If you've ever tried to use baking powder in place of baking soda, or vice-versa, you've discovered that the two don't work the same. But what's the difference between baking soda and baking powder?
The short answer: Baking soda needs an acidic ingredient like lemon juice to activate it. Baking powder is basically baking soda with the acid already built in.
But you can't use the two interchangeably in your baking. If you try, your recipe probably won't turn out the way you want.
In a moment we'll talk about the problems that substituting one for the other can cause. But first, here's a bit more background on how these substances work.
Quick Breads: Baking Powder or Baking Soda
Both baking powder and baking soda work by releasing carbon dioxide gas. This gas forms bubbles in the dough, causing it to rise. While the dough is cooking, these bubbles harden as it's baked.
The release of gas is caused by a chemical reaction. The reaction happens quickly, which is why banana bread, zucchini bread and so on, which are made with baking soda and/or baking powder, are known as "quick breads."
How Do Baking Soda and Baking Powder Work?
So, how do baking soda and baking powder actually work? Baking soda is an alkaline, and when you mix in something acidic, like vinegar, it will release gas. The key here is that baking soda needs some sort of acid to activate the reaction. So it will work in recipes that include acidic ingredients like buttermilk, sour cream, lemon juice, yogurt and so on.
Molasses is also acidic, and so, believe it or not, is honey. So any of these ingredients would activate the baking soda. But if you were to try to substitute baking soda for baking powder in a recipe where no acidic ingredient is present, there will be no release of gas and the dough won't rise.
Baking powder, on the other hand, is nothing more than baking soda with some sort of acidic compound (different brands of baking powder use different compounds) already included. The baking soda and the acidic compound won't react together until they are moistened, which causes the two chemicals to mix.
So-called "double-acting" baking powder is also activated by the heat of the oven or griddle, and thus has greater leavening powers.
Using Baking Powder Instead of Baking Soda
So now let's say you were to use baking powder instead of baking soda. This should create some leavening, because a recipe that calls for baking soda should already include some sort of acidic ingredient as described above.
But here's where the problem lies: Baking powder is about one-third baking soda, and about two thirds other ingredients. So while you will indeed get some rise, you won't get enough, because you would essentially only be using one-third the amount of baking soda as the recipe actually requires.
If you were determined to do this, you could triple the amount of baking powder, but because of the additional ingredients in the baking powder, you'd probably notice a bitter flavor. There's also a chance that because of the extra acids in the recipe, the batter would quickly rise and then fall before the bubbles had a chance to bake in. Either way, the results are not good.
Make Your Own Baking Powder
You can, however, make a batch of baking powder yourself. All you need to do is combine one teaspoon of baking soda with two teaspoons of cream of tartar. This will yield one tablespoon of baking powder. You should use it right away, however — don't make up a batch in advance. And if you don't have cream of tartar, you're going to have to go to the store anyway, so you might as well just buy yourself some baking powder.
(But note that cream of tartar is a good thing to have around. For instance, it will help stabilize egg whites when you whip them for making meringue or soufflé.)
One last note: Chemical leavening agents like baking powder and baking soda will lose their potency after a while, especially if they are stored in a warm place (like a kitchen!) or if the containers are not sealed tightly. The good news is that both are pretty cheap, so for best results, replace them every six months or so.