CHOCOLATE
Milk Chocolate
S T Beckett, Formerly Nestlé Product Technology Centre York, York, UK
ª 2011 Elsevier Ltd. All rights reserved.
Introduction He was able to do this because condensed milk had
recently been made commercially available, so he had
Chocolate is almost unique as a food in that it is a solid at less water to remove. Also he had cheap water power
room temperature, yet melts easily in the mouth, so that available to him to carry out the remainder of the drying.
it can be swallowed as a smooth liquid. It originated as a Most chocolate contains about 1% of moisture.
drink and took its present form only in the last 150 years. White chocolate is an even more recent develop-
In most countries, milk chocolate far outsells plain and ment. The main ingredients are sugar, milk powder,
white chocolate. The physical and chemical properties and cocoa butter. This means that it does not contain
of the milk components affect the making of the any of the brown cocoa material found in cocoa
chocolate as well as its flavor and texture. Many plain powder, but has more milk than the other main types
chocolates contain milk fat in order to retard the devel- of chocolate.
opment 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 confec-
tionery, and new products, specifically for chocolate Composition of Milk Chocolate
production, are continually being developed by the
milk-processing industry. 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
History them are smaller than 30 mm. Larger particles are easily
detected by the tongue and would make the chocolate feel
To be called chocolate, a product must contain some gritty. This solid material is surrounded by fat, which is a
cocoa-derived ingredients. The cocoa tree (Theobroma mixture of cocoa butter and milk fat (vegetable fats made
cacao) will only grow within 20 of the equator. It origi- from special nuts that mimic cocoa butter are also used in
nated in South and Central America where the Aztecs and some countries). This fat, which normally makes up
Incas roasted and ground the beans to make them into a between 27 and 32% of the weight of chocolate, must
drink. The Spanish introduced this to Europe and cocoa coat the surface of all the solid particles, to enable them to
drink houses became popular in London at the time of move past one another. This is needed to produce a
Samuel Pepys. In 1727, Nicholas Sanders is said to have smooth-flowing liquid, which can be poured into molds
been the first to add milk to the drink. or poured over center ingredients such as wafers, toffees,
Over half of the cocoa bean consists of a fat, called and fondants. The fat then sets to produce the products
cocoa butter. This fat tended to spoil the drink, and so a that are found in shops.
Dutchman called Van Houten developed a press to When the chocolate is placed in the mouth, the fat
remove most of it and leave cocoa powder. In 1847, the melts and it is now even more important that it coats the
UK company, Joseph Fry, combined cocoa beans, cocoa solid particles. Otherwise, instead of having a smooth
butter, and sugar to produce a plain eating chocolate. liquid that can be swallowed easily, it would be much
If water is added to chocolate, it becomes soft and more pasty and would tend to feel gritty due to solid
pasty and does not have a snap when you break it, nor particles sticking together to form agglomerates.
the hard bite associated with chocolate. The addition of It is not easy to coat sugar with fat, however, as the
milk to chocolate was not therefore easy and it was only in sugar surface tends to be lipophobic. In order to help this
1875 that Daniel Peter in Switzerland made the first bars. wetting process, surface-active agents are added, which
856
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 by making a chocolate with full cream milk powder
to flow. The most widely used surface-active agent produced by roller drying and comparing it with an
(emulsifier) is lecithin, which is normally obtained identical one made with spray-dried powder. The latter
from soybeans. Milk also contains some lecithin and in contains much more bound-up fat and so the chocolate is
addition the proteins can have an emulsifying effect, much thicker. Most milk powder producers prefer to
both of which can affect the flow properties of chocolate. make a product with a high level of bound fat as this has
This coating action is normally carried out in a large better flow and keeping properties. This is contrary to the
mixing machine, peculiar to the industry, which is called requirements of the confectionery industry and so several
a conche and which typically holds from 3 to 10 tonnes methods have been patented to free the fat from the
of chocolate. amorphous lactose. One of these involves adding crystal-
line lactose before spraying, to try to stop the formation of
lactose glass. An alternative approach is to moisten the
Flow Properties of Liquid Chocolate milk powder before redrying it in a fluidized bed. The use
of high homogenization pressures during the manufacture
How liquid chocolate flows has a major effect on its of whole milk powder has also been shown to increase the
processing and eating properties. Incorrect viscosity can free-fat content, although not as much as by crystalliza-
lead to misshapen or overweight products, or to poor tion techniques.
flavor and texture. Chocolate, like tomato ketchup and Small amounts of surface-active agents usually have a
non-drip paint, has a viscosity that varies depending upon big effect on the yield value of chocolate. Most chocolates
how quickly it is being poured or stirred. This is known as contain about 0.4% of lecithin and as can be seen in
non-Newtonian flow. It cannot be described by a single Figure 2, this amount is very beneficial in reducing
number, and traditionally the viscosity is described by both flow parameters. If more is added, however, the
two parameters: a yield value, which relates to the force yield value increases again. This may be due to the for-
required to start the mass of liquid chocolate flowing, and mation of a bilayer around the sugar, or to the lecithin
a plastic viscosity, which is more concerned with keeping molecules joining together to form micelles. The lecithin
the flow moving. in milk forms part of the lecithin content of the chocolate.
Milk affects both these parameters. The butterfat com- Normally, it is at a low level, but may become important
bines with cocoa butter to coat the solid particles and this if buttermilk powder is used. Some chocolates, particu-
helps lower both. However, if the butterfat is contained larly in the United States, contain high levels of
within cells within the non-fat milk solids, for example, buttermilk, and in these cases the level of soy lecithin
surrounded by amorphous lactose, then it cannot affect may have to be reduced to avoid the thickening effect
the viscosity of the chocolate. This can be demonstrated 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 sweetness of the chocolate. It can also be used to replace
emulsifying effect. Their effect depends upon the some of the sucrose, when a reduction in sweetness is
amount used and the other ingredients present. The required. Care must be taken, however, to ensure that the
moisture of the chocolate is also important. Although lactose is free from off-flavors. Metallic or cheesy notes
this is present at around 1%, it significantly thickens can very quickly make the chocolate unpalatable.
the chocolate, probably by ‘sticking’ the sugar particles The milk fat has little effect on the creaminess of the
together. Lecithin and proteins, being hygroscopic, help product compared with the non-fat components. It does,
to reduce this effect. however, alter very significantly the texture and melting
The processing and the structure of the various types properties of chocolate.
of milk powders also play a significant role in determining The milk components have a very significant effect on
the final flow properties of chocolate. Several in-depth the color of the chocolate, making it a much lighter
studies have been carried out by Prof. Tscheuschner and brown. Other factors such as the type of cocoa bean and
co-workers in Germany. 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 Chocolate obtains its characteristic texture/mouthfeel
acidic/fruity notes. This comes from numerous chemical from the cocoa butter. This is a triglyceride, that is, it
compounds, which in turn relate to the bean type, its has three fatty acids attached to a glycerol backbone. In
growing conditions, fermentation, roasting, and other the case of cocoa butter, oleic (about 35%), stearic (about
processing. The milk solids tend to counter the acidity 34%), and palmitic (about 26%) acids make up most of
and produce a more creamy taste. This is particularly true the fatty acids present, with oleic acid normally (80%)
for the milk proteins. For a particular chocolate flavor, being located in the central position. This in fact makes it
a careful balance must be maintained between these a relatively simple fat and is the reason why it melts over
proteins and the cocoa content. A reduction by a few the relatively narrow range of temperature between room
percent of the caseinates can produce a significant temperature and that of the mouth. However, it can
increase in cocoa flavor. crystallize in six different forms, depending on the
The flavor of a chocolate depends upon the speed with temperature and how it is processed (see Figure 3).
which the flavor components reach the different receptors Forms I–IV are unstable and would give chocolate a
in the mouth and nose. This in turn depends upon the crumbly texture and a dull appearance, rather than the
viscosity of the chocolate and how it melts. This means solid bite and gloss preferred by the consumer.
that chocolates with the same amount of milk can taste Form V is produced in the factory by machines called
very dissimilar if they flow differently or have a different temperers, which take the chocolate through a cooling/
particle size. Chocolate from a refrigerator will taste dif- heating cycle while vigorously mixing it. Although
ferent from a bar that has been kept at room temperature. Form VI is more stable, it normally forms only by a
The lactose in the milk does not affect this cocoa/ solid-to-solid transition, unlike the other forms, which
creaminess balance, but can be used to adjust the can be formed in liquid chocolate.
Chocolate | Milk Chocolate 859
Loose compacting Dense a dilution effect, that is, 50% solid. It is in fact less than
unstable compacting 35% solid, which would give a very pasty product.
stable At 20 C, a mixture containing 25% milk fat has a solid
γ α β′1 β′2 β2 β1 fat content of only about 60%. This is relatively soft and is
I II III IV V VI about the limit that can be used, unless of course the fat is
16–18 °C 22–24 °C 24–26 °C 26–28 °C 32–34 °C 32–34 °C 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 choco-
Liquid chocolate late becomes soft and easy to melt. Increasing the amount of
Figure 3 The temperature ranges for the stable formation of
milk fat also makes the color of the chocolate lighter.
the six different forms of cocoa butter. Milk fat can be fractionated into elements with different
hardnesses, usually to provide high-, medium-, and low-
melting fractions. These change the hardness of the choco-
The different forms are due to the individual mole- late according to their different dilution and eutectic
cules of fat packing themselves together in different ways. effects. The fractionation may also change the milk flavor
If milk fat is present, it cannot fit exactly within this of the chocolate. The hard fraction normally gives a harder
packing, so the structure formed is not so compact and product, although there is some evidence that extra-hard
the texture is much softer. For this reason, milk chocolate fractions may upset the crystallization (tempering) process
is normally much easier to bite into than the plain varie- and thereby give the opposite result by causing the cocoa
ties and has a more easily melting creamy texture. The butter to set in its unstable forms.
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. Fat Bloom on Chocolate
Anhydrous milk fat is partially liquid at room
temperature, whereas cocoa butter is largely solid. It Chocolate bloom has the appearance of a white powder,
would be expected therefore that additions of milk fat like a frost, which can be mistaken for mold. It is in fact
would increase the liquid fat content, but this is magnified composed of large cocoa butter crystals that have been
by what is known as a eutectic effect, which limits the formed on the surface. There are three different causes of
amount of butterfat that can be used in chocolate. fat bloom.
The eutectic effect arises from the fact that the two fats Perhaps the main cause is that the fat has changed its
are not compatible in their structures. This is illustrated in crystal form. This may be due to the manufacturer not
Figure 4. At 20 C, about 80% of the cocoa butter is solid, setting it in Form V, in which case the product may go
which is sufficient to give it a hard bite. An equal mix of white in a few days. Alternatively, as the chocolate ages, it
cocoa butter and butterfat (20% solid) would be expected changes from Form V to Form VI. This may take months
to have an average solid content of about half of this due to or even years if the chocolate is stored correctly.
90
80
70
60 Dilution effect
Solid fat (%)
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Milk fat in cocoa butter (%)
Figure 4 The relative hardness of mixtures of cocoa butter and milk fat at 20 C.
860 Chocolate | Milk Chocolate
However, the transformation is much faster at higher Crumb is manufactured by drying sweetened con-
temperatures. densed milk with finely milled cocoa beans (without the
A second cause is when the product has been melted, shell). Here, the sugar and the cocoa help to preserve the
perhaps by being left in the sun. The fat resets leaving the milk fat, which would otherwise go rancid. It is interesting
white crystals on the surface. that the antioxidant properties of cocoa have only been
In a box of chocolates with several different types of highlighted in the last few years, even though chocolate
centers, those containing nuts or nut-based pastes are crumb was developed more than 60 years ago.
usually the first to bloom. This is because the nut fat, The antioxidant properties tend to be in the non-fat
like milk fat, is mainly liquid. This migrates through the brown cocoa powder. This enables milk chocolate to be
chocolate, making it softer and pushing some of the fat sold in transparent packaging if desired. White choco-
onto the surface, where it crystallizes. late, on the other hand, must have opaque wrapping as
The addition of milk fat to the chocolate reduces the otherwise the light will accelerate the rancidity of the
cocoa butter’s tendency to change its crystalline form and milk fat.
thereby slows down bloom formation. This may be due to The presence of proteins, moisture, and reducing
the way the different molecules of liquid fat are contained sugars during drying is ideal for the Maillard reaction,
within the structure. This is also able to slow down the which introduces a cooked note into the product. This is
formation of bloom due to nut oil. The effect is indepen- the main reason why the chocolates in countries that
dent of the other milk components and so can be applied traditionally use crumb, like the United Kingdom, taste
to plain chocolates. Some plain chocolates in fact contain very different from those where milk powders are mainly
more milk fat than milk chocolates. used, for example, France.
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
Whey Powder
being the best for this purpose.
This powder is normally used at a level up to about 5% of
the chocolate mass to increase the milkiness of the pro-
duct. It is used at higher levels in coatings and chocolate-
Milk-Based Ingredients Used in Chocolate like products. In general, demineralized whey is used so as
Making not to impart unwanted flavors into the chocolate.
Whole Milk Powder
Both spray- and roller-dried powders are used to make
Lactose
milk chocolate. Specially processed spray-dried powders
with a higher level of free fat are produced for use in Lactose can be used as a partial alternative to sucrose in
confectionery. 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 choco-
High-Fat Powders
late. This means that all the fat is free, so the viscosity is
lower and the texture softer than in a product made with Whole milk powders are available with more than 55%
an equivalent amount of whole milk powder. The taste is milk fat. This anhydrous fat is largely in a free form and so
also different from that of a chocolate made with whole aids chocolate flow. The high-fat powders enable the
milk powder. Sometimes, lipase-free milk powders are manufacturer to add all the milk fat as a powder and
requested. This is because the lipase can accelerate thereby avoid the cost and inconvenience of additional
decomposition of some of the milk fat into free fatty liquid fat metering systems.
acids, which produce a soapy or cheesy flavor.
Chocolate Crumb Buttermilk Powder
This ingredient was developed at a time when the keep- As with whey powder, this can be used in smaller propor-
ing properties of milk powders were poor. The chocolate tions to adjust the flavor and flow properties of a
industry has peak sales at Christmas, which coincides with chocolate. It is also used in chocolate-flavored coatings
low milk production, so an ingredient with a long shelf and, in the United States, a special type of product known
life was developed. as buttermilk chocolate is manufactured.
Chocolate | Milk Chocolate 861
Legislation Concerning Milk Chocolates See also: Analytical Methods: Principles and
Significance in Assessing Rheological and Textural
There are very distinct legal definitions of what can be Properties. Butter and Other Milk Fat Products: The
called chocolate. These vary from country to country, Product and Its Manufacture. Flavors and Off-Flavors in
although most markets apply either the European Union Dairy Foods. Hazard Analysis and Critical Control
or Codex Alimentarius or United States regulations. Points: Processing Plants. Liquid Milk Products:
Chocolate-like products that do not meet the appropriate Recombined and Reconstituted Products. Milk Protein
criteria must be labeled as chocolate-flavored coatings or Products: Functional Properties of Milk Proteins. Whey
a similar name and may contain milk components, such as Processing: Utilization and Products.
whey, at any level.
Most milk chocolate legislation has minimum milk fat
solids and non-fat milk solids levels. The non-fat milk Further Reading
solids must normally be in the ratio at which they are
Beckett ST (2003) Is the taste of British milk chocolate different?
found naturally. This means that skim milk powder can- International Journal of Dairy Technology 56(3): 139–142.
not just be replaced by whey or lactose. Beckett ST (2008) The Science of Chocolate, 2nd edn. Cambridge:
In most legislation, the minimum milk fat level is Royal Society of Chemistry.
Campbell LB and Pavlasek SJ (1987) Dairy products as
between 2.5 and 3.5% and the total milk content must ingredients in chocolate and confections. Food Technology
be between 12 and 14% of the chocolate. Several tradi- 41(10): 78–85.
tional UK chocolates contain a minimum of 20% milk of Cook R (1984) Chocolate Production and Use. New York: Harcourt
Brace.
which at least 5% is milk fat. Because of the higher milk Full NA, Yella Reddy S, Dimick PS, and Ziegler GR (1996) Physical
content, there is normally less non-fat cocoa solids, which and sensory properties of milk chocolate formulated with
is regarded as inferior in some countries. This means that anhydrous milk fat fractions. Journal of Food Science
61: 1068–1084.
in all countries within the European Union, except the Hartel RW (1996) Applications of milk-fat fractions in confectionery
United Kingdom and Ireland, they have to be labeled as products. Journal of the American Oil Chemists Society
family milk chocolate or its equivalent. 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.
Future Developments 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
Although the chocolate industry is a relatively small user bloom in dark chocolate. Journal of the American Oil Chemists
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Minifie BW (1980) Chocolate, Cocoa and Confectionery, 2nd edn.
one. It is also one where specialist ingredients can be used Westport, CT: Avi Publishing Co. Inc.
in an economic way. This means that the development of Mohler MR, Huginin AG, and Ebers K (1981) Whey-based nonfat milk
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that aid liquid chocolate flow or reduce fat bloom is likely Scheruhn E, Franke K, and Tscheuschner H-D (2000) Merkmale des
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