What is done with the skin and mucilage from the coffee cherry is what determines or defines the processing method.
The wet, or washed process is a method of removing the mucilage from the cherries using water in one of two possible ways:
- The cherries can be mechanically de-pulped to remove the skin and some mucilage and the beans are then fermented in water tanks to remove the remainder of the mucilage, or
- The cherries are processed by an aquapulper, which mechanically removes the mucilage without the need for fermentation.
Here is a video of an aquapulper in action:
The fermentation process is one way to affect a coffee’s flavor at origin. Doing it right can add a bit of lively acidity and even a hint of wine-like attributes like floral and fruity aromas and flavors to a coffee. Doing it wrong can make the ferment flavors and aromas dominant, even overbearing and unpleasant. Fermentation done properly is one way a mill or washing station can add uniqueness, and thus value to the end product.