Maillard reaction
The browning chemistry between sugars and amino acids that makes toasted spices and seared food taste rich.
Also: browning, Maillard browning, non-enzymatic browning
The Maillard reaction, described by French chemist Louis-Camille Maillard in 1912, occurs when amino acids and reducing sugars react at temperatures above about 140 degrees Celsius, producing hundreds of new aroma and colour compounds. In spice cooking it appears when cumin is toasted, when onions are fried to deep brown in a bhuna, and when meat is seared before a spice rub flavours the crust. Dry heat favours it, and water slows it, which is why a wet pot does not brown. A pinch of baking soda speeds it. Spices can also scorch, a different process, and burnt spice tastes acrid.