How Does the Wet-Hulling Process Shape Aged Mandheling?
Aged Mandheling is one of Indonesia's most distinctive coffees, combining Sumatra's wet-hulling tradition with the mellowing that comes from long storage. The beans, varieties like Caturra, Typica, and Sidikalang grown at around 1,500 meters on volcanic soil, end up less wild and more composed. The article traces the origin, wet-hulling steps, aging logic, roast points, and flannel-filter brewing.
Sumatra Mandheling carries two well-known grade names: Mandheling DP Grade 1, with a long wild-forest aftertaste, and Vintage Sumatra Mandheling, the aged type discussed here. Cultivation centers on Sumatra, Java, and Sulawesi. Around Lake Tawar in northern Sumatra the coffee may be called Aceh or Lake Tawar coffee, while Lintong and Lake Toba production also falls under the Mandheling category.
Aged Mandheling is one of the most distinctive Indonesian coffees. It not only carries Sumatra's unique wet-hulling tradition but has also undergone a mellow transformation gifted by time. This article will comprehensively trace the origins and development of this coffee, from the producing region's background, the causes and steps of the wet-hulling method, the storage logic for aged beans, changes in green beans, and roasting key points, to the practical operation of pour-over brewing with a flannel filter cloth. Front Street Indonesian Aged Mandheling serves as an example throughout the article, helping coffee enthusiasts understand why Aged Mandheling is less wild and more composed, and how to present its best flavors through proper extraction methods.
Aged mandheling
Front Street Indonesian Aged Mandheling
Variety: Caturra, Typica, Sidikalong
Soil: Volcanic soil
Altitude: 1500m
Processing method: Aged bean processing
01 | Producing Region Introduction
In the Asian coffee landscape, several large islands of the Malay Archipelago occupy a pivotal position, including Sumatra, Java, and Kalimantan. What made Sumatra Mandheling renowned far and wide is precisely its rich and heavy flavor profile. Sumatra Mandheling has two well-known grade names: Sumatra Mandheling DP Grade 1 and Vintage Sumatra Mandheling. The former has a long-lasting aftertaste with a wild forest character, like the scent of damp soil in a primeval rainforest.
Coffee cultivation in Indonesia is mainly concentrated on Sumatra, Java, and Sulawesi, with Sumatra's "Mandheling" being the most famous. Take the exceptional Front Street PWN Golden Mandheling as an example—it undergoes three rounds of hand sorting and one round of machine screening, greatly reducing the defect rate while ensuring the uniformity and consistency of green bean size, reaching a specification of 18 mesh and above.
Mandheling is sometimes also called "Sumatra coffee." Around Lake Tawar in northern Sumatra, it can be called Aceh coffee or Lake Tawar coffee; while coffee produced in the Lintong and Lake Toba areas can be classified within the Mandheling category.
Mainly from two producing regions:
One is the Aceh region, which includes five origins: Lake Tawar, Gayo Mountain, Gayo people, Aceh Mandheling, and Takengon Mandheling;
The other is the North Sumatra region, composed of four origins: Lake Toba, Lintong, Mandailing people, and Batak people.
02 | Processing Method
Mandheling's unique wet-hulling method
Wet Hulling, known locally as Giling Basah, is a traditional method in Indonesian coffee processing. Judging by name alone, wet hulling seems similar to wet processing (i.e., washed processing), but the cupping performance of the two is completely different. Coffee processed by wet hulling tends to have high body, strong impact, and extremely prominent character.
Wet Hulling Processing Steps
① Remove the skin and pulp, retaining the parchment and mucilage
② Fermentation in water tank
③ Wash off the mucilage
④ Sun-dry with parchment for 2-3 days to 20-24% moisture content
⑤ Remove the parchment
⑥ Dry the green beans to 12-13% moisture content
⑦ Ready for export
Why use wet hulling?
a. Climate reasons
Indonesia's adoption of wet hulling is closely related to local weather conditions. Indonesia maintains humidity between 70% and 90% year-round, with frequent typhoons, and annual rainfall in some areas can even reach 2,000 mm. Green coffee beans are most vulnerable to moisture, so how does Indonesia still produce rich and full-bodied Front Street Mandheling coffee under such unfavorable climate conditions? The answer is wet hulling.
In tropical climates, coffee cherries typically need 2 to 3 weeks to complete drying. In Indonesia's exceptionally humid environment, drying coffee becomes a major challenge. Coffee drying has to be extended, and during this period, the beans still maintain high moisture content, making it easier for bacteria to invade the interior of the green beans.
The drying stage of conventional washed processing retains the parchment, which to some extent protects the green beans from external damage. But wet hulling is different—it removes the parchment before the final drying, allowing sunlight to directly hit the surface of the green beans, causing them to rapidly dehydrate, with drying speed 2 to 3 times faster than washed processing.
b. Economic benefits
Dutch colonists first brought coffee to Indonesia in the 17th century, and these colonists pursued faster and greater economic returns. Wet hulling dramatically compressed the time spent on the farm and significantly reduced labor costs, which highly aligned with the mindset of investors seeking quick profits and cost control. This is also a reason driving the popularity of wet hulling.
c. Defects and kuku kambing (goat's foot beans)
When wet hulling removes the parchment, the coffee beans still have moisture content as high as 20% to 24%, whereas general processing methods wait until moisture content drops to 10% to 12% before hulling. In a "semi-dry" state, the parchment easily adheres to the surface of the green beans, making it more difficult to remove than in a "fully dry" state, and the hulling process requires greater friction.
From another perspective, the "semi-dry" green beans are very fragile at this point, with far less hardness than "fully dry" green beans, so the beans are easily crushed, forming small indentations. These are what we commonly call horse hoof or goat's foot beans, known locally as kuku kambing.
The extremely fast processing speed of wet hulling also leads to Mandheling often having a relatively high defect rate. Processing plants arrange workers to hand-sort defects, generally divided into DP (double-picked) and TP (triple-picked). Front Street Mandheling, having undergone three rounds of hand sorting, will be superior to double-picked in terms of defect rate.
Aged Bean Processing Method
Aged coffee beans are not simply green beans left to sit for a long time. Green beans left too long will also spoil, turning from fresh green to white, then yellow, becoming bland and tasteless, or even getting infested with insects. Just like aged wine, green beans must undergo proper processing and long-term storage before they can be called true 【Aged Coffee】.
The so-called Aged bean means:
Subjecting green beans to extended storage time to achieve natural aging (usually 2 to 3 years)
These changes include reduced acidity, color change, and increased bean density.
The storage environment must be cool and well-ventilated.
Because the storage environment is darker and the time is longer,
Aged coffee always struggles to escape
Complex flavors resembling mustiness or what is commonly called burlap or leather~
03 | Green Bean Analysis
Properly stored coffee beans will change in taste and appearance, such as reduced acidity, darker color with lack of moisture, fuller and thicker mouthfeel, sweetness with honey fragrance, and some original defects of the green beans becoming less noticeable. Because the storage environment is dark and the time is long, aged coffee always struggles to escape complex flavors resembling mustiness or what is commonly called burlap or leather.
Aged beans must be strictly and carefully controlled during storage, regularly and evenly turned, with humidity and ventilation adjusted, to prevent insect damage or mold.
The storage of aged beans generally does not occur in producing regions or estates, but is a commercial practice of green bean distributors or brokerage companies.
Properly stored coffee beans
Will change their taste and appearance,
For example, reduced acidity, dark color lacking moisture,
Fuller mouthfeel with good thickness, sweetness with honey fragrance,
Some original defects of the green beans also become less noticeable.
04 | Roasting Analysis
The appearance of Front Street Aged Mandheling is not attractive, but the baptism of time wears away the acidity of Front Street Mandheling, increasing its purity, and the medium-dark roast profile is rounder.
Because Front Street Mandheling green beans are high in density and aged beans have less moisture, heat adjustments at each stage must be made with special care. With Front Street Mandheling coffee, be careful not to scorch the oils on the surface of the beans.
Yangjia 800N, 550g green beans charged, specific operation:
Charge when drum temperature reaches 200°C, air damper set to 3, after 1 minute of soaking, adjust heat to 160°C, air damper unchanged, adjust heat once when drum temperature reaches 165°C, dropping to 140°C, roast until 5'35'', temperature 146°C, bean surface turns yellow, grassy smell completely disappears, dehydration complete, open air damper to 4;
At the 9th minute, ugly wrinkles and dark streaks appear on the bean surface, the toast aroma clearly turns to coffee fragrance, which can be defined as the prelude to first crack. At this point, listen carefully for the sound of first crack. At 9'30'' first crack begins, reduce heat to 80°C, air damper fully open to 5 (heat adjustment must be very careful, not so low that there is no crackling sound) 40°C, at 194°C reduce heat, drop at 197.4°C.
【Front Street Aged Mandheling】Through the settling of time, it has less of Mandheling's wildness and more mellowness and refinement in the mouthfeel. After aging, the coffee beans have weaker acidity but higher body, thicker texture, with a sense of mature steadiness, completely different from the lively brightness of new beans. Roasted aged coffee beans require a longer development time to reveal their richness.
04 | Brewing Analysis
Flannel recommended
Step 1
A brand new flannel filter cloth must first be removed and soaked in boiling water for 5 minutes, then placed on the metal ring.
If it is a used filter cloth, it should also be boiled in water for at least 3 minutes to disinfect.
Step 2
Grind the beans while the filter cloth is soaking. Due to the special material of the flannel dripper, pour-over with flannel filter cloth uses slightly more coffee beans than with paper filters, and the brewed flavor will be better. Of course, still load an appropriate amount of coffee grounds according to the size of the filter cloth. For 2 cups (240c.c. of coffee), use 40 grams of beans. It is recommended to grind the coffee beans to a coarseness between granulated sugar and fine sugar.
Step 3
Dry the filter cloth, first wring it by hand, then place the filter cloth between a clean dry towel to absorb moisture.
Step 4
Rinse with hot water, preheat the filter cloth and drip device, then pour out the water.
Step 5
Loosely pour the coffee grounds into the filter cloth, no need to press them compact.
Step 6
Use a wooden stirring spoon or butter knife to gently stir the coffee grounds from the very bottom upward, finally pull the bottom of the bag to adjust the shape.
Step 7
Make a dent at the top of the coffee grounds about one coin wide and one thumbtack deep. This is because the coffee bed is relatively deep, making it easier for hot water to spread in all directions and evenly saturate the coffee grounds.
Step 8
Let the hot water sit and cool to about 80-85°C, then begin pouring from near the dent, starting very slowly at first, pouring 60 grams of water within 30 seconds. No need to deliberately soak all the coffee grounds; capillary action will slowly spread the water. After pouring, wait about 30 seconds.
Step 9
Begin the second pour, this time a bit faster than the first, pouring 140 grams of water within 60 seconds. At this point the coffee will begin producing a large amount of bubbles, somewhat like a cosmic explosion scene in a movie. After pouring, wait 20 seconds, the water level drops slightly.
Step 10
Final pour, this time pouring 120 grams of water within 30 seconds. The entire process requires pouring 320 grams of water over 3 minutes. Because the filter cloth and coffee grounds absorb roughly twice the weight of the coffee grounds in water, you can ultimately collect about 240 grams of coffee, with a coffee-to-water ratio of 1:6.
Brewing coffee with a flannel filter bag is time-consuming, so the resulting coffee temperature is lower. Preheating the coffee cup can slightly raise the coffee temperature. But never reheat the coffee in any form.
The above content is compiled by CoffeeHunters, a coffee news website.
