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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.
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.
The proportion of these ingredients that is usually effective in batters and doughs for hot breads is 1 level teaspoonful of soda to 1 pint of sour milk. So as to derive the best results in using these chemical leavening agents, it will be well to observe that if they are mixed together in a cup the milk will bubble and may, provided the quantity is sufficient, run over. These bubbles are caused by the gas that is formed when the acid and soda meet, and when they break gas escapes, with the result that some of it is lost. Formerly, it was the custom to mix these leavening substances in this way, and then to add them to the other ingredients. Now, however, in order that all gas produced may be kept in the dough mixture, the soda is sifted in with the dry ingredients and the sour milk is added with the liquid ingredients.
A point well worth remembering is that sour milk and soda may be substituted for sweet milk and baking powder in a recipe that calls for these ingredients by using 1 teaspoonful of soda to each pint of sour milk. This information should prove valuable to the housewife, especially if she has accumulated a supply of sour milk that should not be wasted. Occasionally it will be found that baking powder and soda are required in the same recipe, but this occurs only when an insufficient amount of soda to produce the desired result is specified.
SODA AND MOLASSES - Although molasses, which is a product of sugar cane, is sweet, it contains an acid that is formed by the fermentation that continually occurs in it, an evidence of which is the tiny bubbles that may be seen in molasses, especially when it is kept in a warm place. Because of the presence of this acid, molasses may be used with soda to form a chemical leavening agent, and when they are combined in hot breads or cake, the chemical action of the two produces carbon dioxide. However, accurate results cannot always be obtained when these ingredients are used, for the degree of acidity in molasses is as uncertain as it is in sour milk. Molasses that is old or has been kept in a warm place will contain more acid than molasses that has been manufactured only a short time or that has been kept cool to retard fermentation.
The proportion of soda to molasses that can usually be relied on for hot breads and cakes is 1 teaspoonful of soda to 1 cupful of molasses, or just twice the quantity of soda that is generally used with sour milk. To produce the best results, the molasses should be mixed with the liquid ingredients and the soda sifted in with the dry ones. As molasses burns very quickly in a hot oven, all breads or cakes containing it as an ingredient should be baked in an oven of moderate temperature.
