Clear Lake Coffee Roasters - What’s the Deal with Wet Hulled Coffee Processing? September 10, 2020

Indonesia is every sort of wet and always all kinds of “Basah.” Rain? Plenty of it, more than most places on earth. Humidity? Oh, heck yeah. Humidity will often reach well above 90% throughout most of Indonesia. Ocean? Everywhere. Everywhere, there is ocean.

The story behind “Giling Basah” (grind or mill wet) coffee is, start to finish, a story about moisture. Although you might hear tell that wet hulled coffee is a processing expediency related to cash flow, the fact that producers can be paid sooner rather than later for wet hulled coffee is simply a reality that coincides with the necessity of battling the relentless presence of moisture and the impracticability—economic, logistic, structural—of drying coffee efficiently in that environment, combined with the prevalence of smallholder farmers. The story goes like this …

Let’s say you are a small coffee farmer in Sulawesi (though you could be in Flores, Sumatra, Java, Bali or even Laos.) Like 9 out of 10 coffee farmers in Sulawesi you grow coffee on less than 1 hectare of land. Like your coffee farming neighbors, you don’t have access to a coffee mill or production facility of any kind other than a small, shared, hand-cranked pulper manufactured long ago by E. H. Bentall and Co. that has been rebuilt and repainted many times over the decades.

Founded in 1805, E.H. Bentall & Co., of England, began manufacturing plows and was known for innovative design. By WWI the company had expanded into manufacturing all kinds of farming implements, including a wide variety of milling equipment. Following WWII, the company found a significant growth niche manufacturing coffee processing machinery. Bentall was acquired by a company named Acrow in 1961, but the Bentall brand remained. Acrow closed its doors in 1984, so when you see small milling equipment, like these Bentall pulpers in Sulawesi, they are at least 40 years old and possibly much older. Photo by Clear Lake Coffee Roasters during a 2019 sourcing trip.

After you harvest coffee cherries you run them through the hand pulper, spinning a cylindrical “cheese grater” that removes the outer skin and the bulk of the flesh of the cherry, or pulp. But this leaves a layer of fruitiness, the “mucilage,” or, if you’re the kind of person who uses a lot of starch in your lab coat, what you might call the “pectin.” To break down that pesky pectin, you soak the sticky coffee in water overnight inside … well, whatever you have, from bags to buckets. This is fermentation and it makes it easier to wash off the mucilage to get to the clean parchment.

After pulping the mucilage remains, so the coffee is fermented overnight to make it easier to remove.

But wait, you say, this sounds like wet-processing. But wait, I reply, yes it does, but I’m not finished. At this point, you have wet parchment coffee. We need the green bean inside the parchment to lose some of its “water weight” because then it will be easier to remove the parchment. This means drying the coffee because as the green coffee bean inside the parchments loses moisture it shrinks and separates from the parchment, making it easier to remove. The difference between wet-processed coffee and wet-hulled coffee is how we get from point A (wet parchment) to point B (dry green coffee).

After the mucilage is washed off you dry the parchment wherever you can to get the moisture content down to 50%.

In wet processing, or washed coffee, the wet parchment now begins a lengthy drying process, a distance measured in moisture but not necessarily time. Wet parchment will have a moisture content well above 50% and it needs to be in the neighborhood of 11% to remove the dry parchment after it has separated from the bean. This is accomplished by drying the coffee in parchment on patios or mechanical dryers or a combination.

You don’t have a drying patio. Even if you did, between rain and relentless humidity, it would take a long time to get coffee down to 11-13% moisture for dry hulling. So, you spread the coffee out as best you can, wherever you can, to get the moisture content closer to 50%. The time can vary from one to several hours depending on circumstances.

Coffee collectors buy coffee from farmers and then sell to the mill at the same price per standard size can. The difference is, when they buy the coffee, they buy a heaping can full (like a heaping spoonful), but when they sell the coffee they sell a level can. That tiny hill of coffee on each can is their profit.

After this brief period of drying you take your coffee into town on market day and sell it to a buyer or “collector.” If your coffee isn’t too wet and it’s clean of mucilage, you’ll get a better price than otherwise.The collector has the means to transport coffee to a mill with a “wet hulling” machine. They wait for the coffee to lose another 20% moisture, give or take, but even so the parchment remains tightly adhered to the bean.

A wet huller is a large milling machine designed to apply the extra friction required to remove parchment that is still, relatively speaking, damp, and doesn’t want to go anywhere. A wet huller works on the same principle as a dry parchment huller except it applies great friction and is designed to operate in a much wetter environment, drawing off water in addition to parchment.  Imagine you are removing leaves from your driveway with a leaf blower. Now imagine how much easier it is to remove dry leaves than it is to remove wet leaves and you have some idea of the difference between dry hulling and wet hulling. Finally, after wet hulling, the green coffee is laid out to dry, but without the parchment it dries much faster. As a result, your coffee can go from picking to shipping in around a month; whereas, in most coffee growing regions this takes several months.

This process can be abbreviated, usually depending on geography (i.e. the farmer might sell directly to a mill) or elongated (i.e. their might be more “middle-people” between the farmer and the mill). Wet hulling can be more unforgiving than other processing methods but can also provide opportunities to deliver the best of traditional Indonesian profiles without the negative aspects sometimes associated with poor quality. Wet hulling emphasizes body over brightness, and savory over sugary sweetness. Because the final drying is done without the protection of parchment, care must be taken with the drying environment. Mills with an eye on improving quality use raised, screen beds in greenhouse-like structures to protect the green coffee, and to keep the moisture content from creeping back up.