Named after Louis-Camille Maillard*, the chemist who first described the process over 100 years ago, put simply the Maillard reaction is the caramelisation of the natural sugars within a protein when exposed to heat. Just think of the browning that occurs when baking bread or searing meat.
To take the more scientific approach, there are two ways that browning can occur: enzymatic and non-enzymatic.
The former is when the avocado or banana you’ve cut up begins to discolour after their flesh has been exposed. Not necessarily desirable or attractive, is it?
The latter takes place from the application of heat. It not only changes the appearance, but the flavour compounds too.
So as enjoyable as that marshmallow might be straight from the pack, when you stick it on a fork and hold it over a flame until it bubbles and browns, you experience a whole different taste – this is a direct result of the Maillard reaction.
So while you can eat and enjoy a marshmallow without utilising this reaction, some foods definitely need to undergo this reaction. Coffee is one of them. A raw green bean, compared to roasted, is essentially flavourless and unusable.
But add some heat, cause the Maillard reaction to take place and voila, you have the wonderful product that we enjoy so much!
*As Monsieur Maillard was French, the correct pronunciation of his name is Mayar, though the ‘Anglicised’ Mayard is widely used.