What is Coffee Wet-Hulled Flavor? What is Indonesia's Wet-Hulled Processing Method?

What is the difference between wet hulling and washed processing?

After guests visit FrontStreet Coffee and order a cup of Golden Mandheling coffee, they often ask out of curiosity: Why do Indonesian coffee beans mostly use the wet hulling method instead of washed or natural processing? In this article, FrontStreet Coffee will explain what wet hulling is.

What is wet hulling?

Wet hulling, also known as Wet Hulling or Giling Basah in the local language, is a unique processing method exclusive to Indonesian origins, and is sometimes called semi-washed processing. Unlike the washed processing method, where coffee is fermented with the mucilage, then cleaned with water and dried directly with the parchment intact, wet hulling uses washed processing for fermentation, then performs semi-drying before removing the parchment mechanically and proceeding to final drying. The coffee beans enter storage "naked" without parchment.

Why does Indonesia choose to use wet hulling for green coffee beans?

The choice of green bean processing method generally depends on factors such as the natural climate and resources of the region. Natural processing is common in dry, hot areas with scarce water resources, while washed processing is common in areas where water is easily accessible. Indonesia's humid and rainy climate makes natural processing difficult, as it requires long periods of sun drying. FrontStreet Coffee believes that wet hulling gives Indonesian coffee beans a richer flavor, making the herbal and spice notes of Indonesian coffee more pronounced.

Detailed explanation of the wet hulling process

1. Depulping

Similar to washed processing, coffee cherries need to be processed as quickly as possible after picking. In Indonesia, coffee cherries are typically depulped by small farmers at their homes. This step removes the skin and some pulp from the coffee cherry.

2. Washing

After depulping, the coffee beans are soaked in water for 1-2 hours and rubbed against each other to remove some of the mucilage.

3. First Drying

The soaked coffee beans undergo their first drying at the farmers' homes. At this point, the moisture content of the coffee beans will drop to between 20% and 35%.

4. Collection

After the first drying, the coffee beans are sent to the market for sale. At this point, the mucilage layer of the coffee beans has not yet solidified and is in a sticky state. These coffee beans are purchased, collected, and sent to processing plants for the next steps of processing.

5. Second Drying

The collected coffee beans sent to the processing plant undergo a second drying. This step reduces the moisture content of the coffee beans to about 18%.

6. Hulling/Wet Hulling

After the second drying, the coffee beans are put into a coffee hulling machine for wet hulling. This process removes the mucilage and parchment layers from the coffee. Unlike other processing methods, wet hulling removes the parchment layer before the final drying, while washed processing retains the parchment layer until drying and exports.

7. Final Drying & Storage

Finally, the coffee beans are sent to the drying patio again for the final drying process. This step reduces the moisture content of the coffee beans to 11%. The dried coffee beans are bagged and stored in warehouses waiting for transport and export.

Characteristics of wet-hulled green beans

After receiving multiple batches of wet-hulled Mandheling green beans, FrontStreet Coffee noticed they share a common characteristic in appearance: "sheep hoof shape." This is because when the semi-hard, semi-soft moist green beans are mechanically hulled to remove the mucilage and parchment, they are easily compressed and injured, causing the beans to crack open in a sheep hoof shape, commonly known as "sheep hoof beans." This "sheep hoof shape" is a very significant characteristic of Mandheling and is not considered a defect bean.

Flavor characteristics of wet-hulled coffee beans

Teacher Han Huaizong once described the flavor characteristics of wet-hulled coffee beans in his book: "This is also a rare processing method in the world, which accidentally created Mandheling's special low acidity, thick body, and mellow flavor."

Through years of cupping different wet-hulled Indonesian coffee beans, FrontStreet Coffee has found that these coffees have lower acidity, thicker body, and unique flavors such as herbal spices. However, the disadvantage is that the quality is relatively inconsistent. Of course, the inconsistent quality cannot be entirely attributed to the wet hulling method; in most cases, it might be due to the relatively lower quality of some green coffee beans.

So with all that said, how are wet-hulled coffee beans roasted and brewed? Next, FrontStreet Coffee will use PWN Golden Mandheling coffee beans for roasting and brewing demonstrations.

FrontStreet Coffee: PWN Golden Mandheling Coffee Beans

Region: Aceh Gayo Mountains, Sumatra

Altitude: 1100-1600 meters

Variety: Ateng

Grade: G1, triple hand-sorted

Processing: Wet Hulling

How does FrontStreet Coffee roast wet-hulled Golden Mandheling coffee beans?

Golden Mandheling belongs to green beans with higher moisture content, with a relatively high deviation in moisture compared to natural processed beans, so special attention is needed during dehydration. For green beans with high moisture content, you can close the damper immediately after dropping the beans, steam for 30 seconds, then open to 3, until the beans turn light green or white, open the damper to 4, and after first crack, open to 5 (maximum). FrontStreet Coffee suggests keeping detailed records before roasting: the moisture content and density of the coffee beans, origin, processing method, roasting environment temperature and humidity in the roasting room, etc., and plan your roasting curve. 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, set the damper to 3. After 1 minute, adjust the heat to 160°C, keeping the damper unchanged. Roast until 5 minutes 40 seconds, when the temperature reaches 148°C, the bean surface turns yellow, and the grassy smell completely disappears, indicating dehydration is complete. Adjust the heat to 140°C and the damper to 4. At 9 minutes 40 seconds, ugly wrinkles and black spots appear on the bean surface, and the toasted bread smell clearly transforms into coffee aroma, which can be defined as the prelude to first crack. At this point, listen carefully for the sound of first crack. At 9 minutes 54 seconds, first crack begins, adjust the heat to 60°C, open the damper fully (be very careful when adjusting the heat, not so low that there's no cracking sound), and drop the beans at 204.5°C.

How does FrontStreet Coffee brew medium-dark roasted Golden Mandheling coffee beans?

When brewing medium-dark roasted coffee beans, FrontStreet Coffee generally uses the KONO Meimon dripper because this dripper's only exhaust area is in its quarter ribs. When the water level passes the rib area, the water level in the dripper continuously increases, creating pressure through the weight of the water. Since the outlet is relatively small, it can extend the contact time between coffee particles and water. As the water flow drives this, it can more effectively extract soluble substances, generally achieving the high body thickness that customers expect.

Water temperature: 88°C

Coffee amount: 15g

Water-to-coffee ratio: 1:15

Grind size: 65% pass-through rate with 0.85mm mesh sieve

FrontStreet Coffee first uses a bloom amount that is twice the coffee amount, that is, 30g of water for blooming, with a bloom time of 30 seconds. Using a small stream, pour water in circles to 125g, then segment. When the water level drops and is about to expose the coffee bed, continue pouring to 225g and stop pouring. When the water level drops and is about to expose the coffee bed, remove the dripper (timing starts from the beginning of blooming). Extraction time is 2'00".

PWN Golden Mandheling brewing flavors: nuts, spices, herbal plants, licorice, chocolate, caramel, with clean and soft flavor profile.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473