Is the Wet-Hulled Coffee Processing Method the Same as Washed Processing? What Are the Specific Steps of Wet-Hulling?

Introduction to Coffee Processing Methods by FrontStreet Coffee

In traditional washed processing methods, fresh coffee cherries have their pulp removed and are left to ferment in concrete pools overnight, undergoing acidification and pectin decomposition. Next, the parchment coffee beans are sun-dried for about 20 days until reaching 11% moisture content. They can then be packaged, with the parchment layer removed, and the coffee is graded by density and size, and manually sorted for export.

The green beans remain within the parchment layer, continuously "washed." Protected by the parchment, the green beans are placed in a relatively clean small environment that stabilizes moisture, mitigates diurnal temperature fluctuations, and reduces the impact of direct sunlight.

In washed processing, these beans are typically dried to 11% moisture content. The beans become what we know as dried green beans, with the thin parchment easily removed.

What is Wet Hulling?

So what exactly is wet hulling processing? What are the specific procedures?

Wet hulling, also known as Wet Hulling, is called Giling Basah in the local language and is a traditional Indonesian coffee processing method. Judging by name alone, wet hulling seems similar to washed processing, however, the cupping flavors of these two processing methods are completely different. Coffee processed using wet hulling is typically full-bodied and intense, with a very distinct character.

Wet Hulling Process

Because there is a significant space gap between the parchment shell and green beans, farmers sell their beans to local collection stations that buy wet parchment coffee when the beans reach their first drying stage at 35-40% moisture content. During the collection process, some beans are packaged in separate bags, others are mixed, resulting in varying moisture levels among the beans. This may be due to incomplete fermentation forms or partial mucilage still adhering to the parchment layer in a partially dry state. However, quality assessment is not performed when collecting the beans; they are all mixed and bagged together.

The beans with parchment are sun-dried for 2-3 days until reaching 20-24% moisture content, then processed through a specially designed wet hulling machine. This machine uses significant friction to tear away the parchment layer tightly attached to the green beans. During this stage, white or green mucilage typically flows out. Due to long-term mucilage soaking and humid conditions, the beans appear soft, pale and swollen, taking on a grayish-green color. Through the friction and agitation, they are easily crushed or bruised, especially at the ends, forming small gaps that create horsehoof or goat hoof beans (locally known as kuku kambing).

Final Processing

Before export, the hulled green beans are placed directly in courtyards, on tarps, or on roads for drying. Without parchment protection, the green beans dry very quickly, eventually reaching 12-13% moisture content. At this point, the beans exhibit a deep green or bluish-gray color. The beans are then sorted, bagged, and prepared for export.

Without parchment protection, the green beans are directly exposed to the environment and may be affected by environmental molds, yeasts, and bacteria. When directly exposed to sunlight, moisture evaporates rapidly, causing uneven drying with spots (which may further lead to inconsistent roasting levels when the beans are roasted). Excessive heat during the hulling process can also cause rapid aging of the coffee, leading to the woody, earthy flavors we often taste in Sumatran coffee.

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