Washed – also known as the wet method requires equipment and large quantities of water. When properly processed it produces a green coffee which is homogeneous with crisp, clean flavor and great snap with only a few defective beans. As in the natural method, preliminary sorting and cleaning the cherries is necessary. It is performed after harvesting by washing the cherries in tanks filled with flowing water. Screens may also be used to improve the separation between the ripe and unripe, large and small, cherries.
After sorting and cleaning, the pulp is removed from the cherry. This is a key difference between the dry and the wet methods. Unlike the dry method, the wet method separates the pulp of the fruit from the beans before the drying stage. The pulping is done by a machine which squeezes the cherries between fixed and moving surfaces. The flesh and the skin of the fruit are left on one side and the beans, enclosed in their mucilaginous parchment covering, shift to another. The clearance between the surfaces can be adjusted to avoid damage to the beans. The pulping is done as soon as possible after harvesting to avoid any deterioration of the fruit.
The pulped beans then go on to a series of vibrating screens which separate them from any un-pulped or imperfectly pulped cherries, as well for any large pieces of pulp that might remain. The separated pulped beans then pass through water-washing channels and move on to further separation that takes place within flotation tanks before they can be hulled.
Wet process pulping leaves some residual flesh as well as the sticky mucilage adhering to the surrounding parchment that needs to be completely removed. To accomplish this the pulped beans are dunked into fermentation tanks where the mucilage is broken down by natural enzymes until it is dispersible and can be washed away. The process takes between 24 and 36 hours, depending on the temperature, thickness of the mucilage layer and concentration of the natural enzymes.
When the fermentation is complete, the coffee is thoroughly washed with clean water in tanks or in special washing machines. At this stage the wet coffee parchment contains approximately 57% moisture which has to be reduced further by the drying process, this process is the same as described in the natural method.. After drying, the wet-processed coffee, or parchment coffee as it is commonly known, is stored and remains in this form until it’s hulled shortly before export.
