Re: how does the crust form on bread?

How does crust form on bread?

There are two parts to my answer.

1. The chemical reaction that makes the crust brown is called the "Browning or Maillard reaction". It has rather complex chemistry but is basically a reaction between the sugars in the bread dough and the proteins in the dough. It occurs at the rather high temperatures that are found at the surface of the bread in baking (see below) or at the surface of the bread slice in toasting.

2. The bread dough is a rather poor conductor of heat, thus when the dough is exposed to the high heat of baking, the surface of the bread attains the temperature of baking and the Maillard reaction occurs. However, since the bread dough is such a poor conductor of heat, these high temperatures found at the surface of the bread are not found in the interior of the bread dough, even only a few millimeters into the bread dough. Since the high temperatures are required for the Maillard reaction, there is no browning in the interior of the bread dough.