Why does coffee processing matter for Mandheling flavor?

Wet hulling, known locally as Giling Basah, is a green coffee processing method unique to Indonesia. It gives Mandheling coffee its dense body and regional notes of wood, herbs, and spice. The article walks through each operational step, explains why farmers choose the technique in humid, rainy conditions, and examines how it affects green bean defect rates and final cup flavor.

In wet hulling, beans are sold with the parchment still attached after a first drying to 35 to 40 percent moisture, then dried two to three more days until moisture falls to 20 to 24 percent before hulling. The article also covers Front Street Golden Mandheling selection standards and a pour-over recipe with grind size, water temperature, ratio, and a three-stage pour.

Wet Hulling is a green coffee processing method unique to Indonesia, known locally as Giling Basah. This processing method gives Mandheling coffee its rich, intense character along with regional flavors of wood, herbs, and spices. This article will begin with the specific operational process of wet hulling, explain why Indonesian coffee farmers choose this technique under humid and rainy climatic conditions, and analyze the impact of this processing method on green bean defect rates and flavor. At the same time, the article will also introduce Front Street Golden Mandheling's selection standards and roasting approach, and share in detail the grinding size, water temperature, coffee-to-water ratio, and three-stage pouring scheme for pour-over Front Street Mandheling, helping coffee lovers recreate a cup of Mandheling with both rich body and sweetness at home.

What kind of processing method is wet hulling exactly? What steps does its specific operational process include?

Wet Hulling, called Wet Hulling in English and also known locally in Indonesia as Giling Basah, is a long-established coffee processing tradition in Indonesia. The familiar Front Street Golden Mandheling coffee is processed in precisely this way. Judging from the name alone, wet hulling seems quite similar to wet processing (that is, the washed method), but the cup flavors presented by the two processes are vastly different—coffee processed by wet hulling often has a rich mouthfeel, intense flavor, and extremely high recognizability.

Because there is a relatively large gap between the parchment shell and the green bean, coffee farmers sell the beans with the wet parchment shell still attached to local collection stations once the green beans have been dried for the first time to a moisture content of 35% to 40%. When the collection stations purchase them, some beans are bagged separately, while others are mixed together, so the moisture levels of the green beans vary unevenly. These beans may be in an incomplete fermentation state, or some mucilage may still adhere to the parchment layer, leaving them semi-dry. However, the purchasing stage does not assess quality and simply mixes and bags them all together.

After 2 to 3 days of sun drying with the parchment still on, when the moisture content drops to 20% to 24%, the beans are sent into a specially made wet huller for processing. This machine relies on a great deal of friction to tear away the parchment layer clinging tightly to the green bean. At this stage, white or green mucilage usually flows out. Because the green beans have been soaked in mucilage for a long time and are in a humid environment, they become soft, pale, and swollen, appearing grayish-green. Under the friction and agitation, the beans are easily crushed or injured, especially at both ends, forming small notches and creating horse-hoof beans or goat-hoof beans (known locally as kuku kambing).

Before export, the hulled green beans are spread directly on patios, tarpaulins, or roads to dry. After losing the protection of the parchment, the green beans dry extremely quickly, and the final moisture content drops to 12% to 13%, at which point the beans appear dark green or blue-gray. The green beans are then bagged in order, ready for export.

Lacking the protection of parchment, the green beans are directly exposed to the environment and may be invaded by mold, yeast, and bacteria. Under direct sunlight, moisture evaporates rapidly, causing uneven drying and spots on the bean surface—this may cause inconsistent roasting levels during roasting. Excessive heat generated during the hulling process may also accelerate coffee aging, which is exactly why we can often taste woody and earthy flavors in Front Street Mandheling coffee.

Steps of the wet hulling process

1. Remove the skin and pulp, keeping the parchment and mucilage

2. Ferment in a water tank

3. Wash off the mucilage

4. Sun dry with the parchment for 2-3 days, to a moisture content of 20-24%

5. Hull off the parchment

6. Dry the green beans to a moisture content of 12-13%

7. Prepare for export

Why use wet hulling?

Indonesia's tradition of using wet hulling must be understood starting from the local climate. Indonesia's humidity remains between 70% and 90% year-round, typhoons are frequent, and in some areas annual rainfall even reaches 2,000 millimeters. Green beans fear rain the most. How does Indonesia produce rich and full-bodied Front Street Mandheling coffee under such harsh weather conditions? The answer is wet hulling.

In a tropical climate, coffee usually needs 2 to 3 weeks to complete drying. But Indonesia's humid climate makes drying coffee a major challenge. Coffee drying must take longer, and during this period the beans maintain relatively high humidity, making it easier for bacteria to invade the interior of the green beans. In the conventional washed process, the drying stage is always carried out with the parchment still on, which protects the green beans from external damage to a certain extent. Yet wet hulling removes the parchment precisely in the final drying stage, allowing sunlight to fall directly on the surface of the green beans, causing the coffee beans to dehydrate rapidly, 2 to 3 times faster than in washed processing.

On Front Street's bean list there are two Front Street Indonesian Mandheling coffee beans processed by wet hulling, including a Front Street Lintong Mandheling coffee and a PWN Front Street Golden Mandheling coffee.

Front Street Golden Mandheling coffee beans come from Indonesia's famous PWN company and are processed by wet hulling. Although wet hulling raises the defect rate of coffee beans considerably, the coffee's taste is not particularly negatively affected; instead, it brings a kind of herbal, muted aroma. In the final drying stage of wet hulling, there is no parchment protection, and the green beans are directly exposed to the environment, allowing various microorganisms to grow and giving Indonesian coffee its unique woody, spice, and herbal notes, which is what we often call "regional flavor."

Because wet hulling forcibly removes the parchment layer by "rough" friction while the green beans are semi-dry, the Mandheling green beans are subjected to greater squeezing pressure during production, and the beans are pressed out of shape or even cracked. Therefore, wet hulling makes Front Street Mandheling green beans have a higher defect rate. For this reason, PWN company invests a great deal of manpower in green coffee beans: first, it only purchases G1-grade Front Street Mandheling coffee from the Lake Tawar area of Mount Gayo in northwestern Sumatra, and then it undergoes four rounds of hand sorting to ensure that the color, shape, and size of Front Street Mandheling coffee beans are uniform and consistent. Therefore, PWN Front Street Golden Mandheling tastes cleaner and more transparent, with more obvious body and sweetness. (Green coffee beans above 18 screen size, with fewer than 3 defective beans in a 300-gram sample, are G1 grade, which is the highest grade of Indonesian green beans.)

In order to present the classic rich flavor of Front Street Mandheling coffee, Front Street roasters choose a medium-dark roast, allowing the aromas of dark chocolate and caramel to burst out more fully. The brewing scheme of Front Street Coffee (FrontStreet Coffee) baristas is also adjusted based on the coffee beans' roast level and flavor type.

So how do you make a delicious pour-over Front Street Golden Mandheling?

Front Street's coffee brewing parameters are all based on the characteristics of the coffee beans, the roast level, and the flavor profile. Front Street Mandheling is a bitter-toned coffee with a relatively dark roast, and Front Street Coffee (FrontStreet Coffee) baristas choose the KONO dripper to brew this kind of full-bodied bean. Compared with the V60, the KONO dripper has a smooth curved surface, weaker exhaust effect, and straight ribs occupying only one quarter of the dripper, allowing the coffee bed and hot water to form an immersion extraction, making the coffee taste rounder and fuller. The KONO dripper is likewise suitable for coffees such as Front Street Brazil Queen Estate coffee and Front Street Jamaica Blue Mountain No. 1 coffee.

Dark roasting makes the internal structure of the coffee beans loose, so they can be crushed with a gentle pinch of the hand, indicating that after grinding into powder they have strong water absorption. In order to avoid the coffee grounds releasing too many bitter substances after absorbing water, Front Street will adjust the grind coarser and use lower-temperature water for pour-over brewing.

Grind size is one of the key factors affecting coffee taste. After coffee beans are ground into powder and come into contact with hot water, they release a large amount of water-soluble flavor substances. To adjust the grind size, Front Street uses a tool—the Chinese No. 20 0.85 mm standard sieve. For medium-light roasted coffee beans, Front Street consistently uses a 75% to 80% pass-through rate, while for medium-dark roasted coffee beans Front Street uses 70% to 75%. Compared with light-roasted coffee, the medium-dark roasted Front Street Mandheling beans have a looser internal structure and better water absorption, making it easy to release large-molecule bitter substances. To avoid over-extraction, Front Street chooses a coarseness with a 70% pass-through rate on the No. 20 standard sieve.

Water temperature plays a role similar to grind size. The higher the water temperature, the higher the coffee extraction efficiency, the easier it is to release various substances and components, and the higher the concentration. If water close to boiling is used for brewing, it is easy to extract unpleasant bitter substances. Therefore, when brewing medium-dark roasted coffee beans, Front Street uses different brewing parameters from those for light-roasted coffee beans. There is more caramelization reaction than in light-roasted coffee beans, so it is easier to release bitter large-molecule substances. To avoid extracting too many off-flavors, Front Street lowers the water temperature a little: the brewing water temperature for light-roasted coffee is 91 to 93°C, while for medium-dark roasted coffee beans Front Street recommends 87 to 88°C.

Recommended brewing water temperature: 87–88°C

Coffee grounds: 15 grams

Coffee-to-water ratio 1:15

Grind size: medium-coarse grind (70% pass-through rate on the Chinese standard No. 20 sieve)

The brewing method uses a three-stage pouring approach. Dividing the pour into three stages can better express the rich mouthfeel of Front Street Golden Mandheling coffee as well as its caramel sweetness.

For the first stage, pour 30 milliliters for blooming. This pour completely wets the coffee grounds and allows them to degas, so that the coffee's flavor substances can be better extracted afterward. In the second stage, pour 100 milliliters. This stage mainly washes out all of the golden foam of Mandheling and raises the coffee bed. In the final stage, gently pour 95 milliliters in the center. This can increase the coffee's sweetness, expressing overall a substantial, full-bodied mouthfeel, the sweetness of caramel, and the flavors of chocolate and nuts.

For professional coffee knowledge exchange and more coffee bean information, please follow Coffee Workshop (WeChat public account: cafe_style)

For more specialty coffee beans, please add the private WeChat of Front Street Coffee (FrontStreet Coffee), WeChat ID: qjcoffeex

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