The Amorphous Gel of mucilage around the bean consists of hemicelluloses, pestic substances and sugars and is soluble in water. It can therefore be removed by use of chemicals, warm water or by an Agua Pulper.
For small scale units, fermentation is the most feasible. Fermentation involves the beans being placed in plastic buckets or tanks and left until the mucilage has been broken down. Natural enzymes in the mucilage and feasts bacteria in the environment work together to break down the mucilage. The beans should be stirred occasionally and a few beans tested by washing them in water. The beans are ready when the mucilage can be washed off and the beans feel gritty.
After this, the wet processed beans are dried to prevent cracking and this should be done slowly to 10% moisture content level and similar drying methods can be used for this as for the dry processed coffee.
After drying, the coffee should be rested for 8 hours in a well ventilated place and the thin parchment around the coffee removed by hand, pestle and mortar or in a small huller.
- Mainly for Robusta coffee although it can also be used for Arabica coffee.
- It involves the freeing of the wet parchment of mucilage at moisture contents of 50 – 60 % to the required 12 % to ensure their conservation.
- Dry processing involves coffee cherries drying either by the sun (solar drying) on raised stands or on mats or in solar driers immediately after harvest.
- The bed depth should be less than 40 mm in case of open drying and 30 mm for solar driers and the cherries should be raked frequently to prevent fermentation or discoloration.
- Care should also be taken to prevent dust and dirt blown onto the produce as well as preventing damage from unexpected rainstorms that can soak the produce very quickly without warning.
- Investment in solar driers helps overcome this problem.
After coffee drying, HULLING commences. This is the removal of the pericarp either by a pestle and mortar or in a mechanical huller. The mechanical hullers usually consist of a steel crew, the pitch of which increases as it approaches the outlet so removing the pericarp.