In contrast to the other Mutana experiments, we find a unique, syrupy sweetness in the 72hr that points to the extended time this lot spent in the Afri-tank container. Sweet hay, black tea, and maraschino cherry aromatics introduce a cup with deep molasses-like sweetness and additional notes of apricot and baking spices.
Thanks to the support of our friends at the Long Miles Coffee Project, we are thrilled to share four experimental lots from Mutana hill that, following de-pulping, were kept sealed in plastic Afri-tank containers for four distinct fermentation times, providing a unique opportunity to explore the impact of “reduced oxygen” processing on eventual cup profile.
"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 many instances of 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 cherries 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, wet processing 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!
Over the past decade, there has been growing interest within the specialty coffee industry in experimental processing approaches that seek to manipulate the “fermentation stage” in various ways. Whether employed to pursue a desirable standard of control and repeatability in coffee processing, or to develop interesting new flavor profiles in the cup, these techniques have been increasingly trendy in recent years, and words such as “anaerobic”, “aerobic”, and “carbonic maceration” have become marketing buzzwords on producer, importer, and roaster coffee descriptions around the world. Among these terms, “anaerobic” is perhaps the most commonly used - often as a description of coffee fermentation that occurs in a sealed container or other low oxygen environment.
At Passenger, it continues to be the case that the majority of the coffees that we are most excited to drink, most inspired to roast, and most proud to share are examples of traditional processing approaches (mostly washed, sometimes honeys, sometimes naturals). This is simply and purely a reflection of our team’s subjective taste preferences and absolutely not a judgment of what anyone else enjoys or is motivated to produce. But while we may have slightly conservative tastes in today’s coffee market, we are also committed to learning, and fascinated by experimentation - especially in collaboration with producers with whom we have cultivated trust through long term partnership.
Near the start of 2021, as a part of Burundi harvest planning discussions with our friends and partners at the Long Miles Coffee Project, we learned more about the “reduced oxygen process” that the team at Heza washing station was developing. We were interested to pursue a comparative tasting experiment to explore this processing approach, and asked the team at Long Miles if it would be possible to forward-book four bags of coffee from Mutana hill for this purpose. At the time of writing, we are proud to share the results of this 2021 experiment: four distinct microlots from the same cherry delivery that were fermented for different durations in sealed Afri-tank containers (creating a reduced oxygen environment).
The reduced oxygen process employed by the Long Miles team is a simple variation of traditional wet processing in Burundi. Freshly harvested coffee cherry is delivered to the washing station where it is sorted for ripeness and weighed for farmer payment. The coffee is then de-pulped - at which point the experimental phase begins: rather than undergoing a fermentation stage in an open air tank, the mucilage-coated parchment is placed in a sealed Afri-tank container. The four microlots that Passenger contracted for this experiment were kept sealed in the Afri-tank containers for four different time periods: 36hrs, 48hrs, 60hrs, and 72hrs. When the target fermentation time was reached, the parchment was removed from the tanks, washed in grading channels with fresh water, and then dried on raised beds.
We find each of these experimental lots to be thoroughly enjoyable when brewed individually. And taking advantage of a limited chance to taste more than one of them side by side provides a unique opportunity to assess the impact of differing fermentation times (in a reduced oxygen environment) on eventual cup profile.