Sumatra coffees are famous for their peculiar flavor profile, low acidity, thick body, and rustic flavors that can often be described as earthy. Much of the flavor comes from the way Sumatras are processed, the wet-hull method , not to be confused with wet-processed coffee. The flavor of typical wet-hull Sumatra is polarizing among buyers. Some love it, but they must bracket this type of flavor profile because it would be considered unacceptable from any other origin besides Indonesia. Each coffee drinker has to discover if this type of flavor is right for them, or not; whether it's a go-to daily drinker, an occasional diversion, or flat-out unacceptable.
On a cupping table of well-processed Central American coffees, a Sumatra would immediately be thrown out. The earthy and foresty flavors - herbal, sometimes mossy or even mushroomy - would be attributed to processing errors, and the coffee labeled defective. So why this schism in the way the coffee trade treats wet-hull Indonesia coffees, and Sumatra in particular?
It comes down to taste: If a Sumatra supplier can consistently provide the same coffee, processed the same way, be it fruity or earthy, there are buyers who see this as a uniquely different flavor profile, and a welcome break from the Central America, Colombia or Kenya coffees. And of course the bottom line is that their customers like it. Those who like minimally-processed wines, or those wines with complex flavors of leather, peat moss, fir, cedar, humus, tannins, will see something in the Sumatra flavor profile.
Indonesian coffees like Sumatra are nearly always processed by the wet-hull method. Wet-hulled coffee is called Giling Basah in Bahasa language. Most coffee in Indonesia is grown on small-holder farms, a family with anywhere between 100 trees to a few hectares of land. They pick the coffee and pulp it, which means that they run it through a hand-crank drum with a surface like a cheese grater that peels off the skin of the fruit. Then they will ferment the coffee in any number of ways - either in a polypropylene bag, a plastic tub, or a concrete tank - to get the fruit layer (mucilage) to break down. After overnight fermentation, the mucilage can be washed off, and you have wet parchment coffee - the green bean inside the parchment layer that encompasses it, still swollen with water.
Sometimes origins like Sumatra are available as a true wet-processed coffee (although this term would probably not apply well, a better description would be dry-hulled). In wet-processing a farm would slowly dry this coffee for days or weeks, usually on a patio or raised bed, or sometimes in a mechanical dryer, down to 10-11.5 % moisture. In this process, the green bean would become the small dried seed we know, and the thin parchment shell is removed, preparing the coffee for export.
But in Sumatra and other parts of Indonesia, the farmer doesn't want to wait for all this to happen - they want to get paid! They want to do as little work to process the coffee, and get cash. And who can blame them? So they take their clean wet parchment coffee, dry it a few hours until it has 50% moisture content, and sell it to a collector middleman, or deliver it to a mill. They get paid faster, and do less work this way.
The mill might dry the coffee a little bit more, a day or two, but in general they send it to a special machine (the wet-huller) when the coffee still has 25-35% moisture content. This machine uses a lot of friction to take the tightly-attached parchment layer and tear it from the water-swollen green bean, which at this stage is often white and looks nothing like the green bean we finally see. Then the coffee is laid out to dry, totally unprotected by any outer layer, on a patio, on a tarp, on the road, or sometimes on the dirt! Drying without the shell is rapid, so the mill is able to sell the coffee and get paid with rapidity.
What does this do to the coffee? It creates a lower-acid cup, less brightness, and seems to enhance body. But the risk is great: the wet and unprotected green bean can easily be damaged in the hulling, or on the drying patio. No farmer in Central America would think of exposing their green bean direct to the patio or bed without the parchment layer. This layer protects the coffee from taints, keeps it clean, and allows a slower, gentler, more uniform drying. And coffees that are dried well will last longer when they arrive at the buyers; good tastes won't fade quickly into papery or burlap bag flavors.
This might make is sound like all wet-hulled coffee is bad, since this method isn't rooted in creating good-tasting coffee, but rather speeding up the process. But there is good vs. bad wet-hulled coffee. There are mills drying coffee on patios so clean you could eat off them, covered in a green-house like structure to protect from the unpredictable Sumatra rains, treating the coffee with great respect, and consistently producing great lots. It takes a lot of cupping, and identifying a different set of reference points to determine what a really good wet-hull Sumatra should be.
We look for sweetness in the cup, an expanded definition of sweetness than one might use when cupping other origins. This could be raw sugar, like muscavado, or molasses. It could be unique syrups like brown rice syrup, or sorghum syrup. In any case, a coffee with no sweetness is rarely, if ever a good coffee. We look at the rustic elements to distinguish gross flavors like dirt from positive clean-earth, humus or other positive and relatively clean natural scents and tastes. While slight green herb and mossy is good, vegetal notes that are too bittering hint at poor processing or under-ripe fruits. In our lab we also check the defect count, ultra-violet appearance of the coffee, water activity, humidity and density of the bean. These tell the story of the coffee, but ultimately we find that cupping reveals the truth just as well.
Sumatra was planted in coffee after the crop was introduced to Java in Indonesia. Arabica production in Sumatra began in the 18th century under Dutch colonial domination, introduced first to the northern region of Aceh around Lake Tawar. Coffee is still widely produced in these northern regions of Aceh (Takengon, Bener Mariah) as well as in the Lake Toba region (Lintong Nihuta, Dairi-Sidikalang, Siborongborong, Dolok Sanggul, and Seribu Dolok) to the southwest of Medan.
In the past, Sumatra coffees have not been sold by region, because presumably the regional differences are not that distinct. Rather, the quality of the picking, preparation and processing of the coffee determines much of the cup character in this coffee. In fact, Sumatras are sold as Mandheling (Mandailing) which is simply the Indonesian ethnic group that was once involved in coffee production. The coffee is scored by defects in the cup, not physical defects of the green coffee. So a fairly ugly-looking green coffee can technically be called Grade 1 Mandheling. A grade 1 coffee can be a good cup or a very dirty and ugly-tasting coffee. The grading sometimes seems arbitrary by any standard. The way coffee is shipped via the humid port of Medan also damages quality as it can gain moisture before shipping, then flash dried in the hot, hot sun to get it back down to an acceptable level. This ruins cup quality.
The main story behind the coffee here is processing, but the varieties of coffee grown do factor into the cup, and certainly into the farming practice. Sumatra has a range of cultivars. The original Typica type was brought from Yemen or Ethiopia via India. This is sometimes called Jember Typica. There are 2 main Typica types: Bergandal and Sidikalang. Hibrido de Timor, a cross between arabica and robusta, is sometimes found with the name "TimTim" ... we offered TimTim Blangili a while back. The majority of coffees are arabica types that have robusta inputs, like the Catimor coffees found in Central America. Ethiopia strains were reintroduced with the names Rambung and Abyssinia, which were brought to Java in 1928, and later to Aceh, Sumatra. Another group of Ethiopian varieties found in Sumatra are called “USDA". Knowing the specific cultivar is nearly impossible, and they are often a mix of many. In Sulawesi for example, Djember means S-795 from India, not a pure Typica. Many Aceh coffees are Ateng types of catimor, although there is still old varieties of coffee tucked away in this zone. Our Lintongs are a mix of Onan Ganjang, Djembers, and Ateng types. All of this is really second fiddle to the process flavors, the Indonesia wet-hull method called Giling Basah. Process flavors trump all in the Sumatra cup.
Sumatra faces many problems in coffee cultivation. There are types of fungus such as leaf rust. But the most damage to the crop and the livelihood of the small farmer is CBB - the Coffee Berry Borer - or Broca, as it is called in Latin America. Broca runs rampant in most areas of Sumatra. The small beetle drills into the fruit and seed while it is on the tree, and these beans must be sorted out from top grade coffees before they are exported. It is forced from the bean in processing, so the insect itself is not a risk but the damage it does to the bean and the plant's reaction to the attack will result in a whole host of defect flavors in the cup.
On my last trip to Sumatra I was shocked at the amount of Broca I saw on the plant, and also on the wet parchment coffee. They were all over the bags in the local markets where coffee is traded. It was very sad both for the damage to the cup quality, as well as the value and volume of the crop. There are natural control methods, like alcohol traps made from used 2 liter soda bottles. But one of the best prevention methods is to pick coffee promptly when it is mature, and not let coffee fall to the ground. The borer only wants to live in the ripe fruit. But Sumatra has a poorly defined crop cycle and weather patterns, meaning the coffee shrub often has ripe fruit on it. It's like a Broca motel - the borer always find a room available.
There is a tendency to over-roast Indonesians. The reason is that they don't show as much roast color, and have a mottled appearance up until 2nd crack and even a bit into it. Don't let this make you think you have to roast them dark (although they can be nice this way too). Great Indonesians will be wonderful roasted just to the verge of 2nd crack but NOT into it at all. So ignore the weird beans you see green, and ignore the mottled appearance of lighter roasts, and only focus on the what you get in the cup.
With prices high, you expect quality would be up too. But in general this is not the case. What's the incentive to pick and prepare coffee better when the market guarantees a premium anyway? It's why we buy very selectively from Sumatra and cup our lots hard. What I have seen is blends of old crop and new crop early in the Grade 1 window (Nov-Jan in particular), which is a deceptive practice. Nonetheless, roasters need Sumatra and I am sure someone buys it ... someone who doesn't cup their lots that is! Problems aside, we have been able to find great Sumatras in both the traditional rustic flavor category, and cleaner, well-processed types, because we have established good relations directly with the sources.