Once the cherries are picked, the beans are removed and then dried. Processing involves separating the coffee beans from the cherry.
Removing the beans from the cherry can be done in several ways:
- Ferment-and-Wash Method
- Machine-assisted Wet Processing
- Dry Process
Ferment-and-Wash is used mainly at large coffee processing factories. On the farm, the crop was processed with the machine-assisted wet process. Cherries that were too small to be machine processed were rejected, then dry processed by hand.
To fully understand processing, you need to understand the parts of a coffee cherry. This illustration from Wikipedia shows the cherry anatomy.
Structure of coffee berry and beans:
- center cut
- bean (endosperm)
- silver skin (testa, epidermis)
- parchment (hull, endocarp)
- pectin layer
- pulp (mesocarp)
- outer skin (pericarp, exocarp)
Sections 1, 2 and 3 form the final green coffee bean.
When coffee is roasted, a paper-like peal is released that is referred to as chaff. This is the roasted silver skin (3).
Parchment (4) is a hard white shell covering the green bean. In this picture, I broke away part of the dried parchment (4) to reveal the green bean (1,2,3) inside.
The skin and the mucilage (5,6,7) are removed by the processing machine. The specific unit Matias uses is a Penagos Hermanos’ UCBE model 500. The Penagos company has a patent on the peeler, which runs vertically instead of horizontally. That characteristic, and the fact that there is a centrifuge that washes the bean makes this machine very effective and ecofriendly.
Penagos Hermanos was established as a Columbian company in 1892. In the 1980s, Penagos developed the ecologic wet coffee process plant called UCBE. The UCBE 500 can process up to 500 kgs of coffee cherries per hour using a 3 H.P. electric motor and water for washing.
This picture shows the UCBE at the plantation.
Cherries are poured into the top hopper (1). The cherry skin is cut and the beans squeezed out. The skins are routed to the red slide, where they drop into a waiting wheelbarrow (2). The skins are piled and composted for fertilizer. The cherries that are not split because they are too small are screened out and sent out the reject chute, falling into the reject bag (3). The beans still coated in mucilage are sent to a spinning grate where water is added to wash the beans. The spinning throws off the mucilage/water mixture, which is cast off to flow down the chute to the black holding tank (4). The washed coffee beans go into the bag (5), ready for drying.
Water and mucilage flow to the holding tanks where a two week long process with bacteria starts. By the time the water is sprayed on the property, the PH is back at 6.8 and the organic matter has practically been eaten up by the bacteria.
Cherry skins are collected for composting. In a regular operation, they will come out of the process mixed with the mucilage, causing an awful odor due to the low PH of the mucilage. In Matias’s process, the coffee skins are separated from the mucilage thus avoiding fermentation of the pile and the awful odor that is common in coffee processing.
Bacteria will also be applied to it and in a matter of 6 weeks, the volume of the composting pile will go down 80% and be ready to be applied to the coffee trees.
The front pile has been decomposing for a few days. A new pile is started for this batch. The black plastic is to cover the pile at night and keep it dry. It is off during the day so the sun hits the pile of peels and dries them up quicker.
Just-processed Wet Coffee Beans that have gone thru the centrifuge and are washed and ready to lay down under the sun to dry.
Processing coffee cherries