Protein Coagulation

Appears in
On Food and Cooking

By Harold McGee

Published 2004

  • About

There are several general consequences of denaturation that follow for most food proteins. Because the molecules have been extended in length, they’re more likely to bump into each other. And because their side groups are now exposed and available for forming bonds, denatured proteins begin to bond with each other, or coagulate. This happens throughout the food, and results in the development of a continuous network of proteins, with water held in the pockets between protein strands. The food therefore develops a kind of thickness or density that can be delicate and delightful, as in a barely set custard or perfectly cooked piece of fish. However, if cooking or other denaturing conditions continue, given the extreme physical or chemical environment that caused the proteins to denature in the first place, only the stronger bonds can form and survive, which means that the proteins bond together more and more tightly, densely, and irreversibly. And as they do so, they squeeze the pockets of water out from between them. The custard gets dense and a watery fluid separates from the solid portion; the fish gets tough and dry.