n their passage through
the serum, either as they rise to the surface in gravity creaming,
or in the separator bowl. If these clusters are broken up, so
that the globules are uniformly distributed, the milk will cream
much less rapidly and completely. In the process known as
"homogenization" of milk, the individual fat globules are broken
into such small globules, that they cannot overcome the viscosity
of the serum, and they remain distributed throughout the milk. In
such cases, no cream rises, and even the cream separator is unable
to remove the fat from such milk.

In selling bottled milk, it is highly desirable that the cream line
should show distinctly. In normal milk, this line forms in a few
hours, but where milk is heated to a high temperature, and agitated
at the same time, the clusters of fat globules are broken apart and
the creaming power injured. This physical change is dependent not
only on the temperature, but also on the time of exposure. A
momentary exposure at 160 deg. F., or for 20 minutes at 145 deg. F., is
about the maximum limit which can be applied to milk without
material injury to the creaming property.

[Illustration: Fig. 25.--Fat Globules in Raw Milk.

In raw milk the fat globules are in masses of varying sizes. These
rise to the surface quickly in gravity creaming.]

The body or consistency of pasteurized cream may be restored by
allowing the cream to stand for several days at low temperatures,
or by the addition of a small amount of sucrate of lime. This
substance, known to the dairy trade as "viscogen," is made by adding
to a thick solution of cane sugar, some freshly slaked lime. The
sugar solution permits of the dissolving of a much larger amount of
the lime than is possible in water. When the liquid is allowed to
settle, the clear solution is then decanted off and is used at the
rate of about one part to 100 to 150 parts of cream. The fat
globules are, by its action, brought into aggregates and the body of
the cream thus restored. Viscogen contains nothing that is at all
harmful, but milk and cream to which it is added must be sold under
some distinctive name as "visco-cream," since the laws of
practically all states do not allow the addition of any substance
whatever to milk or cream.

[Illustration: Fig. 26.--Fat Globules in Heated Milk.

When milk is heated the masses of globules are broken up and fat
globules are uniformly distributed throughout the milk.]

[Illustration: