When coffee is processed using a wet or washed method, the pulp of the coffee cherry must be mechanically removed. Many small holders utilize a small hand-cranked pulper that can alternatively be attached to a small motor via a pulley.
The machine has a knuckled drum that as it rotates, presses the cherries against an iron faceplate. The pressing action squeezes the seeds from the cherry and the machine utilizes channels that discard the seeds from one side and the pulp from the other side of the machine.
To adjust the machine to accommodate different sized cherries, the iron faceplate can be moved closer or further away from the drum. The opening at the bottom of the hopper can also be adjusted.
Whole cherries are fed into the top via the hopper and seeds and pulp are discarded via opposite sides of the machine. I have a video at the bottom of the page showing how a pulper is used.
Watch this video of a pulper machine in action: