A metabolic process through which microorganisms such as yeasts and bacteria consume sugars and produce different substances (carbon dioxide, alcohols and acids, for example) that are important for the production of bread and several other food items such as beer, pickles or chocolate.

The most notable contribution of fermentation to bread making is the "rising" effect, which is produced by the accumulation of carbon dioxide in the gluten network of the dough. Fermentation also benefits the flavor and texture of bread by the production of some acids and esters and improves the health benefits by breaking down some substances that can't be normally digested.