Egg Coagulation Science

An egg is a complex mixture of water and tightly folded protein bundles. As you apply heat, these protein bundles gain thermal energy and begin to bump into each other. Eventually, the weak bonds holding the bundles in their folded shape break apart—a process called denaturation.

Once unfolded, these long protein strands begin to tangle and bond with one another, forming a three-dimensional mesh that traps the surrounding water. This coagulation turns the liquid egg into a solid gel.

The various proteins in an egg denature at slightly different temperatures. Egg whites begin to set around 140°F (60°C) and become totally firm at 149°F (65°C). Yolks, containing different proteins and fats, begin to thicken at a slightly higher temperature, around 149°F (65°C), and set fully by 158°F (70°C).

This is why a perfectly cooked sunny-side-up egg with a set white and runny yolk requires precise heat management (much like achieving the perfect doneness for salmon). Overcooking pushes the proteins to bind too tightly, squeezing out the trapped water (syneresis), which results in a rubbery, weeping scramble.