No matter where you are on your baking journey, at some point you’ve probably asked yourself, “what’s the difference between baking soda and baking powder?” It’s a reasonable question: They’re both plain white powders and their names certainly sound similar. We’d be lying if we said we hadn’t wondered the same thing once or twice in the past before tying on our aprons.
It’s totally fair to be confused because baking powder and baking soda actually do have a lot in common: They’re both “chemical leaveners,” which means that they add volume to baked goods by generating gas during the mixing and baking of a batter or dough. Cakes, muffins, scones, quick breads, and basically anything you’re baking that doesn’t include yeast (a biological leavener) or beaten eggs (a mechanical leavener) rely on these compounds to produce a light texture or “crumb.”
Still, while they look the same, sound the same, and do virtually the same job, they aren’t substitutes for one another—at least, not entirely.
So, what’s the difference between baking soda and baking powder?
Let’s start with the science: Baking soda is the commercial name for sodium bicarbonate. When sodium bicarbonate comes into contact with an acidic liquid—think buttermilk, yogurt, sour cream, molasses, coffee, citrus juice, or vinegar—it produces carbon dioxide gas, and those bubbles produce the lift that you’re looking for. (If you’re having flashbacks to the papier maché volcanoes you made for the science fair, you’re on the right track.)
Definitely worth keeping in mind: This reaction starts as soon as the two ingredients are mixed together, and weakens with time. A good rule of thumb is that if a recipe calls for leavening with baking soda only, you should get the batter or dough into the oven as quickly as you can, before the reaction peters out. Otherwise you might end up with flat cupcakes or muffins, even if you did everything else perfectly.
Baking powder comprises sodium bicarbonate and powdered acid—often cream of tartar. When moisture is added to baking powder, the same gaseous reaction can occur without the need to introduce a separate acidic ingredient. If you’re really in a pinch, you can make a “single-acting” baking powder at home by mixing cream of tartar and baking soda, although we wouldn’t recommend it for every recipe. That’s because most of the baking powder you find at the grocery store is “double-acting.” This means that the mix includes a secondary powdered acid and cornstarch, which acts as a drying medium. With double-acting baking powder, the first reaction begins immediately when the powder dissolves in the batter, but the second reaction (driven by that secondary acid) occurs more slowly when heated.
Thanks to that delayed reaction, double-acting baking powder gives bakers a bit more flexibility. The batter or dough can sit for a little while without the baker worrying whether or not it will rise in the oven. It also allows you to bake light, airy confections in the absence of an acidic ingredient. Powder has the leavening power to puff all on its own.
Why do some recipes contain both baking soda and baking powder?
If it’s really as simple as whether or not a recipe has an acid in it, then why all the fuss about when to use baking soda vs. baking powder—and why do some recipes call for both? Well, it turns out that reality is a bit more complicated. For one, when you mix baking soda with an acid, it doesn’t just create CO2. It also neutralizes the acid, raising the overall pH and making the batter more alkaline. In practical terms, this lessens the sour flavor of ingredients like lemon juice and apple cider vinegar, meaning less tartness in your final dish. Push this too far by adding too much baking soda, and the recipe could end up with an unpleasant soapy flavor. Not good, right? The amounts of acid and sodium bicarbonate in baking recipes must work in perfect equilibrium for the baked item to reach the right level of airiness. In most cases that means soda plus powder.