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.
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