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.
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