What's the difference between baking soda and baking powder? Are they interchangeable?
Baking soda and baking powder both help create a reaction that causes doughs to rise. This chemical reaction is dependent on the interaction of a base and an acid.
Baking soda is the common name for sodium bicarbonate, which is a base. When combined with an acid plus some moisture, such as buttermilk, the reaction releases carbon dioxide bubbles, causing dough to expand.
Baking powder contains sodium bicarbonate, but it also contains the acid necessary to produce the chemical reaction, usually in the form of cream of tartar. It only needs to be combined with moisture to begin working.
This chemical reaction has the effect of neutralizing the acid. So if you want the acid in your dough to retain its strength and flavor, such as when using buttermilk in pancakes, always use baking powder instead of baking soda. The only acid that will be neutralized will be the one contained in the baking powder, instead of the one in your dough that is working to create acidic flavors. On the other hand, if you want to reduce the acidity in your dough — say, when using a sourdough starter to make a sweeter dish — opt for baking soda.
Both baking soda and baking powder work quickly, so if you're making anything out of a batter or dough that relies on them for leavening, it's best to cook them right away. However, when working with whole grain doughs, it helps to let the dough rest for a while before use (so the whole grains will have a chance to absorb enough moisture). So if you're using a whole grain dough that also requires baking soda or baking powder, wait until after the dough has had a chance to rest for at least 15 minutes before adding the leavening agent.
— Tabitha Alterman, senior associate editor