The three browning reactions in food

TL;DR

Food browning has three distinct reactions — enzymatic oxidation, caramelization, and the Maillard reaction — each with different triggers and chemistry.

Key Points

• 1.Enzymatic browning is a plant defense, not heat-related. Cutting fruit releases polyphenol oxidase, which oxidizes phenols into quinones that react with amino acids to produce melanin — the same pigment that darkens human skin.
• 2.Caramelization requires only heat and sugar, no protein. Different sugars caramelize at different temperatures: fructose just above 100°C, glucose at low baking temps, sucrose at normal baking temps, and maltose above the common 350°F/180°C default.
• 3.The Maillard Reaction, described by French chemist Maillard in 1912, requires both sugar and amino acids. It produces melanoidins (brown color), plus toasty, nutty, and umami-flavored volatile compounds depending on exact conditions.
• 4.pH critically differentiates caramelization from Maillard. Maillard is enhanced by alkaline conditions (lye-soaked pretzels brown fast) and inhibited by acid (yogurt in naan reduces browning), while caramelization is enhanced by extreme pH in either direction.
• 5.In practice, both reactions occur simultaneously in almost all cooking. All foods contain some sugar and protein; calling everything 'browning' is the safest, most accurate term to avoid pedantic errors.