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Indonesia Sumatra Coffee Beans and Mandheling Coffee Beans: Flavor Characteristics and Processing Methods

Published: 2026-01-27 Author: FrontStreet Coffee

Last Updated: 2026/01/27, Professional coffee knowledge exchange. For more coffee bean information, please follow Coffee Workshop (WeChat public account: cafe_style). Indonesia, the world's largest archipelagic nation, has more than 400 volcanoes within its territory, with over one-third being active volcanoes, accounting for about 16% of the world's total. However, the optimistic residents are not at all concerned

Indonesian Mandheling coffee is the representative coffee of Indonesia in Asia. Mandheling is not the name of a coffee producing region, but rather a homophone of the Mandheling tribal group in northwestern Sumatra, Indonesia. During World War II when Japan occupied Indonesia, a Japanese soldier drank an incredibly fragrant and mellow coffee at a café. When he asked the owner the name of the coffee, the owner misunderstood and thought he was asking "Where are you from?" and replied: "Mandheling." After the war, the Japanese soldier recalled the coffee he drank in Indonesia was called "Mandheling," and later people began referring to the Arabica beans produced in Sumatra as Mandheling coffee.

Mandheling coffee originates from Sumatra Island in Indonesia. Indonesia is a Southeast Asian country and the world's largest archipelagic nation, with Jakarta as its capital. It shares borders with Papua New Guinea, East Timor, and Malaysia. Indonesia was one of the first places to grow coffee outside of Yemen.

Historical Development

At the end of the 17th century, the Dutch first introduced Arabica seedlings to Ceylon (today's Sri Lanka) and Indonesia. The Dutch first transplanted Arabica Typica to Jakarta in Java Island. Due to the suitable local climate and soil conditions, Arabica quickly spread to Sumatra in northwest Java and Sulawesi, another large island in the northeast. In 1877, a large-scale disaster struck the Indonesian islands when coffee rust disease destroyed nearly all coffee trees. People had to abandon the Arabica varieties they had cultivated for years and introduced Robusta coffee trees from Africa, which had stronger disease resistance.

Today, Indonesia has become a major coffee-producing country, with coffee mainly grown in Java, Sumatra, and Sulawesi. Robusta varieties account for 90% of total production. Sumatra Mandheling, however, is the rare Arabica variety. Today, Mandheling coffee generally refers to the Arabica coffee beans from Sumatra Island in Indonesia.

Indonesian Coffee Bean Growing Environment

Indonesia has a typical tropical rainforest climate with an average annual temperature of 25-27°C, no distinct seasons, and annual precipitation of 1600-2200mm. Indonesia is located in a volcanic zone with fertile, mineral-rich soil that is conducive to coffee bean cultivation and growth. Indonesia's elevation ranges from 900-2100 meters, with main coffee growing areas concentrated around 1200 meters.

Indonesian coffee beans have two main harvest seasons. The primary harvest season is approximately from September to October, while the secondary harvest season is from May to June. This year, Indonesia's coffee bean export volume has increased significantly compared to last year. Analysis suggests this is due to last year's high Indonesian coffee prices leading to reduced exports, combined with increased production in the current growing season leading to increased exports—this combination of factors has resulted in a significant increase in Indonesia's coffee exports this year.

Major Coffee Growing Regions

Indonesia's main coffee-producing regions include Sumatra Island, Java Island, and Sulawesi Island, with "Mandheling" from Sumatra Island being the most famous. In the northern Lake Tawar area, it can be called Aceh coffee or Lake Tawar coffee. The Lintong and Lake Toba areas can be called Mandheling. The region is divided into eight provinces, but only two provinces grow coffee extensively—Aceh Province and North Sumatra Province. The most representative coffee growing areas in these two provinces are the Gayo mountains surrounding Lake Tawar in Aceh Province, where coffee is grown by local indigenous Gayo people. Coffee in North Sumatra Province is grown around Lake Toba. This lake is extremely large and is the world's largest volcanic lake. The Mandheling produced by Lake Tawar and Lake Toba is the famous "Two Lakes, Two Mandhelings," and to the south of Lake Toba lies the Lintong growing region.

Lake Toba

Lake Toba is located north of Medan, the capital of Sumatra Island, and is a high-altitude freshwater lake with an average elevation of about 900 meters. The lake is diamond-shaped, 100 kilometers long and 30 kilometers wide, covering an area of 1,130 square kilometers. It is a highland lake at an average elevation of 1100-1600 meters and is also the world's largest volcanic lake. The commonly referred Mandheling typically refers to Typica or its variant coffee beans grown in the mountainous areas around Lake Toba. Among these, Lintong is the most famous Mandheling coffee producing region in the Lake Toba area, also known as Lintong Mandheling coffee.

Lintong Mandheling with unsorted green beans can sometimes exhibit inconsistent quality, but it largely retains the flavor characteristics of Sumatra coffee—strong, rich taste with distinctive spicy and herbal aromas. Therefore, FrontStreet Coffee also lists Lintong Mandheling as part of FrontStreet Coffee's high cost-performance daily bean series, allowing everyone to experience the unique taste of Indonesian coffee.

Aceh Gayo Mountain Growing Region

The Gayo Mountain region is located in Aceh Province in northern Sumatra Island. Coffee in the Gayo Mountain region is grown on the slopes surrounding the town of Takegon and Lake Tawar. The growing altitude averages between 1,110 and 1,600 meters in the production areas. Coffee is grown by small farmers under shade trees, and the wet-hulled processing method brings out unique flavors with deep and lively richness. Aceh, at the northernmost tip of Sumatra Island, is a fascinating and complex place.

Due to long-term political instability, Aceh is not a region that ordinary people typically visit. The Gayo Mountains are located in the Aceh growing region of northern Sumatra Province. Most coffee farmers working in Gayo are local farmers. The term "Gayo" originates from a tribe in the Aceh region of Indonesia. This region has ideal growing conditions, a long historical culture, and unique flavors. The region widely employs organic methods for coffee cultivation without using chemical fertilizers and is considered a world green coffee production area. Therefore, Gayo coffee is often called green coffee or Gayo organic coffee.

Lake Toba

Lake Toba is located in central North Sumatra Province. In 1888, Dutch colonists moved "Java Mandheling" north to the Lake Toba area. Lintong in South Sumatra and the Lake Toba area can be called Mandheling. The Lintong area is the true Mandheling growing region. Mandheling is produced from the mountainous areas surrounding Lake Toba. This lake is located north of Medan, the capital of Sumatra Island, and is a high-altitude freshwater lake with an average elevation of about 900 meters. The commonly referred Mandheling typically refers to Typica or its variant coffee beans grown in the mountainous areas around Lake Toba.

Lake Tawar

Lake Tawar is located in central Aceh Special Administrative Region. Situated at the northern tip of Sumatra Island, most coffee produced in North Sumatra is Gayo, primarily of the Ateng variety. Coffee from Lake Tawar at the northern tip can be called Aceh coffee or Lake Tawar coffee. Its area is less than one-tenth that of Lake Toba. However, in recent years, its coffee quality and production have surpassed those of Lake Toba.

Because Indonesia has thousands of islands, not all coffee from the country tastes the same. Besides Java Island, coffee beans from Sumatra Island in Indonesia are renowned worldwide for their heavy body, low acidity, and earthy, spicy, and herbal aromas that make Mandheling coffee beans famous.

Indonesia's Unique Coffee Processing Method—Wet Hulling

Wet hulling, also known as Wet Hulling or Giling Basah in the local language, is the traditional Indonesian coffee processing method. From the name alone, wet hulling appears similar to wet processing (washed processing), however, the cupping flavors of these two processing methods are completely different. Coffee processed with wet hulling typically has a rich, strong flavor with a very distinct personality.

The uniqueness of Mandheling coffee flavor originates from the local unique post-processing method for green coffee beans. Due to the year-round rainfall and high air humidity in Sumatra, if the dry processing method were used, coffee cherries might become contaminated by rainwater or even over-fermented, leading to spoilage. Therefore, this cannot meet the conditions required for dry processing.

Additionally, washed processing requires sufficient water resources and adequate funding, but local economic conditions are limited and cannot fully meet the requirements of complete washing. Therefore, the distinctly Sumatran wet hulling processing method emerged, which requires a short drying time and uses less water during the process.

Wet Hulling Process

After removing the skin and pulp of coffee cherries, the parchment beans with sticky mucilage are briefly washed and then placed in water tanks for short-term fermentation. The longer the fermentation time, the more acidic the taste becomes. Some processing plants or estates even skip the fermentation step entirely, directly spreading the parchment beans evenly for drying. This both inhibits acidity and increases the viscosity of the taste. The parchment layer serves as a protective layer for green coffee beans to some extent, protecting them from external damage.

However, the local climate in Sumatra is too humid, and coffee drying takes a longer time. In this short period, coffee maintained at higher humidity can attract bacterial contamination, leading to spoiled coffee beans. Removing the parchment layer allows sunlight to directly reach the surface of green coffee beans, enabling them to dry quickly.

During the process of removing the parchment layer, significant friction occurs between coffee beans and between beans and machinery, generating excessive heat that may cause coffee to age rapidly, resulting in the woody and earthy special flavors found in Sumatra coffee.

This special wet hulling method causes Mandheling coffee beans to appear cracked and asymmetrical in shape—what we call "goat hoof shape." This is not considered a defect but is normal. Some coffee friends even say that the uglier Mandheling coffee beans look, the better their flavor tastes.

Gold Mandheling Coffee

Another frequently mentioned Mandheling coffee bean is called "Gold Mandheling"—the word "Gold" reflects the high quality of this coffee bean. FrontStreet Coffee's Gold Mandheling comes from PWN company. PWN company uses extremely strict standards when producing Gold Mandheling—coffee green beans must be size 18 or larger, with fewer than 3 defects per 300-gram green bean sample. Meeting G1 grade standards and undergoing three rounds of manual selection ensure complete removal of defective beans, thereby maximizing flavor clarity and enhancing sweetness.

Traditional Mandheling coffee flavor has a rich taste due to its relatively dark roast level. To present the traditional Mandheling flavor, FrontStreet Coffee uses a medium-dark roast level when roasting Mandheling.

FrontStreet Coffee's Mandheling Brewing Parameters

The special feature of the Kono dripper is that its "rib" flow channels extend to the bottom of the hole where coffee liquid flows out. Because the ribs are at the bottom and short, they fit well with filter paper, so the flow rate is slower than V60, which can increase coffee extraction rate and enhance coffee richness.

Dripper: KONO dripper, Water temperature: 88°C, Coffee amount: 15 grams, Coffee-to-water ratio: 1:15, Grind size: Medium-coarse grind (Chinese standard #20 sieve with 75% pass-through rate).

Using segmented extraction, bloom with twice the coffee weight in water—that is, bloom with 30 grams of water for 30 seconds. The blooming process is needed to allow coffee grounds to release internal carbon dioxide gas, thereby making the subsequent extraction more stable. With a small water stream, pour in a circle until reaching 125 grams, then continue pouring to 225 grams and stop. Remove the dripper once all water has dripped through. Start timing from the beginning of pouring, with an extraction time of 2'00". Next, pick up the entire cup of coffee and shake it evenly before pouring into cups for tasting.