Why are there black spots in baking? The problem of blackhead scorched spot roasting coffee beans espresso

Blackheads (or blackspots) are common in coffee roasting, especially in the early stages of roasting. Generally appear at both ends of the coffee bean, deeper baking degree of the case, but also often appear on the back of the coffee bean. Why are there blackheads? First of all, we can be sure that it must have something to do with heating, when the baking temperature is too high.