fat has been removed from cream by churning is known by the name
buttermilk. Such milk is similar to skim milk in composition, and unless
butter is made of sweet cream, buttermilk is sour. Buttermilk is used
considerably as a beverage, but besides this use there are numerous ways
in which it may be employed in the preparation of foods, as is pointed
out in various recipes. An advantage of buttermilk is that its cost is
less than that of whole milk, so that the housewife will do well to make
use of it in the preparation of those foods in which it produces
satisfactory results.

17. ARTIFICIAL BUTTERMILK.--Several kinds of sour milk that are called
buttermilk are to be had, particularly at soda fountains and
restaurants. While they are similar to buttermilk they are not the same,
because they are produced artificially from whole or skimmed sweet milk.
The usual method employed in the making of these artificial buttermilks,
as they may well be called, consists in adding to sweet milk tablets
containing lactic acid or a certain culture of bacteria that induce
fermentation, very much as yeast does, and then keeping it at about body
temperature for a number of hours in order to allow the milk to thicken
and sour. Such milks exert a beneficial action in the digestive tract,
and their food value, provided they are made from whole milk, is just as
high as that of the original sweet milk. Artificial buttermilks
therefore prove a valuable source of food supply for persons who find
them palatable and who do not care for sweet milk. Their food value may
be increased by adding cream to them.

18. SOUR MILK.--Ordinary milk contains large numbers of bacteria that
produce fermentation. When it is allowed to stand for some time, these
bacteria act upon the sugar, or lactose, contained in the milk and
change it into lactic acid. This acid gives to the milk a sour taste and