Conventional chemistry wisdom says that something which starts out as a liquid should either remain liquid or evaporate when heat is applied. Why do eggs go in the opposite direction?
In: Chemistry
Longer answer:
Eggs have protein in them. Proteins are molecules that are like long chains, and different parts of the chain have different positive and negative electric charges on different sides. These charges attract and repel each other, which causes the chain to roll up and fold in on itself in a predictable way that gives the protein a particular shape when it’s first formed. Most of the functional parts of plants and animals are made of of proteins.
When you heat up a protein, the molecules start vibrating and bouncing around a lot, ricocheting off each other. (That’s basically what heat *is* – faster-moving molecules.) These bounces are stronger than the electric forces that hold the protein in its shape, so the proteins start to unravel.
At that point, things get messy pretty quickly. The parts of the proteins that are supposed to stick to themselves start sticking to other nearby proteins instead, and they all become one big solid clump.
It’s not just eggs that do that. When you bake bread or cake or anything with flour, the proteins do the same thing, and that’s what turns your soft dough or liquid batter into something much firmer. When you cook meat, the proteins do the same thing too, which is why overcooked meat can get tough and dry.
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