If you’ve baked long enough, you’ve probably screwed up a recipe at some point by putting the wrong one in the batter and ended up with a metallic tasting cake or an overflowing quick bread.
Want to just cut to the chase?
Both baking power and baking soda are leaveners. They will both give your baked goods lift but they are not equivalent. They work in different ways and you really shouldn’t try to substitute.
Baking soda needs a sour
Baking soda on a chemical level is sodium bicarbonate. When baking soda is mixed with both a liquid and an acid (like buttermilk, brown sugar, or vinegar) it produces carbon dioxide gas, and those bubbles produce the lift in the baked goods.
The important thing to remember is that this reaction starts as soon as the ingredients are mixed together, so you want to get recipes with baking soda into the oven as soon as possible before the reaction fizzles out.
Baking powder has the power
If this where a venn diagram, baking powder would be the encompassing big circle around baking soda. Think of baking powder as an all-in-one solution. It’s baking soda with the acid built right in (usually cream of tarter).
Therefore baking powder just needs the liquid to start the reaction. Most of the baking powder in stores today is called “double-acting,” meaning it has a two-part reaction. The first occurs immediately when the powder dissolves in the batter (the liquid), but a second occurs more slowly when it’s heated.
Baking powder allows for more flexibility because you can let the batter or dough sit for a little while before baking and still get the rise you’re after.
Why use both?
In recipes that use both baking soda and baking powder, it’s usually a question of balancing the flavor and texture. When baking soda reacts with the acid, it neutralizes it. This takes away the sour flavor that the acid lends and sometimes you actually want a little tartness.
Beyond flavor, sometimes you need the additional lift that the powder can bring. Often when the baking soda reacts with the acid to form the carbon dioxide, it’s not enough to produce the right texture. The amounts of acid and baking soda need to be in balance for flavor so you’ll need to add more powder for texture, or airiness.