Why does angel food cake use egg whites instead of whole eggs?

Angel food cake relies exclusively on egg whites because they are essential for creating the cake's characteristic low-density, airy structure.12

When whipped, the protein in egg whites forms a stable foam that provides the necessary volume and lift for the cake. In contrast, egg yolks contain a high concentration of emulsified fat. Because fats and oils significantly diminish the foaming power of egg whites, using whole eggs would prevent the batter from achieving the light, elastic structure required for an angel food cake.21

To ensure this foam remains stable during the baking process, bakers often add cream of tartar, which is acidic, and gently fold in the dry ingredients to avoid collapsing the delicate air bubbles. While whole eggs are used in other types of cakes to provide richness, color, and a different texture, the specific goal of an angel food cake is to maximize volume and lightness through the unique properties of pure protein foam.312