Washed coffee is distinguished by the clarity of the flavours and attributes that it can achieve. This clarity need not suggest timidity, as the best washed coffees combine nuance and complexity with great intensity. Clarity should also not be regarded merely as simplicity. Rather, it is exactly the transparency of wet processed coffees that allows for perception of the remarkable complexity of acids and other compounds present in the coffee beverage- complexity that is frequently masked in alternately processed coffees.
During this process, the sugars present in the mucilage are removed through natural fermentation or mechanical scrubbing. Fermentation can be done by stacking the coffee outside or placing them under water and allowing nature to take its course. After the sugars are removed, the beans then can be taken through a secondary washing to remove any additional debris, or taken immediately to the patios or beds for drying.
During wet processing, the pulp (i.e.the exocarp and a part of the mesocarp) is removed mechanically. The remaining mesocarp, called mucilage, sticks to the parchment and is also removed before drying. Hulling of dry parchment coffee leads to green coffee.
Mucilage is insoluble in water and clings to parchment too strongly to be removed by simple washing. Mucilage can be removed by fermentation followed by washing or by strong friction in machines called mucilage removers. Fermentation may be natural or accelerated by chemicals or enzymes. Mechanical mucilage removers operate by rubbing parchment beans against each other and against the mobile and static parts of the machines.
Fermented coffee can be washed manually in the [fermentation] tank itself or in channels, by centrifugal pumps or by several types of specific machines.