Baking powder is a fine white powder used to make cakes and biscuits leaven (rise). Cooks add baking powder to flour mixtures before baking them. Chemicals in baking powder react with air and a liquid (usually water or sweet milk) to form carbon dioxide gas. Bubbles of carbon dioxide become trapped in the flour mixture. The bubbles expand when they are heated and make the mixture rise.
All baking powders contain starch, baking soda (sodium bicarbonate), and acid-forming ingredients. The starch keeps the powder dry and prevents it from acting until a liquid is added. Baking soda reacts with the acid-forming ingredient to produce carbon dioxide. Different kinds of baking powders contain different acid-forming ingredients. Tartrate baking powders contain cream of tartar and tartaric acid as acid-forming ingredients. Phosphate powders have calcium dihydrogen phosphate. Sulfate powders contain sodium aluminum sulfate, or alum. Combination, or double-acting, powders have phosphate and sulfate.
Baking powders differ in speed of reaction. Sulfate powder is the slowest baking powder. It does not react fully until heated. Tartrate and phosphate powders are the fastest. They react as soon as they are mixed with a liquid. Combination powders are the most widely used type. They react equally well in both the mixing and baking processes. Baking soda and sour milk have the same rising effect on flour mixtures as baking powder and sweet milk.
