Coffee Production and Trade

Coffee processing

Coffee drying

Sun-drying of parchment coffee using 'elbas' - Colombia

Wet parchment coffee has a moisture content (m.c.) of approximately 60%, and fresh cherry coffee is obviously higher. The optimum m.c. coffee beans must be dried to is 12.5%, the maximum level recommended by the International Coffee Organization.

From the perspective of OTA reduction, and product quality, the drying step (for both dry and wet processed coffee) is one of the most critical. The main aim is to minimise the time the drying coffee remains within the window of opportunity for fungal growth and OTA production, and to avoid the rewetting of the product (by either dew or rain).

Drying methods basically consist of sun-drying and mechanically assisted drying, or a combination of the two. There is a large variety of drying equipment designs that can be used (including solar dryers, raised mesh tables, drying patios, hybrid drying terraces, and drying ovens and silos). The drying process must be carefully controlled to ensure satisfactory drying without damage to quality. The various advantages and disadvantages of drying methods and associated equipment are discussed in more detail in Section 3 of the training tool 'Good Hygiene Practices along the coffee chain'.

'Hybrid' drying terrace - Brazil

It can take up to four weeks to dry cherry coffee and approximately eight to ten days to sun-dry parchment coffee, though these times will vary according to prevailing ambient temperatures and humidity. As indicated above, the faster drying to 12.5% m.c. occurs, the better.

From an OTA reduction perspective, coffee drying yards should have adequate capacity, smooth drying surfaces, good drainage provision, and full exposure to sunlight. Drying coffee should be covered overnight, and whenever rain is likely, to avoid re-wetting. Equally, any machinery used for drying should be subject to regular maintenance and inspection to ensure that the risk of fungal growth is minimised.