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CHOCOLATE | Milk Chocolate
CHOCOLATE
Milk Chocolate S T Beckett, Formerly Nestle´ Product Technology Centre York, York, UK ª 2011 Elsevier Ltd. All rights reserved.
Introduction Chocolate is almost unique as a food in that it is a solid at room temperature, yet melts easily in the mouth, so that it can be swallowed as a smooth liquid. It originated as a drink and took its present form only in the last 150 years. In most countries, milk chocolate far outsells plain and white chocolate. The physical and chemical properties of the milk components affect the making of the chocolate as well as its flavor and texture. Many plain chocolates contain milk fat in order to retard the development of a white mold-like appearance, known as chocolate bloom. Milk-derived ingredients, such as lactose and whey, are used in a wide variety of confectionery, and new products, specifically for chocolate production, are continually being developed by the milk-processing industry.
History To be called chocolate, a product must contain some cocoa-derived ingredients. The cocoa tree (Theobroma cacao) will only grow within 20 of the equator. It originated in South and Central America where the Aztecs and Incas roasted and ground the beans to make them into a drink. The Spanish introduced this to Europe and cocoa drink houses became popular in London at the time of Samuel Pepys. In 1727, Nicholas Sanders is said to have been the first to add milk to the drink. Over half of the cocoa bean consists of a fat, called cocoa butter. This fat tended to spoil the drink, and so a Dutchman called Van Houten developed a press to remove most of it and leave cocoa powder. In 1847, the UK company, Joseph Fry, combined cocoa beans, cocoa butter, and sugar to produce a plain eating chocolate. If water is added to chocolate, it becomes soft and pasty and does not have a snap when you break it, nor the hard bite associated with chocolate. The addition of milk to chocolate was not therefore easy and it was only in 1875 that Daniel Peter in Switzerland made the first bars.
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He was able to do this because condensed milk had recently been made commercially available, so he had less water to remove. Also he had cheap water power available to him to carry out the remainder of the drying. Most chocolate contains about 1% of moisture. White chocolate is an even more recent development. The main ingredients are sugar, milk powder, and cocoa butter. This means that it does not contain any of the brown cocoa material found in cocoa powder, but has more milk than the other main types of chocolate.
Composition of Milk Chocolate Figure 1 is a schematic diagram of a section through a piece of chocolate. Just under half the weight is sugar, and about one-quarter is the non-fat cocoa and milk particles. All these particles must be milled so that the majority of them are smaller than 30 mm. Larger particles are easily detected by the tongue and would make the chocolate feel gritty. This solid material is surrounded by fat, which is a mixture of cocoa butter and milk fat (vegetable fats made from special nuts that mimic cocoa butter are also used in some countries). This fat, which normally makes up between 27 and 32% of the weight of chocolate, must coat the surface of all the solid particles, to enable them to move past one another. This is needed to produce a smooth-flowing liquid, which can be poured into molds or poured over center ingredients such as wafers, toffees, and fondants. The fat then sets to produce the products that are found in shops. When the chocolate is placed in the mouth, the fat melts and it is now even more important that it coats the solid particles. Otherwise, instead of having a smooth liquid that can be swallowed easily, it would be much more pasty and would tend to feel gritty due to solid particles sticking together to form agglomerates. It is not easy to coat sugar with fat, however, as the sugar surface tends to be lipophobic. In order to help this wetting process, surface-active agents are added, which
Chocolate | Milk Chocolate
857
Figure 1 Schematic diagram of the solid particles and fat within a piece of milk chocolate.
form a layer on the sugar surface and help the chocolate to flow. The most widely used surface-active agent (emulsifier) is lecithin, which is normally obtained from soybeans. Milk also contains some lecithin and in addition the proteins can have an emulsifying effect, both of which can affect the flow properties of chocolate. This coating action is normally carried out in a large mixing machine, peculiar to the industry, which is called a conche and which typically holds from 3 to 10 tonnes of chocolate.
Flow Properties of Liquid Chocolate How liquid chocolate flows has a major effect on its processing and eating properties. Incorrect viscosity can lead to misshapen or overweight products, or to poor flavor and texture. Chocolate, like tomato ketchup and non-drip paint, has a viscosity that varies depending upon how quickly it is being poured or stirred. This is known as non-Newtonian flow. It cannot be described by a single number, and traditionally the viscosity is described by two parameters: a yield value, which relates to the force required to start the mass of liquid chocolate flowing, and a plastic viscosity, which is more concerned with keeping the flow moving. Milk affects both these parameters. The butterfat combines with cocoa butter to coat the solid particles and this helps lower both. However, if the butterfat is contained within cells within the non-fat milk solids, for example, surrounded by amorphous lactose, then it cannot affect the viscosity of the chocolate. This can be demonstrated
by making a chocolate with full cream milk powder produced by roller drying and comparing it with an identical one made with spray-dried powder. The latter contains much more bound-up fat and so the chocolate is much thicker. Most milk powder producers prefer to make a product with a high level of bound fat as this has better flow and keeping properties. This is contrary to the requirements of the confectionery industry and so several methods have been patented to free the fat from the amorphous lactose. One of these involves adding crystalline lactose before spraying, to try to stop the formation of lactose glass. An alternative approach is to moisten the milk powder before redrying it in a fluidized bed. The use of high homogenization pressures during the manufacture of whole milk powder has also been shown to increase the free-fat content, although not as much as by crystallization techniques. Small amounts of surface-active agents usually have a big effect on the yield value of chocolate. Most chocolates contain about 0.4% of lecithin and as can be seen in Figure 2, this amount is very beneficial in reducing both flow parameters. If more is added, however, the yield value increases again. This may be due to the formation of a bilayer around the sugar, or to the lecithin molecules joining together to form micelles. The lecithin in milk forms part of the lecithin content of the chocolate. Normally, it is at a low level, but may become important if buttermilk powder is used. Some chocolates, particularly in the United States, contain high levels of buttermilk, and in these cases the level of soy lecithin may have to be reduced to avoid the thickening effect described above.
858 Chocolate | Milk Chocolate
Figure 2 The effect of the addition of different amounts of lecithin upon the chocolate viscosity parameters. PV, plastic viscosity (Pa s); YV, yield value (Pa).
The proteins, both whey and caseinates, have an emulsifying effect. Their effect depends upon the amount used and the other ingredients present. The moisture of the chocolate is also important. Although this is present at around 1%, it significantly thickens the chocolate, probably by ‘sticking’ the sugar particles together. Lecithin and proteins, being hygroscopic, help to reduce this effect. The processing and the structure of the various types of milk powders also play a significant role in determining the final flow properties of chocolate. Several in-depth studies have been carried out by Prof. Tscheuschner and co-workers in Germany.
sweetness of the chocolate. It can also be used to replace some of the sucrose, when a reduction in sweetness is required. Care must be taken, however, to ensure that the lactose is free from off-flavors. Metallic or cheesy notes can very quickly make the chocolate unpalatable. The milk fat has little effect on the creaminess of the product compared with the non-fat components. It does, however, alter very significantly the texture and melting properties of chocolate. The milk components have a very significant effect on the color of the chocolate, making it a much lighter brown. Other factors such as the type of cocoa bean and its roasting conditions also affect this parameter.
Flavor of Milk Chocolate
Effect of Milk Fat on Chocolate Texture
Plain chocolate has a distinctive cocoa flavor, with some acidic/fruity notes. This comes from numerous chemical compounds, which in turn relate to the bean type, its growing conditions, fermentation, roasting, and other processing. The milk solids tend to counter the acidity and produce a more creamy taste. This is particularly true for the milk proteins. For a particular chocolate flavor, a careful balance must be maintained between these proteins and the cocoa content. A reduction by a few percent of the caseinates can produce a significant increase in cocoa flavor. The flavor of a chocolate depends upon the speed with which the flavor components reach the different receptors in the mouth and nose. This in turn depends upon the viscosity of the chocolate and how it melts. This means that chocolates with the same amount of milk can taste very dissimilar if they flow differently or have a different particle size. Chocolate from a refrigerator will taste different from a bar that has been kept at room temperature. The lactose in the milk does not affect this cocoa/ creaminess balance, but can be used to adjust the
Chocolate obtains its characteristic texture/mouthfeel from the cocoa butter. This is a triglyceride, that is, it has three fatty acids attached to a glycerol backbone. In the case of cocoa butter, oleic (about 35%), stearic (about 34%), and palmitic (about 26%) acids make up most of the fatty acids present, with oleic acid normally (80%) being located in the central position. This in fact makes it a relatively simple fat and is the reason why it melts over the relatively narrow range of temperature between room temperature and that of the mouth. However, it can crystallize in six different forms, depending on the temperature and how it is processed (see Figure 3). Forms I–IV are unstable and would give chocolate a crumbly texture and a dull appearance, rather than the solid bite and gloss preferred by the consumer. Form V is produced in the factory by machines called temperers, which take the chocolate through a cooling/ heating cycle while vigorously mixing it. Although Form VI is more stable, it normally forms only by a solid-to-solid transition, unlike the other forms, which can be formed in liquid chocolate.
Chocolate | Milk Chocolate
Dense compacting stable
Loose compacting unstable γ
β′1
α
β′2
β2
III IV V I II 16–18 °C 22–24 °C 24–26 °C 26–28 °C 32–34 °C
β1 VI 32–34 °C
Liquid chocolate Figure 3 The temperature ranges for the stable formation of the six different forms of cocoa butter.
The different forms are due to the individual molecules of fat packing themselves together in different ways. If milk fat is present, it cannot fit exactly within this packing, so the structure formed is not so compact and the texture is much softer. For this reason, milk chocolate is normally much easier to bite into than the plain varieties and has a more easily melting creamy texture. The latter is, however, in part due to the fact that it melts more easily as there is proportionately less solid fat present at normal ambient temperatures. Anhydrous milk fat is partially liquid at room temperature, whereas cocoa butter is largely solid. It would be expected therefore that additions of milk fat would increase the liquid fat content, but this is magnified by what is known as a eutectic effect, which limits the amount of butterfat that can be used in chocolate. The eutectic effect arises from the fact that the two fats are not compatible in their structures. This is illustrated in Figure 4. At 20 C, about 80% of the cocoa butter is solid, which is sufficient to give it a hard bite. An equal mix of cocoa butter and butterfat (20% solid) would be expected to have an average solid content of about half of this due to
a dilution effect, that is, 50% solid. It is in fact less than 35% solid, which would give a very pasty product. At 20 C, a mixture containing 25% milk fat has a solid fat content of only about 60%. This is relatively soft and is about the limit that can be used, unless of course the fat is bound up within the lactose of the milk and so cannot affect the crystallization of cocoa butter. Chocolate contains approximately 30% of fat overall, which means that most recipes contain less than 7.5% of free milk fat or the chocolate becomes soft and easy to melt. Increasing the amount of milk fat also makes the color of the chocolate lighter. Milk fat can be fractionated into elements with different hardnesses, usually to provide high-, medium-, and lowmelting fractions. These change the hardness of the chocolate according to their different dilution and eutectic effects. The fractionation may also change the milk flavor of the chocolate. The hard fraction normally gives a harder product, although there is some evidence that extra-hard fractions may upset the crystallization (tempering) process and thereby give the opposite result by causing the cocoa butter to set in its unstable forms.
Fat Bloom on Chocolate Chocolate bloom has the appearance of a white powder, like a frost, which can be mistaken for mold. It is in fact composed of large cocoa butter crystals that have been formed on the surface. There are three different causes of fat bloom. Perhaps the main cause is that the fat has changed its crystal form. This may be due to the manufacturer not setting it in Form V, in which case the product may go white in a few days. Alternatively, as the chocolate ages, it changes from Form V to Form VI. This may take months or even years if the chocolate is stored correctly.
90 80
Solid fat (%)
70 Dilution effect
60 50 40 30 20 10 0 0
10
20
30
40
859
50
60
Milk fat in cocoa butter (%) Figure 4 The relative hardness of mixtures of cocoa butter and milk fat at 20 C.
70
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90
100
860 Chocolate | Milk Chocolate
However, the transformation is much faster at higher temperatures. A second cause is when the product has been melted, perhaps by being left in the sun. The fat resets leaving the white crystals on the surface. In a box of chocolates with several different types of centers, those containing nuts or nut-based pastes are usually the first to bloom. This is because the nut fat, like milk fat, is mainly liquid. This migrates through the chocolate, making it softer and pushing some of the fat onto the surface, where it crystallizes. The addition of milk fat to the chocolate reduces the cocoa butter’s tendency to change its crystalline form and thereby slows down bloom formation. This may be due to the way the different molecules of liquid fat are contained within the structure. This is also able to slow down the formation of bloom due to nut oil. The effect is independent of the other milk components and so can be applied to plain chocolates. Some plain chocolates in fact contain more milk fat than milk chocolates. The more milk fat that is added, the stronger will be the antibloom effect. In addition, some milk fat fractions are better than others, with the harder fractions usually being the best for this purpose.
Milk-Based Ingredients Used in Chocolate Making
Crumb is manufactured by drying sweetened condensed milk with finely milled cocoa beans (without the shell). Here, the sugar and the cocoa help to preserve the milk fat, which would otherwise go rancid. It is interesting that the antioxidant properties of cocoa have only been highlighted in the last few years, even though chocolate crumb was developed more than 60 years ago. The antioxidant properties tend to be in the non-fat brown cocoa powder. This enables milk chocolate to be sold in transparent packaging if desired. White chocolate, on the other hand, must have opaque wrapping as otherwise the light will accelerate the rancidity of the milk fat. The presence of proteins, moisture, and reducing sugars during drying is ideal for the Maillard reaction, which introduces a cooked note into the product. This is the main reason why the chocolates in countries that traditionally use crumb, like the United Kingdom, taste very different from those where milk powders are mainly used, for example, France.
Whey Powder This powder is normally used at a level up to about 5% of the chocolate mass to increase the milkiness of the product. It is used at higher levels in coatings and chocolatelike products. In general, demineralized whey is used so as not to impart unwanted flavors into the chocolate.
Whole Milk Powder Both spray- and roller-dried powders are used to make milk chocolate. Specially processed spray-dried powders with a higher level of free fat are produced for use in confectionery.
Lactose Lactose can be used as a partial alternative to sucrose in order to make the chocolate less sweet. As with whey, it must not contain any off-flavors.
Skim Milk Powder This is used in combination with milk fat to make chocolate. This means that all the fat is free, so the viscosity is lower and the texture softer than in a product made with an equivalent amount of whole milk powder. The taste is also different from that of a chocolate made with whole milk powder. Sometimes, lipase-free milk powders are requested. This is because the lipase can accelerate decomposition of some of the milk fat into free fatty acids, which produce a soapy or cheesy flavor.
High-Fat Powders Whole milk powders are available with more than 55% milk fat. This anhydrous fat is largely in a free form and so aids chocolate flow. The high-fat powders enable the manufacturer to add all the milk fat as a powder and thereby avoid the cost and inconvenience of additional liquid fat metering systems.
Chocolate Crumb
Buttermilk Powder
This ingredient was developed at a time when the keeping properties of milk powders were poor. The chocolate industry has peak sales at Christmas, which coincides with low milk production, so an ingredient with a long shelf life was developed.
As with whey powder, this can be used in smaller proportions to adjust the flavor and flow properties of a chocolate. It is also used in chocolate-flavored coatings and, in the United States, a special type of product known as buttermilk chocolate is manufactured.
Chocolate | Milk Chocolate
Legislation Concerning Milk Chocolates There are very distinct legal definitions of what can be called chocolate. These vary from country to country, although most markets apply either the European Union or Codex Alimentarius or United States regulations. Chocolate-like products that do not meet the appropriate criteria must be labeled as chocolate-flavored coatings or a similar name and may contain milk components, such as whey, at any level. Most milk chocolate legislation has minimum milk fat solids and non-fat milk solids levels. The non-fat milk solids must normally be in the ratio at which they are found naturally. This means that skim milk powder cannot just be replaced by whey or lactose. In most legislation, the minimum milk fat level is between 2.5 and 3.5% and the total milk content must be between 12 and 14% of the chocolate. Several traditional UK chocolates contain a minimum of 20% milk of which at least 5% is milk fat. Because of the higher milk content, there is normally less non-fat cocoa solids, which is regarded as inferior in some countries. This means that in all countries within the European Union, except the United Kingdom and Ireland, they have to be labeled as family milk chocolate or its equivalent.
Future Developments Although the chocolate industry is a relatively small user of milk products, it is also a stable and slightly increasing one. It is also one where specialist ingredients can be used in an economic way. This means that the development of products with special flavors or which have components that aid liquid chocolate flow or reduce fat bloom is likely to increase. In addition, the sales of organic and fair trade products and those with ingredients from specific locations have increased dramatically over recent years and this trend is likely to continue.
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See also: Analytical Methods: Principles and Significance in Assessing Rheological and Textural Properties. Butter and Other Milk Fat Products: The Product and Its Manufacture. Flavors and Off-Flavors in Dairy Foods. Hazard Analysis and Critical Control Points: Processing Plants. Liquid Milk Products: Recombined and Reconstituted Products. Milk Protein Products: Functional Properties of Milk Proteins. Whey Processing: Utilization and Products.
Further Reading Beckett ST (2003) Is the taste of British milk chocolate different? International Journal of Dairy Technology 56(3): 139–142. Beckett ST (2008) The Science of Chocolate, 2nd edn. Cambridge: Royal Society of Chemistry. Campbell LB and Pavlasek SJ (1987) Dairy products as ingredients in chocolate and confections. Food Technology 41(10): 78–85. Cook R (1984) Chocolate Production and Use. New York: Harcourt Brace. Full NA, Yella Reddy S, Dimick PS, and Ziegler GR (1996) Physical and sensory properties of milk chocolate formulated with anhydrous milk fat fractions. Journal of Food Science 61: 1068–1084. Hartel RW (1996) Applications of milk-fat fractions in confectionery products. Journal of the American Oil Chemists Society 73: 945–953. Haylock SJ and Dodds TM (2009) Ingredients from milk. In: Beckett ST (ed.) Industrial Chocolate Manufacture and Use, 4th edn., pp. 76–100. Oxford: Wiley Blackwell. Liang B and Hartel RW (2004) Effects of milk powders in milk chocolate. Journal of Dairy Science 87: 20–31. Lohman MH and Hartel RW (1994) Effect of milk fat fractions on fat bloom in dark chocolate. Journal of the American Oil Chemists Society 71: 267–276. Minifie BW (1980) Chocolate, Cocoa and Confectionery, 2nd edn. Westport, CT: Avi Publishing Co. Inc. Mohler MR, Huginin AG, and Ebers K (1981) Whey-based nonfat milk replacers in light chocolate flavoured compound coatings. Food Technology 35: 79–81. Scheruhn E, Franke K, and Tscheuschner H-D (2000) Merkmale des Milchpulvers beeinflussen die Viskosita¨t. Zucker und Su¨sswarenwirtschaft 5: 131–136. Wells MA (2009) Chocolate crumb. In: Beckett ST (ed.) Industrial Chocolate Manufacture and Use, 4th edn., pp. 101–119. Oxford: Wiley Blackwell.
Milk Chocolate S T Beckett, Formerly Nestle´ Product Technology Centre York, York, UK ª 2011 Elsevier Ltd. All rights reserved.
Introduction Chocolate is almost unique as a food in that it is a solid at room temperature, yet melts easily in the mouth, so that it can be swallowed as a smooth liquid. It originated as a drink and took its present form only in the last 150 years. In most countries, milk chocolate far outsells plain and white chocolate. The physical and chemical properties of the milk components affect the making of the chocolate as well as its flavor and texture. Many plain chocolates contain milk fat in order to retard the development of a white mold-like appearance, known as chocolate bloom. Milk-derived ingredients, such as lactose and whey, are used in a wide variety of confectionery, and new products, specifically for chocolate production, are continually being developed by the milk-processing industry.
History To be called chocolate, a product must contain some cocoa-derived ingredients. The cocoa tree (Theobroma cacao) will only grow within 20 of the equator. It originated in South and Central America where the Aztecs and Incas roasted and ground the beans to make them into a drink. The Spanish introduced this to Europe and cocoa drink houses became popular in London at the time of Samuel Pepys. In 1727, Nicholas Sanders is said to have been the first to add milk to the drink. Over half of the cocoa bean consists of a fat, called cocoa butter. This fat tended to spoil the drink, and so a Dutchman called Van Houten developed a press to remove most of it and leave cocoa powder. In 1847, the UK company, Joseph Fry, combined cocoa beans, cocoa butter, and sugar to produce a plain eating chocolate. If water is added to chocolate, it becomes soft and pasty and does not have a snap when you break it, nor the hard bite associated with chocolate. The addition of milk to chocolate was not therefore easy and it was only in 1875 that Daniel Peter in Switzerland made the first bars.
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He was able to do this because condensed milk had recently been made commercially available, so he had less water to remove. Also he had cheap water power available to him to carry out the remainder of the drying. Most chocolate contains about 1% of moisture. White chocolate is an even more recent development. The main ingredients are sugar, milk powder, and cocoa butter. This means that it does not contain any of the brown cocoa material found in cocoa powder, but has more milk than the other main types of chocolate.
Composition of Milk Chocolate Figure 1 is a schematic diagram of a section through a piece of chocolate. Just under half the weight is sugar, and about one-quarter is the non-fat cocoa and milk particles. All these particles must be milled so that the majority of them are smaller than 30 mm. Larger particles are easily detected by the tongue and would make the chocolate feel gritty. This solid material is surrounded by fat, which is a mixture of cocoa butter and milk fat (vegetable fats made from special nuts that mimic cocoa butter are also used in some countries). This fat, which normally makes up between 27 and 32% of the weight of chocolate, must coat the surface of all the solid particles, to enable them to move past one another. This is needed to produce a smooth-flowing liquid, which can be poured into molds or poured over center ingredients such as wafers, toffees, and fondants. The fat then sets to produce the products that are found in shops. When the chocolate is placed in the mouth, the fat melts and it is now even more important that it coats the solid particles. Otherwise, instead of having a smooth liquid that can be swallowed easily, it would be much more pasty and would tend to feel gritty due to solid particles sticking together to form agglomerates. It is not easy to coat sugar with fat, however, as the sugar surface tends to be lipophobic. In order to help this wetting process, surface-active agents are added, which
Chocolate | Milk Chocolate
857
Figure 1 Schematic diagram of the solid particles and fat within a piece of milk chocolate.
form a layer on the sugar surface and help the chocolate to flow. The most widely used surface-active agent (emulsifier) is lecithin, which is normally obtained from soybeans. Milk also contains some lecithin and in addition the proteins can have an emulsifying effect, both of which can affect the flow properties of chocolate. This coating action is normally carried out in a large mixing machine, peculiar to the industry, which is called a conche and which typically holds from 3 to 10 tonnes of chocolate.
Flow Properties of Liquid Chocolate How liquid chocolate flows has a major effect on its processing and eating properties. Incorrect viscosity can lead to misshapen or overweight products, or to poor flavor and texture. Chocolate, like tomato ketchup and non-drip paint, has a viscosity that varies depending upon how quickly it is being poured or stirred. This is known as non-Newtonian flow. It cannot be described by a single number, and traditionally the viscosity is described by two parameters: a yield value, which relates to the force required to start the mass of liquid chocolate flowing, and a plastic viscosity, which is more concerned with keeping the flow moving. Milk affects both these parameters. The butterfat combines with cocoa butter to coat the solid particles and this helps lower both. However, if the butterfat is contained within cells within the non-fat milk solids, for example, surrounded by amorphous lactose, then it cannot affect the viscosity of the chocolate. This can be demonstrated
by making a chocolate with full cream milk powder produced by roller drying and comparing it with an identical one made with spray-dried powder. The latter contains much more bound-up fat and so the chocolate is much thicker. Most milk powder producers prefer to make a product with a high level of bound fat as this has better flow and keeping properties. This is contrary to the requirements of the confectionery industry and so several methods have been patented to free the fat from the amorphous lactose. One of these involves adding crystalline lactose before spraying, to try to stop the formation of lactose glass. An alternative approach is to moisten the milk powder before redrying it in a fluidized bed. The use of high homogenization pressures during the manufacture of whole milk powder has also been shown to increase the free-fat content, although not as much as by crystallization techniques. Small amounts of surface-active agents usually have a big effect on the yield value of chocolate. Most chocolates contain about 0.4% of lecithin and as can be seen in Figure 2, this amount is very beneficial in reducing both flow parameters. If more is added, however, the yield value increases again. This may be due to the formation of a bilayer around the sugar, or to the lecithin molecules joining together to form micelles. The lecithin in milk forms part of the lecithin content of the chocolate. Normally, it is at a low level, but may become important if buttermilk powder is used. Some chocolates, particularly in the United States, contain high levels of buttermilk, and in these cases the level of soy lecithin may have to be reduced to avoid the thickening effect described above.
858 Chocolate | Milk Chocolate
Figure 2 The effect of the addition of different amounts of lecithin upon the chocolate viscosity parameters. PV, plastic viscosity (Pa s); YV, yield value (Pa).
The proteins, both whey and caseinates, have an emulsifying effect. Their effect depends upon the amount used and the other ingredients present. The moisture of the chocolate is also important. Although this is present at around 1%, it significantly thickens the chocolate, probably by ‘sticking’ the sugar particles together. Lecithin and proteins, being hygroscopic, help to reduce this effect. The processing and the structure of the various types of milk powders also play a significant role in determining the final flow properties of chocolate. Several in-depth studies have been carried out by Prof. Tscheuschner and co-workers in Germany.
sweetness of the chocolate. It can also be used to replace some of the sucrose, when a reduction in sweetness is required. Care must be taken, however, to ensure that the lactose is free from off-flavors. Metallic or cheesy notes can very quickly make the chocolate unpalatable. The milk fat has little effect on the creaminess of the product compared with the non-fat components. It does, however, alter very significantly the texture and melting properties of chocolate. The milk components have a very significant effect on the color of the chocolate, making it a much lighter brown. Other factors such as the type of cocoa bean and its roasting conditions also affect this parameter.
Flavor of Milk Chocolate
Effect of Milk Fat on Chocolate Texture
Plain chocolate has a distinctive cocoa flavor, with some acidic/fruity notes. This comes from numerous chemical compounds, which in turn relate to the bean type, its growing conditions, fermentation, roasting, and other processing. The milk solids tend to counter the acidity and produce a more creamy taste. This is particularly true for the milk proteins. For a particular chocolate flavor, a careful balance must be maintained between these proteins and the cocoa content. A reduction by a few percent of the caseinates can produce a significant increase in cocoa flavor. The flavor of a chocolate depends upon the speed with which the flavor components reach the different receptors in the mouth and nose. This in turn depends upon the viscosity of the chocolate and how it melts. This means that chocolates with the same amount of milk can taste very dissimilar if they flow differently or have a different particle size. Chocolate from a refrigerator will taste different from a bar that has been kept at room temperature. The lactose in the milk does not affect this cocoa/ creaminess balance, but can be used to adjust the
Chocolate obtains its characteristic texture/mouthfeel from the cocoa butter. This is a triglyceride, that is, it has three fatty acids attached to a glycerol backbone. In the case of cocoa butter, oleic (about 35%), stearic (about 34%), and palmitic (about 26%) acids make up most of the fatty acids present, with oleic acid normally (80%) being located in the central position. This in fact makes it a relatively simple fat and is the reason why it melts over the relatively narrow range of temperature between room temperature and that of the mouth. However, it can crystallize in six different forms, depending on the temperature and how it is processed (see Figure 3). Forms I–IV are unstable and would give chocolate a crumbly texture and a dull appearance, rather than the solid bite and gloss preferred by the consumer. Form V is produced in the factory by machines called temperers, which take the chocolate through a cooling/ heating cycle while vigorously mixing it. Although Form VI is more stable, it normally forms only by a solid-to-solid transition, unlike the other forms, which can be formed in liquid chocolate.
Chocolate | Milk Chocolate
Dense compacting stable
Loose compacting unstable γ
β′1
α
β′2
β2
III IV V I II 16–18 °C 22–24 °C 24–26 °C 26–28 °C 32–34 °C
β1 VI 32–34 °C
Liquid chocolate Figure 3 The temperature ranges for the stable formation of the six different forms of cocoa butter.
The different forms are due to the individual molecules of fat packing themselves together in different ways. If milk fat is present, it cannot fit exactly within this packing, so the structure formed is not so compact and the texture is much softer. For this reason, milk chocolate is normally much easier to bite into than the plain varieties and has a more easily melting creamy texture. The latter is, however, in part due to the fact that it melts more easily as there is proportionately less solid fat present at normal ambient temperatures. Anhydrous milk fat is partially liquid at room temperature, whereas cocoa butter is largely solid. It would be expected therefore that additions of milk fat would increase the liquid fat content, but this is magnified by what is known as a eutectic effect, which limits the amount of butterfat that can be used in chocolate. The eutectic effect arises from the fact that the two fats are not compatible in their structures. This is illustrated in Figure 4. At 20 C, about 80% of the cocoa butter is solid, which is sufficient to give it a hard bite. An equal mix of cocoa butter and butterfat (20% solid) would be expected to have an average solid content of about half of this due to
a dilution effect, that is, 50% solid. It is in fact less than 35% solid, which would give a very pasty product. At 20 C, a mixture containing 25% milk fat has a solid fat content of only about 60%. This is relatively soft and is about the limit that can be used, unless of course the fat is bound up within the lactose of the milk and so cannot affect the crystallization of cocoa butter. Chocolate contains approximately 30% of fat overall, which means that most recipes contain less than 7.5% of free milk fat or the chocolate becomes soft and easy to melt. Increasing the amount of milk fat also makes the color of the chocolate lighter. Milk fat can be fractionated into elements with different hardnesses, usually to provide high-, medium-, and lowmelting fractions. These change the hardness of the chocolate according to their different dilution and eutectic effects. The fractionation may also change the milk flavor of the chocolate. The hard fraction normally gives a harder product, although there is some evidence that extra-hard fractions may upset the crystallization (tempering) process and thereby give the opposite result by causing the cocoa butter to set in its unstable forms.
Fat Bloom on Chocolate Chocolate bloom has the appearance of a white powder, like a frost, which can be mistaken for mold. It is in fact composed of large cocoa butter crystals that have been formed on the surface. There are three different causes of fat bloom. Perhaps the main cause is that the fat has changed its crystal form. This may be due to the manufacturer not setting it in Form V, in which case the product may go white in a few days. Alternatively, as the chocolate ages, it changes from Form V to Form VI. This may take months or even years if the chocolate is stored correctly.
90 80
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Milk fat in cocoa butter (%) Figure 4 The relative hardness of mixtures of cocoa butter and milk fat at 20 C.
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860 Chocolate | Milk Chocolate
However, the transformation is much faster at higher temperatures. A second cause is when the product has been melted, perhaps by being left in the sun. The fat resets leaving the white crystals on the surface. In a box of chocolates with several different types of centers, those containing nuts or nut-based pastes are usually the first to bloom. This is because the nut fat, like milk fat, is mainly liquid. This migrates through the chocolate, making it softer and pushing some of the fat onto the surface, where it crystallizes. The addition of milk fat to the chocolate reduces the cocoa butter’s tendency to change its crystalline form and thereby slows down bloom formation. This may be due to the way the different molecules of liquid fat are contained within the structure. This is also able to slow down the formation of bloom due to nut oil. The effect is independent of the other milk components and so can be applied to plain chocolates. Some plain chocolates in fact contain more milk fat than milk chocolates. The more milk fat that is added, the stronger will be the antibloom effect. In addition, some milk fat fractions are better than others, with the harder fractions usually being the best for this purpose.
Milk-Based Ingredients Used in Chocolate Making
Crumb is manufactured by drying sweetened condensed milk with finely milled cocoa beans (without the shell). Here, the sugar and the cocoa help to preserve the milk fat, which would otherwise go rancid. It is interesting that the antioxidant properties of cocoa have only been highlighted in the last few years, even though chocolate crumb was developed more than 60 years ago. The antioxidant properties tend to be in the non-fat brown cocoa powder. This enables milk chocolate to be sold in transparent packaging if desired. White chocolate, on the other hand, must have opaque wrapping as otherwise the light will accelerate the rancidity of the milk fat. The presence of proteins, moisture, and reducing sugars during drying is ideal for the Maillard reaction, which introduces a cooked note into the product. This is the main reason why the chocolates in countries that traditionally use crumb, like the United Kingdom, taste very different from those where milk powders are mainly used, for example, France.
Whey Powder This powder is normally used at a level up to about 5% of the chocolate mass to increase the milkiness of the product. It is used at higher levels in coatings and chocolatelike products. In general, demineralized whey is used so as not to impart unwanted flavors into the chocolate.
Whole Milk Powder Both spray- and roller-dried powders are used to make milk chocolate. Specially processed spray-dried powders with a higher level of free fat are produced for use in confectionery.
Lactose Lactose can be used as a partial alternative to sucrose in order to make the chocolate less sweet. As with whey, it must not contain any off-flavors.
Skim Milk Powder This is used in combination with milk fat to make chocolate. This means that all the fat is free, so the viscosity is lower and the texture softer than in a product made with an equivalent amount of whole milk powder. The taste is also different from that of a chocolate made with whole milk powder. Sometimes, lipase-free milk powders are requested. This is because the lipase can accelerate decomposition of some of the milk fat into free fatty acids, which produce a soapy or cheesy flavor.
High-Fat Powders Whole milk powders are available with more than 55% milk fat. This anhydrous fat is largely in a free form and so aids chocolate flow. The high-fat powders enable the manufacturer to add all the milk fat as a powder and thereby avoid the cost and inconvenience of additional liquid fat metering systems.
Chocolate Crumb
Buttermilk Powder
This ingredient was developed at a time when the keeping properties of milk powders were poor. The chocolate industry has peak sales at Christmas, which coincides with low milk production, so an ingredient with a long shelf life was developed.
As with whey powder, this can be used in smaller proportions to adjust the flavor and flow properties of a chocolate. It is also used in chocolate-flavored coatings and, in the United States, a special type of product known as buttermilk chocolate is manufactured.
Chocolate | Milk Chocolate
Legislation Concerning Milk Chocolates There are very distinct legal definitions of what can be called chocolate. These vary from country to country, although most markets apply either the European Union or Codex Alimentarius or United States regulations. Chocolate-like products that do not meet the appropriate criteria must be labeled as chocolate-flavored coatings or a similar name and may contain milk components, such as whey, at any level. Most milk chocolate legislation has minimum milk fat solids and non-fat milk solids levels. The non-fat milk solids must normally be in the ratio at which they are found naturally. This means that skim milk powder cannot just be replaced by whey or lactose. In most legislation, the minimum milk fat level is between 2.5 and 3.5% and the total milk content must be between 12 and 14% of the chocolate. Several traditional UK chocolates contain a minimum of 20% milk of which at least 5% is milk fat. Because of the higher milk content, there is normally less non-fat cocoa solids, which is regarded as inferior in some countries. This means that in all countries within the European Union, except the United Kingdom and Ireland, they have to be labeled as family milk chocolate or its equivalent.
Future Developments Although the chocolate industry is a relatively small user of milk products, it is also a stable and slightly increasing one. It is also one where specialist ingredients can be used in an economic way. This means that the development of products with special flavors or which have components that aid liquid chocolate flow or reduce fat bloom is likely to increase. In addition, the sales of organic and fair trade products and those with ingredients from specific locations have increased dramatically over recent years and this trend is likely to continue.
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See also: Analytical Methods: Principles and Significance in Assessing Rheological and Textural Properties. Butter and Other Milk Fat Products: The Product and Its Manufacture. Flavors and Off-Flavors in Dairy Foods. Hazard Analysis and Critical Control Points: Processing Plants. Liquid Milk Products: Recombined and Reconstituted Products. Milk Protein Products: Functional Properties of Milk Proteins. Whey Processing: Utilization and Products.
Further Reading Beckett ST (2003) Is the taste of British milk chocolate different? International Journal of Dairy Technology 56(3): 139–142. Beckett ST (2008) The Science of Chocolate, 2nd edn. Cambridge: Royal Society of Chemistry. Campbell LB and Pavlasek SJ (1987) Dairy products as ingredients in chocolate and confections. Food Technology 41(10): 78–85. Cook R (1984) Chocolate Production and Use. New York: Harcourt Brace. Full NA, Yella Reddy S, Dimick PS, and Ziegler GR (1996) Physical and sensory properties of milk chocolate formulated with anhydrous milk fat fractions. Journal of Food Science 61: 1068–1084. Hartel RW (1996) Applications of milk-fat fractions in confectionery products. Journal of the American Oil Chemists Society 73: 945–953. Haylock SJ and Dodds TM (2009) Ingredients from milk. In: Beckett ST (ed.) Industrial Chocolate Manufacture and Use, 4th edn., pp. 76–100. Oxford: Wiley Blackwell. Liang B and Hartel RW (2004) Effects of milk powders in milk chocolate. Journal of Dairy Science 87: 20–31. Lohman MH and Hartel RW (1994) Effect of milk fat fractions on fat bloom in dark chocolate. Journal of the American Oil Chemists Society 71: 267–276. Minifie BW (1980) Chocolate, Cocoa and Confectionery, 2nd edn. Westport, CT: Avi Publishing Co. Inc. Mohler MR, Huginin AG, and Ebers K (1981) Whey-based nonfat milk replacers in light chocolate flavoured compound coatings. Food Technology 35: 79–81. Scheruhn E, Franke K, and Tscheuschner H-D (2000) Merkmale des Milchpulvers beeinflussen die Viskosita¨t. Zucker und Su¨sswarenwirtschaft 5: 131–136. Wells MA (2009) Chocolate crumb. In: Beckett ST (ed.) Industrial Chocolate Manufacture and Use, 4th edn., pp. 101–119. Oxford: Wiley Blackwell.