Coffee drying is the post-harvest last step before we get new lots into our warehouse. This process is crucial for maintaining the quality developed during fermentation and will help to preserve the coffee while it reaches the final destination.
We had an interesting conversation with Francisco Quezada, one of our producer partners and part of La Familia Microlot Series from Finca Vizcaya and Finca La Labor about different drying systems and their convenience for producers according to their volumes and quality.
Keep on reading, this might be a conversation piece to fully understand how your beans are being treated before they reach your roastery!
Drying Systems
According to Coffee Research, coffee must be dried from approximately 60% moisture content to 11%-12% moisture content. It takes between 12 to 20 days depending on the drying system and weather conditions. Francisco explains that he chooses the most convenient drying system based on volume and final quality.:
Raised Beds / Marquesina: this drying system consists of suspended wood frames with a mesh that holds the beans in order to avoid any contact of the mass of coffee with the ground. These raised beds are placed inside a greenhouse. While it does require some investment, this system protects the beans and is mostly used for microlots.
This method allows producers to measure different variables that help to take action in case one of them is out of the correct range. One way of measuring is by implementing a digital thermo hygrometer which tracks temperature and humidity and records when both variables were at their highest and lowest point. This becomes crucial information for producers and helps to create solutions in order to reduce humidity and temperature inside the greenhouse.
Additionally, as well as with the other drying systems, it is important to constantly turn the mass and let airflow run in order to control temperature and humidity increase.
Sun Drying / Patios: this has been the traditional system for countries like Brazil and large farms. This drying system relies completely on optimal weather conditions such as sun and low humidity. Additionally, some logistics are required such as constantly turning the mass in order to prevent mold in the coffee beans.
Mechanical Driers: known as Guardiolas and consist of rotary drums that allow monitoring temperature (no more than 38°C) and drying time. It takes from 2 to 3 days to dry coffee using this method and has been used for large amounts of coffee and standard quality. It is becoming a more consistent way of drying as producers can control certain variables without relying on weather conditions.
Variables
There are three crucial variables that help monitoring and controlling the drying process: temperature, airflow and humidity. Francisco explains that coffee should be dried at no more than 40°C in order to get a homogeneous drying. Additionally, the mass should be at maximum 25°C and this is where other variables such as airflow play an important role in order to keep the mass at a stable temperature.
Humidity might be a difficult variable to deal with as it depends on weather conditions. However, building systems such as extractors that help reduce relative humidity in close drying systems like with marquesinas is an efficient way of protecting the beans from mold.
Getting the right measurements of temperature and relative humidity also help to create drying curves that provide information about the evolution of the drying process which help to take action on how to prevent any damage to the coffee beans.
Interrupted Drying Process
This has become a common practice during the drying process specially for those super exotic coffees and microlots. It means that when the coffee beans have reached 15% moisture content it is stored for 10 to 14 days in order to homogenize and enhance the coffee attributes.
Sounds like a long process right?
This is what quality is about, taking care of every single detail that improves and keeps the physical and sensory qualities of coffee and finding strategies that keep improving the process in the long run.
Once the drying process has come to the end. Coffee beans need some stabilization time in good storage conditions. According to Francisco, coffee needs to stabilize for about 3 months before being milled. It will ensure that the moisture content and water activity will remain consistent on its way to the roasteries around the world.
Coffee drying systems vary from farm to farm based on production, infrastructure and quality. It is key to measure the variables involved that will help the producer adjust and improve the process and this way deliver a product of quality that will pass all the physical and sensory analysis at the lab.