Double-acting baking powder has two types of acids, which react at different times during baking. The reaction adds volume to baked goods that don’t have acid in them, such as cookies or cakes.
Baking powder is a leavening agent that contains a combination of alkali, acid and a moisture absorber. Double-acting baking powder contains two types of acids. The first acid reacts by creating gases when mixed with the liquid in the recipe. The second type reacts by creating gases when the batter is exposed to oven heat.