Coffee processing is the act of breaking open coffee cherries after they have been harvested, removing the beans, and drying the beans. There are two methods of processing coffee cherries – the wet method and the dry method.
Wet Method: Every coffee cherry contains either one or, more commonly, two beans. Each bean, inside the cherry, is coated with a filmy substance called silver skin and surrounded by a husk called parchment (pergamino). Harvested cherries are fed into machines that break the surface of the cherries without damaging the parchment. Most of the cherries skins are washed away with water and the beans are allowed to ferment in concrete tanks for 24 to 48 hours. The fermentation process breaks down the gummy mucilage and whatever cherry skin still surrounds the beans. Water is again used to wash the beans after fermentation. The beans are then spread out in the sun on concrete patios or drying racks (In more modern mills, giant drum dryers are used to finish the process.). The beans are then allowed to rest for three to four weeks (reposado) in their parchment. The parchment and silver skin are milled off the beans prior to bagging and shipping.
Dry Method: This method is generally used where water is not abundant or where it has become the local tradition. The cherries are picked and then allowed to dry on concrete patios. When fully dry, the beans are milled to remove cherry skin, parchment, and silver skin all at once. Subsequent sorting for defects and size is extremely important for dry method processed beans.