What is Wet-Hulling? Characteristics of Indonesian Mandheling Coffee Bean Wet-Hulling Process and Flavor Profile

What is Wet Hulling?

Every coffee bean processing method is related to the local climate. The coffee beans we drink must undergo processing methods before being roasted, including washed, natural, honey, anaerobic processing, etc. With the advancement of specialty coffee, coffee bean processing methods continue to increase. The processing method directly affects the flavor of coffee. Indonesian coffee beans use a unique processing method—wet hulling, also known as Wet Hulling. In the local language, it's also called Giling Basah, and is sometimes referred to as semi-washed processing.

The reason Indonesia uses this unique coffee bean processing method is entirely because the local weather is predominantly rainy with continuous typhoons, making it impossible to achieve the good weather required for natural drying. Moreover, the local economy is not prosperous, making it difficult to use the more expensive washed processing method. Indonesia has consistently high temperatures and humidity year-round, lacking long periods of sunlight, with humidity ranging between 70-90%. Therefore, relying solely on natural processing is clearly unrealistic. For the ever-changing weather of Sumatra island, even using washed processing for coffee beans makes it difficult to find a week of sunny weather for drying. Thus, wet hulling emerged as a solution. By accident, it became a unique processing method in the world, also creating the distinctive herbal, mellow, nutty, and pine flavor profile of Indonesian Mandheling coffee.

The difference between wet hulling and washed processing is: washed processing retains the pectin for fermentation, then uses clean water to wash away residual pectin before direct sun drying, with coffee beans stored with parchment intact. Wet hulling, however, uses washed processing for fermentation, then undergoes partial drying before machine removal of parchment for final drying. Coffee beans enter storage "naked" without parchment protection.

Mandheling Coffee

Mandheling coffee is considered one of the mellowest coffees in the world. Mandheling coffee characteristics include rich flavor and mellow mouthfeel, bringing people a very intense coffee experience and feeling. At FrontStreet Coffee, Mandheling coffee is a very popular variety. Before Blue Mountain coffee appeared, Mandheling coffee was called the mellowest coffee by coffee connoisseurs, and FrontStreet Coffee certainly agrees with this point. Mandheling coffee's body ranks among the top in specialty coffee, with heavy mouthfeel and low acidity as its characteristics, while the smoothness and sweetness of dark chocolate and caramel provide a very long-lasting aftertaste with complex flavor layers.

Indonesia is the world's largest archipelagic country, known as the "country of a thousand islands." The islands are relatively scattered, with rugged mountains and hills dominating the interiors, only narrow coastal plains, surrounded by shallow seas and coral reefs. Indonesia has a typical tropical rainforest climate with average annual temperatures of 25-27°C and no distinct seasons. The north is affected by Northern Hemisphere monsoons with abundant rainfall from July to September, while the south is affected by Southern Hemisphere monsoons with abundant rainfall in December, January, and February, with annual precipitation of 1600-2200mm. Because of these geographical conditions and climate characteristics, Indonesia's higher altitude, volcanic ash soil, and its climate features are excellent conditions suitable for Arabica coffee tree growth.

Indonesia's main coffee producing regions include Sumatra, Java, and Sulawesi islands, with Sumatra's "Mandheling" being the most famous.

Mandheling is also called "Sumatra coffee," with coffee from Lake Tawa in the northern part being called Aceh coffee or Lake Tawa coffee, while coffee from the Lintong and Lake Toba areas can be called Mandheling. FrontStreet Coffee has two Mandheling coffees: the daily bean series Indonesian Mandheling coffee and single-origin Golden Mandheling coffee.

Lintong Mandheling

Lintong Mandheling comes from the Lintong mountain area in north-central Sumatra, near Lake Toba. Lintong Mandheling is the regular version of Mandheling. Lintong Mandheling also uses conventional wet hulling, creating its characteristics of low acidity and high body. FrontStreet Coffee's daily bean Indonesian Mandheling comes from Lintong.

Golden Mandheling

Golden Mandheling specifications are Typica variety with 18 mesh or larger, with fewer than 3 defective beans (300g green bean sample), belonging to the highest G1 grade, with color leaning toward dark green, and flat bean shape. After strict selection, Golden Mandheling not only eliminates the characteristic earthy impurities of regular Mandheling but also tastes cleaner and brighter, with stronger sweetness and aroma. FrontStreet Coffee's Golden Mandheling comes from PWM company. Golden Mandheling is actually produced from Mandheling acquired locally in Indonesia by Pwani Coffee Company, which then registered the name Golden Mandheling, so actually the Mandheling produced by this company is the authentic Golden Mandheling.

Mandheling Coffee Bean Varieties

Mandheling coffee specifically refers to Arabica coffee beans grown on Sumatra island in Indonesia, with varieties mostly being timtim or ateng. Timtim is Timor, an Arabica variety with Robusta bloodline, while Ateng is Catimor, a hybrid of Caturra and Timor.

Specific Steps of Mandheling Coffee Bean Wet Hulling:

1. Coffee farmers first harvest mature coffee cherries and place them in water tanks, using flotation to remove debris and unripe coffee cherries.

2. Then use a depulper to remove the pulp and skin, retaining the endocarp and pectin for brief fermentation to decompose the pectin.

3. The washed coffee green beans undergo drying treatment, placing parchment coffee beans under direct sunlight for 1-2 days, reducing the moisture content of green coffee beans to 30%-50%.

4. Then use machines to remove pectin and parchment layers. Coffee beans with endocarp removed undergo another drying process for 2-4 days, reducing moisture content to about 12-13%, completing the processing.

Although wet hulling creates the unique flavor of Mandheling coffee, one issue that occurs with wet hulling is that the semi-hard, semi-soft moist green beans are easily crushed when the pectin and parchment layers are removed. The beans crack open like sheep's hooves, commonly known as "goat hoof beans." FrontStreet Coffee considers this a very significant characteristic of Mandheling coffee beans, not considered defective beans.

FrontStreet Coffee Brewing Suggestions:

To brew a delicious cup of coffee, FrontStreet Coffee believes that coffee bean freshness is a very important part of brewing. Coffee beans shipped by FrontStreet Coffee are all roasted within 5 days. FrontStreet Coffee's roasting philosophy is "freshly roasted good coffee," ensuring every customer receives the freshest coffee when they receive their order. The coffee degassing period is about 4-7 days, so when customers receive it, the flavor is at its best.

For friends who need ground coffee, FrontStreet Coffee warmly reminds: if coffee beans are ground in advance, there's no need for further degassing, because during transportation, the pressure from carbon dioxide in the packaging also helps round out the coffee flavor, so you can brew a cup immediately upon receiving the coffee grounds. However, coffee grounds need to be brewed promptly, because coffee grounds oxidize relatively quickly after contact with air, meaning the coffee flavor will dissipate faster, and the coffee flavor won't be as good. Therefore, FrontStreet Coffee recommends buying whole beans and grinding fresh for each brew to better taste the coffee's flavor.

FrontStreet Coffee's Mandheling Brewing Parameters:

FrontStreet Coffee uses a KONO dripper for brewing Mandheling coffee. The KONO's ribs stop before reaching halfway up the dripper height. This design actually ensures that after wetting the filter paper, it clings tightly to the dripper wall to restrict airflow, thereby increasing water absorption time for coffee particles, resulting in more uniform extraction and enhanced mellow mouthfeel.

KONO dripper, 88°C water temperature, 1:15 coffee-to-water ratio, 15g coffee grounds, grind size (75% pass-through rate on No. 20 standard sieve), three-stage extraction.

Using segmented extraction, bloom with twice the amount of water as coffee grounds, that is, 30g water for 30 seconds bloom. The blooming process is necessary to allow coffee grounds to release internal carbon dioxide gas, thereby making later extraction more stable. Use small flow circular pouring to 125g, then continue pouring to 225g and stop. Wait for all water to drip through the dripper, then remove the dripper. Time from the start of pouring, extraction time is 2'00". Next, pick up the entire cup of coffee and shake well, then pour into cups for tasting.

[Lintong Mandheling Coffee] Herbal, chocolate, caramel, overall quite balanced.

[Golden Mandheling Coffee] Nuts, spices, herbal plants, licorice, chocolate, caramel.

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