Have you ever wondered how freshly baked bread gets its a golden brown crust and why it smells so good? Or how nondescript green berries turn into beautiful brown coffee beans with a rich alluring aroma?
The answers to these questions lie in a series of complex of chemical reactions, known as Maillard reactions, which give many foods their familiar flavours and colours. These sensory properties even guide us in how we choose foods and help create our initial perceptions of their quality.
As the name suggests, Maillard reactions were first described by a French physician and biochemist, Louis-Camille Maillard, in 1912. These reactions produce hundreds of chemical compounds that give colour and aroma to some of our favourite foods such as roast meat, potato chips, bread and other bakery products, coffee, chocolate and confectionery.
These reactions occur most rapidly under conditions of low moisture and at temperatures above about 130℃. Hence, they tend to kick in when we fry, bake, grill or roast.
Maillard reactions are also referred to as browning reactions because of the colour they impart to foods cooked in this way. When meat is grilled or roasted, only the surface is usually hot enough to cause browning. The interior can retain a pinkish colour because the cooking temperature stays below that required for Maillard reactions to occur rapidly.
Foods cooked by boiling or steaming do not turn brown or acquire the complexity of flavours because the temperature only reaches about 100℃. Likewise with cooking in a microwave oven.
The colour of chocolates, fudges and toffees are produced by the reaction of sugars with milk proteins.