Maillard reaction

The Maillard reaction is the chemistry behind almost everything that tastes “roasted”: amino acids from proteins react with sugars to form hundreds of new aroma and colour compounds. It's named after the French chemist Louis Camille Maillard, who described it in 1912. It gets going noticeably from around 140 °C and needs a dry surface – which is why nothing browns while it's boiling in water (100 °C), and why wet meat turns grey rather than brown in the pan.

Not to be confused with caramelisation: there, sugar reacts with itself, from around 160 °C, with no protein involved at all. When you sauté onions, both happen at the same time. A dark bread crust, the edges of fried potatoes, crispy fried onions, coffee, cocoa and the crust on a steak are all Maillard products – as is the colour of pretzels, which are dipped in lye before baking, because an alkaline environment speeds up the reaction.

This knowledge is especially useful for light cooking: roasted flavours replace fat as a carrier of taste. Oven-roasted vegetables at 200 °C with a teaspoon of oil, spread out well on the baking tray (not piled up, otherwise they steam), meat patted dry and seared in a very hot pan, roasted chickpeas, tomato purée fried off for sauces – all of this adds depth with hardly any extra calories. A pinch of bicarbonate of soda makes onions brown faster.

The downside: too much heat produces unwanted substances, above all acrylamide in starchy foods and so-called AGEs (advanced glycation end products – essentially sugar-bound proteins that can put a strain on the body in large amounts) in heavily browned meat. The rule of thumb from the German Federal Institute for Risk Assessment (BfR), “golden, not charred”, therefore applies to food lovers too: golden brown is the goal; black is too much.

An experiment for children: two slices of toast, one light, one dark – smell, compare, describe. That's how you understand chemistry with your nose.