; but if
the milk is quickly cooled, it enhances the keeping quality very
materially. It is unfortunate that this same term is used in connection
with the heating of cream as a preparatory step to the use of pure
cultures in cream-ripening in butter-making. The objects to be
accomplished vary materially and the details of the two processes are
also quite different.

While pasteurizing can be performed on a small scale by the individual,
the process can also be adapted to the commercial treatment of large
quantities of milk. The apparatus necessary for this purpose is not
nearly so expensive as that used in sterilizing, a factor of importance
when other advantages are considered. In this country pasteurization has
made considerable headway, not only in supplying a milk that is designed
to serve as children's food, but even for general purposes.

~Requirements essential in pasteurization.~ While considerable latitude
with reference to pasteurizing limits is permitted, yet there are
certain conditions which should be observed, and these, in a sense, fix
the limits that should be employed. These may be designated as (1) the
_physical_, and (2) the _biological_ requirements.

~Physical requirements.~ _1. Avoidance of scalded or cooked taste._ The
English and American people are so averse to a scalded or cooked flavor
in milk that it is practically impossible for a highly heated product to
be sold in competition with ordinary raw milk. In pasteurization then,
care must be taken not to exceed the temperature at which a permanently
cooked flavor is developed. As previously observed, this point varies
with the period of exposure. A momentary exposure to a temperature of
about 170 deg. F. may be made without any material alteration, but if
the heat is maintained for a few minutes (ten minutes or over), a
temperature of 158 deg. to 160 deg. F. is about the maximum that can be
employed with safety.

_2. Normal creaming of the milk._ It is especially desirable that a
sharp and definite cream line be evident on the milk soon after
pasteurization. If this fails to appear, the natural inference of the
consumer is that the milk is skimmed. If the milk be heated to a
temperature sufficiently high to cause the fat-globule clusters to
disintegrate (see Figs. 22 and 23), the globules do not rise to the
surface as readily as before and the cream line remains indistinct.
Where the exposure is made for a considerable period of time (10 min