Artificial Fermentation

Carbonates are compounds from which gas can be set free; the addition of an acid to a compound that sets gas free proves that such compound is a carbonate. That soda is a carbonate may be proved by the addition of several acids, any one of which will set free carbon dioxide. Carbon dioxide may also be evolved from soda simply by heating it, but when soda is used alone in batters and doughs, though lightness is secured, other essentials are lacking; the "cake" is yellow, and the unchanged carbonate neutralizes the acid in the digestive fluids, and thus impedes digestion.

Sour milk, lemon juice, and molasses, through the lactic, citric, and acetic acids involved in their composition, when used with soda generate carbon dioxide; but the quantity and strength of the acids are variable. Nor is any one of these ingredients such as would be available or suitable at all times and under all circumstances.

The muriatic acid of the chemist seemed at first to be the ideal acid, combined with soda, to set free carbon dioxide, as the residue after fermentation was common salt; but the liberation of the gas was instantaneous when the acid and soda met. So this combination was dismissed as impractical. Acid phosphates, the residue from which are mineral matters, were tried, and are still in use; but finally cream-of-tartar came to be considered the sine qua non, for which the culinary world was seeking to complete the necessary chemical reaction in the process of lightening food. There were several reasons for these conclusions, and these hold good to-day.

Cream-of-tartar is a harmless substance, which does not unite chemically with soda until the application of heat, as well as moisture; and the residue (Rochelle salts) is harmless, taken in the quantity used in food, even when a large amount of such food is eaten.

There is, however, one objection to the use of soda and cream-of-tartar. The proportion of each must be measured with the greatest accuracy. Rather more than twice as much of cream-of-tartar as soda, by measure, is called for. If the quantity of soda be too great the caustic unneutralized carbonate will neutralize the acid of the gastric juice and hinder digestion. In this case the yellow color of the food tells the story, and the food may be avoided; but, on account of this necessary accuracy in measurement, baking-powder has come into general use.

Baking-Powder

The best approved baking-powder is a composition of bicarbonate of soda and cream-of-tartar, mixed in such proportion that one exactly neutralizes the other. A small quantity of cornstarch, or flour is added to separate the ingredients. These three ingredients are mixed together by sifting many times (ten or more) so that each little particle of carbonate and acid be surrounded by a thin coating, or film, of starch. There are many grades of soda, cream-of-tartar and flour, and, of course, the best give the best results.