43. Besides milk that is commonly sold by dairymen and milk dealers, it
is possible to buy in the market many grades of so-called PRESERVED
MILK. Such milk is produced by driving off all or part of the water
contained in milk, and it is sold as _condensed, evaporated,_ and
_powdered milk_. Usually, it is put up in tin cans, and while it is not
used so extensively as regular milk, many firms are engaged in its
preparation.
44. CONDENSED AND EVAPORATED MILK.--As has just been mentioned,
condensed and evaporated milk is produced by the complete or partial
evaporation of the water contained in milk. Such milk can be shipped
long distances or kept for long periods of time, because it does not
contain sufficient moisture to permit the growth of bacteria. In
evaporating milk to produce these preserved milks, each gallon is
diminished in quantity to about two and one quarter pints, the original
87 per cent. of water being reduced to about 25 per cent. Therefore, in
order to use such milk, sufficient water must be added to restore it to
its original composition. Sometimes comparatively large amounts of cane
sugar are added to such milks, which, besides sweetening them, assist in
their preservation. If cane sugar is not used, the milks are usually
made sterile in order to prevent them from spoiling.
45. POWDERED MILK.--The form of preserved milk known as powdered milk
is the result of completely evaporating the water in milk. Such milk has
the appearance of a dry powdered substance. It does not spoil easily and
is so greatly reduced in quantity that it can be conveniently stored.
Because of these characteristics, this product, for which skim milk is
generally used, is extensively manufactured. It is used chiefly by
bakers and confectioners, and, as in the case of evaporated or condensed
milk, the water that has been evaporated in the powdering process must
be supplied when the milk is used.