A Trip to the Wet Mill

High-quality, specialty coffees require special processing for the unique flavor qualities to come through in the cup. One aspect of processing is how the "cherry" pulp on the outside of the bean is removed. Wet-processing is the preferred method for many high quality coffee. In Africa, Kenya has a long history of producing washed coffees. Many other countries do not. This field visit took us to an established wet mill in Kenya.

The process starts with the farmer bringing their ripe (hopefully)cherry to the receiving station. Here, they weigh the load and the farmer gets a receipt for what was delivered.

From there it is dumped into a hopper. All of the hoppers, tanks and conveyance channels are arranged along the slope of a hill. This allows the system to be gravity-fed. With a bit of assistance from water here and there, it all flows down hill.

At the base of the hopper, a grinding machine forces cherries past grinding blades adjusted to strip the pulp and pass the bean. Most cherries contain two beans (except peaberries). The beans pass down these channels while the pulp is carried away for composting (hopefully).

While the pulp is stripped away, a thin layer of mucilage still coats the bean. It's that slippery stuff that prevents you from picking up a tomato seed. In this type of mill, rows of tanks hold the beans while fermentation breaksdown the mucilage.

After standing for the right length of time, the beans are "tested" to see when they are ready. One test involves prodding the heap with a stick to see whether the hole stands up when the stick is removed (sorta like a toothpick in the middle of a cake). Another, rubs beans between your hands to listen for a distinctive rasping sound.

Once "done," the beans are then released into washing channels. In addition to washing, these channels are used to sort tainted beans. Infected beans or those that did not develop properly are less dense, floating to the surface. "Floaters" are washed down the channel, allowed to float over the top of weirs. The denser high-quality beans sink. These beans are agitated counter-current in the channel to leave a clean bean, or parchment.

Parchment is screened at the end of the channel. Wet

parchment is carried to drying beds to air dry on screens in the sun. Dried parchment is then collected up and stored in the warehouse where it is bagged to await shipping.