Baking powder is a chemical leavener that is used to produce carbon dioxide in baked goods. The most common type of baking powder available commercially is double acting. This type contains baking soda and two different types of acids (sodium aluminum sulfate and monocalcium phosphate—usually), which act in two stages. The monocalcium phosphate reacts with the baking soda on contact with water in the first stage. The second stage occurs upon heating and is a reaction between the rest of the baking soda and sodium aluminum sulfate. These ingredients are calibrated to allow all of the acids and bases to neutralize after heating.