Role: let the dough fermentation, so as to make the production of more fluffy and soft pastry, is an essential additive in the production of pastry.

Use: fast baking powder for water when a large number of reactions, in the baking, steaming and frying when the puffing and loosening effect is no longer obvious, and slow baking powder in the heating stage, the need for pasta and other food began to solidify, only to begin to occur the effect of puffing, the effect is not ideal. Thus, it is recommended to do pasta type of fermentation, try to choose double-effect baking powder.

Expanded Information:

The baking powder, although it has baking soda as an ingredient, is a precision-tested addition of acidic powders (such as cream of tartar) to balance out its pH, so, basically, the Although baking soda is a base-carrying substance, commercially available baking powder is a neutral powder, so baking soda and baking powder can't be replaced arbitrarily.

As for the cornstarch that is used as a filler in baking powder, it is mainly used to separate the acidic powder from the alkaline powder in baking powder to avoid them reacting prematurely. Baking powder should also be stored in a way that prevents it from getting wet and failing prematurely.

Baidu Encyclopedia - Baking Powder