"Wet Method" Expensive But Pays Off in Long Run

We will now turn to a description of the "wet method" for processing beans. The wet process requires a greater monetary investment and more care, but it better helps preserve the intrinsic qualities of the bean and causes less damage.

The main difference between the wet method and the dry is that in the wet method the pulp is removed from the bean almost immediately instead of allowing the cherries to dry first.

After the green coffee is picked, the coffee is sorted by immersion in water. Bad or unripe fruit will will float on the surface and good ripe fruit will sink to the bottom. The pulp is removed in a pulping machine that crushes the cherries. In order to preserve the quality of the beans, pulping has to be done as soon after harvesting as possible, ideally within 12 hours, but no later than 24 hours after picking. If the beans are left too long before processing, the pulpy flesh of the cherry becomes more difficult to separate from the bean.

According to Wikipedia, removal of the beans from the cherry in the wet method is accomplished via two ways: the classic ferment-and-wash method or a newer method called machine-assisted wet processing. In the ferment-and-wash method, the remaining pulp is removed by breaking down the cellulose by fermenting the beans with microbes and then washing them with large amounts of water. This process has to be carefully monitored to ensure that the coffee does not acquire undesirable, sour flavours. For most coffees, the process takes between 24 and 36 hours, depending on temperature, thickness of the rind and the concentration of the microbes. The final result is assessed by feel, as the parchment surrounding the bean loses its slimy texture and acquires a rougher, "pebbly" feel.
When the fermentation is complete, the coffee is thoroughly washed with clean water.

In machine-assisted wet processing, fermentation is not employed to separate the beans from the pulp. Instead this is accomplished by mechanical scrubbing. This process can cut down on the use of water and is thus more environmentally friendly. It can however affect the flavour of the coffee adversely, since the fermentation process is eliminated. Wikipedia further adds that the ecological argument has been rendered "moot" because newer machinery in the ferment- and-wash method has also cut down on the use of water.

After the pulp has been removed through one of these two described methods, the remaining rind and parchment is removed in the "hulling" process. Coffee is occasionally shipped without the hulling process having taken place, but most often a machine called a huller is used to crunch off the parchment skin before the beans are shipped.