Wet-Hulled (aka Semi-Washed, Sumatra Process, Giling Basah)
Fruit Removal: Coffee is generally depulped within 24–48 hours; mucilage remains on the seeds until it is purchased by a collector and/or delivered to a mill
Fermentation: Occurs in the coffee from the moment it is picked, and is accelerated during the piled or sack phase, will continue until the coffee is completely dry to 11% moisture for export.
Drying Time: 12–15 days
Profile: Earthy, savory, herbaceous, heavy body, dark chocolate, nutty
Areas of Indonesia,—including Sumatra, where it is best-known—are famous for this rather specific and flavor-altering processing method, which is vastly different from other commonly used styles. Broadly speaking, the Wet-Hulled process is a result of a combination of environmental conditions, market access, and traditions found in Indonesia which sets these coffees apart from the rest of the world.
The process can be simplified to a set of peculiar and particular steps: After harvesting, the coffee is often depulped in small machines on-site at a farm or household, and then the depulped seeds are stored in plastic tanks or jute sacks to await delivery to a collection point. (Sometimes cherry is delivered to the mill instead, depending on the producer’s available resources.) While in these containers, the mucilage is available for microorganisms to begin to metabolize the sugars, acids, moisture, and other compounds in the mucilage, which remains clinging to the seeds. The coffee is then delivered at high moisture to a market, collector, or receiving point, where it is purchased and then transported and/or sold to a mill for hulling. At this point, the coffee is typically between 35–50% moisture—quite a bit higher than the 10–12% moisture at which most coffees are hulled. The mucilage and parchment layers are removed simultaneously using specialized machines, and then the coffee is typically laid tarpaulins for drying.
It is important to recognize that while it is parchment coffees that are typically spread to dry in other producing countries, it’s what we call “green coffee” that is dried in the Wet-Hulled process. Removing the protective parchment layer so comparably early in the process creates not only the very distinct flavor profile from these regions, but also adds a bit of risk, as the seeds themselves are more vulnerable to environmental factors (such as rising and falling relative humidity) and other interference or taints (animals, for instance, or dirt and debris). However, part of the effectiveness of Wet-Hulling, or Giling Basah, is the rapidity of drying after the coffee is hulled: The damp climate and cloud cover over Sumatra can render other drying methods difficult or inviable for commercial production. Wet-Hulling also allows producers and mills slightly more flexibility when it comes to selling and delivering their yield, which is especially significant to smallholder farmers in rural, remote areas.