August 26, 2009

Hot Bread Leavening Agents Part 2

CHEMICAL LEAVENING.–Chemical leavening is brought about by the action of gas produced by an acid and an alkali. All chemical leavening agents are Similar in their action, and they are composed of an acid and an alkali. When an acid and an alkali are brought together in the presence of moisture and heat, the result is the rapid production of carbon dioxide, a gas that expands on being heated, just as all other gases do. In expanding, the gas pushes up the batters or doughs, and these, when baked, set, or harden, into porous shapes. In addition to forming the gas, the acid and the alkali produce a salt that remains in the bread, and it is this salt that is responsible for the harmful effect usually attributed to chemical leavening agents.

The first chemical leavening agents were devised by bread makers themselves. They consisted of a combination of salts, 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 bread maker, especially if they 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.