Why are egg whites used in souffles?

Egg whites act as a leavening agent in souffles. When beaten, egg whites trap air bubbles, which expand and lighten the souffle during baking. This gives souffles their characteristic fluffy texture.

Structure

The proteins in egg whites coagulate when heated, which helps to set and stabilize the structure of the souffle. This prevents it from collapsing after baking.

Tenderness

Egg whites also contribute to the tenderness of a souffle. The fat content in egg yolks can make a souffle heavy, so using mostly or only egg whites results in a lighter, fluffier texture.