Maillard reaction

The Maillard reaction is a set of non-enzymatic reactions in which the carbonyl group of a reducing sugar reacts with the amino group of an amino acid or protein. Via Amadori products it yields brown melanoidins and a great number of aroma compounds. It is named after the French chemist Louis-Camille Maillard, who described it in 1912 while heating a solution of a sugar with an amino acid.

It differs from caramelisation in needing an amino compound, whereas caramelisation is the breakdown of carbohydrates alone. In baking, roasting and grilling, however, both reactions commonly run side by side; a review of baking puts crust browning typically at around 160 °C.

The reaction rate rises sharply with temperature and also depends on pH, water content and the kind of sugar and amino acid. It proceeds slowly even in frozen storage over months. It slows down in an acidic medium; below pH 6, according to a review, it is very slow. Above roughly 120 °C acrylamide can form as a by-product, classed by the IARC as a probable carcinogen.