Double Acting Baking Powder (Aluminum Free) consists of baking soda, one or more acid salts (cream of tartar and sodium aluminum sulfate) plus cornstarch to absorb any moisture so a reaction does not take place until a liquid is added to the batter. Double-acting baking powder reacts to liquid and heat in two stages. The first reaction takes place when you add the baking powder to the batter and it is moistened. The second reaction takes place when the batter is placed in the oven.
Baking powder should always be stored in a cool, dry place away from exposure to heat or moisture. Once opened, baking powder can be kept for six months, up to a year. It will gradually lose its leavening ability over time so some people prefer to replace their baking powder sooner. We do not recommend refrigerating or freezing this product because condensation can cause the powder to react and lose its effectiveness.