Mandheling: Robusta or Arabica? A Guide to Indonesian Mandheling Coffee Bean Varieties and Brewing Methods

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Mandheling is a coffee variety grown in Sumatra, Indonesia, Asia, so it's also known as Sumatra coffee. The main producing regions include Java Island, Sulawesi Island, and Sumatra Island, with Mandheling from Sumatra Island being the most renowned.

Among the refined traditional Arabica coffees produced in northern Sumatra, the finest are marketed under the names Lintong and Mandheling. Specifically, Lintong refers to coffee grown in a small area located in the southwestern part of Lake Toba within the Lintong administrative region. The coffee smallholder plots are scattered across a high, undulating clay plateau covered in ferns. Lintong coffee is grown without shade, without chemicals, and is almost entirely owned by small private growers.

FrontStreet Coffee—Indonesia Sumatra Lintong Mandheling

Region: Indonesia Sumatra, Lintong Region
Altitude: 1100-1600m
Processing: Wet Hulling
Varieties: Timtim, Ateng
Flavor Description: Toasted bread, nuts, caramel, herbs, chocolate

FrontStreet Coffee believes that Mandheling coffee has rich aroma, solid and mellow mouthfeel, low acidity, and is quite intriguing. When deep roasted, one can experience both its lingering bitter notes and enjoy its elegant sweetness, simultaneously feeling its unique earthy aroma through smell and taste.

Based on their understanding of Mandheling coffee, FrontStreet Coffee's roasters decided to maximize the expression of Mandheling's flavors, preferably while preserving Mandheling's own character and making it suitable for most people's tastes. Each specialty coffee shop has its own unique characteristics. FrontStreet Coffee hopes to showcase the best Mandheling to customers while retaining FrontStreet Coffee's distinctive features, guided by our unique understanding of coffee. FrontStreet Coffee currently sells two types of Mandheling coffee beans: one is the Lintong region Mandheling mentioned above, and the other is the Golden Mandheling coffee beans from PWN company in Aceh Gayo Mountain.

FrontStreet Coffee—Indonesia Sumatra PWN Golden Mandheling Coffee Beans

Region: Indonesia Sumatra, Aceh Gayo Mountain
Altitude: 1100-1600m
Processing: Wet Hulling
Varieties: Ateng
Flavor Description: Spices, nuts, pine, caramel, herbs, chocolate

The difference between the two lies in that PWN Golden Mandheling coffee beans undergo at least three rounds of pure manual selection after harvesting and drying processing, ensuring that the coffee bean specifications reach above 18. Defective beans are fewer than 3 (in a 300g green bean sample), belonging to the highest grade G1 level. PWN beans are darker green in color and have uniform flat shapes.

What are the differences between Mandheling coffee beans of different roast levels?

For this purpose, FrontStreet Coffee tested light roast, medium-dark roast, and dark roast Mandheling coffee beans using drip extraction (pour-over) ~ single serving, with slight adjustments in grind size and water temperature due to different roasts.

1. Light Roast: 80% pass-through rate on national #20 sieve, water temperature 90°C, water-to-coffee ratio 1:15
2. Medium-Dark Roast: 75% pass-through rate on national #20 sieve, water temperature 88°C, water-to-coffee ratio 1:15
3. Dark Roast: 70% pass-through rate on national #20 sieve, water temperature 86°C, water-to-coffee ratio 1:15

The test results are as follows:

1. Light Roast: Mandheling at this roast level has heavier fruit acidity and slight bitterness. The fruit acidity is obvious but comfortable on the palate, with a sensation of saliva production on both sides of the mouth, and average smoothness.

2. Medium-Dark Roast: Very well-balanced, rich and mellow, with more pronounced bitterness. Chocolate notes and subtle sweetness are more prominent, with obvious licorice aroma and weaker fruit acidity. Smoothness is better than light roast, with strong aroma and noticeably enhanced fruit acidity.

3. Dark Roast: Almost no acidity, with very heavy bitterness. If direct fire roasting is slightly improper, it may also produce burnt flavors.

All coffee beans sold by FrontStreet Coffee are freshly roasted and shipped within 5 days after roasting ~ The optimal flavor enjoyment period for freshly roasted coffee beans is 30-35 days after roasting completion.

The deeper the roast level, the more carbon dioxide is produced inside the coffee beans. After roasting completion, coffee beans contain abundant carbon dioxide, so don't rush to drink them. You can first let the beans rest for 3-5 days (counting from the roast date), allowing the coffee beans to naturally release some carbon dioxide in their original packaging, reducing the likelihood of uneven extraction due to excessive carbon dioxide bubbles during the extraction process.

Mandheling Coffee Bean Processing Method—Sumatra Wet Hulling

March to May and September to December are the seasons for harvesting Mandheling in Sumatra. Nowadays, most coffee farmers only harvest fully red coffee cherries. After collecting coffee cherries in the morning, they remove the skin and pulp in the afternoon. Sumatra's natural environment is superior, and most of the water used is mountain spring water.

1. Coffee Cherry Depulping: Place the parchment coffee beans into large water-filled tanks or troughs, scooping out defective parchment beans floating on the liquid surface.

2. Fermentation: The dense parchment beans that sink to the bottom are briefly cleaned, removed, and placed in buckets or plastic bags for a brief dry fermentation process, allowing the mucilage sugars on the seed coat surface to ferment and enhance flavor. Basically, the longer the fermentation time, the heavier the acidity. Fermentation duration varies among producers, generally only a few hours, but some estates omit the dry fermentation stage and directly sun-dry the parchment beans, which can reduce acidity and increase viscous mouthfeel. For full mucilage sugar fermentation to enhance flavor, fermentation time is typically between 12-36 hours, depending on specific conditions.

3. Wet Hulling and Drying: The parchment beans are sun-dried for one to two days until the bean moisture content reaches 30%-50%, when the beans are still semi-hard and semi-soft. Use a hulling machine to remove the parchment shell and continue drying, accelerating the drying process. About two days later, when moisture content reaches 12%-13%, the coffee beans are collected into woven bags, typically 40kg and 80kg per bag, and sent to coffee processing factories for hulling. The process is completed in about four days total.

The hulling process involves using a hulling machine to grind off the parchment shell, then sun-drying until moisture content reaches approximately 12%-15%. Then, the coffee beans are sent for mechanical sorting to remove various impurities and sorted by particle size. Of course, accidents can happen. During the hulling process, coffee bean temperatures rise to 30-60°C and completely damage the parchment, likely triggering bean germination. Wet hulling can also result in higher rates of defective beans such as moldy beans compared to washed and natural processing methods, because the fruit skin is removed during processing, allowing beans direct contact with air. Mold brings good flavors because coffee beans have four protective layers: fruit skin, mucilage, parchment, and silver skin.

In the washed processing method, only the first two layers are removed, preserving the parchment and silver skin for sun-drying. However, wet hulling removes the third and fourth protective layers midway, exposing them directly to sunlight, which is why Sumatra green beans appear blue-green. Although wet hulling shortens drying time, the likelihood of mold, fungi, and yeast contamination significantly increases. Interestingly, contamination isn't necessarily bad—it depends on the specific microbial species. Dr. Martha Taniwaki from the Brazilian Food Technology Research Institute once tried inoculating coffee beans with different microbial strains and produced various flavors including putrid, oily, moldy, woody, iodine, caramel, chocolate, and floral aromas.

Academics believe that the woody, herbal, earthy, banana, and spicy flavors of Sumatra coffee are likely created by mold. Roasting plant managers often report to academia that some mold-contaminated coffee beans taste better after thorough cleaning, while others become difficult to swallow—this depends on the microbial species. Perhaps it's possible to suppress harmful molds while introducing beneficial ones, controlling wild yeasts while cultivating elegant yeasts. But which molds help enhance coffee flavor? Which are harmful? This awaits further research.

Elephant Beans: The "ID Card" of Mandheling Coffee Beans!

Wet hulling may trigger the germination mechanism of green beans, thereby affecting flavor. Because coffee beans that have lost their four protective layers are in an exposed state, they are more likely to trigger germination compared to washed beans that only lose two protective layers. This means activating the metabolism of sugars, proteins, and fats—these components are all precursor aromatic compounds in coffee. Additionally, the friction generated during hulling raises bean temperatures to 30°C-60°C, which also promotes germination and mold growth.

Moreover, the semi-hard and semi-soft moist green beans are easily damaged by mechanical force during parchment removal, making the beans prone to cracking open in an elephant-hoof shape. This is why Sumatra has a higher proportion of elephant beans. However, whether elephant beans are good or bad remains undecided to this day. The key control point is maintaining clean equipment and beans. Once hulled, drying must be rapid to produce the mellow, low-acid, and sweet Sumatra flavor; if control is improper, it may result in tasteless Sumatra coffee or even moldy earthy flavors. If you prefer stronger acidity, Aceh can also undergo washed processing, depending on customer requirements.

Summary of Wet Hulling Flavor Characteristics

To summarize the flavors of wet hulling, aside from subtle differences, we generally believe that wet-hulled beans have earthy, smoky, and chocolate flavors. They are mellow yet seem quite muted, with low acidity stemming from the shorter, less effective fermentation process and longer drying time—if you forget about wet hulling fermentation, go back and review.

As for the earthy and herbal flavors of wet-hulled beans, opinions vary widely. Some say this is related to the bean varieties used in wet hulling regions (Timtim & Catimor: with Robusta heritage), some say this is the result of organic interaction between green beans and the external environment, and some even say it's because there are too many defective beans!

There are numerous sources of defective beans in wet hulling. First, natural defects present in coffee cherries are unavoidable, and another contributor to defects is the hulling process. Additionally, there's corrosion during transportation of wet parchment beans, damage to exposed green beans from sunlight and moisture, and irregular weather causing uneven drying speeds, which also detracts from flavor. This is why Mandheling requires so many rounds of manual selection.

Finally, FrontStreet Coffee summarizes the characteristics of various green bean processing methods:

Production Risk: Wet Hulling / Natural > Washed / Honey > Semi-Washed
Equipment Cost: Washed / Semi-Washed > Honey / Wet Hulling > Natural
Water Usage: Washed > Semi-Washed > Honey / Wet Hulling

How to Brew Mandheling Coffee Beans?

Different brewing methods with different equipment will result in different taste profiles. Next, FrontStreet Coffee will use the store's PWN Golden Mandheling coffee beans as an example, using four different brewing methods to compare and analyze their flavor characteristics.

Pour-Over

Flavor: Multi-layered, clean, balanced, with persistent caramel sweetness in the aftertaste

1. Equipment Choice: Hario V60
2. Water Temperature: 88°C
3. Grind Size: Medium-coarse (70% pass-through rate on standard #20 sieve)
4. Roast Level: Medium-dark roast
5. Bloom Time: 25 seconds

Specific Technique: Three-stage pour-over for Mandheling, using 15g coffee ground with Fujiyama grinder's serrated burrs #4, V60 dripper, water temperature 88-89°C. First pour 30g water for 25s bloom, then pour to 104g and pause, wait until the water level drops to half before continuing the pour, slowly pour until reaching 220g, discarding the last 5g. Water-to-coffee ratio 1:15, extraction time around 2:00.

Volcanic pour-over extraction is also suitable for Mandheling, as are flannel or Kono filters!

Specific Technique: High-temperature extraction, water temperature 90-92°C, small water flow in the early stage, pouring at a spot the size of a coin, pause, bloom, pause, bloom, keeping the grounds in a continuous blooming state. Bloom time 1:30, finally use large water flow for rapid extraction, total extraction time 2:30.

AeroPress

FrontStreet Coffee believes that Mandheling coffee brewed with AeroPress has rich and complex flavors, prominent spice notes, and the fresh aroma of forest woods.

1. Equipment Choice: AeroPress
2. Water Temperature: 85°C
3. Grind Size: Medium-coarse (70% pass-through rate on standard #20 sieve)
4. Roast Level: Medium-dark roast
5. Bloom Time: 2 times, first 20 seconds, second 50 seconds

Specific Technique: Standard AeroPress preparation, recommend adding 20g coffee grounds, water-to-coffee ratio 1:17. First pour 83°C hot water to 100g, stir 3-5 times to fully wet the coffee grounds, let rest for 20s, add remaining hot water to reach 240g, let rest for 40s, stir for 5s, and when the time reaches 1 minute 50 seconds, attach the plunger and press down. Total time: 2 minutes 5 seconds.

Siphon

Flavor: Mellow, rich, prominent herbal and bitter notes, accompanied by prominent caramel sweetness

1. Equipment Choice: Hario Siphon
2. Water Temperature: 90°C
3. Grind Size: Medium-coarse (70% pass-through rate on standard #20 sieve)
4. Roast Level: Medium-dark roast
5. Bloom Time: 30 seconds

Specific Technique: Side-burn extraction, recommend 20g coffee for 2 servings, water-to-coffee ratio 1:12, water level mark 2, using post-addition method. Wait for bubbling before adding coffee, stir 4-5 times, extract for about 30 seconds then turn off heat. Finally, stir twice and let the coffee liquid fall naturally.

French Press

Flavor: Balanced, mellow, with good texture and oils, carrying a slight sweetness

1. Equipment Choice: French Press
2. Water Temperature: 92°C
3. Grind Size: Medium-coarse (70% pass-through rate on standard #20 sieve)
4. Roast Level: Medium-dark roast
5. Bloom Time: 2 minutes 30 seconds

Specific Technique: 20g coffee beans, pour hot water (approximately 92-93°C) into the French press to the marked capacity of 300ml, start timing. Place the lid on the French press with the filter stopped at the highest position, wait for 2.5 minutes. Press the filter to the bottom.

Conclusion

Recommended methods are Pour-Over and AeroPress, which showcase the rich and mellow flavors of PWN Golden Mandheling. Siphon and French press methods more easily cause over-extraction, and once over-extracted, you can only taste sour and bitter flavors.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473