alternative form of express- ing such information is as speciﬁc volume (SV) which is simply the reciprocal of density, that is sample volume divided by sample mass, SV = v/m. Both density and SV terms are encountered in discussions of baked-product quality, the lower the product density, the higher its speciﬁc volume and vice versa. Measurement of colour Product colour may be determined using comparisons with standard colour charts, such as the Munsell chip system (Munsell, undated), or by using Tristimulus colorimeters (Anderson, 1995). Such techniques for the measurement of crust colour are relatively straightforward, since the surface texture of a loaf or roll has only a limited impact on the measurement. The basic concept for Tristimulus readings is to be able to express a given colour using three attributes: one comes from a scale of 0–100 that represents black to white; one covers red to green hues; the third covers yellow to blue. In baking, our interests lie mainly in the red-yellow part of the colour spectrum for crust colour. Crumb colour on the other hand presents a greater problem. The cellular structure of the product will have a direct impact on the mea- surements because of the shadows which are cast by the individual cells. The Tristimulus colorimeters are able to provide a reading on the intrinsic colour of the crumb. For crumb colour we will be mostly interested in the yellow to white regions of the colour spectrum. The measurement of crumb brightness is of particular importance, because, in the case of white-ﬂour products, the brightness of the product crumb is one of the factors which consumers use to make their judgement of product quality. In the case of Tristimulus data, this would be covered by concepts such as the Y and Whiteness Index values. Crumb brightness may be measured using C-Cell (Calibre Control International, Warrington, UK) and is directly related to the perception of sample brightness as perceived by human observers. In addition to the measurement of slice brightness, C-Cell provides data on the contrast between the shadow cast by the cells and the brightness of the cell-wall material. Both measurements provide useful data on how consumers will view crumb quality. Texture properties Measurements of product texture properties fall into two broad groups: sensory and mechanical. The latter category includes compression 24 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups testing, Texture Proﬁle Analysis (TPA) and crispness testing. One of the most common methods used by consumers to make an assessment of product quality is the ‘squeeze test’. This is particularly the case with wrapped bread. They do this to try and get an impression of the fresh- ness of the product. On the store shelf the bread is most often cold, but consumers have learned that fresh bread is easy to squeeze and will spring back to its original shape when the compressing force is removed. A similar test method is applied by experts when they assess bread texture. You will see them gently compress the surface of the loaf with their ﬁnger tips and watch the spring-back of the crumb (Fig. 2.5). This is a classic example of a sensory test of the subjective kind because the methodology used and the interpretation of the results depend on the individual carrying out the test. It should be recognised that sensory science is not an exact science and the data provided in many cases are only indicators and not guar- antees of commercial success. Sensory tests can also be an expensive business, because of the large numbers of people and time involved in such activities. It is not surprising, therefore, that objective instrumen- tal methods for the routine testing of product softness and texture have been developed. It is important that appropriate and strong links are Figure 2.5 Compression of bread crumb. Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 25 established between objective and sensory tests so that results from one type of testing may be related to other forms of testing. The use of sensory, or taste, panels provides a disciplined approach to subjective texture analysis. Sensory panels may be untrained or trained in sensory science. In the case of the latter, assessments are carried out by individuals who have received training to help them deliver greater objectivity in the context of the texture or taste ques- tions which need to be answered. Commonly, sensory panels are called upon to identify differences between samples with different formula- tions or to evaluate changes in product quality. It should be noted that sensory analysis need not be conﬁned to the testing or eating of products – appearance can also be assessed in this way. The subject of sensory science is too extensive to be covered in this book and so readers are referred elsewhere for more detailed information (Kilcast, 2004). Many of the tests which are used to assess product softness or texture are designed to mimic the approach that consumers and experts use and so commonly use some form of controlled compression of the sample. Various forms of compressimeter have been evolved over the years (Bourne, 1990), but all operate using similar features and provide similar data. There are two main ways in which tests are carried out: one is based on compressing the whole slice and the other on compress- ing a core taken from the product. A typical compression test will either subject the product to a stan- dard force applied for a ﬁxed time or compress the sample through a given distance and measure the force required to achieve a given per- centage thickness compression (Cauvain, 2004a). Both techniques provide useful information on the softness of the sample. Resilience data or sample springiness can be determined by removing the com- pressing force and measuring the degree to which the sample recovers, usually after a ﬁxed time. To some degree, the ability of the sample to recover depends on the level of compressing force that was ﬁrst applied. The greater the compressing force the less likely the sample is to show signiﬁcant resilience. A wide range of tests can be designed to provide texture information on baked products. The form of the test depends on the information being sought and can encompass composite bakery products. For example, a puncture method may be used to evaluate the crispness of apple pie pastry (Fig. 2.6). A needle-shaped probe is driven at a ﬁxed speed through the lid pastry, ﬁlling and base pastry in one continuous movement and the forces encountered recorded. This technique has been used to follow the migration of moisture from the apple ﬁlling to the base pastry during the storage of apple pies (Cauvain, 1991) and to 26 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups Figure 2.6 Puncture testing of composite apple pies. evaluate the effects of stabilisers added to the ﬁlling to restrict this moisture migration. It is important to recognise that the sample moisture content and density will have an effect on both the perception of softness and its objective measurement. Since both vary between samples, test com- parisons between different products are best made on a basis of stan- dardised moisture content. It is fair to say that this does not reﬂect the situation that will be observed by consumers who perceive breads and cakes of different moisture content as being different, even if they were made on the same day. They will also tend to assess products with different densities as being different, even if they have the same mois- ture content. In general terms, consumers perceive bread and cake products with higher moisture contents and lower densities as being fresher, provided that they also show the required resilience. The value of being able to correct sample data for differences in moisture content and density is that the underlying contributions, posi- tive or negative, of ingredient, recipe or process changes can be identi- ﬁed. A knowledge of which changes make positive contributions to the textural properties of baked products is invaluable for countering the negative impacts. One of the ways correction for sample moisture and density may be made involves sub-sampling a whole product slice. One Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 27 technique for this involves the removal of a cylindrical core from a bread or cake slice (Cauvain, 1991). The location of the core is ﬁxed relative to the product base, since the density and moisture content will vary according to the location of the core in the slice cross-section. However, the exact location may be varied depending on the type of product being assessed (but not between test samples). The core has ﬁxed dimension (radius and height) so that a simple weighing can be used to obtain the sample density (from density = mass/volume) and the moisture content of the sample can be measured (see below). Measurement of cellular structure The cellular structure of the crumb of the product may be assessed by eye or by using objective image analysis. A more detailed description of the techniques that may be used and their importance in under- standing the nature of baked-product structure is given in Chapter 5. Measurement of moisture content The techniques most commonly used to assess moisture content are based on driving off water with heat (Cauvain and Young, 2000). Relatively little equipment is required: an oven ﬁtted with fan and thermostat, a desiccator to hold the samples, some lidded sample pans and an accurate balance. Sample moisture is based on the loss of weight that occurs when a known weight of sample is heated. Standard methods are readily available (AACC, 1995; ICC, 1995). Oven-drying methods are usually favoured because they are not directly affected by product formulation, structure or density. Alternative methods are available including nuclear magnetic resonance, near infrared, direct heating with infrared and the use of an electrical current passed through the sample to measure its electrical conductance or capaci- tance (Cauvain and Young, 2000). Water activity and its relevance The water activity of a product (aw), or its equilibrium relative humid- ity (ERH), is an important property that is related to many aspects of product shelf-life. Water activity and ERH are related by the relation- ship ERH = aw × 100. ERH is expressed on a scale of 0–100 and expressed as a percentage, while aw is expressed on a scale of 0–1. Thus, an ERH of 80% equals an aw of 0.8. The ERH of a product may be deﬁned as: The ERH is that unique humidity at which moisture is neither gained nor lost from a product, or at which the rate of evaporation of moisture 28 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups from a product equals the rate at which moisture is absorbed by the product In other words, the humidity within the product is in equilibrium with that of the atmosphere surrounding it. If the product ERH is higher than the relative humidity of the surrounding atmosphere then it will lose moisture and dry out, but if the product ERH is lower than the relative humidity of the surrounding atmosphere it will gain moisture. The loss or gain of water during storage can have a profound impact on the eating qualities of the bakery products. ERH is also important for understanding the potential for moisture migration within prod- ucts or between different components in a composite product. The ERH of a product is a critical factor in its spoilage-free shelf-life. Its impact on microbial activity has been discussed in detail in many other publications (Cauvain and Young, 2000). It is sufﬁcient at this point to recognise that the lower the product ERH the longer its spoilage-free shelf-life. Product ERH may be measured directly or may be calculated from ingredients and recipe data (Cauvain and Young, 2000). The latter technique is useful in the context of product development because it is not necessary to make up samples for testing. However, in order to ensure that the ERH calculations are relevant it is necessary to have appropriate data on the ingredients. The data required depend on the calculation method being used. There are two main methods, known as the sucrose equivalence and sucrose concentration methods. In the former, the assumption is that there is sufﬁcient water in the recipe to solubilise all of the ingredients. If there is not, then the sucrose-concentration method gives more rele- vant results. There are inaccuracies associated with both the direct measurement of ERH and its calculation. The relationship between product ERH and spoilage-free shelf-life is not an absolute one and any prediction should be made with care. For a more detailed discussion of the issues surrounding the ERH of bakery products the reader is referred elsewhere (Cauvain and Young, 2000). Key physical characteristics of bread and fermented goods Bread is characterised by a crust, a dry thin layer that encloses a soft, sponge-like cellular structure. The crust will usually have a light golden-brown colour. In some bread products the colour may be darker, as when wholemeal (wholewheat), brown or non-wheat ﬂours are used in its production. Rye breads, which are especially popular Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups 29 in Scandinavia, eastern and northern Europe, tend to produce darker crust colours. Many different factors affect crust colour, which appears during baking because of the Maillard reaction (Manley, 2000) and is based on a reaction between proteins and sugars present in the dough. The reaction starts when the product surface temperature exceeds 115°C. This can only happen when sufﬁcient water has evaporated from the crust surface. It takes a few minutes of exposure to heat in the oven before this happens. The depth of bread-crust colour achieved during baking is inﬂuenced by the pH of the dough, with lower pHs (i.e. more acid conditions) yielding darker crust colour. This effect of lower dough pH accounts, in part, for the darker crust often seen with sponge- and-dough or sour-dough breads. Bread crust has considerably lower moisture content than that of the crumb. On leaving the oven, and for some while after cooling, the crust moisture content will remain lower than that of the crumb. Typically, crust moisture contents are in the range 12–17%, while for bread crumb they will be in the range 35–40%, depending on bread type. Variations in crust character may be signiﬁcant. In general, bread crusts will have a hard and brittle eating character. Two major factors contributing to that character are the low moisture content and the thickness of the crust. Typically the latter is 1–3 mm, though only the ﬁrst mm or so will be coloured brown. Regional and product variations in crust character are signiﬁcant and major contributors to differences in bread quality between the regions of the world. The variations in crust character extend to surface decoration though in many cases the marking or cutting of the dough surface actually has a process control function and contributes to product quality, as will be discussed later. All bread types are characterised by having an open, cellular crumb structure and (by comparison with other foods) an intermediate mois- ture content. A key contribution to the cellular structure of breads comes from the release of carbon dioxide gas from baker’s yeast fer- mentation. As has already been described, key characteristics of bread crumb are a relative softness combined with a degree of resilience or springiness and a degree of chewiness. Moisture plays a signiﬁcant contributory role to these eating characteristics, with lower moisture contents resulting in an increase in ﬁrmness and losses in springiness and chewiness. Such changes in eating quality are commonly associ- ated with bread staling, though moisture losses are not the sole reason for bread staling (Pateras, 1998; Chinachoti, 2003). An equally important contributor to the character of bread crumb is the nature of the cellular structure. Bread crumb cell structure is com- prised of two components, the small holes or ‘cells’ and the cell walls 30 Key Characteristics of Existing Bakery-Product Groups and Typical Variations within Such Groups (i.e. the material surrounding the cells), the crumb itself. The size of the cells and their spatial distribution within a loaf have a signiﬁcant impact on the thickness of the cell-wall material. The formation of the cells and wall material are determined by the qualities of the ingredi- ents used (primarily wheat ﬂour, which is the contributor of gluten- forming proteins), the formulation used and many aspects of dough processing (most importantly dough mixing). The variations in the cellular structures in bread products are sig- niﬁcant and are major contributors to variations in eating qualities. The tendency is for bread-cell structures with small cell sizes uniformly distributed within the slice, commonly referred to as ﬁne, to be soft- eating and slightly chewy in character. Bread crumb characterised by larger cell sizes, thicker cells walls and a more random distribution of cell size within the slice, commonly referred to as open or coarse, tend to yield bread with ﬁrmer and more chewy eating characteristics. There are major differences between the densities of different breads (Table 2.2). Product density is directly related to the expansion of the dough during proving and baking and the retention of gases within the gluten structure, up to the point of foam-to-sponge conversion. Many ingredient, formulation and processing fa

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