Leavening

Leavening is the process by which dough or batter increases in volume and develops a porous, light crumb as gas is produced or trapped within the mixture. The expanding gas creates air pockets that lift the structure, while the surrounding proteins and starches set to form a stable matrix. Leavened products range from bread and buns to cakes and pastries, and the method used affects flavor, texture, and crumb structure.

Biological leavening relies on microorganisms, most notably baker's yeast, which ferment sugars to produce carbon dioxide and alcohol. In doughs, gas produced by fermentation is trapped by a gluten network, gradually inflating the loaf during fermentation and baking. Sourdough uses a surrounding culture of wild yeasts and lactic acid bacteria. Chemical leavening uses acids and bases that react to release carbon dioxide; baking soda requires an acidic ingredient to activate, while baking powder contains both an acid and a carbonate and often a drying agent, with some powders designed to release gas in two stages. Physical leavening relies on heat to generate steam; moisture in the batter or dough vaporizes during baking, inflating the mixture, as seen in pastries, popovers, and choux pastry.

Practical considerations include temperature and time: yeast activity increases with warmth but declines with excessive heat or overproofing, which weakens structure. Quick breads rely on chemical leavening for speed, while yeast breads develop flavor and chew from fermentation. Proper mixing, moisture, and ingredient temperatures influence gas formation and retention; storage instructions for leavening agents advise dryness and expiration dates.