The proteins in eggs enable them to act as leavening agents. Proteins unwind and stretch to form the flexible, elastic film that encases air bubbles. Because of this, when eggs are beaten, they can expand to a foam that’s up to eight times their original volume! Beaten egg whites hold millions of tiny air bubbles – which leavens angel food, sponge cakes, meringues, and soufflés. They can even act as an additional source of leavening in batters containing baking powder.