The use of two acidic components is the basis of the term "double acting".The acid in a Baking Powder can be either fast-acting or slow-acting.A fast-acting acid reacts in a wet mixture with baking soda at room temperature, and a slow-acting acid does not react until heated. When the chemical reactions in Baking Powders involve both fast- and slow-acting acids, they are known as "double-acting"; those that contain only one acid are "single-acting".
By providing a second rise in the oven, double-acting Baking Powders increase the reliability of baked goods by rendering the time elapsed between mixing and baking less critical. This is the type of Baking Powder most widely available to consumers today. Double-acting Baking Powders work in two phases; once when cold, and once when hot.
For example,Jianshi Baking Powder is a double-acting product that contains sodium acid pyrophosphate and monocalcium phosphate as leavening acids. With these acid,gas releases twice, first is in making dough, the second time is in the oven.
Common low-temperature acid salts include cream of tartar and monocalcium phosphate (also called calcium acid phosphate). High-temperature acid salts include potassium aluminium sulfate, sodium aluminium phosphate, and sodium acid pyrophosphate,etc.
