This is the age-old method of processing coffee and is still used in many countries where water resources are limited. The freshly picked cherries are simply spread out on huge surfaces to dry in the sun. In order to prevent the cherries from spoiling, they are raked and turned throughout the day, then covered at night, or if it rains, to prevent them from getting wet. Depending on the weather, this process might continue for several weeks for each batch of coffee. When the moisture content of the cherries drops to 11 percent, the dried cherries are moved to warehouses where they are stored.
The Wet Method
In wet method processing, the pulp is removed from the coffee cherry after harvesting and the bean is dried with only the parchment skin left on. There are several actual steps involved. First, the freshly harvested cherries are passed through a pulping machine where the skin and pulp is separated from the bean. The pulp is washed away with water, usually to be dried and used as mulch. The beans are separated by weight as they are conveyed through water channels, the lighter beans floating to the top, while the heavier, ripe beans sink to the bottom. Next they are passed through a series of rotating drums which separate them by size.
After separation, the beans are transported to large, water-filled fermentation tanks. Depending on a combination of factors — such as the condition of the beans, the climate and the altitude — they will remain in these tanks for anywhere from 12 to 48 hours. The purpose of this process is to remove the slick layer of mucilage (called the parenchyma) that is still attached to the parchment; while resting in the tanks, naturally occurring enzymes will cause this layer to dissolve. When fermentation is complete the beans will feel rough, rather than slick, to the touch. At that precise moment, the beans are rinsed by being sent through additional water channels. They are then ready for drying.
Grading & Sorting
Before being exported, the coffee beans will be even more precisely sorted by size and weight. They will also be closely evaluated for colour flaws or other imperfections.
Typically, the bean size is represented on a scale of 10 to 20. The number represents the size of a round hole’s diameter in terms of 1/64’s of an inch. A number 10 bean would be the approximate size of a hole in a diameter of 10/64 of an inch and a number 15 bean, 15/64 of an inch. Beans are sized by being passed through a series of different sized screens. They are also sorted pneumatically by using an air jet to separate heavy from light beans.
Next defective beans are removed. Though this process can be accomplished by sophisticated machines, in many countries, it is done by hand while the beans move along an electronic conveyor belt. Beans of unsatisfactory size, colour, or that are otherwise unacceptable, are removed. This might include over-fermented beans, those with insect damage or that are unhulled. In many countries, this process is done both by machine and hand, insuring that only the finest quality coffee beans are exported
Machines are used to remove the parchment layer (endocarp) from wet processed coffee. Hulling dry processed coffee refers to removing the entire dried husk — the exocarp, mesocarp & endocarp — of the dried cherries.
This is an optional process in which any silver skin that remains on the beans after hulling is removed in a polishing machine. While polished beans are considered superior to unpolished ones, in reality there is little difference between the two.