What Kind of Green Bean Processing Method is Sumatra's "Wet-Hulling"? The Correct Way to Drink Wet-Hulled Coffee Beans

In the world of green coffee processing, some terms have become familiar to us, such as "sun-dried" and "washed." Whether or not we ever get the chance to visit coffee-producing regions, understanding green coffee processing helps guide what we do as consumers, from roasting and brewing to reading regional flavors during tasting.

The Sumatran "wet hulling" process, much like "honey processing," often trips up coffee lovers who are new to the field. Unlike the sun-dried and washed methods, it cannot be understood from its literal meaning alone.

What Are "Wet Hulling Coffee Beans"

"Wet Hulling" in English is "Wet Hulling," where "Hull" [hʌl] means shell or pericarp, so the full name is the "wet dehulling method."

This is a processing method best known from Sumatra, and similar techniques appear in Sulawesi and Papua New Guinea. It was inherited from the Dutch colonial era and later improved.

Two Characteristics of Wet Hulling

1. It rarely uses large fermentation tanks to remove mucilage.

2. Dehulling is performed when moisture content is between 30%-50%.

That second characteristic is what gave the method its name.

The Processing Steps of Wet Hulling Coffee Beans

1. After ripe coffee cherries are harvested, the outer skin and pulp are removed, leaving what we know as "parchment coffee." Once the pulp is off, the beans still hold a thin layer of skin, the inner pericarp, and this state, wrapped in the inner pericarp, is called "parchment coffee."

2. The "parchment coffee" is fermented, for as little as half a day and as long as 36 hours, then briefly sun-dried. When the moisture content reaches 30%-50%, it goes to the processing facility for dehulling, and the final green beans are dried afterward.

Compared with other processing methods, wet hulling takes a relatively shorter drying time. After a long soak in mucilage and time in a humid environment, the resulting green beans are soft, pale and swollen. This is why Mandheling green beans show up with distinctly light green, dark green or gray-green colors.

The Shortcomings of Wet Hulling Coffee Beans

Because wet hulling strips the "parchment" during the final drying stage, the beans come into direct contact with air, and the share of defective beans such as moldy beans runs much higher than with washed and sun-dried methods. That, in turn, creates real headaches for bean selection before roasting.

During post-processing of the green beans still carrying the parchment layer, the beans are also easily crushed or bruised by friction and stirring, especially at both ends, forming small gaps that become horse-hoof or goat-hoof shaped beans.

Different Preferences

In the specialty coffee world, many people prefer the stable quality of FrontStreet Coffee's Mandheling, while others enjoy the stimulating spiciness it brings. Some describe it as a mysterious, herb-like aroma. Driven by the market's pursuit of a "CLEAN" cup, Sumatran coffee has become an "addiction" that people chase for its bold, rich character.

In our roastery's product line there are also espresso blends built on Mandheling. Wet-hulled Mandheling at the beginning of the second crack has a fascinating creamy aroma and appears more gentle and reserved among the other aromatic-blend coffee beans. Perhaps this is the charm of coffee: from green beans to the cup, with many layers of steps in between, each step giving coffee a different expression. Could this be the ultimate taste in the world?

FrontStreet Coffee Recommendation

To taste wet hulling at its most typical, start with the FrontStreet Indonesia Wet-Hulled Mandheling. It comes from the Toba Lake area of the Lintong region, is medium-dark roasted for the classic Mandheling profile, and lands low in acidity and full in body with caramel, dark chocolate and toasted bread aromas and a long finish. For a cleaner, higher-grade expression of the same process, the FrontStreet PWN Golden Mandheling is screened more strictly for density, size, shape and color, which tames the earthier notes, and it drinks with sandalwood, herbs, spice, roasted hazelnut, caramel and dark chocolate. An easy daily cup for anyone who likes their coffee bold and not sour.