Sumatran Coffee Processing: Why You Should Know Giling Basah

A guide to understanding the Giling Basah method, a Sumatran coffee-processing tradition.

In the Bahasa language of IndonesiaUSDA is (obviously) the United States Department of Agriculture. USDA also had coffee plant breeding programs in the past and one variety they distributed to Indonesia and was..., Giling Basah means “wet-hulled.” That’s not very exciting in itself … but understanding the processingThe removal of the cherry and parchment from the coffee seed.: Coffee is either wet-processed (also called washed or wet-milled) or dry-processed (also called wild, natural or natural... method is key to understanding why you might like (or dislike) a certain coffee. Processing is a huge part of determining the cup character of a coffee. Yet we hear much less about it than we do other aspects of a coffee’s originIn coffee talk, it refers to a coffee-producing region or country; such as, "I was just at origin." Of course "Origin" for most product we use is not..., such as altitudes, varieties of plants, etc.

Giling Basah refers to a coffee process that is specific to Indonesia and creates a signature flavor. Wet-hulled coffees can have more bodyAssociated with and sensed by mouthfeel, body is sense of weight and thickness of the brew, caused by the percentage of soluble solids in the cup, including all... and lower acidityAcidity is a positive flavor attribute in coffee, also referred to as brightness or liveliness. It adds a brilliance to the cup, whereas low acid coffees can seem..., but they also fall short of the sweetnessSweetness is an important positive quality in fine coffees, and is one of five basic tastes: Sour, Sweet, Salty, Bitter, Savory (Umami). In coffee, sweetness is a highly... and aromaAroma refers to sensations perceived by the olfactory bulb and conveyed to the brain; whether through the nose or "retro-nasally": The aromatics of a coffee greatly influence its... uncovered by other methods.

If you have any interest in coffees from Indonesia, and are looking for some reason why you like them (or perhaps why you don’t like them), it’s worth your time to learn about Giling Basah.

While it’s more attractive to discuss coffee in a vocabulary validated by the wine discourse (varietal, terroir), these matter little when viewed through the lens of processing. If a coffee is “wet hulled” versus “wet processed,” whether it is a Typica or BourbonA coffee cultivar; a cross between Typica and Bourbon, originally grown in Brazil: Mundo Novo is a commercial coffee cultivar; a natural hybrid between "Sumatra" and Red Bourbon,..., cultivarCultivar is a term used interchangeably with Varietal in the coffee trade to indicate plant material, although there are distinctions.: The naming of a cultivar should conform to... will be secondary to the way the cup flavors were shaped by processing.

Identical Twins

“Wet-hulled” versus “wet-processed”: They sound similar, but judging by the results they could not be farther apart. Wet-processed coffee (also called washed coffee) is the most common method the world over for high quality specialty coffeeSpecialty coffee was a term devised to mean higher levels of green coffee quality than average "industrial coffee" or "commercial coffee". At this point, the term is of.... Most everything you taste from Latin America is wet-processed coffee. Kenyas, Rwandas, BurundiBurundi coffee bears resemblance to neighboring Rwanda, in both cup character, but also the culture surrounding coffee. Burundi is a small landlocked country at the crossroads of East... are also all wet-processed.

Indonesia has islands that have historically produced wet-process coffees: JavaThere are several types of Abyssinia variety coffee, but they are not from Ethiopia but rather Indonesia. Abyssinia 3 = AB3.  PJS Cramer, a Dutch plant researcher, introduced this variety..., BaliCoffee from the Indonesian island of Bali was formerly sold mainly to the Japanese market. Perhaps it is the changing face of world economics that finds the first..., FloresFlores is an Indonesian island, and as a coffee bears more resemblance to the coffees of Timor-Leste, New Guinea and Java than to the wet-hulled coffees of Sumatra.... But the biggest origin, SumatraIndonesians are available as a unique wet-hulled or dry-hulled (washed) coffees. Giling Basah is the name for the wet-hulling process in Bahasa language, and will have more body..., as well as SulawesiSulawesi coffees are low-acid with great body and that deep, brooding cup profile akin to Sumatra. The coffee is sometimes known as Celebes, which was the Dutch colonial..., have typically produced Giling Basah, wet-hulled coffee.

In the traditional wet-process method, the fresh coffee fruit has its skin removed (pulped) and it is left in concrete tanks to fermentAs an aroma or flavor in coffee, ferment is a defect taste, resulting from bad processing or other factors. Ferment is the sour, often vinegar-like, that results from... overnight. By a process of acidification and the breakdown of pectins the persistent, sticky fruit layer can be “washed” off of the inner green bean (still coated by a parchmentGreen coffee still in its outer shell, before dry-milling, is called Parchment coffee (pergamino). In the wet process, coffee is peeled, fermented, washed and then ready for drying... shell). Next, the coffee is dried by the sun for 20 days or so, until it reaches an 11% moisture level. It can then be bagged up, warehoused for a 30 day restingEither the resting of parchment coffee after drying, or for the home roaster, post-roast resting.: Resting might refer to "reposo", the time after drying the parchment coffee, when... period, at which time the parchment layer is shelled off, the coffee is graded by densityThe density of a coffee bean is often taken as a sign of quality, as a more dense bean will roast more with a better dynamic. The density... and size and hand-sorted for export.

Wet-hulling shares the same initial steps as wet-processing. In much of Indonesia it is small-holder farmers who carry out the first steps of the process. Farmers 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 ferment the coffee in any number of ways – in a polypropylene bag, a plastic tub, or a concrete tank, to get the fruit layer (mucilageMucilage indicates the fruity layer of the coffee cherry, between the outer skin and the parchment layer that surrounds the seed. It readily clings to the inner parchment...) to break down. After overnight fermentationFermentation in coffee processing traditionally referred to the stage in wet-processing of the coffee. We now understand that fermentation happens more broadly in nearly all processes, including honey..., the mucilage can be washed off and you then have wet parchment coffee. The green bean is inside the parchment layer, still swollen with water. It’s basically identical to wet-processing up to this point.

As mentioned, in wet-processing a farm would now slowly dry this coffee to 11% moisture. The green bean would become the small dried seed we know and the thin parchment shell is easily removed, as there is a substantial spacial gap between the parchment shell and the much smaller dried green bean.

But in Indonesia, the farmer doesn’t want to wait for all this to happen. Is it because they want to create a unique flavor profileFlavor Profile implies a graphical impression of a particular coffee, whether it be an artistic portrait or data graph of the perception of flavor compounds. In the case..., to shape the cup character, to get more body out of the coffee? No! It’s because they want to get paid! They want to do as little work as possible to process the coffee and get cash. And who can blame them? Coffee is a cash crop after all.

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 at a local coffee market. They get paid faster and do less work this way. Each town in the coffee producing areas has a section where the collectors compete to buy the wet parchment coffee. The coffee market coincides with the town’s weekly market day.

The collector accumulates the humid parchment, sometimes mixing it, and sometimes keeping it in separate bags. It matters little; they might pay differently based on the wetness of the coffee, or penalize for a lack of cleanliness (usually in the form of incomplete fermentation, a reddish partially dried mucilage still clinging to the parchment layer). But in any case there is no discrimination for quality and it is all eventually mixed.  Collectors buy based on the “litera”, a standard 1 or 2 liter volume, typically using a can found in the area. They often buy the coffee from farmers and sell it to a larger collector or mill at the same price, but they buy using a heaped can-full (called a Bocho, a hill) and sell by the level can-full. The difference is their profit.

The mill might dry the coffee a little bit more for 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.

The wet-huller is massive, generates a lot of friction and transfers heat to the coffee. It is powered by a car or truck engine, often times! The heat it imparts to the coffee is not good for resulting cup quality.  Coffee is soft when it is wet, not the hard dried seed we know well, and is prone to being crushed. It is rubberyA taste fault giving the coffee beans a highly pronounced burnt-rubber character. Result of continued enzyme activity in the coffee bean when it remains in the fruit and... like a pencil eraser, but sadly it is not resillient like one. The friction of the wet huller can mangle the coffee and crush the ends in particular.

After hullingHulling is the step at the dry mill where the green coffee bean is removed from the parchment shell. (See Wet Hulled for the Indonesia method). 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. In no other coffee origin would they consider laying the green bean out to dry without the parchment shell protecting it.

But this is Indonesia, the great exception.    In the best mills, the coffee is treated with care in this state, dried on very clean patios. In the worst case it is laid out on the road. In any case, direct contamination isn’t the only concern for quality. Overly rapid drying is bad for coffee, and the parchment shell creates a neat little environment for each green bean to dry. It stabilizes moisture, moderates diurnal temperature swings, and lessens the impact of direct sun. Take that away and you have the possibility of harsh and uneven drying.

Coffees that are dried well, with an even and slow loss of moisture, will last longer when they arrive at the importing country; good tastes won’t fade quickly into papery or burlap bag flavors. The soft coffee is also damaged on the patio by being crushed underfoot, or in the process of unbagging and rebagging it daily.

So why is the coffee stripped of it’s parchment shell when it is wet? Why is the green bean laid out to dry without this protective layer? Again, time is money. The longer you have coffee in your possession, the more money you lose. The quicker you can sell it, the quicker you make back your investment and keep your cash flowing, and the quicker you can take your profit.

Drying coffeeAfter coffee is picked, it must be dried. In both dry-process and wet-process (and the other hybrid processes like pulp natural and forced demucilage) the coffee must always... without the parchment is fast! Consider that in Central America the time from harvest of coffee cherryOriginally coffee literature referred to the fruit of the tree as a "berry" but in time it became a cherry. It is of course neither. Nor is the... to export might be 2 to 3 months, including 20-25 days to try on the patio, then 30 days of “rest” (called repose) in the warehouse for the coffee moisture to stabilize. In Indonesia coffee is often exported in under 1 month from picking the cherryEither a flavor in the coffee, or referring to the fruit of the coffee tree, which somewhat resembles a red cherry.: Either a flavor in the coffee, or... to loading the vessel at port!

The Crazy Indonesian Climate

To attribute Giling Basah to greed is false. Yes, people want to get paid quickly, but that is a factor in any coffee system. Indonesia faces a challenge in coffee production that few countries encounter to such a dramatic extent: weather. To be more specific, in Indonesia the farmer is trying to grow coffee in a humid climate. This means that the cherry is on the tree for many more months than in climates with clear weather patterns, with one or two blooms of the coffee flower per year. There are places in Central America where a coffee picker might visit a tree 3 times in the harvest to select the ripe fruit, and one last time to “clean” the tree of everything remaining. In Indonesia the farmer is harvesting the coffee weekly for up to 8 months of the year, revisiting a tree countless times to remove the ripe coffee.

More importantly, drying coffee in Indonesia is a nightmare. A “good” day for drying might have 4 hours of partial sun in the morning, and then rain in the afternoon. The coffee has to be collected from the patios before rains come, and the labor to get the coffee even slightly drier each day is taxing on the business of the coffee millA coffee mill might mean a coffee grinder, but we usually use the term to refer to a coffee processing facility, either a Wet-Mill or a Dry Mill..... Many of the mills we work with are building covered drying patios to increase drying times, since even in a rain shower there is heat and air movement to dry the coffee.

Keeping the parchment shell on each green bean would slow this process radically, and when coffee in parchment has been drying more than 30 days it shows problems in the cup. So in this light, stripping off the parchment shell when wet guarantees a better outcome than leaving it on in most coffee regions of Indonesia. Dry-processing coffee, where the entire fruit layer is left on the bean, is even more impractical in Indonesia as it would take even longer to dry the green bean. Mechanical drying or covered drying in hotter climates might make it feasible.

The Indonesian port cities that coffee is exported from, such as Medan in Sumatra, are exceptionally hot and humid. Oftentimes, coffee dried to 11% moisture at altitude in a place like Lintong gain water content in Medan as they are being prepared for export. There are logistic and legal reasons that specialty grade coffees cannot be exported with high moisture, especially when they are to be bagged per 60kg unit. The importer would be cheated of a large volume of coffee if it was shipped wet.

So in Medan they often “flash dry” the coffee for several hours in the intense sun, and quickly bag it up for export in jute. You can bring the moisture level back down from 14% or 15% to 11 or 12% quickly, but it is terrible for the cup quality of the coffee and something they would do nowhere else. They wouldn’t have to anywhere els either, because other coffee origins don’t suffer such humid climates.

The “Indo Coffee” Taste

Let’s be honest: On a cuppingCupping is a method of tasting coffee by steeping grounds in separate cups for discrete amounts of ground coffee, to reveal good flavors and defects to their fullest.... table of well-processed Central American coffees, an Indonesia wet-hulled coffee would likely be thrown out as defective. The earthyEarthy is a flavor term with some ambivalence, used positively in some cases, negatively in others.: Sumatra coffees can have a positive earthy flavor, sometimes described as "wet... and forestyA flavor found in rustic Indonesia coffees, wet-hulled types from Sulawesi and Sumatra in particular, reminiscent of a walk in the woods.: A flavor found in rustic Indonesia... flavors – herbalA flavor descriptor in coffee reminiscent of herbs, usually meaning aromatic, savory, leafy dried herbs. Usually, more specific descriptions are given, whether is is a floral herb, or..., sometimes mossy or even mushroomy – would be attributed to processing errors, and the coffee labeled as substandard.

So why this schism in the way the coffee trade treats wet-hull Indonesia coffees?   It comes down to taste: If a Sumatra supplier can consistently provide the same coffee processed the same way, be it fruityIn some coffee taster’s lexicon, “fruity” means the coffee is tainted with fruit, and “fruited” means a coffee is graced by positive fruit notes. We don't exactly see... or earthy, there are buyers who see this as a uniquely different flavor profile, and a welcome break from Central America, ColombiaColombian coffee is highly marketed and widely available in the US. They have been largely successful at equating the name Colombian Coffee with "Good" Coffee. This is half-true.... or KenyaKenya is the East African powerhouse of the coffee world. Both in the cup, and the way they run their trade, everything is topnotch.: Kenya is the East... coffees. And of course the bottom line is that their customers like it. Those who like minimally-processed wines or wines with complexThe co-presence of many aroma and flavor attributes, with multiple layers. A general impression of a coffee, similar to judgments such as "balanced" or "structured" flavors of leather, peat moss, fir, cedar, humus, tannins, will see something in the Sumatra flavor profile.

Peets and, in earlier days, Starbucks, made a signature flavor out of dark-roasted Indonesia coffee. The black oily cup was perfect for overloading with cream and customers saw this as “strong” coffee, something they identified as special because it wasn’t like Grandma’s can of Folgers. Light roast coffee was seen as “weak.” The thick body and low acidity of Indonesia further advanced the idea of a deep, brooding character (referring to both the cup, and the customer … or at least how they wished to be seen).

The fact is, dark roast levels obscure a multitude of defects in the cup. When Sweet Maria’s started back in ’97, right in the middle of this “specialty coffee as carbon-water” era, the samples of Sumatra coffees I looked at were hideous. And for perhaps a decade after that, many Indonesian coffees were exported with impunity, as “Grade 1 Mandheling” seemed to mean nothing, and 100+ physical defects per 350 gram sample of green beans was common. Indonesian exporters, perhaps as the most dubious in the coffee world, were not only given a free pass on the cupping table, but in terms of cleanliness of coffee preparationPreparation refers to the dry-milling steps of preparing coffee for export: hulling, grading, classifying, sorting.: Preparation refers to the dry-milling steps of preparing coffee for export: hulling, grading,... as well.

Recovering Giling Basah from the Dustbin

This might make it sound like all wet-hulled coffee is bad, since this method isn’t really rooted in creating good tasting coffee, but rather speeding up the process and mitigating weather problems.

But there is good versus 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-hulled 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 rusticA general characterization of pleasantly "natural" flavors, less sophisticated and less refined, but appealing. : What is Rustic? This is a general term we came up with... Dried... elements to distinguish gross and off-putting flavors like dirt from positive “clean-earth,” like humus or other relatively clean, natural scents and tastes. While slight green herb and mossy is good, vegetal notes that are too bitterBitterness is one of 5 basic tastes: Sour, Sweet, Salty, Bitter and Umami (savory flavors). There are many types of bitterness, hence not one avenue to tracking down... hint at poor processing or under-ripe fruits.

In our lab we also check the defectIn coffee, a defect refers to specific preparation problems with the green coffee, or a flavor problem found in the cupping process. Bad seeds in the green coffee... 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. Samples are cupped at lighter roast levels so nothing is obscured by the roast tasteThe set of flavors that result from the degree-of-roast.: Roast Taste is a term we started to distinguish it from "Origin Flavor". We use the "roast taste" term..., as well as more developed levels to show what flavors are possible with a darker treatment.

New Directions in Old Coffee Tradtions

Sumatra and Sulawesi have traditionally been Indonesia origins that were wet-hulling all their coffee. There have been instances of fully-washed coffee mills operating in Sumatra, like those of the dubious Holland Coffee operation in AcehThe northernmost district in SumatraL Aceh District is north of North Sumatra and produces some very classic Sumatra coffees. The center of coffee in Aceh is Lake Tawar.... In Sulawesi there was the plantation and wet millThe wet mill is a processing center where coffee cherry from the tree is brought for initial processing.: The wet mill goes by many names (Beneficio, Factory, Washing... of Sulatco and the forced demucilageDemucilage refers to a method to remove the fruity layer of coffee cherry... the called mucilage. Mucilage is the layer between the outer skin and the parchment layer,... (i.e. machine washed) coffee of Toarco’s Pedemeran plantation.  Other islands were producing fully wet-processed coffee like the PTP Government EstateA "coffee estate" is used to imply a farm that has its own processing facility, a wet-mill. In Spanish this is called an Hacienda. A Finca (farm) does... coffees of East Java: Jampit, Blawan, Kayumas. Bali coffee was often wet-processed, and newer coffee projects in places like Flores, and East TimorTimor-Leste (East Timor) is a tiny island between Australia and Sulawesi, annexed by Indonesia and liberated in a referendum several years ago. Small scale coffee farming was jump-started... are washed coffee.

The market likes wet-hulled flavor from Indonesia so some retrograde buyers are requesting Giling Basah process from places like Bali and Flores that did not historically do this method. This is part of a shift from an orientation to the Japanese market, which wanted cleaner cup character, to a part of the American market that operates with the ’80s mentality serving up French roastSugars are heavily caramelized (read as burned) and are degraded; the woody bean structure is carbonizing, the seed continues to expand and loose mass, the body of the... Indo coffee.  We have a new designation for our coffee projects in West Java, Sulawesi and Sumatra. We call it dry-hulled coffee. We could call it wet-processed, but we mean to distinguish it from wet-hulling. Dry-hulled coffees cupped next to their wet-hulled counterparts show more brightnessA euphemistic term we use often to describe acidity in coffee. A bright coffee has more high, acidic notes. : A euphemistic term to describe acidity in coffee.... and a lighter body.

But dry-hulling also fails to hide bad cultivars, and a vast percentage of Indonesia is planted in these ignoble plant types. The most popular is AtengAn improved Ateng selection of Timor variety with Bourbon reportedly. The specifics are a little doubtful (Timor x Bourbon) as it is not the result of a plant..., a type of coffee with robustaAteng is a common name for Catimor coffees widely planted in Sumatra and other Indonesia isles.: Ateng, with several subtypes, is a common name for Catimor coffees widely... inputs to give it disease resistance, and even worse is TimTimHibrido de Timor abbreviated HdT is the interspecies hybrid of C. Arabica and C. Canephora (Robusta) that was found in Timor Leste in the 1940s. This was presumed..., which is pure Timor hybrid, a spontaneous cross of arabicaArabica refers to Coffea Arabica, the taxonomic species name of the genus responsible for around 75% of the worlds commercial coffee crop.: Arabica refers to Coffea Arabica, the... and robustaRobusta usually refers to Coffea Robusta, responsible for roughly 25% of the world's commercial coffee. Taxonomy of Robusta is debated: some sources use “Robusta” to refer to any.... In wet-hulling, the processing flavors mask these varietals and their woodyGenerally a taste defect from age; old green coffee, perhaps yellowing in color. This is due to the drying out of the coffee over time, and as the... or metallic taste in the cup. But if you improve your wet-process method and dry coffee to 11% before hulling, you start to taste the bad plant material.

In our projects we have had farmers sort out Ateng and TimTim, to plant better types like JemberS-795 is a variety based on the " S-Line" coffees of  India, and stands for Selection 795,  It has a very fine cup, one of the best in... or S-linea, or old local Typicas that are still present from the Dutch era.  The ascendency of Indonesian coffeeIndonesian coffee is known for its unique earthy, potent flavors. Some like it, some hate it, but it's certainly distinctive. Much of the coffee in Indonesia is processed... will necessitate buyers to make these demands, to stop accepting defect-riddled coffees, to roast in a way that reveals the character of the green coffeeGreen coffee refers to the processed seed of the coffee tree fruit. Coffee is a flowering shrub that produces fruit. The seeds of the fruit are processed, roasted,..., and to teach coffee customers what a clean, well-prepared Indonesia coffee can truly be.

–Thompson

A few more Sumatra resources in our coffee library:

Here’s a video Tom put together discussing coffee trading and cultivation traditions in Aceh

Check out Tom’s photo travelogue from a 2019 visit to Aceh, Sumatra