The skill of grinding or shelling coffee beans

Coffee beans should be ground before they are exported, that is, the endocarp of Arabian and Robbite coffee beans to be sold should be removed. The residual shell of coffee beans after removal and cleaning of endocarp and drying process is also known as peeling or peeling.

It is more difficult to remove the endocarp of coffee beans in the wet treatment than in the drying process, so different shelling machines are needed. There are mainly two types of machines: friction sheller and compaction sheller. Engelberg and African models of friction shellers are suitable for dry or wet coffee beans: in a cylindrical box, the coffee beans are squeezed between a linear strip and a knife, and the shell is scraped by a knife to reveal the beans.

Parchment coffee beans are usually shelled on a Smout friction sheller. Jules Smout is of Belgian and Scottish descent. He was born in Koenigsberg, Prussia, and settled in Guatemala. In 1844, he developed a coffee peeling machine with a rotating body with a screw, which rotates in a box with a screw, which rotates in the opposite direction. When the coffee bean is driven along the rotation, the endocarp is peeled off the coffee bean. Because the rotating body rotates relatively slowly, it produces less heat than other types of shelling machines.

Other shellers include rolling shellers (mainly used for dried coffee beans produced in South America) and crossbar shellers (with knives inside).

In other places except Brazil, the parchment coffee beans are treated with a pressing sheller instead of rubbing the sheller. Coffee beans must have moderate water content when shelling, or they may break. The pressing sheller consists of a horizontal disk rotating in a ring, and the edge of the plate is surrounded by an iron needle or rod. When the machine is running, the coffee bean comes into contact with the iron needle due to the action of centrifugal force, which makes the endocarp shell fall off.