The coffee pulp is obtained either by subjecting fruit to a depulping operation using water, or by first drying it, followed by a dehulling operation.
For the wet process, after harvest, the coffee berries are transported to the coffee processing plant, where they are dumped into a tank of water to remove spoiled, green fruits and foreign material. With the help of water, used as a transport mechanism, the berries are taken to the pulping machines that by pressure separate the beans from the coffee pulp. Running water moves the beans into a fermentation tank that removes the remaining mucilage and allows further processing. The coffee pulp is transported by water to be stock-piled for later removal or simply allowed to ferment naturally. Coffee pulp can be used as a feedstuff or as an organic fertilizer to be applied to coffee trees (Bressani, 1991).
The dry process consists in either allowing the fruit to dry on the trees, or by harvesting fresh fruit and drying it. Once it is dried, the fruit is dehulled. The high water content of the pulp from the wet process causes problems in handling, transport, stability and processing. For feed applications, the pulp should be dried as quickly as possible to avoid spoilage, or should be preserved, e.g. by ensiling. The wet coffee pulp is subjected to a drying operation with or without partial water removal, by pressure, with or without the addition of calcium hydroxide. Drying is accomplished by solar dehydration, by forced hot air-drying, or a combination of both. The product obtained is dried coffee pulp (Bressani, 1991).
An alternative process is ensiling with 4-6% sugar cane molasses. Although fresh coffee pulp can be directly ensiled, better quality is obtained if the moisture content is around 75%. A well-packed trench silo holds an average of 325 kg of coffee pulp per cubic metre. Additives, such as urea (10%), sodium metabisulphite (0.3-0.5%), calcium hydroxide (2%), and mixtures of inorganic acids (10% HCl + H2SO4), can be included. A different and attractive ensiling process is to mix grasses, sorghum or corn, with coffee pulp in layers of about 30 cm with or without sugar cane molasses (4-6%). The silage, whether of coffee pulp alone, or mixed with grasses, is ready to be used in about 3 weeks and if well packed, it can be preserved for up to 18 months. The silage from coffee pulp alone or mixed with other forages can be used as it is, or it can be dehydrated (but this operation is not necessary)(Bressani, 1991).