Designing a Modern Wet Mill

Combining Technologies For Consistency, Quality, and Efficiency by Alec Lee


The GCC’s vision of an integrated production model at scale requires us to look for new ways to approach coffee production. From this perspective, our team saw an opportunity for innovation in the wet mills by implementing technology that promotes more efficient and more consistent post-harvest processes. Multiscan technology borrowed from the olive industry combined with the latest wet mill machinery and automation will allow us to process 30,000 kg of cherries per hour and separate lots according to quality and origin, providing full traceability from the farm level up. Construction is under way on our two primary wet mills and should be completed before the main harvest begins this fall.

Our president, Boris Wüllner, was heavily involved in the design process, and his goal was to design a state-of-the-art wet mill that would give the GCC team maximum control over the post-harvest process while using less water, energy, and manpower. Few, if any, producers in Colombia operate such wet mills, so Boris looked to modern Brazilian producers as well as Spanish olive producers, who have already shifted away from traditional machinery, for inspiration. 

Creating an energy efficient, quality focused wet mill required coordination between our team, the architects, and the producers of the individual technologies that we sought to integrate.

Let’s start from the beginning: when cherries arrive at a wet mill via cafeductos or a truck, they are typically washed and go straight to the depulper. In our beneficios, the cherries are first rinsed for cleaning and to remove floaters. Cherries are then sent through a multi-scanner that sorts by 5 sizes, 3 colors (from ideal ripeness to unripe or overripe), and a minimum density. Unripe, small, and low density cherries are separated and processed apart as low quality coffee, or corriente. Multiscan initially developed this technology for large scale olive producers in Spain, but they have successfully adapted it to process coffee cherries and a number of other agricultural products.

Introducing the multi-scanner at the beginning of the wet mill process flow creates a high degree of separation by quality and yields a consistent and clean final product in the form of dry parchment.

Boris Wullner explaining the multiscan machine.
Boris Wüllner, GCC president, was heavily involved in the wet mill design process. His goal was to make sure the GCC team has maximum control over the post-harvest process while using less water, energy, and manpower.

After sorting, the streams of cherries move through five size-adjusted depulpers that minimize the number of seeds damaged and cherries not depulped (due to small size). Coffee is moved to the delpupers and through the rest of the wet mill on conveyor belts. No water is used to move cherries between processes, as is typically done in traditional beneificios

Our water consumption will decrease 79% overall, dropping from 14 liters of water for every kilogram of dry parchment produced to 3 liters of water.

Stainless steel fermentation tanks of different sizes will allow us to produce our Estate coffees with a standard 12-hour fermentation, as well as varying “recipes” to highlight the profiles of different varieties or processes. When ready, coffees are quickly blasted with high pressure water to remove any remaining mucilage before entering the two-stage drying process.

Vertical silos efficiently lower the humidity level of the parchment to around 25% in around 8 hours, however they are not well designed for even drying down to the ideal 11%. For consistent water activity levels and uniform humidity through each coffee seed, horizontal tumblers are far superior. The two part drying process will take place over 24 hours at 45℃ (115℉).

In addition to the latest processing technologies, both facilities will be automated. A control panel will allow our beneficio manager to adjust processes as needed in real time, but the wet mill will operate seamlessly when left alone. This means our team can focus its attention on the details and continue our journey towards perfecting our coffee and modernizing Colombia's coffee production.

Expect further news from the GCC team come harvest time, as we put our wet mills to use during the peak months of production. We’ll dive deeper into the sustainability and quality implications of the facilities as soon as they are operational. Until then, we’d appreciate any comments or questions you have regarding the wet mill process or the technologies described here. Email us at [email protected].