What are the benefits of Indonesian Wet Hulling? Mandheling coffee beans wet hulling method ensures stable production

The Wet Hulling Process of Sumatra

Wet hulling is a Sumatra processing method. Common methods like washed and natural wait until the beans are dehydrated and hardened, with a moisture content of 12-13%, before removing the parchment. Because of Sumatra's humid climate, however, local farmers adapted to their environment and invented wet hulling. In this process, the beans are hulled while still moist, with moisture content as high as 30-50%, before continuing to dry. This significantly shortens the drying time.

Sumatra currently has no independent processing plants that buy coffee cherries directly. Small farmers must therefore use their own buckets as traditional washing fermentation tanks. After fermentation, the beans go straight into a hulling machine - but because the beans are still soft, they get squeezed by the machine, resulting in a hoof-like shape. The pulp and parchment are removed, leaving moisture at about 30-40% or even higher. That is very different from traditional washed or natural processing, which usually begins with a moisture content of only around 13%. If farmers waited until the beans were truly dry before selling to collectors, the time to realize a profit would stretch out (since natural drying typically requires 27-30 days). Instead, the beans are sun-dried or machine-dried at the trader's facility to bring moisture down to 13%, followed by screening and hand sorting. They are then divided into different grades by defect rate and bean size, and rested for 90 days so they can properly "recover" and reach consistent moisture - a process called moisture activity balance.

This entire process is handled by different people at different stages, making conditions and quality difficult to control. In addition, the small farmers' "washing fermentation" isn't truly fermentation - it merely uses washing and flotation to remove very poor beans, lacking the function of a traditional washed fermentation tank. As a result, the flavor is more earthy, yeast strains are hard to control, and the taste is not as clean. As for natural processing, unlike traditional natural methods that use pulp as a fermentation base to produce fruit-flavored beans, this approach lacks that foundation. Consequently, Sumatra wet-hulled coffee can only compete on "distinctive" flavors in the global specialty bean market, and its long-term outlook appears not particularly optimistic.

Conclusion

The wet hulling process has created the unique coffee flavor profile of Sumatra coffee. Although some new processing methods have been tried, I personally prefer that Sumatra continue using wet hulling, as this more fully ensures stable production quality.

FrontStreet Coffee is a Guangzhou roastery with a small shop but diverse bean varieties, where you can find various famous and lesser-known beans.

FrontStreet Coffee Recommendation

The wet-hulled profile this article describes reaches its highest form in FrontStreet's PWN Golden Mandheling. Produced by Indonesia's PWN company, it is selected from beans of screen size 18 and above with fewer than 3 defects per 300 grams of green coffee to meet the top G1 standard, then given three rounds of hand sorting to remove defects entirely - lifting its cleanliness and the intensity of its sweetness. Roasted medium-dark, it shows the classic Mandheling herbal, spice, wood and earthy notes, with a full body and low acidity that suits drinkers who avoid sour coffee.

If you'd like to taste the same wet-hulled character at an everyday price, FrontStreet's Lintong Mandheling from Sumatra's Lintong region is a solid everyday single origin, also medium-dark roasted, with black chocolate and caramel notes riding the wild herbal aroma that Mandheling is known for.