How Baking Powder WorksBaking powder contains baking soda (sodium bicarbonate) and a dry acid (cream of tartar or sodium aluminum sulfate). When liquid is added to a baking recipe, these two ingredients react to form bubbles of carbon dioxide gas.
The reaction that occurs between sodium bicarbonate (NaHCO3) and cream of tartar (KHC4H4O6) is:
NaHCO3 + KHC4H4O6 → KNaC4H4O6 + H2O + CO2
Sodium bicarbonate and sodium aluminum sulfate (NaAl(SO4)2) react in a similar manner:
3 NaHCO3 + NaAl(SO4)2 → Al(OH)3 + 2 Na2SO4 + 3 CO2
Using Baking Powder CorrectlyThe chemical reaction that produces the carbon dioxide bubbles occurs immediately upon adding water, milk, eggs or another water-based liquid ingredient. Because of this, it's important to cook the recipe right away, before the bubbles disappear. Also, it's important to avoid over-mixing the recipe so that you don't stir the bubbles out of the mixture.
Single-Acting and Double-Acting Baking PowderYou can buy single-acting or double-acting baking powder. Single-acting baking powder makes carbon dioxide as soon as the recipe is mixed. Double-acting powder produces additional bubbles as the recipe is heated in the oven. Double-acting powder usually contains calcium acid phosphate, which releases a small amount of carbon dioxide when mixed with water and baking soda, but much more carbon dioxide when the recipe is heated.
You use the same amount of single-acting and double-acting baking powder in a recipe. The only difference is when the bubbles are produced. Double-acting powder is more common and is useful for recipes that might not get cooked right away, such as cookie dough.