Gas bubbles

Breads and cakes are aerated to the point that as much as 80% of their volume is empty space. Bakers use yeast and chemical leavenings to enhance the bubbles in their baked goods. It is important to note that leavenings do not create all of the gas present in the batter or dough. In fact, most of the bubbles form from air introduced when the baker kneads the dough, creams the butter and sugar, or whips the eggs. The carbon dioxide produced by leavenings is released into the water phase of the dough, diffuses to the bubbles already present, and merely enlarges them. Therefore, the initial aeration of doughs and batters strongly influence the final texture of the baked goods.