This is a leavener (something that causes dough to rise). It is composed of baking soda and a mild acid. When these powders react with water, the acid and base react to create gas. A secondary reaction occurs when heated in the oven. Baking soda alone is also a leavening agent, but in order to work there must be something acidic in the dough (eg. buttermilk, lemon, etc.)
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