The Wet Method—Pulping
The wet method of preparation is the more modern form, and is generally practised on the larger plantations that have a sufficient supply of water, and enough money to instal the quite extensive amount of machinery and equipment required. It is generally considered that washing results in a better grade of bean.
In this method the cherries are sometimes thrown into tanks full of water to soak about twenty-four hours, so as to soften the outer skins and underlying pulp to a condition that will make them easily removable by the pulping machine—the idea being to rub away the pulp by friction without crushing the beans.
Niagara Power Coffee Huller
On the larger plantations, however, the coffee cherries are dumped into large concrete receiving tanks, from which they are carried the same day by streams of running water directly into the hoppers of the pulping machines.
At least two score of different makes of pulping machines are in use in the various coffee-growing countries. Pulpers are made in various sizes, from the small hand-operated machine to the large type driven by power; and in two general styles—cylinder, and disk.
The cylinder pulper, the latest style—suggesting a huge nutmeg-grater—consists of a rotary cylinder surrounded with a copper or brass cover punched with bulbs. These bulbs differ in shape according to the species, or variety, of coffee to be treated—arabica, liberica, robusta, canephora, or what not. The cylinder rotates against a breast with pulping edges set at an angle. The pulping is effected by the rubbing action of the copper cover against the edges, or ribs, of the breast. The cherries are subjected to a rubbing and rolling motion, in the course of which the two parchment-covered beans contained in the majority of the cherries become loosened. The pulp itself is carried by the cover and is discharged through a pulp shoot, while the pulped coffee is delivered through holes on the breast. Cylinder machines vary in capacity from 400 pounds (hand power) to 4,800 pounds (motive power) per hour.
Some cylinder pulpers are double, being equipped with rotary screens or oscillating sieves, that segregate the imperfectly pulped cherries so that they may be put through again. Pulpers are also equipped with attachments that automatically move the imperfectly pulped material over into a repassing machine for another rubbing. Others have attachments partially to crush the cherries before pulping.