Washing soda has already been discussed. Since baking powders in some
form are used in almost all homes for the raising of cake and pastry
dough, it is essential that their helpful and harmful qualities be
clearly understood.
The raising of dough by means of baking soda--bicarbonate of soda--is
a very simple process. When soda is heated, it gives off carbon
dioxide gas; you can easily prove this for yourself by burning a
little soda in a test tube, and testing the escaping gas in a test
tube of limewater. When flour and water alone are kneaded and baked
in loaves, the result is a mass so compact and hard that human teeth
are almost powerless to crush and chew it. The problem is to separate
the mass of dough or, in other words, to cause it to rise and lighten.
This can be done by mixing a little soda in the flour, because the
heat of the oven causes the soda to give off bubbles of gas, and these
in expanding make the heavy mass slightly porous. Bread is never
lightened with soda because the amount of gas thus given off is too
small to convert heavy compact bread dough into a spongy mass; but
biscuit and cake, being by nature less compact and heavy, are
sufficiently lightened by the gas given off from soda.
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