Before shipment, the coffee is dried and a coffee moisture meter is used to measure the moisture content of the coffee beans. Coffee should be dried from about 60% humidity to 11-12% humidity. The coffee is usually dried on large terraces of asphalt or cement and then transferred to mechanical dryers. The coffee in the drying terraces is moved every 30-40 minutes and is shaped in long rows no more than 5 cm high. Next to each row is an open field, which is heated and dried by the sun. Then the coffee is moved to the dry part of the terrace, and the section where it was previously is now left to dry in the sun. This helps to speed up the drying process of coffee and prevents the development of fermentation and moldy beans.
This method is widely used in Brazil, but less used in Guatemala or Costa Rica, where coffee is more often stacked perpendicular to the old piles. Drying coffee only on the terrace takes 6-7 days for washed coffee, 8-9 days for natural pulp, and 12-14 days for natural coffee. This is why coffee beans are usually dried on a patio until they reach a moisture content of 15% and are then transferred to mechanical dryers. Once the coffee reaches a moisture content of 25% or less, it can be piled up at night and covered with cotton cloths to allow the coffee to breathe. If it rains, these piles can also be covered with plastic. Coffee should not be covered with cloth bags, as this will give a distinct aroma and aroma of coffee.
Coffee Drying Stages
In a study conducted in Kenya, Kamau reports that there are six stages of coffee drying.
- Skin drying. Moisture 55-45%.
- White Stage drying. Moisture 44-33%.
- Soft Black stage. Moisture 32-22%.
- Medium Black Stage. Moisture 21-16%.
- Hard Black Stage. Moisture 15-12%.
- Fully dry coffee and conditioning. 11-10%.
In this study, he found that sun-drying coffee for the third stage is mandatory for coffee quality. As long as the temperature was between 40-50 °C, which means a bean temperature of 35 °C, then the quality of the coffee will not be severely compromised during the other stages of coffee drying.
The last two stages of coffee drying (15-11% humidity) last only six hours at 40 °C in a mechanical dryer.
Coffee Drying Equipment
There are several coffee dryer systems available. Many older dryers are converted grain dryers that are not as efficient as the new horizontal barrel dryers. The new coffee dryers are designed to mix the coffee evenly to ensure even drying. Drying coffee using mechanical dryers accelerates the slowest part of the coffee drying process and helps prevent fermentation. In some environments with high humidity, the whole drying process must take place in mechanical dryers. Mechanical dryers should never be set at temperatures above 40-45 °C and this question should be asked before buying coffee that has been mechanically dried. At higher temperatures, the germ is killed and the aroma potential of the coffee is destroyed. At extreme temperatures the grain crystallizes and, when crushed with a hammer, will break like glass.