Chemistry Reference
In-Depth Information
Flocculation
Coalescence
Partial coalescence
Actually during the process of churning, one may conclude that the process of butter
making can be described as an inversion of the original cream emulsion. The system
of fat droplets dispersed in water is converted into a continuous phase of fat that
contains water droplets. The final product is about 80% milk fat, 18% water, and 2%
milk solids, mainly proteins and salts carried in the water. The physical structure of
butter is found to be a bit more complicated. The continuous, amorphous phase of
solid fat surrounds not only water droplets but also air bubbles, intact fat globules,
and highly ordered crystals of milk fat that have grown during the cooling process.
The proportion of continuous or “free” fat can vary from 50% of the total to nearly
100%, and it has a direct influence on the behavior of butter. The more fat there is in
discrete globules or crystals, the harder and more crumbly the butter, even to the point
of brittleness. The difference is a matter of both large-scale and molecular arrange-
ments. In a mass where the free fat merely fills the small interstices between globules
and crystals, the texture will be largely that of the separate particles. Further, it takes
more energy to separate the molecules ordered in a crystal than it does to disrupt
an already disordered phase of the same molecules. Mostly crystalline butter, then,
will be relatively stiff and not as smooth as mostly amorphous butter. The ideal, of
course, lies somewhere between the two extremes and is attained by manipulating
the cooling process (much as one controls the texture of candy).
9.5.3.1 milk—composition and emulsion chemistry
The role of milk in nature is to nourish and to provide immunological protection to
the mammalian young. The nutritional value of milk is high. It comes from vari-
ous sources, such as human, goat, buffalo, sheep, and yak, and has been a food for
humans since prehistoric times. It is also a very complex food with many thousands
of different molecular species found in it. There are several factors that can affect
milk composition. An approximate composition of milk can be given as follows:
Water
87%
Milkfat
4%
Solids-not-fat
9%
Protein
3%
Lactose
5%
Minerals
0.6% (Ca, P, citrate, Mg, K, Na, Zn, Cl, Fe, Cu,
sulfate, bicarbonate, and other kinds)
Acids
0.1% (citrate, formate, acetate, lactate)
Enzymes
peroxidase, catalase, phosphatase, lipase
Gases
oxygen, nitrogen
Vitamins
A, C, D, thiamine, riboflavin, etc.
The following terms are used to describe milk and its fractions:
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