Delicately complex aromatics of mild florals, brown sugar, melon, and citrus lead to a juicy and beautifully complex cup profile with flavors of black cherry, marzipan, caramel, and tropical fruit. While perhaps not offering quite the depth of sweetness or overall flavor balance that we find in the Gaharo Dry Fermentation experiment, we think this lot exhibits better flavor clarity and possesses a slightly cleaner, more sparkling acidity.
When preparing “wet processed” coffee, the coffee seeds undergo a fermentation stage - sometimes underwater and described as “wet” and sometimes in the open air and described as “dry” - to facilitate the removal of the sugary mucilage that remains following the mechanical removal of the fruit. Thanks to the support of our friends and partners at the Long Miles Coffee Project in Burundi, we can now offer the unique opportunity to taste two experimental lots, one wet fermented and one dry fermented, that were processed from a single delivery of cherry harvested on Gaharo Hill in June, 2020.
"Fermentation” is a tricky and potentially misleading term in the context of specialty coffee production. While it is understandable that many coffee enthusiasts have drawn parallels between the use of fermentation in coffee processing and, say, fermentation techniques in winemaking, the function and impact of fermentation in coffee is really quite different from the central role that it plays in the production of wine and other fermented beverages such as beer and kombucha. With that said, while coffee is not a fermented beverage, spontaneous fermentation involving natural yeasts and bacteria certainly plays a key role in most coffee processing around the world.
As many readers will already be aware, the roasted coffee “beans” that we know and love originate as the seeds of small cranberry-sized fruits that are often collectively referred to as coffee “cherry”. At harvest, coffee pickers collect ripe cherry in large sacks and the fruit is delivered to a mill where “processing” (the necessary steps that transform fresh picked cherry to exportable, ready-to-roast “green coffee”) begins. One of the most commonly employed approaches to coffee processing is referred to as “washed” or “wet” processing. While the specifics of this approach vary widely from country to country and farm to farm, the washed process includes a fermentation stage in the vast majority of situations.
The role of fermentation in this context is to help remove the sticky, sugary layer of mucilage that remains on the surface of the coffee seed after its fruit has been removed by a pulping machine. Yeasts and bacteria in the air, on the fruit, or in the water if the freshly pulped coffee is soaking in a tank, play a key role in breaking down the sugars in the coffee’s mucilage. With a little time and agitation, the mucilage can be completely removed and a handful of formerly sticky coffee seeds begin to feel smooth like river pebbles. Once it reaches this stage, the coffee is ready to be dried. So, when we talk about fermentation in coffee processing, we are not specifically stating that the coffee is itself fermented, but more that microbes have been employed to “demucilaginate” freshly pulped coffee so that it can be successfully dried, milled, exported, roasted, ground, brewed, and enjoyed!
While some kind of fermentation stage occurs in all versions of the wet process (except in cases where the mucilage is mechanically removed), specific approaches vary in different parts of the coffee producing world. At some processing sites, the freshly pulped coffee ferments in a tank in the open air, while at others the fermentation stage occurs with the coffee fully submerged under water. The former approach is often referred to as “dry fermentation” while the latter is generally described as “wet fermentation”. While both approaches can result in excellent quality coffee, they certainly differ in terms of the type of fermentation environment that the coffee navigates during processing and different fermentation environments can certainly impact the cup profile that the coffee ultimately exhibits.
On our last trip to visit our friends at the Long Miles Coffee Project in Burundi in February 2020, we asked the coffee quality team if they would be willing to help us conduct an initial experiment to explore the impact of wet and dry fermentation on eventual cup profile. Thanks to their generosity and willingness to support us with this project, the experiment was completed last year and we purchased four distinct experimental lots that were processed from cherry harvested on Gaharo Hill and processed at the Bukeye washing station.
The initial two experiments that we are currently adding to the Education Lot menu originated as a single allotment of cherry that was delivered to the washing station on June 8th, 2020. Half of the delivery underwent wet fermentation following pulping, and the other half was dry fermented in the open air. Both lots were soaked in clean water following fermentation before being moved to raised beds for drying. Tasting these two lots, which in our opinion are both quite delicious in subtly different ways, is a fascinating experience, and we’re already dreaming up new experiments for the upcoming harvest!