Maillard reaction
also: Maillard browning
Heat-driven reactions between sugars and amino acids during roasting that build savory, toasty, complex brown flavors and aromas.
The Maillard reaction is a family of browning reactions between reducing sugars and amino acids (the building blocks of proteins) that kick in under heat. It is the same chemistry that browns toast, seared meat, and bread crust, and in coffee roasting it generates a huge range of aroma and flavor compounds.
Why it matters: Maillard browning is where much of coffee’s savory, toasty, nutty, chocolatey, and complex character is born. It happens during the middle phase of the roast, broadly before and around first crack, at temperatures roughly above 140 to 150 C (284 to 302 F). How long and how hot a roaster runs this phase strongly shapes the final cup.
It works alongside caramelization, which is sugar browning on its own; the two overlap but are distinct. Together they drive the color change and aroma development a roaster manages through development time. Get the Maillard phase right and you build depth and sweetness; rush it and the coffee can taste thin, flat, or harsh even at the same roast level.