🧪 Food chemistry

Cooking is really a set of chemical reactions, heat rearranges the molecules inside food, breaking some bonds apart and forming new ones, which changes texture, colour and flavour all at once. Proteins, like those in egg white or meat, unfold and clump together as they heat, which is why raw and cooked versions of the same food can look and feel completely different. Sugars and proteins on a food's surface can also react together under high heat in a process that creates hundreds of new flavour compounds, which is part of why a seared or toasted surface tastes so different from a boiled one.

Toasting bread triggers a chemical reaction between sugars and proteins on its surface, called the Maillard reaction, which only kicks into gear once the surface gets hot and dry enough. That reaction creates hundreds of new flavour and aroma compounds, along with a range of brown colours, which is exactly why toasted bread tastes so much richer and more complex than plain untoasted bread. The inside of a slice usually stays pale because it is protected by moisture, and moisture keeps a food's temperature from climbing high enough for that browning reaction to properly happen.

Cutting a fruit like an apple breaks open its cells and exposes certain natural chemicals to the oxygen in the air, which triggers a reaction that produces brownish compounds on the surface. This is a completely different process from the browning that happens during cooking, since it happens even in cold, raw fruit without any heat at all. A splash of lemon juice can slow the browning down, since its acid interferes with the reaction, which is why recipes sometimes suggest it for sliced fruit left sitting out.

Salt does more than add its own flavour, it actually suppresses bitterness and boosts other flavours already in the food, which is why even sweet foods, like caramel or melon, can taste noticeably better with just a tiny pinch. Your taste buds detect salt easily even in small amounts, and that little jolt can make other flavours, like sweetness or savouriness, feel sharper and more present. Chefs rely on this constantly, seasoning food gradually and tasting along the way, rather than adding all the salt at once at the very end.