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
Because you’re looking at a chemical reaction instead of a phase change. The proteins in the eggs unfold because of the heat and then combine with and wrap around each other so that they become a solid.
Eggs have a lot of protein, and protein is a chain of amino acids. These amino-acid strings fold back on themselves. The proteins are held in place by weak bonds (non-covalent) between different parts of the amino-acid string. When you heat an egg, the proteins gain energy and literally shake apart the bonds between the parts of the amino-acid strings, causing the proteins to unfold. As the temperature increases, the proteins gain enough energy to form new, stronger bonds (covalent) with other protein molecules. When you boil an egg, the heat first breaks (unfolds) the proteins, and then allows the proteins to link to other proteins. That’s why the egg turns hard.
[removed]
[ON FOOD AND COOKING](https://www.amazon.com/Food-Cooking-Science-Lore-Kitchen/dp/0684800012) by Harold McGee: This is THE book for the questions you have!!!!
Why do my friends turn solid after I cook them?
You are denaturing proteins with heat, and can never re-nature them again. Using the opposite of heat won’t turn them back to the opposite of cooked. Using more heat won’t either. Tread lightly, there is no reset button in life. You are taking part in activities that can never be undone. The consequences of your actions in this case are permanent, and IRREVERSIBLE!
Because it’s a chemical reaction. I mean, cakes don’t melt into liquid when you bake them. Steak doesn’t melt into a puddle when you cook it.
You’re equating a gas/liquid/solid phase change to an egg’s chemical reaction.
They turn solid because proteins unfurl
Adding on to what other people said, [here’s an AMA](https://www.reddit.com/r/science/comments/2tu16v/science_ama_series_im_gregory_weiss_uc_irvine/) from a scientist that successfully “uncooked” an egg by undoing the unfolding of proteins
An interesting backward approach to answering your question: https://www.iflscience.com/scientists-work-out-how-unboil-egg-whites-26987
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.
Latest Answers