The main ingredient of a meringue is egg whites, which, when whisked, become light and airy due to the incorporation of air. This process is known as foaming, and it transforms the proteins in the egg whites, allowing them to hold air. Typically, granulated sugar is added gradually to stabilize the foam and create the desired texture. Meringue can be used as a topping for pies, incorporated into cakes, or baked into crisp cookies. The delicate balance of beating the egg whites to the correct consistency is crucial to achieving a successful meringue.