The coffee grinding process comes after the roasting process. Destoned roasted beans are inserted into the grinder silo, which is connected to the grinder itself. A roller mill grinder is a coffee grinding machine that mills coffee beans with two rotating grooved steel cylinders. In this process, you adjust the size of the coffee grounds - coarse to fine. It is important to adjust the particle size as the flavor, depth, and body of your coffee can change. Also, the particle size decides if the coffee ground is appropriate for certain coffee extraction methods.