Angel food cake gets its signature airy texture entirely from millions of air bubbles trapped in whipped egg whites.

The culinary science of angel food cake centers on the denaturation of egg white proteins, primarily ovalbumin and ovotransferrin. When egg whites are whipped, physical agitation causes these protein molecules to uncoil and bond together, forming a protective network around air bubbles. This process creates a colloidal dispersion known as a foam. To stabilize this foam, cream of tartar is often added to lower the pH, which prevents the protein bonds from becoming too tight and squeezing out the trapped air.The absence of fat is critical to this chemical process. Even a tiny trace of egg yolk or oil can interfere with protein bonding, preventing the foam from reaching its full volume. Unlike sponge cakes that use baking powder, angel food cake relies solely on the physical expansion of trapped air and steam during baking to rise. This is why the cake is traditionally baked in a specialized ungreased tube pan, which allows the batter to climb the walls and center chimney for maximum height.According to food scientists at institutions like America's Test Kitchen, the cooling process is equally vital as the baking itself. Because the cake's structure is primarily composed of delicate protein and starch walls, it is highly susceptible to gravity while still warm. Suspending the pan upside down stretches the protein network while it cools and solidifies, ensuring the cake maintains its height and preventing the cell walls from buckling under their own weight. This technique has been a staple of American baking since the late 19th century.