The Difference Between Wet Hulling and Wet Processing - Why Use Wet Hulling for Mandheling Coffee Beans?

This guide explains how wet hulling differs from standard wet processing, walks through the wet-hulling steps, and looks at why Indonesia relies on it - including the climate and economic reasons, plus the defects it can create.

Are Wet Hulling and Wet Processing Methods Similar Yet Different?

In traditional wet processing, fresh coffee cherries are pulped and left to ferment overnight in concrete pools, undergoing acidification and pectin decomposition. Next, the green beans are dried in the sun with their parchment still on for about 20 days, until they reach 11% moisture content. They can then be packaged, the parchment layer removed, and the coffee sorted by density and size and hand-graded for export.

During this stage the green beans keep "washing" inside the parchment layer. Protected by the parchment, the beans sit in a relatively clean microenvironment that stabilizes moisture, moderates the day-to-night temperature swings, and softens the effects of direct sunlight.

So far, wet hulling and wet processing are basically the same.

As noted above, in wet processing, beans in this state are typically dried to 11% moisture content. The green beans become what we know as dry green beans, with thin parchment that comes off easily.

Next, you see the other side of wet hulling.

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 the name alone, wet hulling sounds similar to wet processing (washed), yet the two produce distinctly different cup flavors. Coffee processed by wet hulling is typically full-bodied and intense, with a very distinct character.

Because there is considerable space between the parchment shell and the green beans, farmers sell the beans to local collection stations that buy wet-parchment coffee when the beans first reach 35-40% moisture content. During collection, some lots are bagged separately and some are mixed, so the moisture content of the green beans can vary. Either the fermentation is incomplete or mucilage still partly clings to the parchment in a semi-dry state. In any case, no quality assessment is made when the green beans are collected; they are all mixed and bagged together.

Dried in the sun with the parchment for 2-3 days until they reach 20-24% moisture content, the beans then pass through a specially made wet-hulling machine. This machine uses heavy friction to tear away the parchment layer still tightly attached to the beans. At this stage a white or green mucus typically flows out. Because of the long mucilage soak and the humid conditions, the resulting green beans are very soft, pale, and swollen, taking on a gray-green color. The friction and stirring crush and squeeze them easily, especially at the ends, forming small notches that create "horseshoe beans" or "goat hoof beans" (locally called kuku kambing).

Before export, the hulled green beans are spread directly in courtyards, on tarps, or on roads to dry. Without the protection of parchment, they dry very quickly, finishing at 12-13% moisture content. At this point the beans look dark green or blue-gray. They are then sorted, bagged, and made ready for export.

Without parchment, the green beans are exposed directly to the environment and can be affected by molds, yeasts, and bacteria. Under direct sunlight, moisture evaporates fast, causing uneven drying with spots (which can further lead to inconsistent roast levels). Excessive heat during hulling can also age the coffee quickly, producing the woody, earthy flavors we often taste in Sumatran coffee.

Wet Hulling Processing Steps

Remove skin and pulp, keeping parchment and mucilage

Pool fermentation

Wash away mucilage

Sun-dry with parchment for 2-3 days until reaching 20-24% moisture content

Hull off the parchment

Dry green beans to 12-13% moisture content

Prepare for export

Why Use Wet Hulling?

Climate Reasons

Indonesia's wet-hulling tradition has to be understood against local weather. Humidity stays between 70-90% year-round, typhoons are continuous, and in some regions annual rainfall can reach as much as 2,000mm. Green beans fear rain most of all, so how does Indonesia overcome such harsh conditions to produce rich, full-bodied Mandheling coffee? That is where wet hulling comes in.

Under tropical conditions, coffee takes an average of 2-3 weeks to dry. In Indonesia's especially humid climate, drying becomes a major problem: it has to take longer, and during that time the coffee holds more moisture, letting bacteria penetrate the green beans more easily. In ordinary washed processing, drying is done with the parchment on to protect the beans from external damage. But wet hulling removes the parchment for the final drying step, letting sunlight hit the bean surface directly so the coffee dries quickly - 2-3 times faster than washed processing.

Economic Benefits

Dutch colonists first introduced coffee to Indonesia in the 17th century. These colonists wanted faster, bigger economic returns. Wet hulling greatly reduced time spent on farms and significantly lowered labor costs. That fit the investor mindset of chasing quick profits and cutting costs, and it is another driving force behind wet-hulling processing.

Defects and Kuku Kambing (Goat Hoof Beans)

When wet hulling removes the parchment, the coffee's moisture content is still as high as 20-24%, whereas in general processing the moisture is reduced to 10-12% before hulling. In this "semi-dry" state, the parchment tends to stick to the bean surface, making hulling harder than "fully dry" hulling and requiring greater friction. On the other hand, "semi-dry" green beans are very fragile, far softer than "fully dry" beans, so they are easily squeezed into small notches. This is what we commonly call "horseshoe beans" or "goat hoof beans" (locally called kuku kambing).

The ultra-fast speed of wet hulling also results in higher defect rates. Staff are assigned at the processing plants for manual defect sorting, typically including DP (double picking) and TP (triple picking). Mandheling that undergoes triple picking has a better defect rate than double picking.

FrontStreet Coffee is a roastery in Guangzhou with a small storefront but a diverse range of beans, where you can find both famous and lesser-known origins.

FrontStreet Coffee Recommendation

No bean shows off wet hulling quite like Golden Mandheling, and FrontStreet Coffee's comes from PWN in Indonesia, a company that applies extremely strict standards. It selects only beans of screen size 18 and above and requires fewer than 3 defect beans per 300g of green-bean sample, meeting the top G1 grade. On top of that, three rounds of hand sorting remove every defect, raising the cup's cleanliness and intensity of sweetness. Those standards make the quality high and the production limited, which is why FrontStreet PWN Golden Mandheling stands at the top of Mandheling coffee. Golden Mandheling is famous, but it is mainly supplied to Japan and the US, and only a limited amount of genuine Golden Mandheling is imported each year.

Wet hulling creates that heavy body and distinctive earthy, herbal flavor - a mother-nature kind of taste that has captivated many seasoned coffee drinkers. To experience it, FrontStreet Coffee's Lintong Mandheling is rich and intense, sweet-bitter on the palate, with clove and woody aromas: a medium-dark roast, low in acidity, with spice and mint notes and a strong, lingering, full sweetness.

FrontStreet Coffee's Mandheling line comes from Sumatra in Indonesia and is a single-origin bean, usually brewed as pour-over for a rich aroma and full body, though it also makes espresso with generous crema, an intense taste, and a pronounced caramel note. Mandheling is normally dark roasted to soften the acidity and play up that full, aromatic character. FrontStreet's Lintong Mandheling and PWN Golden Mandheling come from the Lintong and Aceh regions of Sumatra respectively, both medium-dark roasted. FrontStreet aims to present black chocolate and caramel while preserving Mandheling's wild herbal note, that distinctive fragrance born of its growing environment and processing.

For the best of FrontStreet PWN Golden Mandheling, a pour-over shows it off most clearly. Use water at 87-88°C, 15g of coffee, a 1:15 coffee-to-water ratio, a grind like coarse sugar, and a three-pour method, which reveals the full body and caramel sweetness. For the first pour, bloom with 30ml to wet all the grounds and let them degas, so the later extraction is cleaner. For the second pour, add 100ml to flush out the golden foam and lift the bed. For the final pour, use a gentle center pour of 95ml to raise sweetness, delivering a thick, full body with caramel sweetness and chocolate and nut flavors.

Many people who try FrontStreet Mandheling want to use it on an espresso machine. For that, FrontStreet Coffee's classic blend is the most reordered choice: it layers a medium-dark Mandheling on top of Brazil's creamy nut flavor, bringing butter, roasted chestnut, and caramel to the front. Mandheling not only lifts the body of the whole cup but adds distinctive sandalwood, herbal, and spice notes, and a little Robusta is included to boost crema richness. Latte art or a layered Dirty are both easy with it.