A leavening agent (sometimes called just leavening or leaven) is a substance used in doughs and batters that causes a foaming action intended to lighten and soften the finished product. The leavening agent reacts with moisture, heat, acidity, or other triggers to produce gas (usually carbon dioxide and sometimes ethanol) that becomes trapped as bubbles within the dough. 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 fu… (More on Leavening)