You might've noticed that the canister of baking powder in your pantry has the phrase double-acting or single-acting written on the side. But what does it mean for baking powder to be "double-acting," and what is the difference between double-acting and single-acting baking powder?
What Is Baking Powder?
Baking powder, like baking soda, is a leavening agent, meaning it helps doughs and batters rise. But unlike baking soda, baking powder is a complete leavening agent. That means it contains both the alkaline baking soda and the acid needed to create lift in one packaged ingredient.
The difference between double-acting and single-acting baking powder comes down to what type of acid is paired with the alkaline baking soda to make baking powder.
Single-Acting vs. Double-Acting Baking Powder
Double-acting baking powder will react and create gas bubbles twice: once when added to liquid, and again when exposed to heat. "That is, they inflate an initial set of gas bubbles upon mixing the powder into the batter, and then a second set during the baking process," explains food scientist Harold McGee in On Food and Cooking.
"There are several different acids used in baking powders, each with a different pattern of gas production," explains McGee, adding, "Most double-acting supermarket baking powders are a mixture of sodium bicarbonate [baking soda], MCP [monocalcium phosphate], and SAS [sodium aluminum sulfate]." These ingredients allow double-acting baking powder to react when added to the batter and when heat is applied.
The alkaline baking soda in baking powder will always immediately react with liquid, creating that initial lift in the batter. For single-acting baking powder, that initial lift when added to liquid is all there is—a single reaction, right at the beginning.
Because single-acting baking powder only produces a single reaction upon being combined with liquid batter, it's especially important to work quickly and get the batter in the oven soon after mixing. This will ensure your baked goods rise nicely and you don't lose any of the valuable bubbles from the reaction.
The Best Baking Powder for Home Baking
Fortunately for the still-confused bakers out there, you're more likely to run into double-acting baking powder in the grocery store, since most single-acting baking powders are only available for commercial use. And double-acting baking powder is what's commonly used for at-home baking.
If you do stumble upon a canister of the commercial-grade stuff, or have a recipe that calls for single-acting baking powder but only have double-acting, feel free to use the two types of baking powder interchangeably. When recipes refer simply to "baking powder," it's usually the double-acting stuff, and that's the best kind to keep on hand for all of your home baking needs.