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

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

In: Chemistry
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Milk isn’t just a liquid. There are fats and other things mixed in.

When you heat it, some of those things break apart. The layer you’re referring to, if I remember correctly, is fats that are breaking down into oils.

Hopefully someone with a chemistry or food science/nutrition background will be able to verify or give more explanation.

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!