Characteristics and Story of Mandheling Wet-Hulled Process Coffee Beans from Sumatra, Indonesia

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Indonesia is a large archipelagic country composed of numerous volcanic islands, naturally endowed with excellent coffee growing environments and latitudes. Each island has its own unique characteristics due to different topography and climate. The Indonesian islands that grow coffee include: Sumatra, Sulawesi, Java, Sumbawa, Flores, and Papua. Among these, Sumatra is one of Indonesia's main coffee growing regions, and the most famous FrontStreet Coffee Mandheling coffee comes from here.

Today, FrontStreet Coffee will discuss how Sumatra developed the Wet Hulling processing method and what unique flavors this method brings to Mandheling coffee.

What is Wet Hulling and what are the specific procedures?

Wet Hulling, also known as wet dehulling, is a processing method used for familiar FrontStreet Coffee Golden Mandheling coffee. In the local language, it's called Giling Basah and is a traditional Indonesian coffee processing method. Judging from the name alone, Wet Hulling seems similar to wet processing (washed), however, the cupping flavors of these two processing methods are completely different. Coffee processed with Wet Hulling typically has a thick and strong flavor with a very distinct personality.

Because there is considerable space between the parchment shell and green beans, farmers sell their beans to local collection stations when the green beans reach 35-40% moisture content after initial drying. During the collection process, some beans are packaged in separate bags while others are mixed, resulting in potentially different moisture levels among the green beans. Some may be incompletely fermented or still have part of the mucilage attached to the parchment layer in a partially dry state. However, no quality assessment is made when collecting the green beans, as they are all mixed and bagged together.

The beans with parchment are sun-dried for 2-3 days until reaching 20-24% moisture content, then processed through a specially designed wet huller. This machine uses significant friction to tear off the parchment layer tightly attached to the green beans. During this stage, white or green mucus usually flows out. Due to prolonged soaking in mucus and humid environments, the exposed green beans become soft, pale and swollen, forming a gray-green color. With the stirring from friction, they are easily crushed or damaged, especially at the ends, forming small notches that create what are known as horsehoof or goat hoof beans (called "kuku kambing" locally).

Before export, the hulled green beans are placed directly on courtyards, tarps, or roads for drying. Without parchment protection, the green beans dry very quickly, eventually reaching 12-13% moisture content. At this point, the green beans show a deep green or blue-gray color. The beans are then sorted, bagged, and prepared for export.

Without parchment protection, green beans are directly exposed to the environment and may be affected by environmental molds, yeasts, and bacteria. When directly exposed to sunlight, moisture evaporates rapidly, causing uneven drying with spots (which may further lead to inconsistent roasting levels during baking). Excessive heat during the hulling process can also cause rapid aging of coffee, resulting in the woody and earthy flavors we often taste in FrontStreet Coffee Mandheling coffee.

Wet Hulling Processing Steps

1. Remove skin and pulp, keeping parchment and mucilage
2. Ferment in water tanks
3. Wash off mucilage
4. Sun-dry with parchment for 2-3 days until reaching 20-24% moisture content
5. Hull off the parchment
6. Dry green beans to 12-13% moisture content
7. Prepare for export

Why Use Wet Hulling?

The tradition of using Wet Hulling in Indonesia stems from local weather conditions. Indonesia maintains 70-90% humidity year-round with continuous typhoons, and in some regions, annual rainfall can reach as much as 2,000mm. Knowing that green beans are most vulnerable to rain, how does Indonesia overcome such harsh weather conditions to produce the rich and mellow FrontStreet Coffee Mandheling coffee? The answer lies in Wet Hulling.

Under tropical climate conditions, coffee typically takes 2-3 weeks to dry. In Indonesia's humid climate, drying coffee becomes a major challenge. Coffee drying must take longer, during which time the coffee maintains higher humidity, making it easier for bacteria to penetrate the green beans. In regular washed processing, drying is done with parchment to protect the green beans from external damage. However, we notice that Wet Hulling removes parchment for the final drying stage, allowing sunlight to directly hit the green bean surface, causing the coffee beans to dry 2-3 times faster than washed processing.

FrontStreet Coffee's bean list includes two coffees processed using Wet Hulling: FrontStreet Coffee Indonesian Mandheling coffee beans, including FrontStreet Coffee Lintong Mandheling coffee and PWN FrontStreet Coffee Golden Mandheling coffee.

FrontStreet Coffee Golden Mandheling coffee beans are produced by the famous Indonesian PWN company and processed using Wet Hulling. Although Wet Hulling increases the defect rate of coffee beans considerably, the coffee flavor doesn't become particularly negative; instead, it brings a unique herbal aroma. Without parchment protection during the final drying stage, green beans are directly exposed to the environment and affected by various microorganisms. This gives Indonesian coffee its unique woody, spicy, and herbal notes—what we call "terroir flavor."

Because Wet Hulling uses "rough" friction to forcibly remove the parchment layer when green beans are semi-dry, the production process subjects Mandheling green beans to significant pressure, deforming or even crushing them. Therefore, Wet Hulling results in a higher defect rate for FrontStreet Coffee Mandheling green beans. Consequently, PWN company invests significant human resources in coffee green beans, first only purchasing G1 grade FrontStreet Coffee Mandheling coffee from the Lake Tawa area of Mount Gayo in northwestern Sumatra, followed by four rounds of manual sorting to ensure uniform color, shape, and size of FrontStreet Coffee Mandheling coffee beans. Therefore, PWN FrontStreet Coffee Golden Mandheling tastes cleaner and brighter, with more pronounced body and sweetness. (Coffee green beans above 18 mesh with fewer than 3 defective beans in 300g samples are G1 grade, the highest grade for Indonesian green beans).

To present the classic mellow flavor of FrontStreet Coffee Mandheling coffee, FrontStreet Coffee's roaster chooses medium-dark roasting to enhance the aroma of black chocolate and caramel. FrontStreet Coffee's barista also adjusts brewing methods based on coffee bean roast level and flavor profile.

How to Brew FrontStreet Coffee Golden Mandheling for Best Taste?

FrontStreet Coffee's brewing parameters are based on coffee bean characteristics, roast degree, and flavor profile. FrontStreet Coffee Mandheling belongs to dark-roasted bitter coffee, and FrontStreet Coffee's barista will use a KONO dripper to brew beans with such rich mouthfeel. Compared to V60, the KONO dripper has smooth curved surfaces with weaker exhaust effects, and its straight ribs only cover one-quarter of the dripper, allowing coffee layering and hot water to form immersion extraction, resulting in rounder and thicker coffee flavor. KONO dripper is also suitable for coffees like FrontStreet Coffee Brazil Queen Estate coffee and FrontStreet Coffee Jamaica Blue Mountain No. 1 coffee.

Dark roasting makes the internal structure of coffee beans looser—we can easily crush them with a gentle pinch, indicating strong water absorption after grinding. To avoid excessive bitter substances being released after coffee powder absorbs water, FrontStreet Coffee will adjust the grind to be coarser and use cooler water for pour-over brewing.

Grind degree is one of the key factors affecting coffee flavor. After coffee beans are ground into powder and contact with hot water, they release large amounts of water-soluble flavor substances. FrontStreet Coffee adjusts grind degree using a tool—China No. 20 0.85mm standard sieve. For light-to-medium roast coffee beans, FrontStreet Coffee consistently uses 75-80% pass rate, while for medium-dark roast coffee beans, FrontStreet Coffee uses 70-75%. Compared to light-roasted coffee, the internal structure of medium-dark roasted FrontStreet Coffee Mandheling beans is looser, so water absorption is better, making it easier to release large molecular bitter substances. To avoid over-extraction, FrontStreet Coffee chooses a grind degree with 70% pass rate on the No. 20 standard sieve.

Water temperature plays a similar role to grind degree. The higher the water temperature, the higher the coffee extraction efficiency, making it easier to release various substance components and resulting in higher concentration. If using near-boiling hot water for brewing, it's easy to extract unpleasant bitter substances, so when brewing medium-dark roast coffee beans, FrontStreet Coffee uses different brewing parameters than for light-roast beans. The caramelization reaction is greater than in light-roasted beans, making it easier to release bitter, large molecular substances. To avoid extracting too many impurities, FrontStreet Coffee will slightly lower the water temperature. The brewing water temperature for light-roasted coffee is 91-93°C, while FrontStreet Coffee recommends 87-88°C for medium-dark roasted coffee beans.

Recommended brewing water temperature: 87-88°C
Coffee powder: 15g
Powder to water ratio: 1:15
Grind degree: Medium-coarse grind (70% pass rate on China standard No. 20 sieve)

The brewing method uses three-stage pour-over, which can better express the rich mouthfeel and caramel sweetness of FrontStreet Coffee Golden Mandheling coffee.

The first bloom stage uses 30ml water injection, completely wetting the coffee powder for degassing to better extract coffee flavor substances in subsequent steps. The second stage injects 100ml, mainly to wash out all the golden foam of Mandheling and raise the powder layer. The final stage gently injects 95ml at the center, which can enhance the coffee's sweetness, overall expressing a thick body, caramel sweetness, and chocolate and nut flavors.

Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473