Detailed Introduction to Wet-Hulled Processing: Origin Story and Characteristics

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Indonesia's Unique Coffee Processing: The Wet Hulling Method

Indonesia, a notoriously hot and humid region, has a tropical rainforest climate with high temperatures, abundant rainfall, light winds, and high humidity throughout the year. These conditions make it challenging for humans to avoid developing damp-heat constitution, and drying plants to a mold-resistant state is equally difficult. Yet Indonesia is a major coffee-producing country, with Mandheling coffee grown in the Sumatra region receiving significant attention from the global coffee market. Consequently, Indonesians have devoted considerable effort to improving the drying speed of Mandheling coffee and preventing mold growth during the drying process.

If conventional washed processing were used—fermenting in water tanks to remove pulp and mucilage to reduce drying time—this approach would be environmentally unfriendly, requiring large amounts of water and polluting the environment with acidic post-fermentation water.

Meanwhile, the natural sun-drying method, which involves drying the entire coffee fruit with skin and pulp intact, cannot achieve the moisture levels required for storage. Therefore, the ingenious Indonesian people combined these two processing methods to create the Wet Hulling method, used exclusively in Indonesia.

The Wet Hulling Process

First, coffee farmers harvest ripe coffee cherries and place them in water tanks for flotation selection, removing debris, dust, and unripe coffee cherries. The selected coffee cherries are then put through a depulper to remove skin and pulp while retaining the mucilage. These coffee beans are placed in water tanks for 12 to 36 hours of fermentation, allowing the mucilage layer to decompose and fall off.

The coffee beans are then thoroughly washed with large amounts of water. After cleaning, the beans are placed on the ground for brief drying, approximately two days, until the moisture content reaches 30%-50%. At this stage, the beans are in a semi-soft, semi-hard state, allowing them to be placed in a hulling machine to remove the parchment layer.

Because the beans are in this semi-soft, semi-hard state, more force is required to remove the parchment, which can easily damage the coffee beans under such strong pressure, resulting in what we call "elephant beans" (beans with one side crushed). Finally, the processed coffee beans undergo two days of intense sun-drying until the moisture content reaches 12%, completing the processing.

Characteristics of Wet-Hulled Mandheling Coffee

FrontStreet Coffee has observed that after drying and parchment removal, Mandheling green beans exhibit a blue-green color and smell like fresh grass and herbs. The beans are shaped like hooves, resembling sheep or horse hooves.

Compared to washed processing, beans processed using this method have lower acidity. FrontStreet Coffee believes that Mandheling coffee beans from Indonesia possess such a mellow flavor profile and unique characteristics like herbal and spicy notes not only because of the variety and climate but also because wet hulling is one of the key factors that creates the distinctive taste of Mandheling coffee.

Of course, different qualities of Mandheling coffee beans, even when processed using the same wet hulling method, will show significant differences in flavor and cleanliness. If some coffee beans are of poor quality (grown at low altitudes) or not properly handled during the drying process, they can easily develop earthy or moldy flavors.

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