Why does egg white turn solid when cooked?
Heat changes the shapes of proteins in egg white. They can then join into a network that holds water, turning the runny liquid into a gel.
- The scientific idea
- Protein denaturation
- Fields of science
- Chemistry, Biology
How it works
A cooked egg white does not become firm merely because water has evaporated. Heating changes the shapes of its proteins, exposing regions that can interact with neighboring molecules. As these proteins join, a network forms and holds water within it. The liquid becomes a gel.
Look closer
Unfolding and joining are related steps, but they are not identical: denaturation describes the structural change, while coagulation describes the proteins gathering together. Heat is not the only route. Beating egg whites also changes proteins and lets them stabilize the surfaces of air bubbles. The same ingredient can therefore become either a tender solid or a foam, depending on how its molecules are rearranged.