The Maillard reaction is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. Seared steaks, fried dumplings, cookies, and other kinds of 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 (how the body combines amino acids to form proteins).
The reaction is a form of non-enzymatic browning which typically proceeds rapidly from around 280 to 330 °F. Many recipes call for an oven temperature high enough to ensure that a Maillard reaction occurs. At higher temperatures, caramelization (the browning of sugars, a distinct process) and subsequently pyrolysis (final breakdown leading to burning) become more pronounced.
The reactive carbonyl group of the sugar reacts with the nucleophilic (electron donating) amino group of the amino acid, and forms a complex mixture of poorly characterized molecules responsible for a range of aromas and flavors. This process is accelerated in an alkaline environment (e.g., lye applied to darken pretzels), as the amino groups are deprotonated, and hence have an increased nucleophilicity. This reaction is the basis for many of the flavoring industry’s recipes. At high temperatures, a probable carcinogen called acrylamide can form. This can be discouraged with specific cooking techniques.[4]
In the cooking process, Maillard reactions can produce hundreds of different flavor compounds depending on the chemical constituents in the food, the temperature, the cooking time, and the presence of air. These compounds, in turn, often break down to form yet more new flavor compounds. Flavor scientists have used the Maillard reaction over the years to make artificial flavors.
The Maillard reaction is responsible for many colors and flavors in foods, such as the browning of various meats when seared or grilled, the browning and umami taste in fried onions, and coffee roasting. It contributes to the darkened crust of baked goods, the golden-brown color of French fries and other crisps, of malted barley as found in malt whiskey and beer, and the color and taste of dried and condensed milk, dulce de leche, the Sri Lankan confection milk toffee, black garlic, chocolate, and roasted peanuts.
On particular aroma compoind, 6-Acetyl-2,3,4,5-tetrahydropyridine, is responsible for the cookie or cracker-like flavor present in baked goods such as bread, popcorn, and tortilla products. The structurally related compound 2-acetyl-1-pyrroline has a similar smell, and also occurs naturally without heating and gives varieties of cooked rice and the herb pandan (Pandanus amaryllifolius) their typical smells.
Caramelization may sometimes cause browning in the same foods in which the Maillard reaction occurs, but the two processes are distinct. They are both promoted by heating, but the Maillard reaction involves amino acids, as discussed above, whereas caramelization is simply the pyrolysis of certain sugars.
The Daily Omnivore 
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