Browning and the Maillard reaction

Browning is flavor. The golden crust on bread, the dark sear on a steak, the deep color of roasted onions and the toasty smell of coffee all come from the same chemistry.

The Maillard reaction is a chain of reactions between amino acids (from proteins) and certain sugars. It produces hundreds of new compounds with roasted, meaty, nutty, toasty flavors and brown colors. It happens slowly even at low temperatures (which is why stocks and long braises darken) but only becomes fast enough to brown a surface in minutes above about 140°C (285°F).

Caramelization is the browning of sugars on their own, without protein. It needs higher temperatures — roughly 160–180°C (320–355°F) for table sugar — and gives sweet, buttery and slightly bitter flavors. Onions, carrots and roasted fruit brown through both processes together.

Why water is the enemy of browning. Water can't get hotter than 100°C (212°F) at normal pressure. As long as a food's surface is wet, it stays near 100°C and won't brown; the moisture has to evaporate first. That's why everything in this book that should brown follows the same rules:

• Dry the surface. Pat meat, fish, tofu and vegetables dry with paper towels. Salting meat in advance and leaving it uncovered in the fridge dries the surface even better.
• Use enough heat. Preheat the pan and fat properly (see "Heat").
• Don't crowd. Leave space between pieces so steam can escape.
• Leave it alone. Food sticks at first and releases when a crust forms. Turn it when it lets go easily, not before.
• Use a little fat. Fat conducts heat evenly into the uneven surface of food.

Helping browning along. A little sugar (honey in a glaze) or protein (milk in a bread wash, egg wash on pastry) speeds browning. Alkalinity also speeds the Maillard reaction, which is why a pinch of baking soda helps onions brown faster and why pretzels are dipped in an alkaline bath. Use these tricks sparingly; too much soda gives a soapy taste.

Fond. The browned bits stuck to the pan after searing are concentrated flavor. Dissolve them with a splash of liquid (deglazing) and you have the start of a sauce; see Five-Minute Pan Sauce.

Browned vs burnt. There is a line. Deep mahogany is good; black is bitter. Burnt fat, garlic and spices are especially acrid. Garlic, which is small and full of sugar, burns in seconds over high heat; add it after onions, not before.

When not to brown. Some dishes rely on gentle, pale cooking: a French omelette, poached fish, a blond chicken stock, sweated onions for a delicate soup. Here the aim is to soften without color, so the heat stays low and a lid may help keep moisture in.