Beneficio, Systems Explanation: Solar Dryers

Once coffee is fermented and washed, it must be dried from 46% humidity down to 11%, at which point it is stable to be stored for long period of time. If this drying doesn’t begin within hours of washing, the high humidity levels can cause the coffee to develop off flavors and ruin it. At the beneficio, we will be using solar dryers for this drying process.

When people hear the words “solar dryers” they often think of solar panels, moving parts, or engines; however, solar dryers use the sun’s energy in a much more direct way. Solar dryers look much like small greenhouses, with shelves inside of them to dry coffee. They provide protection from wind and rain, while concentrating the sun’s energy into a force to dry the coffee.

Solar dryers concentrate the sun's energy to dry coffee

Other than solar dryers, there are two main forms of coffee dryers. The highest volume form is mechanical dryers, which load approximately 22,000 lb of coffee into an elevator system and heat coffee by burning wood or coffee shells. The other is patio drying, in which coffee is spread into thin layers on a cement patio.

There are two reasons that we are using solar dryers instead of these other two options: quality and environmental sustainability.

We are configuring our solar dryers to dry coffee in 7-10 days, as opposed to the 4-6 days of patios or the 24 hours of mechanical dryers. High temperatures created by contact with hot cement or passing near the flames of mechanical dryers are damaging to the structure of the coffee bean, lowering the quality. Additionally, coffee is never placed on the ground using our solar dryers. Patios, which must be used for a short amount of time even when mechanically drying coffee, are frequent hosts to trucks, children, dogs, chickens, pigs, and anything else that may be in the area. Finally, there is no way to bring coffee that is on a patio under shelter quickly in the case of a rain storm, and rewetting coffee even slightly can completely ruin the quality. Mechanical dryers cause great physical stress on the coffee—not only because of high temperatures but also because of the large impacts that happen as the coffee falls almost 40 feet from the top of the dryer to the bottom.

Patio drying coffee takes large amounts of space
and dries coffee on the ground, where it is often walked on and driven over

Our second reason for using solar dryers is that they are an important part of making an environmentally sustainable beneficio. Drying patios require extremely large amounts of space and, therefore, a very large amount of cement. Due to the large area necessary, drying patios also represent a reduction in arable land. By installing solar dryers, we are keeping the land surrounding the beneficio available to grow off-harvest plants (from new coffee seedlings to nitrogen fixing beans to hardwood trees to plant in farms).

Mechanical dryers have a tall column (blue in picture) with
large furnaces to heat coffee (silver in picture)

Mechanical dryers, on the other hand take up a relatively small amount of space but require large amounts of energy input. First, they require electrical energy to consistently move the 22,000 lb of coffee inside them. Second, they require large fires to create the temperatures necessary to dry coffee. This requires the use of wood, causing deforestation; or coffee shells, which could otherwise be used to make organic fertilizers; and the burning of either of these produces carbon dioxide which is then released into the atmosphere. Once built, solar dryers require no input other than one person to move coffees every 30 minutes.

We installed our first of four solar dryers in a joint training session with IHCAFE, UMF clients, and members of the COCAQUIL Coffee Cooperative. The other three will be installed in coming weeks as we prepare to ramp up processing at the beneficio.

So there you have it—solar dryers.