What Characteristics Does Wet Hulling Impart to Mandheling? The Unique Herbal Notes of Sumatran Wet Hulling

FrontStreet Coffee - Introduction to Indonesian Wet Hulling

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Typically, coffee-producing countries have distinct dry and rainy seasons. For coffee, a crop that depends on weather, rainy days determine the time period for coffee flowering and fruiting. However, in places like Indonesia where it rains year-round, coffee trees flower and fruit throughout all seasons. This situation not only leaves coffee trees helpless but also confuses coffee farmers.

Coffee flowers are white.

What does this mean? First, farmers must harvest coffee throughout the year. Second, due to lack of sunlight, drying coffee beans in humid Indonesia takes at least fifteen days. Even if the washed method completes coffee fermentation, farmers might move coffee out to sunbathe in the morning, only to have to move it back indoors when afternoon rain arrives.

March to May and September to December are the harvest seasons for Mandheling in Sumatra. Nowadays, most coffee farmers only harvest fully red coffee cherries. After collecting coffee cherries in the morning, they remove the fruit skin and pulp in the afternoon, creating wet parchment beans—what we call parchment coffee. These are then placed in water tanks to remove floating defective beans.

Sumatra's natural environment is excellent, with most water used coming from mountain springs. Next, the dense, sinking beans are taken out and placed in barrels for dry fermentation, allowing the pectin sugars to fully ferment and enhance flavor. Fermentation typically lasts between 12-36 hours, depending on specific conditions.

Then, they are sun-dried for 1-2 days. When the moisture content reaches 35-40%, the coffee beans are collected into woven bags, usually 40 and 80 kilograms per bag, and sent to coffee processing plants for hulling.

The hulling process involves grinding off the husk with a hulling machine, followed by more drying until the moisture content reaches approximately 12-15%. The coffee beans are then sent for mechanical selection to remove various impurities and sorted by particle size.

After mechanical selection, the coffee is sent to hand-sorting warehouses where workers individually pick out defective beans. Only after two to three rounds of hand-sorting are they packed into burlap bags.

Of course, accidents can happen.

During the hulling process, coffee bean temperatures can rise to 30-60 degrees Celsius, completely destroying the parchment and potentially triggering bean germination. Wet hulling can also lead to higher rates of defective beans such as moldy beans compared to washed and natural methods, because the fruit skin is removed during processing, allowing beans direct contact with air. This is the distinctive processing method that creates Sumatra Mandheling's unique flavor. Additionally, the removed fruit skin and pulp can be fermented into fertilizer. When plantations use such ecological fertilizers, they can earn extra points when applying for organic coffee plantation certification.

Key Point: The biggest difference between wet hulling and conventional processing methods is that wet hulling dries the coffee beans after removing the outer husk, while conventional methods dry the beans first before removing the husk.

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