Two different reactions brown food, but they are not the same. Caramelization is the breakdown of sugar on its own and requires high heat. The Maillard reaction occurs when sugar and protein combine; it starts at a lower temperature and produces very different flavors. That is why caramel sauce and a cookie crust may have a similar color but not the same aroma or taste.
Caramelization is a one-ingredient reaction. Only sugar is present; as the heat rises, sugar molecules break down, the fragments bond together again, and that is where the color and aroma come from. It begins at about 160°C / 320°F. That is why nothing but sugar is needed in the pot to make caramel. No ingredient containing water or protein takes part in the reaction; if one is added, the result is no longer pure caramelization. Water in the pot also delays the reaction because the temperature cannot rise until the water evaporates.
The Maillard reaction, by contrast, needs two ingredients: a reducing sugar and an amino acid, the building block of protein. Flour, eggs, milk, and butter supply this protein. The reaction begins at a lower temperature than caramelization and is already underway within the usual oven-cooking range. It produces different compounds; much of the familiar aroma from bread crust, cookie surfaces, and the tops of milk desserts comes from this reaction. A dry surface is also needed: a wet dough surface will not brown, so first let its moisture evaporate.
The distinction has an interesting detail when it comes to granulated sugar. Sucrose, the granulated sugar used in cooking, does not take part directly in the Maillard reaction as it is; it must first break down into glucose and fructose. Some of this breakdown occurs on its own from the heat in the oven and the acid in the dough. Honey, grape molasses, and invert sugar are already broken down, so they produce a faster, darker color in the same dough. For the same reason, recipes that use honey instead of sugar have a slightly shorter baking time.
In the kitchen, the two reactions often happen side by side. As a cookie bakes, some of the sugar on the surface caramelizes while the Maillard reaction also takes place between the sugar and the proteins in the flour and egg; the resulting flavor is the sum of both. Both reactions also occur in desserts where milk and sugar are boiled together for a long time. To see caramelization alone, put only sugar in the pot. The color and aroma of milk caramel are a familiar example of working together.
Where does the distinction help in practice? If something is not browning, first ask which reaction is expected. The fix for a cookie that is not browning is not to raise the heat, but to brush the surface with something that supplies protein and sugar; milk or egg yolk does the job. For caramel sauce, the only remedy is heat. Trying to speed up the wrong reaction will not change the result; it will only burn it. The oven’s upper broiler also speeds up the reaction at the surface but does not heat the inside at all.
A Note for Readers
This content is for informational purposes only and is not a substitute for medical advice. Consult your doctor before making any decision about your health.