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 smallholder 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 quickly.
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.