All about coffee - Initial Processing
After harvesting the next step is to remove the coffee seeds from the ripe fruit and dry them. This can be done in two ways: the dry and the wet methods.
The Dry Method
The dry or ‘natural’ method involves drying the whole cherry. It is the oldest, simplest method and requires little machinery. The harvested cherries are sorted and cleaned, by hand, to remove unripe, overripe and damaged cherries as well as any dirt, soil, twigs and leaves. This can also be done by floating the cherries in water.
The coffee cherries are spread out in the sun, either on large concrete or brick patios, or on matting raised to waist height on trestles. If it rains they are covered up. As the cherries dry, they are raked or turned by hand to ensure even drying. It can take up to 4 weeks before the cherries are dried sufficiently. On larger plantations, machine-drying is sometimes used to speed up the process after the coffee has been pre-dried in the sun for a few days.
Almost all Robustas are processed by this method. The dry method is used for the majority of the Arabica coffee produced in Brazil, most of the coffees produced in Ethiopia, Haiti and Paraguay, and some Arabicas from India and Ecuador. Dried cherries are brittle with a hard outer shell and should have a maximum moisture content of 12.5%. The dried cherries are stored in silos until they are sent to the mill for hulling, where the outer layers of the dried cherry are removed. The ‘green coffee’ beans are then sorted and graded ready for selling.
The Wet Method
The wet method requires the use of special equipment and the availability of water. As with the dry method, the ripe cherries are first cleaned. They are then pulped by a machine that squeezes the cherries so that the flesh and the skin are separated from the beans. The beans are left with a slippery outer skin (the mucilage) and a parchment covering.
The beans are further cleaned to remove lingering bits of pulp and put in large tanks; there the mucilage is broken down by natural enzymes and washed away. This takes between 24 and 36 hours. Then the coffee is thoroughly washed with clean water. At this point the coffee is approximately 57% moisture.
To reduce the moisture to a desirable maximum of 12.5%, the parchment coffee is dried either in the sun, in a mechanical dryer, or by a combination of both. Sun-drying takes from 8 to 10 days. This parchment coffee is then stored.
Just before sale, this coffee is hulled to remove the parchment, and cleaned, screened, sorted and graded. This ‘green coffee’ is now ready for selling.