How Does the Wet Hulling Coffee Process Work?

Wet hulling, called Giling Basah in Indonesia, is a semi-washed coffee processing method. Unlike the washed method, which dries beans inside the parchment layer, wet hulling ferments in washed style, semi-dries the beans, then removes the parchment by machine and finishes drying them bare. The result is Mandheling's low-acid, thick, herb-and-spice flavor and its sheep's hoof green bean shape.

Origin climate drives the choice of coffee processing. Natural processing suits dry, hot areas with scarce water, washed processing suits areas with easy water access, and wet hulling fits Indonesia's humid, rainy conditions, where drying whole parchment is slow and risky. PWN Golden Mandheling follows the process in seven steps, from cherry selection and fermentation through hulling, final drying and sorting.

Wet Hulling is a unique green coffee processing method specific to the Indonesian region, known locally as Giling Basah, and is often classified as a semi-washed method. Its biggest difference from the washed method is that the washed method retains the parchment layer for sun drying, while wet hulling removes the parchment by machine after semi-drying, then completes final drying. This processing method gives Mandheling a low-acid, thick, herb-and-spice-forward flavor, and also creates the green beans' distinctive "sheep's hoof" appearance. Front Street Coffee will combine PWN Golden Mandheling to break down the seven steps of wet hulling in detail, and include roasting and brewing practical records, to take you through a comprehensive understanding of this Indonesian classic coffee from origin to cup.

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What is the difference between wet hulling and washed processing?

Many customers who come to Front Street and order a cup of Golden Mandheling can't help but ask this question. Why do Indonesian coffee beans mostly go the wet hulling route rather than washed or natural? In this article, Front Street will talk about what wet hulling is really all about.

What is wet hulling?

Wet hulling, also called wet hulling (Wet Hulling), is known in the local Indonesian language as Giling Basah. It is a processing method unique to Indonesian production areas and is also classified as a semi-washed processing method. Its difference from the washed method is that the washed method retains the mucilage for fermentation first, then rinses off the remaining mucilage with clean water before direct sun drying, and the coffee beans are stored together with the parchment layer. Wet hulling, on the other hand, first ferments in a washed style, then semi-dries, then uses a machine to remove the parchment layer, and then performs final drying, so the coffee beans enter storage completely bare.

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

The choice of green bean processing method is generally based on factors such as the region's natural climate and resources. Natural processing is generally common in dry, high-temperature areas with scarce water resources, while washed processing is generally common in areas where water resources are easily accessible. Indonesia's humid and rainy climate makes natural processing, which requires long periods of sun drying, difficult to carry out. Front Street believes that wet hulling gives Indonesian coffee beans a fuller flavor and makes the herbal and spice notes of Indonesian coffee beans more pronounced.

Detailed explanation of the wet hulling process

1. Depulping / pulping

As with washed processing, harvested coffee cherries need to be processed as soon as possible. In Indonesia, coffee cherries are generally depulped and pulped independently at smallholder homes. This step removes the skin of the coffee cherries and part of the pulp.

2. Washing

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

3. Drying

After soaking, the coffee beans undergo their first drying independently at the farmer's home. At this point, the moisture content of the coffee beans drops to between 20% and 35%.

4. Collection

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

5. Drying

The coffee beans that are collected and sent to the processing plant first undergo a second drying. This step brings the moisture content of the coffee beans down 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 coffee's mucilage and parchment layer. What differs from other processing methods is that wet hulling removes the parchment layer before the coffee beans' final drying, whereas washed processing and others retain the parchment layer for drying until just before export transport, when the parchment layer is removed.

7. Drying & storage

Finally, the coffee beans are sent once again to the drying yard for final drying. This step brings the moisture content of the coffee beans down to 11%. The dried coffee beans are bagged and stored in warehouses awaiting transport for export.

Appearance characteristics of green beans processed by wet hulling

After receiving several lots of wet-hulled Mandheling green coffee beans, Front Street noticed that they share a common bean appearance characteristic: "sheep's hoof shape." This is because the semi-hard, semi-soft moist green beans are easily crushed when a machine hulls away the mucilage and parchment layer, and the beans crack open like a sheep's hoof, commonly known as sheep's hoof beans. The "sheep's hoof shape" is a very prominent characteristic of Mandheling and is not considered a defective bean.

Flavor characteristics of coffee beans processed by wet hulling

Teacher Han Huaizong once described the flavor characteristics of wet-hulled coffee beans in a book: "This is also a rare processing method in the world, and by accident it created Mandheling's special low-acid, thick, and mellow aroma flavor."

Through years of cupping different wet-hulled Indonesian coffee beans, Front Street has found that the coffee has relatively low acidity, a thick mouthfeel, and unique flavors such as herbs and spices, but the drawback is that quality is relatively unstable. Of course, unstable quality cannot be entirely attributed to wet hulling; in most cases, it may be caused by the fact that some green coffee beans are of relatively lower quality.

Now that we've said so much, how are wet-hulled coffee beans roasted and brewed? Next, Front Street will use Front Street PWN Golden Mandheling coffee beans for a roasting and brewing demonstration.

FrontStreet Coffee: Front Street PWN Golden Mandheling coffee beans Region: Gayo Mountain, Aceh, Sumatra Altitude: 1100-1600 meters Variety: Ateng Grade: G1, 3 times hand-sorted Processing method: Wet hulling

How does Front Street roast wet-hulled Golden Mandheling coffee beans?

Golden Mandheling is a green bean with relatively high moisture, and it has a relatively large moisture deviation compared with natural beans, so special attention is needed during dehydration. For green beans with high moisture content, you can close the airflow immediately after putting in the green beans, steam for 30 seconds, then open it to 3, until the color of the green beans turns light green or white, then open the airflow to 4, and after first crack open it to 5 (maximum). FrontStreet Coffee recommends keeping good data records before roasting, including the coffee beans' moisture content, density, origin, processing method, and the roasting environment's temperature, humidity, and so on in the roasting room. Plan your roasting curve well. Record the relevant chemical and physical changes during the roasting process; this will all help you better understand the final roasting result and help improve the roasting curve.

When the drum temperature reaches 200°C, charge the beans, set the airflow to 3, and after 1 minute adjust the heat to 160°C with the airflow unchanged. Roast until 5 minutes 40 seconds, at a temperature of 148°C, when the bean surface turns yellow, the grassy smell completely disappears, and dehydration is complete. Adjust the heat to 140°C and change the airflow to 4. At 9 minutes 40 seconds, ugly wrinkles and dark streaks appear on the bean surface, and the toast aroma clearly turns into coffee aroma, which can be defined as the prelude to first crack. At this time, listen carefully for the sound of the first crack point. At 9 minutes 54 seconds, first crack begins. Reduce the heat to 60°C and open the airflow fully (adjust the heat very carefully, not so low that there is no crackling sound). Drop the beans at 204.5°C.

How does Front Street brew medium-dark roasted Golden Mandheling coffee beans?

When brewing medium-dark roasted coffee beans, Front Street generally uses the KONO Meimon dripper, because the only exhaust part of this dripper is that one quarter of the ribs. When the water level passes over the rib area, the water volume in the dripper keeps rising, increasing pressure through the weight of the water. Because the outlet is relatively small, it can extend the contact time between coffee particles and water a little longer. As the water flow drives it, this can more effectively extract soluble substances, generally achieving the high body effect that customers expect.

Water temperature: 88°C Dose: 15g Water-to-coffee ratio: 1:15 Grind size: 65% passing rate with a 0.85mm aperture sieve

FrontStreet Coffee first uses a blooming water amount that is twice the amount of coffee grounds, that is, 30g of water for blooming, with a blooming time of 30 seconds. Pour in a small stream in circles until 125g, then pause. When the water level drops and is about to expose the coffee bed, continue pouring until 225g and stop pouring. When the water level drops and is about to expose the coffee bed, remove the dripper. (Start timing from the beginning of blooming.) The extraction time is 2'00".

Brewing flavor of Front Street PWN Golden Mandheling coffee beans : Nuts, spices, herbs, licorice, chocolate, caramel, with a clean and soft flavor.

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