the milk from
the action of rennet enzyms.

_5. Action of rennet._ Heating milk causes the soluble lime salts to be
precipitated, and as the curdling of milk by rennet (in cheese-making)
is dependent upon the presence of these salts, their absence in heated
milks greatly retards the action of rennet. This renders it difficult to
utilize heated milks in cheese-making unless the soluble lime salts are
restored, which can be done by adding solutions of calcium chlorid.

~Sterilization.~ As ordinarily used in dairying, sterilization means the
application of heat at temperatures approximating, if not exceeding,
212 deg. F. It does not necessarily imply that milk so treated is sterile,
i. e., germ-free; for, on account of the resistance of spores, it is
practically impossible to destroy entirely _all_ these hardy forms. If
milk is heated at temperatures above the boiling point, as is done where
steam pressure is utilized, it can be rendered practically germ-free.
Such methods are employed where it is designed to keep milk sweet for a
long period of time. The treatment of milk by sterilization has not met
with any general favor in this country, although it has been more widely
introduced abroad. In most cases the process is carried out after the
milk is bottled; and considerable ingenuity has been exercised in the
construction of devices which will permit of the closure of the bottles
after the sterilizing process has been completed. Milks heated to so
high a temperature have a more or less pronounced boiled or cooked
taste, a condition that does not meet with general favor in this
country. The apparatus suitable for this purpose must, of necessity, be
so constructed as to withstand steam pressure, and consequently is
considerably more expensive than that required for the simpler
pasteurizing process.

~Pasteurization.~ In this method the degree of heat used ranges from 140
deg. to 185 deg. F. and the application is made for only a limited length
of time. The process was first extensively used by Pasteur (from whom it
derives its name) in combating various maladies of beer and wine. Its
importance as a means of increasing the keeping quality of milk was not
generally recognized until a few years ago; but the method is now
growing rapidly in favor as a means of preserving milk for commercial
purposes. The method does not destroy all germ-life in milk; it affects
only those organisms that are in a growing, vegetative condition