In producing coffee, the drying process is just as important as the harvest. The fruits of Arabica coffee plants (known as cherries) ripen at different rates, thus varying the moisture content of the beans within. Caution must be exercised during the drying process to avoid compromising bean quality.
Although Arabica coffee is usually dried on terraces or in dryers, in the pursuit of higher quality, vertical dryers, horizontal/rotary dryers, and other technologies that use direct or indirect heat are growing in popularity. Learn more about the differences between each of these methods in the text below.
In terrace drying (also known as patio drying), coffee cherries are exposed to sunlight and wind over the course of 15 to 30 days, depending on the region of Brazil. In order to ensure even drying, the coffee must be “rotated” or stirred at least ten times daily.
To preserve bean quality, best practice guidelines advise against building terraces in humid places, such as near lowlands or close to bodies of water. In addition, they recommend spreading cherries out in thin layers during the first five days of terrace drying, when the cherries are very moist.
Terraces are usually built out of clay or cement, with cement preferred. The use of a suspended terrace, on which cherries are placed on material above the ground, significantly reduces drying time by allowing sunlight and wind to circulate throughout the cherries.
Once green coffee beans have pre-dried on a terrace, the use of mechanical dryers is a great way to reduce the remaining drying time.
Once cherries have gone through postharvest handling and attained the desired moisture content (between 11 and 12%), they are ready to be processed. Processing yields what we recognize as raw coffee beans, which are separated by type, quality, and size prior to storage.
Ensuring excellence during the drying process
Regardless of the coffee drying method utilized, it is important to avoid unwanted fermentation before and during drying as well as excessively high temperatures. Beans should be dried as quickly as possible to obtain the ideal moisture content. Above all, producers should strive for beans of a uniform coloring, size, and density.
The fruits from which coffee beans are obtained do not ripen uniformly—they ripen in waves—and it is important to avoid mixing unripe and ripe coffees. Coffee producers must draw up a plan that specifies the exact day of harvest, the machinery to be used, the number of people involved, and ensure that the terrace is properly cleaned and ready to receive the beans.
Coffee fruit is highly sensitive to weather and temperature variations. Whether on a terrace or inside a dryer, care must be taken to ensure that the cherries are not exposed to excess temperature or moisture. Prior to roasting, beans must have an adequate moisture content, as very dry beans tend to break, while very wet beans tend to ferment.
In conclusion, the drying process has a direct impact on the quality of Arabica coffee. The right technique has numerous potential advantages, including better harvest planning and longer storage without risking deterioration or loss in quality. The right technique can also prevent bacteria and pests; minimize product loss in fields or terraces during rainy periods; and, in the case of growing coffee for seeds, can increase the germination rate.