Leavening

Leavening is the introduction of gas into dough or batter to make it light and porous. Three gas sources exist — biological (yeast), chemical (baking soda/powder), and physical (steam, mechanical aeration) — and most preparations combine two or more. The choice of leavening system shapes not just texture but flavor, timing, and the entire workflow of baking.

Biological leavening: yeast

Saccharomyces cerevisiae — baker’s yeast — metabolizes sugars to produce CO₂ and ethanol. In the oxygen-poor interior of dough, it ferments rather than respires, generating gas slowly over hours. This slowness is a feature: it allows time for gluten development, enzyme activity, and the accumulation of flavor compounds (organic acids, alcohols, aldehydes) that give bread its complexity.