The crust of bread is the outer layer that forms during baking. It is typically firmer and darker than the soft interior, known as the crumb. The crust develops through a process called Maillard reaction, which occurs when sugars and proteins in the dough react to heat, creating flavor and color. Crusts can vary in texture and thickness depending on the type of bread. For example, a baguette has a thick, crispy crust, while a sourdough may have a chewy, rustic crust. The crust not only adds to the bread's flavor but also helps to retain moisture in the crumb.