Crust color

Browning occurs when sugars caramelize and starches and proteins undergo Maillard browning. A professional baking text adds that milk, sugar and egg increase browning, which also adds flavor.

Timing and temperature drive it. While water keeps evaporating, the crust stays cool, but once evaporation slows significantly the surface temperature rises quickly above 300°F (150°C). The high heat breaks down molecules such as sugars and proteins on the surface of baked goods, producing brown color and a pleasing baked taste. Because essentially all baked goods contain sugars and proteins, these reactions matter across most baking.

Sugars made by enzymes help too: in bread dough, amylase turns starch into sugars that feed the yeast and help brown the loaf.