Semi-wet and wet processed beans are dried after processing. If this drying process is delayed, the beans can become sour and stink, or become infected by bacteria. Therefore, this step is extremely time sensitive and proper monitoring methods should be employed.
The beans are dried until 88% - 90% of the moisture is removed. Drying can be accomplished by spreading the beans out under the sun or in mechanical dryers. The dried beans are known as "parchment coffee", and are stored.
For sun drying, the beans are dried on a drying patio, a clean concrete yard, or on elevated tables. The drying area should always be free of foreign smells (such as smoke or petrol). Since the drying process takes from 7 to 15 days, the risk of rewetting coffee is high. Rewetting coffee beans can later turn into spongy, mouldy or blotchy beans. To prevent this, the coffee beans are dried in rows, and are frequently turned over. They are covered with canvas when rain threatens and also at night to prevent dew.
For mechanical drying, the temperature and moisture need to be monitored closely. A mere 1 C increase in temperature translates into a 2 - 5% reduction in the moisture content of the parchment. If dried at temperatures higher than required, the beans become crystallized. If dried for a prolonged period, they tend to become bleached and fragile. If insufficiently dried, the quality of the beans deteriorates rapidly during storage, and they are likely to become defective.
An article from Sally's Place
Specialty Coffee Association of America
The Coffee and Tea gourmet world
Holland by Mail