Wet processing, whereby the beans are washed, is mainly employed in Central America and parts of Africa (notably Kenya). This process is relatively expensive, but is beneficial to the quality of the coffee. The berries are first fed through a water channel to soak them and to remove any impurities. The unripe berries sink to the bottom, leaving the ripe fruit to float to the top.
The ripe berries can then be processed further. The fruit flesh of the berries is removed with the help of a ‘de-pulper’, a machine that has a roller with a roughened surface. This scours away the fruit flesh (pulp) from the berries under a stream of water. Previously, the remaining pulp was treated as waste, but nowadays it is blended with minerals and turned into fertiliser.
In the second stage of wet processing the coffee beans are fermented in large water containers. The object of the fermentation process is not only to dissolve any remaining fruit flesh, but also to remove the sticky film surrounding the coffee beans, which is not water soluble. This part of the procedure, which lasts approximately two days, is very important. The long period of fermentation is what first gives the coffee its rich aroma and special flavour.