7. CHEMICAL LEAVENING is brought about by the action of gas produced by
an acid and an alkali. All chemical leavening agents are Similar in
their action, and they are composed of an acid and an alkali. When an
acid and an alkali are brought together in the presence of moisture and
heat, the result is the rapid production of carbon dioxide, a gas that
expands on being heated, just as all other gases do. In expanding, the
gas pushes up the batters or doughs, and these, when baked, set, or
harden, into porous shapes. In addition to forming the gas, the acid and
the alkali produce a salt that remains in the bread, and it is this salt
that is responsible for the harmful effect usually attributed to
chemical leavening agents.
8. The first chemical leavening agents were devised by housewives
themselves. They consisted of a combination of saleratus, an alkali made
from wood ashes, and sour milk or molasses. The results obtained were
more or less satisfactory, but never entirely accurate or certain. Later
on, chemists by employing the same idea combined an alkali with an acid
in powder form and produced an accurate and satisfactory leavening agent
in the form of baking powder. The discovery of baking powder, however,
has not displaced the use of other combinations that form chemical
leavening agents, for soda is still combined with sour milk, molasses,
and cream of tartar in the making of various hot breads. Therefore, so
that a proper understanding of the various chemical leavening agents may
be obtained, a discussion of each is here given.
9. SODA AND SOUR MILK.--When soda is used with sour milk for leavening
purposes, the lactic acid in the milk is so acted upon by the soda as to
produce gas. However, these two ingredients--soda and sour milk--do not
make an absolutely accurate leavening agent, because the quantity of
acid in the sour milk varies according to the fermentation that has
taken place. For example, sour milk 48 hours old contains more acid than
sour milk that is kept under the same conditions but is only 24
hours old.
The proportion of these ingredients that is usually effective in batters
and doughs for hot breads is _1 level teaspoonful of soda to 1 pint of
sour milk._ So as to derive the best results in using these chemical
leavening agents, it will be well to observe that if they are mixed
together in a cup the milk will bubble and may, provided the quantity is
sufficient, run over. These bubbles are caused by the gas that is formed
when the acid and soda meet, and when they break gas escapes, with the
result that some of it is lost. Formerly, it was the custom to mix these
leavening substances in this way, and then to add them to the other
ingredients. Now, however, in order that all gas produced may be kept in
the dough mixture, the soda is sifted in with the dry ingredients and
the sour milk is added with the liquid ingredients.
10. A point well worth remembering is that sour milk and soda may be
substituted for sweet milk and baking powder in a recipe that calls for
these ingredients by using _1 teaspoonful of soda to each pint of sour
milk_. This information should prove valuable to the housewife,
especially if she has accumulated a supply of sour milk that should not
be wasted. Occasionally it will be found that baking powder and soda are
required in the same recipe, but this occurs only when an insufficient
amount of soda to produce the desired result is specified.
11. SODA AND MOLASSES.--Although molasses, which is a product of sugar
cane, is sweet, it contains an acid that is formed by the fermentation
that continually occurs in it, an evidence of which is the tiny bubbles
that may be seen in molasses, especially when it is kept in a warm
place. Because of the presence of this acid, molasses may be used with
soda to form a chemical leavening agent, and when they are combined in
hot breads or cake, the chemical action of the two produces carbon
dioxide. However, accurate results cannot always be obtained when these
ingredients are used, for the degree of acidity in molasses is as
uncertain as it is in sour milk. Molasses that is old or has been kept
in a warm place will contain more acid than molasses that has been
manufactured only a short time or that has been kept cool to retard
fermentation.
The proportion of soda to molasses that can usually be relied on for hot
breads and cakes is _1 teaspoonful of soda to 1 cupful of molasses_, or
just twice the quantity of soda that is generally used with sour milk.
To produce the best results, the molasses should be mixed with the
liquid ingredients and the soda sifted in with the dry ones. As molasses
burns very quickly in a hot oven, all breads or cakes containing it as
an ingredient should be baked in an oven of moderate temperature.
12. SODA AND CREAM OF TARTAR.--Some housewives are inclined to use soda
and cream of tartar for leavening purposes; but there is really no
advantage in doing this when baking powder can be obtained, for some
baking powders are a combination of these two ingredients and produce
the same result. In fact, the housewife cannot measure soda and cream of
tartar so accurately as the chemist can combine them in the manufacture
of baking powder. Nevertheless, if their use is preferred, they should
be measured in the proportion of _twice as much cream of tartar as
soda._ As in the case of soda alone, these leavening agents should be
sifted with the dry ingredients. A small quantity of cream of tartar is
used without soda in such mixtures as angel-food cake, in which egg
white alone is used to make the mixture light. The addition of the cream
of tartar has the effect of so solidifying the egg white that it holds
up until the heat of the oven hardens it permanently.
13. BAKING POWDER.--Without doubt, baking powder is the most
satisfactory of the chemical leavening agents. It comes in three
varieties, but they are all similar in composition, for each contains an
alkali in the form of soda and an acid of some kind, as well as a filler
of starch, which serves to prevent the acid and the alkali from acting
upon each other. When moisture is added to baking powder, chemical
action sets in, but it is not very rapid, as is apparent when a cake or
a muffin mixture is allowed to stand before baking. The bubbles of gas
that form in such a mixture can easily be observed if the mixture is
stirred after it has stood for a short time. When both moisture and heat
are applied to baking powder, however, the chemical action that takes
place is more rapid, and this accounts for its usefulness in baking hot
breads and cake.
14. The price of the different kinds of baking powder, which usually
varies from 10 cents to 50 cents a pound, is generally an indication of
the ingredients that they contain. Powders that sell for 40 to 50 cents
a pound usually contain cream of tartar for the acid, the high price of
this substance accounting for the price of the powder. Powders that may
be purchased for 30 to 40 cents a pound generally contain acid phosphate
of lime, and as this substance is cheaper than cream of tartar, a
baking-powder mixture containing it may well be sold for less. The
cheapest grade of powders, or those which sell for 10 to 25 cents a
pound, have for their acid a salt of aluminum called alum. Still other
powders that are sometimes made up to sell for 20 to 30 cents a pound
contain a mixture of phosphate and alum.
15. As baking powders vary in price, so do they vary in their keeping
qualities, their effectiveness, and their tendency toward being
injurious. Most phosphate and alum powders do not keep so well as the
cream-of-tartar powders, and the longer they are kept, the less
effective do they become. The powders that contain phosphate yield more
gas for each teaspoonful used than do the other varieties. Much
controversy has taken place with regard to the different kinds of baking
powder and their effects on the digestive tract, but authorities have
not yet agreed on this matter. However, if foods made with the aid of
baking powders are not used excessively, no concern need be felt as to
their injurious effect. The housewife in her choice of baking powder
should be guided by the price she can afford to pay and the results she
is able to get after she has become well informed as to the effect of
the different varieties. She may easily become familiar with the
composition of baking powder, for a statement of what substances each
kind contains is generally found on the label of every variety. This
information is invaluable to the housewife, as it will assist her
considerably in making a selection.
16. The proportion of baking powder to be used in a batter or a dough is
regulated by the quantity of flour employed and not, as is the case with
soda and molasses or sour milk, by the quantity of liquid, the usual
proportion being _2 level teaspoonfuls to 1 cupful of flour_. Sometimes
this proportion is decreased, 6 or 7 teaspoonfuls being used instead of
8 to each quart of flour in the making of large quantities of some kinds
of baked foods. In adding baking powder to a mixture, as in adding other
dry leavening agents, it should be sifted with flour and the other dry
ingredients.
17. Although baking powder may be purchased at various prices, a good
grade can be made in the home without much effort and usually for less
than that which can be bought ready made. For these reasons, many
housewives prefer to make their own. The following recipe tells how to
make a cream-of-tartar powder that is very satisfactory: