Toast is a
sterile food, while bread often contains various ferments which have not
been destroyed by baking. These undergo incubation during the process of
digestion, particularly in the case of individuals with diseases of the
digestive tract. With normal digestion, however, these ferment bodies do
not develop to any appreciable extent, as the digestive tract disinfects
itself. When the flour is prepared from well cleaned wheat and the
ferment substances which are present mainly in the bran particles have
been removed, a flour of higher sanitary value is secured.

CHAPTER XII

BAKING POWDERS

195. General Composition.--All baking powders contain at least two
materials; one of these has combined carbon dioxid in its composition,
the other some acid constituent which serves to liberate the gas. The
material from which the gas is obtained is almost invariably sodium
bicarbonate, NaHCO_{3}, commonly known as "soda" or "saleratus."
Ammonium carbonate has been used to some extent, but is very seldom used
at the present time. The acid constituent may be one of several
materials, the most common being cream of tartar, tartaric acid, calcium
phosphate, or alum. These may be used separately or in combination. The
various baking powders are designated according to the acid constituent,
as "cream of tartar," "phosphate," and "alum" powders. All of them
liberate carbon dioxid gas, but the products left in the food differ
widely in nature and amount[69].

Baking powder is a chemical preparation which, when brought in contact
with water, liberates carbon dioxid gas. The baking powder is mixed dry
with flour, and when this is moistened the carbon dioxid that is
liberated expands the dough. The action is similar to that of yeast
except that in the case of yeast the gas is given off much more slowly
and no residue is left in the bread. When baking powder is used, there
is a residue left in the food which varies with the material in the
powder. It is the nature and amount of this residue that is important
and makes one baking powder more desirable than another.

[Illustration: FIG. 51.--INGREDIENTS OF A BAKING POWDER.

1, baking powder; 2, cream of tartar; 3, baking soda; 4, starch.]

196. Cream of Tartar Powders.--The acid ingredient of the cream of
tartar powders is tartaric acid, H_{2}C_{4}H_{4}O_{6}. Cream of tartar
is potassium acid tartrate, KHC_{4}H_{4}O_{6}; it contains one atom of
replaceable hydrogen, which im