- 1: a. A substance which is added to dough to produce fermentation; spec. a quantity of fermenting dough reserved from a previous batch to be used for this purpose
- b. In wider sense: Any substance that produces fermentation; = ferment; occasionally applied to the ‘ferment’ of zymotic diseases.
A leavening agent (also leavening or leaven; /ˈlɛvənɪŋ/ or /ˈlɛvən/) is any one of a number of substances used in doughs and batters that cause a foaming action which lightens and softens the finished product. The leavening agent incorporates gas bubbles into the dough—this may be air incorporated by mechanical means, but usually it is carbon dioxide produced by biological agents, or by chemical agents reacting with moisture, heat, acidity, or other triggers. When a dough or batter is mixed, the starch in the flour mixes with the water in the dough to form a matrix (often supported further by proteins like gluten or other polysaccharides like pentosans or xanthan gum), then gelatinizes and "sets"; the holes left by the gas bubbles remain.