This section is from the book "Mrs. Lincoln's Boston Cook Book", by Mary J. Lincoln. Also available from Amazon: Mrs. Lincoln's Boston Cook Book.
This is made without yeast; but the principle is the same as in fermented bread, namely, the liberation of gas within the dough. The gas escapes quickly, and all such bread must be baked as soon as possible after mixing. There are no chemical changes in the starch or sugar; the elastic, glutinous dough is simply expanded by the gas. The starch cells are ruptured by the intense heat in baking; but if the gas bubbles burst before the heat has fixed the gluten wall, the bread will be heavy. This gas is produced in the bread dough in various ways: 1st. By the gas in very cold water, and the air obtained by vigorous beating; 2d. By the introduction of water under pressure, highly charged with gas. The first method is only suitable for mixtures which are to be baked quickly in a very hot oven, and eaten immediately, like gems, puffs, etc. The latter method produces what is known as aerated bread, making a light, sweet, spongy loaf; but it is not practicable for home use. 3d. The usual method is by some gas-generating compound, as the union of an acid and an alkali; usually soda, with either sour milk, cream of tartar, or muriatic acid. This is a convenient form adopted by many people who think it hard work to make yeast bread. When the chemicals used are pure, and in such a proportion that they neutralize each other, and leave only Rochelle salt as a residue, this bread, if used only occasionally, is harmless. But Rochelle salt is a medicine, not a nutritive food; and "those who are well do not need the disturbing influence of a medicine in their daily bread," and those who are ill do not often need this particular form of medicine. Through ignorance or carelessness this bread is often made so that there is an excess of alkali or a residue of alum; and then, if used habitually, it is injurious, and to some extent poisonous. It is convenient to know how to make it well in an emergency, and it helps make variety. It is best, when freshly baked, in the form of small biscuit rather than in loaves, and is not as indigestible, when eaten hot, as hot yeast bread. But for a bread for general use, for bread that will keep well, for bread that will leave a sweet, clean taste in the mouth, for bread that will yield the most in bulk from a given amount of flour, for bread for promoting health, there is nothing equal to perfect, home-made yeast bread. It is not so difficult a task to make perfect bread as most young housekeepers imagine, or old housekeepers assert. It is not impossible for a young girl to succeed as well in her first attempt in this art as the mature housekeeper who counts her loaves by the thousand, provided she learns the best way of making it, and uses a reasonable amount of common-sense.