why does applying heat to a liquid turn it into a solid when cooking (e.g. frying an egg)?


why does applying heat to a liquid turn it into a solid when cooking (e.g. frying an egg)?

In: Biology

In the case of an egg it’s because of the specific shapes of proteins in the egg. The heat from cooking breaks up the bonds that the proteins normally have (called denaturing) and when they form back together they tend to clump up, preventing them from flowing like they used to. Usually when you see that kind of reaction from something this is the core reason, but not all proteins will respond the same way. It also helps that eggs are “barely” liquid. They’re more semi-solid to begin with.

Eggs are full of protein. When you heat a protein up, you ‘denature’ it. That means you change some of the molecules by breaking and making chemical bonds. This changes the structure of the protein, sticks the molecules together, and turns it into a different substance which is a solid at room temperature.

In the case of frying eggs it’s proteins changing (denaturing) because of the heat and causing them to stick together. In other cases like sauces it can sometimes be as simple as boiling off water which will create a more concentrated solution.

Because cooking isn’t something as simple as changing phase from solid to liquid.

Adding heat actually induces a chemical reaction that changes the molecules. It breaks sine up, provides energy to allow other combinations. This is why cooked eggs taste, smell, and feel so very different. They ARE different.

Biological matter is more complex than simple substances like ice or glass or metal that melt when the temperature increases and solidify when it drops. In the case of eggs, much of the non-water mass is protein. Proteins are very large, very special molecules that are essentially long chains that bunch up in specific ways. The protein albumin is built to be suspended in liquid, just floating happily under normal circumstances. Heat it up though and it gets untangled, and then these chains can start to clump to each other. Now they can’t just stay suspended in liquid anymore. The clumps act more like a solid.