Often described as non-enzymatic browning, the Maillard reaction gives a wide range of cooked foods their appealing flavours and colours. Sped along by heat, the Maillard reaction is actually a series of reactions, starting with one between protein and a reducing sugar, such as glucose or fructose. The reactions produce flavour chemicals and browning in foods including fried onions, toast, steak and roasted coffee.


French chemist Louis Camille Maillard first reported the reaction between proteins and sugars in 1912. In recent decades, scientists have unearthed more of Maillard’s detailed mechanisms.

When heat hits food, sugars react with the amino acids that make up proteins to form glycosylamine. This unstable chemical rearranges to create a ketosamine, setting off a cascade of further reactions to produce hundreds of new substances, some of which contribute to flavour and aroma.

What is the Maillard reaction? © Dan Bright
How does the Maillard reaction work? © Dan Bright

These include pyrazines, which have a toasted flavour, along with meaty furans and sweet furanones. Finally, the reaction creates large polymer molecules called melanoidins, which give a brown colour.

In order to obtain Maillard products in a short time, the temperature should exceed 100ºC, with an ideal range between 110ºC and 170ºC. If the temperature is too high, then bitter flavours can develop.

A downside of the Maillard reaction is that it creates a carcinogen called acrylamide as a by-product. Levels of this increase with longer cooking times.

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Asked by: David Walker, via email


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Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.