The Maillard reaction (/maɪˈjɑːr/ my-YAR) is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. Seared steaks, pan-fried dumplings, cookies and other kinds of biscuits, breads, toasted marshmallows, and many other foods, undergo this reaction. It is named after French chemist Louis-Camille Maillard, who first described it in 1912 while attempting to reproduce biological protein synthesis.
In the process, hundreds of different flavor compounds are created. These compounds, in turn, break down to form yet more new flavor compounds, and so on. Each type of food has a very distinctive set of flavor compounds that are formed during the Maillard reaction. It is these same compounds that flavor scientists have used over the years to make artificial flavors.
Aside from taste, in distilling and brewing the Maillard reaction is responsible for the color in grains as they are kilned after malting. The color of a grain, measured in Lovibond, indicates the level of Maillard reaction.
There are negative side effects of the Maillard reaction. It lowers the sugars available for fermentation. Depending on the temperature and time the grain was kiln it will denature conversion enzymes lowering the diastatic power.
It is different than caramelization. Maillard reactions happen at lower temperatures, over longer periods of time, and require an amino acid.