m where the process is used in butter-making that the type
of machinery for each purpose is quite different. The equipment
necessary for the first purpose may be divided into two general classes:

1. Apparatus of limited capacity designed for family use.

2. Apparatus of sufficient capacity to pasteurize on a commercial scale.

~Domestic pasteurizers.~ In pasteurizing milk for individual use, it is
not desirable to treat at one time more than will be consumed in one
day; hence an apparatus holding a few bottles will suffice. In this case
the treatment can best be performed in the bottle itself, thereby
lessening the danger of infection. Several different types of
pasteurizers are on the market; but special apparatus is by no means
necessary for the purpose. The process can be efficiently performed by
any one with the addition of an ordinary dairy thermometer to the common
utensils found in the kitchen. Fig. 24 indicates a simple contrivance
that can be readily arranged for this purpose.

The following suggestions indicate the different steps of the process:

1. Use only fresh milk.

2. Place milk in clean bottles or fruit cans, filling to a uniform
level, closing bottles tightly with a cork or cover. If pint and quart
cans are used at the same time, an inverted bowl will equalize the
level. Set these in a flat-bottomed tin pail and fill with warm water to
same level as milk. An inverted pie tin punched with holes will serve as
a stand on which to place the bottles during the heating process.

3. Heat water in pail until the temperature of same reaches 155 deg. to
160 deg. F.; then remove from source of direct heat, cover with a cloth
or tin cover, and allow the whole to stand for half an hour. In the
preparation of milk for children, it is not advisable to use the
low-temperature treatment (140 deg. F.) that is recommended for
commercial city delivery.

[Illustration: FIG. 24. A home-made pasteurizer.]

4. Remove bottles of milk and cool them as rapidly as possible without
danger to bottles and store in a refrigerator.

~Commercial pasteurizers.~ The two methods of pasteurization practiced
commercially for the preservation of milk and cream have been developed
because of the two types of machinery now in use. Apparatus constructed
on the reservoir or tank principle permits of the retention of the milk
for any desired period of time. Therefore, a lower temperature can be
employed in the treatment. In those mach