Why Food Browns When It Cooks

0:00Bread goes into a toaster pale and comes out brown. Why does food turn brown when it cooks?

0:07Browning is a chemical change: substances in the food react and make new substances.

0:13In toast, seared meat and roasted coffee, much of the brown colour comes from the Maillard reaction.

0:21In this reaction, amino acids, the building blocks of proteins, react with sugars.

0:29The reaction is slow when it is cooler, but fast above about 140 degrees Celsius.

0:36It makes hundreds of new substances: some are brown and colour the food, and many add flavour.

0:44Caramelization is a different reaction: sugar on its own breaks down at high heat.

0:52For table sugar, this happens at about 160 degrees Celsius, and it also makes brown colour and flavour.

1:01A cut apple also turns brown, but at room temperature, with no cooking at all.

1:07An enzyme, a protein that speeds up a reaction, helps compounds in the apple called phenols react with oxygen from the air.

1:16This also gives a brown colour, and it is called enzymatic browning.

1:21But browning is not burning: food heated too hot or for too long breaks down until it is mostly black carbon.

1:31This is called charring, and it tastes bitter.

1:36So food browns when it cooks because heat speeds up reactions, mainly between amino acids and sugars, that make new colour and flavour.