In 1850, British inventor John Walker took out a patent for the drum pulper. Ten years later, he took out a patent for a disc pulper (see below). Drum pulpers usually consist of a rolling pin that is traditionally covered in copper that is bulbed — a bit like the ridges in non-slip copperplate flooring. Cherries are drawn into the pulper from a hopper. Then the bulbs in the rotating drum pull the cherries around to where they press against an adjustable pulping bar. The drum rotates at approximately 120 rpm. (J.N. Wintgens, 2004, pg. 719) Parchment is guided into channels by a carefully calibrated pulping channel whilst most of the pulp is expelled out the side of the pulper on the other side of the machine to the pulping channel.