Yeast is the most widely used biological leavening agent. As yeast grows, it converts sugar food into alcohol and carbon dioxide through fermentation. Yeast should be stored in a cool, dry place, but should always be at room temperature before being dissolved in liquid.
Leavening agents make bread and other baked good rise by causing a foaming action that traps air bubbles in the food as it cooks. The trapped air gives the final product a light and fluffy texture. There are three types of leavening agents.
Leavening agents can be biological or synthetic chemical compounds. The gas produced is often carbon dioxide, or occasionally hydrogen. When a dough or batter is mixed, the starch in the flour and the water in the dough form a matrix (often supported further by proteins like gluten or polysaccharides, such as pentosans or xanthan gum).