What process heats sugar until it browns and develops a rich, nutty flavour?

Caramelization is the process that heats sugar until it browns and develops a rich, nutty flavour. It is a form of non-enzymatic browning caused by heat-driven chemical breakdown and rearrangement of sugar molecules.

As sugar is heated, it undergoes dehydration, fragmentation, condensation, and other reactions that create hundreds of new compounds. Some volatile compounds contribute buttery, toasted, and nutty aromas, while larger molecules called caramelans, caramelens, and caramelins contribute brown colour.

Sucrose caramelizes readily at roughly 170°C, although the temperature varies with the sugar, water content, acidity, and impurities. Fructose begins reacting at a lower temperature than glucose, while brown sugar can caramelize more readily because it contains molasses and other impurities.

Caramelization is often confused with the Maillard reaction. Both brown food, but caramelization involves sugars breaking down through heat; the Maillard reaction involves reducing sugars reacting with amino acids and is especially important when browning proteins such as meat, bread crust, and roasted coffee.