The browned, crispy outer layer of bread, formed by the Maillard reaction and caramelization during baking.
A great sourdough crust is crackly, deeply browned, and full of flavor. It forms when the dough's surface dries out and heats up above 150C (300F), triggering the Maillard reaction between amino acids and sugars. Steam during the first phase of baking keeps the crust flexible long enough for maximum oven spring. Longer fermentation means more available sugars, which means better crust color and flavor.
