Eli5: why does a gooey layer form on top of milk when heating it?

Question

Eli5: why does a gooey layer form on top of milk when heating it?

In: Chemistry

Answer 1

Milk contains a lot of protein. Proteins are complex molecules that are held in very specific shapes by weak bonds. As a protein is heated, those weaker bonds start to break and the protein changes shape in a process called *denaturing*. These denatured proteins are a different consistency, so they form that layer you notice.

The same process is involved when cooking eggs – the liquid, high-protein egg undergoes denaturing and becomes the more rubbery scrambled or fried egg you’re used to.

Hope that helps!