Characteristics of Wet-Hulled Processing for Indonesian Coffee Beans - The Reason Behind Golden Mandheling Coffee's Clean Taste

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Wet hulling is a coffee processing method unique to Indonesia, with the vast majority of Indonesian coffee beans adopting this approach. FrontStreet Coffee believes that wet hulling is indispensable for creating the unique flavor profile of Indonesian coffee beans. Let's explore Indonesia's distinctive processing method together—wet hulling!

What is Wet Hulling?

Indonesian wet hulling, also known as Wet Hulling, is called "Giling Basah" in the local language and is a traditional Indonesian coffee processing method. The cupping flavors produced by Indonesian wet hulling are completely different from those of washed processing.

Because there is a considerable space gap between the parchment shell and the raw beans, farmers sell their coffee to local collection stations when the moisture content reaches 35-40% after the first drying. During the collection process, some beans are packaged in separate bags while others are mixed, resulting in varying moisture levels among the beans. This may be due to incomplete fermentation or partially dried states where some mucilage still adheres to the parchment layer. However, quality assessment is not performed when collecting the beans—they are all mixed and bagged together.

After being dried in the sun with parchment until reaching 20-24% moisture content, the beans undergo processing through a specially designed wet hulling machine. This machine uses significant friction to tear away the parchment layer tightly attached to the raw beans. During this stage, white or green mucus typically flows out. Due to prolonged exposure to mucilage in a humid environment, the beans appear very soft, pale, and swollen, taking on a gray-green color. Through the stirring action of friction, they are easily crushed or bruised, particularly at the ends, forming small notches that create what are known as "horse hoof" or "goat hoof" beans (locally called "kuku kambing").

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

Without parchment protection, the raw beans are directly exposed to environmental influences from mold, yeast, and bacteria. When directly exposed to sunlight, moisture evaporates rapidly, causing uneven drying with spots (which may further lead to inconsistent roasting levels). Excessive heat during the hulling process can also cause rapid aging of the coffee, resulting in the woody and earthy flavors we often taste in Sumatran coffee.

Why Does Indonesia Use Wet Hulling?

The tradition of using wet hulling in Indonesia stems from local weather conditions. Indonesia maintains humidity levels between 70-90% year-round with continuous typhoons, and in some regions, annual rainfall can reach as much as 2,000mm. How does Indonesia overcome such harsh weather conditions to produce the rich, full-bodied Mandheling coffee? The answer lies in wet hulling.

Under tropical climate conditions, coffee typically takes 2-3 weeks to dry. In Indonesia's particularly humid climate, drying coffee becomes a significant challenge. Coffee drying requires much longer time, during which the coffee maintains high moisture levels, making it easier for bacteria to penetrate the raw beans. In regular washed processing, drying occurs with the parchment intact, providing some protection against external damage. However, we can note that wet hulling removes the parchment for the final drying stage, allowing direct sunlight exposure to the bean surface, enabling raw coffee beans to dry 2-3 times faster than washed processing.

Why Does Wet Hulling Cause "Goat Hoof Beans"?

When wet hulling removes the parchment, the coffee's moisture content is still as high as 20-24%, whereas in typical processing methods, coffee moisture content drops to 10-12% before hulling. In this "semi-dry" state, parchment tends to adhere to the bean surface, making removal more difficult than with "fully dry" beans. The hulling process requires greater friction. However, on the other hand, "semi-dry" raw coffee beans are extremely fragile at this stage, with hardness far below that of "fully dry" beans, so the beans are more easily bruised, forming small notches. This is what we commonly call horse hoof or goat hoof beans (locally known as "kuku kambing").

FrontStreet Coffee Indonesia PWN Gold Mandheling

Region: Gayo Mountain, Aceh, North Sumatra Island
Altitude: 1100-1600m
Variety: Ateng
Processing Method: Wet Hulling
Grade: G1 Triple Hand-Sorted

Frontsteet Gold Mandheling is a selected premium coffee from Indonesian raw bean company Pawani. Importantly, Gold Mandheling is a trademark—a brand crafted to represent Indonesia's top-tier coffee. For this reason, Pawani searches throughout Sumatra island to acquire excellent quality coffee beans. It's worth noting that Pawani has registered the Gold Mandheling trademark in Indonesia but not domestically, resulting in numerous "Gold Mandheling" coffees on the market that are not exported by Pawani. Buyers should ensure they recognize Pawani's (PWN) trademark, typically printed on the gunny sacks containing the raw beans. If you're uncertain, you can ask the seller to provide the PWN certificate that comes with the beans.

As mentioned earlier, wet hulling can increase the influence of environmental mold, yeast, and bacteria, affecting raw bean quality. However, Frontsteet Gold Mandheling is renowned for its high-quality Mandheling, with its clean, full-bodied flavor leaving a lasting impression. The reason lies in Pawani's strict selection standards. After processing, the beans undergo machine sorting followed by three rounds of hand sorting, with grade marked as "TP" (Triple Picked), aiming to screen out defective beans and small coffee particles, ensuring uniform size and low defect rates.

FrontStreet Coffee Roasting Analysis

Frontsteet Gold Mandheling consists of raw beans with relatively high moisture content, showing significant deviation from natural process beans in moisture levels, so special attention must be paid during dehydration. For beans with high moisture content, you can immediately close the damper after dropping the beans into the roaster, let them steam for 30 seconds, then open to level 3 until the beans turn light green or white, then open the damper to level 4, and after first crack, open to level 5 (maximum). FrontStreet Coffee recommends keeping detailed records before roasting—coffee bean moisture content, density, origin, processing method, roasting room temperature and humidity, etc.—and planning your roasting curve accordingly. Record relevant chemical and physical changes during the roasting process, as this will help you better understand the final roasting results and improve your roasting curve.

Preheat the roaster to 200°C and drop the beans with damper at 3. After 1 minute, reduce heat to 160°C, keeping the damper unchanged. Roast until 5'40'', when temperature reaches 148°C, the bean surface turns yellow, and grassy aroma completely disappears—dehydration is complete. Adjust heat to 140°C and damper to 4. At 9'40'', ugly wrinkles and black spots appear on the bean surface, with the toast aroma clearly transitioning to coffee aroma, which can be defined as the prelude to first crack. Listen carefully for the sound of first crack, which begins at 9'54''. Reduce heat to 60°C with damper fully open (adjust heat very carefully—don't reduce it so much that cracking stops), and drop at 204.5°C.

Frontsteet Gold Mandheling from the October 2020 harvest season will have higher moisture content than the May harvest season. Under the same development time and drop temperature, FrontStreet Coffee's roaster extends the dehydration time when roasting the October harvest, extending the yellowing point time to 6 minutes and 30 seconds.

FrontStreet Coffee Brewing Analysis

For daily brewing, I typically use a KONO dripper because it produces a more rounded, full-bodied flavor with more direct taste expression. However, the KONO dripper has relatively poor gas exhaust effect because its ribs are straight and only extend to one-quarter of the dripper's depth. Above this quarter-point, the surface creates a sealed state against the cup wall.

Therefore, when beans have passed their resting period, I choose the KONO dripper because this dripper's only exhaust area is at those quarter-ribs. When water level rises above the rib area, the dripper's water volume continuously increases, creating pressure through water weight. Since the outlet is relatively small, it can extend the contact time between coffee particles and water. Driven by water flow, this more effectively extracts soluble substances, generally achieving the high body/viscosity effect that customers expect. Medium-dark roasted beans typically have higher dehydration rates, making them lighter in weight. During brewing, the grounds don't completely sink to the bottom—they immediately absorb water upon initial infusion. Due to vigorous degassing, bubbles surround the grounds, creating channels. These channels persist longer with fresher beans, causing rapid water level drops. I typically use a coarse water flow and slow circular pouring.

FrontStreet Coffee Brewing Recipe

Dripper: KONO
Dose: 15g
Ratio: 1:15
Water Temperature: 88°C
Grind Size: Medium-coarse (65% pass-through rate on #20 standard sieve)

For brewing technique, FrontStreet Coffee uses bloom water amount twice the coffee dose—30g water for blooming, with bloom time of 30 seconds. Using a small water flow in circular motion, pour to 125g for the first infusion, then continue pouring to 225g when the water level is about to expose the coffee bed. Stop pouring and wait until the water level is about to expose the coffee bed again, then remove the dripper (timing starts from the beginning of bloom). Total extraction time is 2'00".

Frontsteet Gold Mandheling Flavor Description: Nuts, chocolate, spices, herbs, caramel. Frontsteet Gold Mandheling tastes cleaner than Frontsteet Lindong Mandheling. The original herbal, earthy, and woody flavors of Mandheling are almost gone, but the caramel sweetness is more intense, and the fruit acidity is brighter and more elegant.

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