The coffee bean is the seed of a coffee cherry. Each winter (dry season) the ripe, red cherries are harvested using a variety of methods. The bean is covered by several layers including the silver skin, parchment (pergamino), mucilage, pulp, and skin. The interaction of the sweet mucilage with the coffee seeds governs much of the flavor of coffee as does the process in which the coffee beans are retrieved from the cherry. There are three processes that are commonly practiced including the wet-process, the dry-process, and the semi-washed method.
The coffee cherries are brought to the processing plant immediately after harvesting. Ripe, overripe, and under-ripe cherries are mixed together at this point. If they were not separated the coffee would have a dusty unpalatable flavor with few desirable attributes. The beans are first washed with water and then passed into tanks filled with water for preliminary separation. The best coffees are dense and will sink in water, whereas the overripe cherries will float and are separated. The low-quality coffees are either slated for internal consumption or sold to instant coffee producers in the United States or Europe. Unfortunately, green (underripe) cherries are also dense and will continue to be mixed with the perfectly ripe cherries. The green cherries can be sorted out during wet-processing, or in the case of dry-processed coffees must be sorted at a later time.
The Dry Method
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.