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The Maillard reaction

The Maillard reaction is a series of chemical reactions that occur during cooking and which release the food’s flavours and aromas. Following on from the work of Hugo Schiff, in the 1910s, the chemist Louis Camille Maillard (1878-1936) worked on the reactions between amino acids and sugars. He recorded his observations and results in his paper Action de la glycérine et des sucres sur les acides amines (The effects of glycerine and sugars on amino acids), published in 1913.
The dark lines left by the grill are the result of the Maillard reaction
© Shutterstock / stockcreations - The dark lines left by the grill are the result of the Maillard reaction

What is it?

The Maillard reaction occurs as food is cooked. It is partly responsible for the browning of food and the release of aromas. During the cooking process, amino acids and certain simple sugars in the food form new molecules, which join together in chains. These groups of molecules reflect light in such a way that we then perceive the surface of the food as being brown.

The Maillard reaction is, in fact, a series of different reactions. The molecules created by the interaction between the sugars and amino acids continue to react and go on to create other molecules, which release powerful aromas. Although some of these molecules are only present in minute quantities, they nonetheless suffice to give grilled meat its succulent flavour. It has in fact been calculated that, if 2 g of this type of substance were dissolved in a lake 2-metres deep and 8 kilometres in diameter, the water would taste of grilled steak! (Myhrvold, 2011)

How does it work?

The Maillard reaction can occur with all methods of cooking, or even at room temperature. The pH level, the water content and the temperature of the food all influence the speed of the reaction and directly influence the aromas that are released. The same foodstuff will therefore produce different aromas depending on whether it is grilled, roasted, fried, boiled or even steamed in a pressure cooker. Food with a high pH (alkaline) provides more favourable conditions for the reaction to take place than food with a low pH (acidic). A marinade, for example, alters the pH of food and, consequently, how it will brown and the aromas it develops during cooking.

At 90°C, the Maillard reaction is rather slow. To speed things up, the surface of the food needs to rise above the boiling point of water (100°C). At temperatures above 115°C, the reaction speeds up and, from 130°C, it takes place very quickly. However, above 180°C, the Maillard reaction stops. Another chain of chemical reactions then commences, called pyrolysis, the decomposition of food by heat. Pyrolysis causes the ‘burnt’ bitter taste of food that has been grilled too much, and the black, charred substances, which are potentially carcinogenic.