Traveling to Sumatra – The Wet Hulling Process

After experiencing the farm and seeing how coffee is picked, we followed the newly bagged cherries to the Jagon Mill in the Takengon region of Sumatra.

Tarantulas Everywhere!

The next step in the process takes place 5,000 feet above sea level and, as we walked breathlessly upward, we spotted palm-sized black and yellow tarantulas lining the gates and branches of the trees. We picked our way past the arachnids and continued on until we smelled an unusual funk in the air. When we arrived, I learned this was the unmistakable aroma of the fermentation process.

Once the cherries are picked, it is imperative that they are processed as quickly as possible to prevent spoilage. Coffee is processed in two different ways, depending on local resources: dry or wet. In Sumatra, most of the local farmers use the wet hulling method, where beans pass through water channels that separate the ripe beans from the unripe. The ripe beans sink to the bottom while the unripe float to the top. The cherries then enter a de-pulping machine which removes the outer husk, leaving only the parchment (a paper-like skin surrounding the bean).

After they are de-pulped, they are placed into fermentation tanks where they remain anywhere from 12- to 48-hours to remove a thin, slimy layer known as mucilage.

Beans in the fermentation tank.

The time varies based on different conditions, such as altitude, ambient humidity, and the temperature of the water being used.

At this point, the beans have only a wet parchment layer left, and are spread out to sun-dry for a couple days, at most. The humidity and high chance of rainfall forces the farmers to make the drying process as fast as possible. The beans are periodically raked in order to assure they are drying evenly and once they drop to a moisture level of 20-23%, they are placed into a hulling-machine. This large and loud machine removes the remaining wet parchment layer in a process known as wet hulling. The bean’s parchment is removed to quicken the drying process (three times as fast) thus reducing the chance of spoilage due to excessive exposure to moisture.

The dry process, less common here because of the natural moisture, is less manual than the wet process and typically involves only three steps instead of five. The beans are picked, laid out to dry, and then dry hulled. This is also referred to as the “natural” process which creates an entirely different coffee than that of Sumatra. Dry-method beans are often called “naturals.”

During the wet hulling process, the delicate, still-moist beans can easily split towards the top, which is so common that the farmers have given it a name: “kuku kambing.” This is also known as goat’s nail because of the resemblance.

Once this is complete, the beans are laid out to dry once more until they reach a moisture content no greater than 11 percent, and are then bagged and set inside to rest. If these beans do not move from the mill after the process is complete, they mold and rot due to the high humidity.

This entire wet-process is one of the biggest factors why we travel half-way around the world to obtain these unique beans. This process, with each step we discussed, is what provides the incomparable richness and body of the Sumatran coffee.


Children play near the mill.

I will never forget all the steps and hard work that goes into quality Sumatran coffee, not to mention the time it takes to travel from one place to another on “roads” – more aptly called mud trails – that are just a string of potholes that even a Donkey would have difficulty passing over. I must give the farmers credit for the incredible feat they perform to bring us this unique cup of coffee that comes from only one place in the world.

Leave a comment

Subscribe Scroll to Top