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Understanding the Complexity of Sumatra Coffee

This distinct, dynamic profile is often a gateway for specialty coffee.

by Ever Meister | November 24, 2020

Far be it from us to wax too poetic about a coffee growing region, but when you stop and consider the great complexity of coffees from Sumatra, maybe you’ll understand why we can’t say enough about — or drink enough of — beans from this region.

Or is it “micro-region?” Sumatra is but one of Indonesia’s more than 17,000 islands, many of which are known for their remarkable coffee. In fact, fellow Indonesian island Java is where one of coffee’s most famous nicknames was born. But nothing about Sumatran coffee can be described as “micro”: It’s one of the top producing regions in Indonesia, representing more than 60 percent of the country’s coffee production, and it is famous the world over for coffees with bold flavor and huge body. In 1922, William H. Ukers, author of the seminal coffee textbook All about Coffee, described the flavor of Sumatran coffee as “exquisite” with a heavy body.

It also has a gigantic following: Many coffee nerds (the author included) will tell you that the unmistakable distinctness of Sumatran coffee was our first introduction into the notion that there’s no such thing as “just coffee.” Back in 2013, coffee luminary Peter Giuliano (now Chief Research Officer for the Specialty Coffee Association) wrote one such tale on his blog, Pax Coffea:

"When I first worked in coffee, Sumatra was the name of the coffee drinker’s coffee; it was a code word for strong, thick, intense coffee. Sumatra meant a certain flavor, a kind of exotic, spicy strength. I still remember the day it dawned on me—standing behind an espresso machine—that Sumatra was a place, and that the coffee was from that place. It seems stupid now, but I had never made the connection before that day. That’s because— in general—we decontextualize coffee’s origins when we use country of origin as simply a label on a coffee."

Thanks for the segue, Peter: It’s true, we often don’t connect the dots between a place and a coffee in ways that make contextual sense for the reasons for certain profiles, and Sumatra is a great example of why taste of place is not only real, but also key to understanding the beautiful complexity of Sumatran coffee. So, if you're a coffee lover, learn why this type of Indonesian coffee should be your new favorite roast.

Processing and profile

For those yet uninitiated to the “classic” Sumatran profile we keep describing, picture this: It’s a drizzly autumn morning, cloud-covered sky as white as an envelope, you’re wearing three layers and they’re all soft jersey cotton. You want a coffee you can curl up on the couch with, one that you’ll want to wrap both hands around. You want it to warm you with notes of nutmeg, spice, and clove with a kiss of zesty fruit, like lemon or dried cherry. You’re longing for something with that smoky-earthy flavor that’s like sitting around a fire pit, and would love a bit of a sweetly herbaceous, leaf-like smell that reminds you of an October walk in the woods.

That, my friend, is the Sumatra mandheling coffee these dreams are made of.

The magic behind this unique flavor combination is not magic at all, but rather the intersection of several significant variables: Climate, processing, and genetics.

Those first two variables are related, as they are in most coffee-growing regions around the world: The local ambient temperature, precipitation patterns, relative humidity, sun exposure, and other goings-on in the atmosphere will have a direct influence on the post-harvest processing that the coffee grown there will undergo. If it’s a sunny, dry climate, for instance, coffee might need less fermentation and a shorter drying time; someplace with shady days and cool overnights might call for a longer fermentation and drying time.

Sumatra’s heavy humidity, rain, and cloud cover slows the drying process significantly, which can cause not only a traffic jam on the drying patios (a big consideration for small coffee farmers), but also a higher potential for mold and other nasty unpleasantries. This is a large part of why the wet-hulling post-harvest process was created: It is a technique used almost exclusively in parts of Indonesia in order to expedite the drying process.

Wet-hulled process — which is sometimes called Sumatra process, semi-washed, or giling basah — starts out similarly to the washed or wet process, in that the coffee is first depulped and then fermented. Sometimes the fermentation is controlled: This typically happens in situations where smallholder coffee farmers are selling Sumatra coffee cherries to a mill. Often the fermentation is not as controlled: Smallholders will depulp the day’s harvest and store it until it’s ready to bring to market, sometimes after a quick “pre-dry” to take some of the stickiness out of the mucilage. The coffee might then be hauled to a marketplace and shopped around to different “collectors,” the word for brokers who buy wet parchment coffee and sell it to a mill. At this point, the coffee is typically at about 50 percent moisture. Once it is at the mill, it will be dried until it’s 30 to 35 percent moisture, at which point the wet hulling process takes place.

The term “wet hull” means that the parchment layer of the coffee is removed by the use of friction or grinding machines before the coffee has reached its exportable moisture content (typically 10 to 12 percent in other places). By removing that protective outer layer, the green coffee seed is exposed, which will allow air and hazy daytime sun to dry it more promptly. This specific process creates seeds that are more of a bluish gray or brown color than the typical green or green-yellow that we see from other places; it also serves to mute acidity and draw out more herbal, savory flavors in the seeds, and is also responsible for creating that big, beautiful body we love in the cup. (If you look at your favorite Sumatran beans closely, you will likely see some evidence of the traumatic process they underwent to be hulled when wet: The machines can create chipped, broken, and scarred Sumatra beans — which, for some people, only adds to the appeal.)

As for the contribution of genetics, we would be remiss if we didn’t mention the fact that the cultivars typically grown in Sumatra also provide a scaffolding for this unique flavor profile: While there are some heirloom varieties like Abyssinia, Bergendal/Bergendahl (aka Indonesian Typica), Bourbon, and Caturra grown throughout the country, most producers have renovated their farms with newer hybrids that are designed for disease and pest resistance, and which tend to have less sweetness and acidity but more body and bass notes. Catimor types — Caturra variety coffees hybridized with the hardy Arabica-Robusta cultivar known as Timor Hybrid — are common: You will see names like Ateng, Tim Tim, Bor Bor, and Adungsari. These coffees, combined with the wet-hulling process, are what we have to thank for that cozy, spicy cup.

The “new” Sumatra

Because the classic Sumatran flavor profile has never ticked the most popular “third-wave” boxes for cupping notes (read: delicate florals, intense acidity, sugary sweetness), wet-hulled coffees have been overlooked in the past as low-quality or unexciting.

However, as processing improves and more and more producers focus on specialty coffee, we are seeing lots that blow expectations out of the water with crisp, clean flavor, light and bright acidity, and yes, even floral notes in concert with those savory complex herbaceous ones. In very recent years, we have seen more experimental processing coming out of Sumatra, including washed lots that show brown sugar, winey fruit acidity, caramel, lemongrass, cola, apple—things you would never have guessed were possible from Sumatra before.

Honey process is also gaining speed in this Indonesian coffee growing region, though it can be tricky due to the climate and requires special attention during the drying period. This extra care can also translate to that “exquisite” quality in the cup that Ukers mentioned. These bold flavor profiles are sure to impress each and every coffee lover.

There’s a wide range of wonderful Sumatran coffees to explore right now, including classic profile expressions from Highwire Coffee Roasters ($22.95), Novo ($20.60) and Atomic Coffee Roasters ($17.65) — and even a sweet, fresh-tasting honey process from Airship ($15.30).

Interested in seeing what other parts of Indonesia have to offer? There’s something for you, too: Gimme! Coffee has a Java Java ($17.65) that will be a good introduction.