Isaac Newton in the Kitchen

Caramelization, [explained Harold McGee, who first bonded rigorous science to popular cookery in his 1984 book, “On Food and Cooking,”] is what happens to sugar — simple sucrose molecules — exposed to high heat. But the browning that takes place in savory foods like onions, potatoes, celery and turkey skin is a “Maillard reaction,” the explosive meeting of a carbohydrate molecule (which may or may not be a sugar) and an amino acid in a hot, dry environment.

Maillard reactions take place when coffee or cocoa beans are roasted or when a bread crust turns brown. Mr. McGee said: “Maillard reactions contribute even more to the pleasures of eating than caramelization does. But of course it doesn’t sound as good on a menu.”