Alkali

Any of several chemical compounds that react when combined with an acid product or ingredient to form a salt, thereby neutralizing the acidic property of the ingredient. The most common example in the pastry kitchen is the use of baking soda (an alkali) to neutralize the acid when using dairy products such as sour cream or buttermilk in a cake batter. As the baking soda neutralizes the acid, the result is the release of carbon dioxide gas, which, in turn, forms air bubbles, causing the cake to rise.