Leavening is any substance that makes dough or batter rise by creating tiny air bubbles throughout it. When you add leavening to bread dough or cake batter, it transforms the dense mixture into something light and fluffy. The word comes from the same root as “levitate,” which makes sense since leavening lifts the dough.

The most common leavening agents are yeast, baking soda, and baking powder. Yeast is actually alive: these microscopic organisms eat sugar in the dough and release carbon dioxide gas, which gets trapped in thousands of tiny pockets and makes bread rise. Baking soda and baking powder work through chemical reactions that also produce gas bubbles. Without leavening, bread would be flat and dense like a cracker, and cakes would be hard and heavy instead of soft and springy.

You can see leavening at work when bread dough doubles in size as it rises, or when pancake batter bubbles on the griddle. The difference between leavened bread (made with yeast or another rising agent) and unleavened bread (like matzo or tortillas) shows just how much leavening changes the final product.