The crust of bread forms where surface moisture evaporates faster than the interior can replace it.

The longer version

The surface of a loaf is exposed to much hotter, drier air than its interior, so water there evaporates rapidly while the crumb beneath stays near the boiling point and remains moist. As the surface layer dries, its temperature climbs past that of the interior, and sugars and proteins react in browning processes that give crust its color and toasty aroma.

Meanwhile the outer structure sets into a firm shell while the inside continues to expand. Steam in the oven during the early minutes delays that setting, which is why humid baking produces thinner, crisper crusts. A dry oven produces a thicker shell and less oven spring.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.