November 24, 2020

A Guide To Coffee Drying

No matter how a coffee is processed, at some point, it will need to be dried. For washed coffees, drying takes place after the cherries have been depulped and their mucilage has been removed. For honey processed coffees, drying occurs while part or all of the mucilage is still present on the parchment; with naturals, the coffee is still dried with both its fruit and mucilage.

Coffee is dried in two main ways. The first is by spreading beans out under the sun on raised beds or patios. The second is by using dedicated mechanical coffee dryers. To learn more about coffee drying and to discuss these two methods, I spoke to Bruno Ribeiro from Pinhalense and Iliana Delgado Chegwin from Azahar Coffee. Here’s what they had to say.

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Coffee drying

Rotary dryers in Lampung, Indonesia

Coffee Drying: An Overview

Coffee drying is a post-harvest process that generally preserves coffee quality rather than improving it. Washed, natural, and honey processed coffees must all be dried at some stage of processing.

There are two main factors that contribute to how a coffee dries: temperature and airflow. Over time, these reduce the moisture within the green coffee.

Throughout the drying process, it is important to keep in mind the temperature limits for each type of processing method; coffees in parchment should not be dried at temperatures higher than 40°C, while naturals should not be dried above 45°C. It is also recommended that the producer keeps temperatures a constant level for certain periods of the drying phase.

Moisture levels should also be monitored to avoid mould developing within the beans. Moisture levels before drying will be between 40 and 50%, and should be reduced to anywhere from 11 to 12%. 

When mechanical dryers are used, coffee will generally be pre-dried under the sun to some extent. Dryers will then be used to complete the process with greater precision and accuracy.

Coffee drying is also one of the longest processes in the post-harvest stage of production, and as a result, it is a major bottleneck point. Drying timelines vary depending on a number of factors, including weather conditions and processing method.

When dried only in the sun, washed and semi-washed coffees will take less time to dry (six to nine days) while natural and honey processed coffees will take longer (10 to 14 days).

While heat and airflow are the two major factors that influence how coffee dries, it is also important to focus on how well moisture can escape from the bean. Bruno Ribeiro manages the North American, Europe, and African markets for Pinhalense. He says: “If you’re drying in humid environments where moisture can’t escape, then the coffees will not lose moisture.”

When coffee beans dry in the sun at scale, humidity is a significant concern. It can delay the drying process and lead to inconsistent moisture levels within a batch of green coffee. However, in mechanical dryers, such as those sold by Pinhalense, the drum is perforated, which allows moisture to escape.

Iliana is the Relationship Manager at Azahar Coffee. She works closely with the team at Finca Isabelita in Sierra Nevada de Santa Marta, Colombia. She says: “Sun-drying is typically limited to very small lots where space and capacity permits.”

However, with newer, smaller-batch rotary dryers and a range of drum sizes on the market, even micro lot coffee production can benefit from mechanical dryers.

Coffee drying

A dryer with a husk feeder in Yunnan, China

Drying Coffee Under The Sun: What Are The Risks?

The risks of sun-drying coffee include uncontrolled fermentation, animal contamination, improper manual drying, and adverse weather conditions, all of which can have a major impact on cup quality.

Uncontrolled fermentation may occur when coffee is not dried quickly enough, as microorganisms break down compounds within the coffee and generate undesirable flavours. Animal contamination includes larger wild animals causing physical damage to the beans and animal droppings (such as those from birds) falling among the drying coffee. Finally, improper manual drying occurs when coffee is not turned properly, leading to uneven exposure to temperature and airflow.

Bruno adds that fluctuating weather is another challenge that affects coffee producers who dry their coffee outdoors. “When coffee is sun-dried, it’s usually not drying at night or in the early hours of the morning,” he says.

“[By] using a drying-patio, producers run the risk of [exposing their coffee] to rollercoaster weather conditions.”

Ultimately, sun-drying relies on consistent heat and low humidity without adverse weather conditions or precipitation. In periods of heavy rainfall, producers may face delays or risk the quality of their coffee (which could cause them to lose at least a year’s worth of hard work).

On the other hand, when temperatures rise, producers run the risk of their coffees overheating and decreasing in quality as a result, especially if they are not frequently turned.

While overheating is a common risk that is associated with mechanical drying, many modern rotary dryers come equipped with internal thermometers or drying control systems, which allow the user to set a maximum temperature and avoid overheating coffee in the drum.

Iliana says: “Sun-drying can be difficult if producers are not in areas where flat spaces [are available] for coffees to be laid out.” Along with taking up more space, she says that sun-drying generally takes longer, and is more likely to cause a bottleneck.

“It can cause labour delays in picking, [which] can also cause cherries to fall off the tree or become overripe, and so on.” As a result, mechanical dryers are useful for producers who have limited space, and can also improve overall farm productivity by saving more time.

“Mechanical dryers have been overlooked and underestimated due to their historical use for commodity coffee,” Iliana adds. However, she says that the advanced technology available in modern mechanical dryers offers new advantages for specialty coffee producers.

Coffee cherries drying on raised beds

Mechanical Dryers: An Overview

The three main advantages that mechanical dryers have over drying coffee in the sun are removing uncontrolled environmental variables which may affect coffee quality, improving accuracy, and minimising delays. 

Furthermore, as mechanical dryers protect coffee against all types of weather, they can also help to combat producers’ anxiety about drying during adverse or unpredictable conditions.

One of the most important features of many modern rotary coffee dryers are drying control systems. These systems offer producers the ability to manage the temperature through three separate variables: the heat source, the air, and the coffee.

By doing so, drying control systems offer producers more control throughout the drying process. Some systems even allow producers to create “drying curves” that interrupt the dryer before it reaches a maximum designated temperature.

“With mechanical drying, parameters such as time and temperature can be controlled,” Bruno says. He explains that this additional control means more consistency in quality, and fundamentally less risk in the drying process.

“In the long term, [mechanical dryers] allow producers to maintain consistency harvest after harvest. [As a result], they will continue to secure loyal buyers who seek out consistent, high-quality coffees.”

While mechanical dryers do require an investment in both equipment and fuel, these costs can be offset by the time and money that producers save in labour.

Bruno adds that this saving can actually lead to farmers improving their productivity and profitability. ”By reducing the drying time and using less labour to revolve the coffees, producers will have more labour time available to harvest and process.”

He adds that for producers who are able to hull their own coffees, mechanical dryers even offer new options for farmers to use some of the byproducts of their crop. Both parchment and coffee husk can be used as fuel for the dryer, or as fertiliser thanks to their high levels of potassium.

Finally, Bruno tells me that some Pinhalense rotary dryers also come equipped with an overhead silo. These, he says, can be used as a pre-drying alternative to minimise the risk of uncontrolled fermentation and optimise the use of spare energy. 

Two small batch dryers in El Salvador

While drying coffees on raised patio beds may still be a suitable option for many coffee producers, mechanical dryers offer a number of different advantages. Technologies such as drying control systems provide the producer with more accuracy and precision throughout the drying process.

Rotary dryers have historically been associated with drying large batches of commercial or commodity-grade coffee. However, today, innovations in mechanical drying mean they can also be suitable for specialty production.

Enjoyed this? Then read Tips for Protecting Coffee During Drying & Storage

Photo credits: Pinhalense

Feature photo caption: Washed coffee on beds at the Balanoor Plantations, Chikmagalur, India

Please note: Pinhalense are a sponsor of Perfect Daily Grind.

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