On farms that have a high proportion of unripe cherry in their mix, the screen pulper makes it possible to separate ripe and unripe cherry by mechanical means. Cherries are forced to pass through a specially designed screen that also acts as a pulper. This screen pulper consists of a horizontal cylinder, with long, slotted holes that form the ‘screen’. Inside the cylinder, a rotor shaped like a worm screw pulls the cherry through the middle of the cylinder. The soft, ripe cherry passes through the holes of the screen and lose their pulp on their way through. Hard, unripe cherries cannot squeeze through the holes. They are forced to travel along the length of the cylinder, where they are pushed out the end by the rotor.
The screen pulper doesn’t separate the skins from the parchment coffee, so this system requires a final phase. An ordinary drum pulper acts as a pulp separator and repasser. The drum pulper separates pulp from parchment and pulps any undersized cherry that have passed through the holes of the screen pulper without being pulped (J. N. Wintgens, 2004, pg. 624).