What is caramelization in coffee roasting?

Caramelization is the thermal decomposition of sugars when exposed to heat - the process by which sucrose and other sugars in the coffee bean break down and reform into hundreds of new aromatic compounds. It begins at around 170-180°C during roasting and is one of the two primary browning reactions, alongside the Maillard reaction, that shape the flavour and colour of roasted coffee.

Caramelization produces the sweet, toffee, caramel, and syrupy notes associated with medium roasts, as well as contributing to the brown colour of the beans. As roasting progresses further, caramelization increasingly gives way to pyrolysis - the destructive breakdown of organic compounds that produces the bitter, charred character of dark roasts.

The distinction between Maillard reaction and caramelization matters in practical roasting because they operate at different temperatures and respond differently to roast curve decisions. Most of the complex aromatic compounds in specialty coffee are Maillard products; caramelization contributes the sweetness and body that round them out.