How Does Wet-Hulling Shape Mandheling Coffee Beans?

Mandheling comes from Sumatra in Indonesia, where Arabica is grown mainly in the higher parts of Aceh and North Sumatra provinces. Humidity stays around 70 to 90% with rainfall above 2,000mm a year, so fully drying parchment to target moisture is slow and difficult, which led locals to the wet-hulled method called Giling Basah.

Wet-hulling shortens the coffee beans process so growers can sell sooner, and it helps explain Mandheling's earthy aroma, herbal and aged-wood notes, full body and low acidity after dark roasting. Aged Mandheling extends this further through deliberate storage, adding the depth that distinguishes these lots on the cupping table.

Sumatra Mandheling coffee from Indonesia has always been loved as the darkest roast on Front Street Coffee's bean list, with a mellow body and low acidity. Behind that unique earthy aroma, notes of herbs and aged wood, what secret is actually hidden? The answer is inseparable from the local hot, rainy environment and the unique wet-hulled method. This article will start from the origin conditions of Front Street Mandheling, analyze every production step of the wet-hulled method, explain the connection between sheep-hoof beans, defect rates, and the taste of place, and further introduce the aging process and time requirements of Aged Mandheling, taking you through a complete understanding of this highly distinctive coffee.

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On Front Street's bean list, Mandheling is the single-origin coffee with the darkest roast. It gives off a rich roast-type aroma, and on the palate it is thick and full-bodied with low acidity. After dark roasting, you can feel both a lasting bitterness and an elegant sweetness within it, while the nose and palate simultaneously pick up that distinctive earthy aroma, leaving a long aftertaste.

At this point, some may wonder: they are all medium-dark roasted beans, so why does Mandheling alone carry this unique smell?

Front Street Mandheling comes from Indonesia's mysterious Sumatra island. The whole of Sumatra is divided into eight provinces, and among them only the higher-altitude Aceh Province and North Sumatra Province grow Arabica coffee on a large scale.

Very different from many coffee-producing regions, Indonesia's weather is unpredictable, humid, and rainy, with year-round humidity maintained between 70 and 90%. Sometimes the morning is clear and sunny, and by the afternoon it is pouring rain. Typhoons can arrive without warning, and annual rainfall even exceeds 2000mm.

Under such harsh climate conditions, trying to thoroughly dry parchment beans to the target moisture content is both difficult and time-consuming. Indonesia is also a large coffee-producing country oriented toward output. In order to shorten the processing cycle and sell the beans for money as quickly as possible, locals developed a unique semi-washed method: the wet-hulled method.

The wet-hulled method (Wet Hulled) is called "Giling Basah" in Indonesian. Like traditional methods such as washed, natural, and honey processing, it has existed and been used in coffee production for many years. At present, wet-hulled coffee still mainly comes from Indonesia, with northern Sumatra and the Sulawesi growing regions being the most concentrated.

At first, locals also mainly used natural processing, but quality fluctuated greatly, so later they shifted to a semi-natural method similar to Brazil's.

Farmers first use a machine to remove the outer skin of the coffee cherries, then pour them directly into a water tank, skim off the defective parchment beans floating on the surface, and take out the beans sunk at the bottom to put into a barrel for brief fermentation. The fermentation time depends on the specific situation, and is usually only a few short hours. After fermentation ends, a small amount of mucilage still remains on the bean shell, which must be scrubbed clean before the parchment beans are moved outdoors to dry.

However, this place is not as dry as Brazil. After removing the fruit skin and taking out the sticky parchment beans, it is simply impossible to dry them outdoors for several consecutive days, because in hot, rainy Indonesia doing so would only make the beans mold directly, so at most they can barely be dried for one or two days.

When the moisture content of the parchment beans drops to 30~50%, they are collected by brokers. At this point the mucilage layer has not yet solidified, and the beans are half-hard and half-soft. They must be sent back to the processing plant in time and have the seed shell ground off with specialized machinery; otherwise, excessive fermentation will make them sour and foul-smelling.

Because hulling is more difficult under the wet-hulled method, the machine needs to apply stronger friction to tear open the parchment layer clinging tightly to the green beans. During this stage, white or green mucilage usually flows out. After prolonged soaking in mucilage and the effects of the humid environment, the green beans eventually become soft, white, and swollen, taking on a gray-green color. Under the friction and stirring, the green beans are also more likely to be crushed or bruised, especially with small notches often appearing at both ends, shaped like sheep hooves. This is precisely why Sumatra coffee has a relatively high proportion of sheep-hoof beans.

You should know that coffee beans originally have four protective layers: fruit skin, mucilage, seed shell, and silver skin. But the wet-hulled method removes the third and fourth layers midway, meaning that coffee beans processed by the wet-hulled method are directly exposed to sunbathing in the state of "inner beans."

After the parchment beans have their seed shell ground off by machine, they still need to continue drying until the moisture content falls between 12% and 15%, and only then are the coffee beans packed into woven bags, usually 40 kg or 80 kg per bag. Finally, these green beans are sent uniformly for machine sorting, to remove various impurities and grade them by bean size.

Not only that, because the four protective layers are removed before drying, the beans are completely exposed in "naked" form to the scorching sun or humid air, and the drying speed is extremely fast. Therefore, whether in fermentation time or drying time, the wet-hulled method is shorter than the traditional washed process, and thus saves a great deal of labor.

Although the wet-hulled method shortens the drying time of green beans, the rough production steps also cause the defect rate to rise sharply.

First, natural defects that already existed when the coffee fruit was harvested cannot be avoided; next is the "crushing" in the hulling stage; there is also the moisture picked up by wet parchment beans during transport, as well as the damage done to the exposed green beans by sunlight and humidity. Finally, uneven drying caused by irregular weather also detracts from the flavor. This is precisely the main reason why high-grade Mandheling must undergo multiple rounds of hand sorting.

Operations directly exposed to a humid environment will inevitably cause the inner beans to pick up various strains of bacteria, thereby affecting the final coffee quality. But interestingly, "contamination" is not entirely a bad thing; certain strains instead give Indonesian coffee its unique flavor. Some academic research suggests that the woody, grass jelly, earthy, and spicy notes of Sumatra coffee should be created by mold. Ultimately, through a series of Maillard reactions and caramelization reactions, the coffee beans transform substances into aromas such as caramel and dark chocolate, and the coffee then presents a highly recognizable earthy aroma, which is what we call the "taste of place."

From this it can be seen that the unique herbal and aged-wood notes of Front Street Mandheling coffee all stem from the local high humidity, which forces the entire post-processing process to be divided into three different stages to dry the coffee beans. If you want to taste Mandheling's unique flavor, you can buy it directly from the Front Street Taobao store or the Front Street Tmall flagship store.

The Aging Process of Mandheling

First, freshly picked coffee cherries must undergo conventional processing. For example, Front Street Coffee's Aged Mandheling coffee beans are processed using the wet-hulled method. In this step, plump, large-screen, defect-free good beans need to be carefully selected for aging. After screening is completed, they must be stored in the warehouse to begin aging.

The aging process must be carried out in the place of origin, placed in a warehouse with temperature and humidity control or good ventilation. During aging, the beans must be turned and inspected frequently, for two purposes: first, to let the coffee beans come into even contact with air and maintain consistent dryness; second, to check whether moldy beans or insect-damaged beans have appeared and prevent large-scale infection.

Today, the aging time for Aged Mandheling is usually 2-3 years. During this period, the acidity of the coffee beans gradually weakens and transforms into sugars, and the color also becomes deeper, mostly yellowish-brown or dark brown, making it highly recognizable.

The above content is compiled by CoffeeHunters, a coffee news website.