at the same time causes the casein of the milk to become a mass known as
_curd_, or _clabber_. This mass continues to grow sour and tough until
all the milk sugar is converted into lactic acid, so that the longer the
milk stands, the more acid it becomes. Sour milk, however, is useful
in the preparation of various dishes, such as hot breads and
griddle cakes.

[Illustration: FIG. 1]

19. WHEY.--When the curd is completely removed from milk, as in making
cheese, a clear, light, yellowish liquid known as whey remains. Whey is
composed of water, minerals, and milk sugar or lactic acid, and is the
least valuable part of the milk. The ingenious housewife will never be
at a loss to make use of this product, for, while its food value is
slight, the minerals it contains are important ones. Whey is sometimes
used to furnish the liquid for bread making and, in addition, it may be
used as a beverage for persons who cannot digest food as heavy as
milk itself.

20. COMPARISON OF FOOD VALUES OF MILK PRODUCTS.--So that the housewife
may become familiar with the food values of milk products, there is here
given, in Fig. 1, a graphic table for the comparison of such products.
Each glass is represented as containing approximately 1 pint or 1 pound
of the milk product, and the figures underneath each indicate the number
of calories found in the quantity represented. The triangle at the side
of each indicates the proportion of ash, protein, fat, carbohydrate, and
water, the percentage composition being given at the side. Housewives as
a rule fully appreciate the food value that is to be found in whole milk
and cream, but such products as skim milk, buttermilk, and whey are
likely to be ignored.