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The weirdest coffee I’ve ever tasted is one I found at a coffee shop in Portland, Oregon, last fall. Like many coffee enthusiasts, I usually buy beans based on the country of origin or the reputation of the roaster, but that day something different beckoned. It was a bag labeled “watermelon co-ferment” from Quindio, Colombia. “Coffee and watermelon flavors eloquently mingle,” promised the label.

I brought the beans home with no idea of what to expect. I’m used to picking up subtle tasting notes in coffee, a hint of cacao, or even blueberry. This was something else entirely. As soon as I opened the bag, aroma of watermelon erupted forth. In the cup, that flavor dominated every other aspect. This was no hint of fruit. This was hyperreal watermelon, amped up to 11. Drinking this coffee felt closer to sucking on a Jolly Rancher candy than sipping a standard cup of joe. I’d never tasted coffee like this. I wasn’t sure coffee should taste like this.

Fresh out of college in the early 2000s, I worked as a barista in the kinds of coffee shops commonly described as “third wave.” These were the shops that sometimes took themselves a little too seriously but that also elevated the quality of coffee in the United States. This was the era of super dark roasts à la Starbucks, rows of pump-bottle syrups, and cloying coffees sprayed with artificial flavors like hazelnut and Irish cream. For many of us, the contrasting purity of lightly roasted single-origin coffee was a revelation. With the zeal of the newly converted, we evangelized for tasting coffee for itself instead of covering it up.

The ethos of this era was “bean to cup,” the idea that everyone involved in coffee production— from farmers to roasters to the barista or the person brewing at home—should aim to bring out the best qualities inherent in the coffee beans. It was a philosophy consciously modeled on winemaking, the goal in both cases being to shepherd an agricultural product through all the processes required to make a complex and nuanced beverage reflective of the place where it was grown, with flavors emerging from factors like the varietal of the plant, the conditions it was grown in, and how it was processed after harvest.

Now, “co-fermentation,” the industry term for processing coffee alongside other fruits or spices, has emerged as a controversial development in the world of specialty coffee. The flavor in my watermelon coffee wasn’t a postproduction addition in the manner of, say, a pumpkin spice latte; it was infused into the beans before they were even roasted. But it’s undeniably a flavor that didn’t come from the coffee beans themselves.

For some, this kind of processing is completely beside the point. “You wipe out the very miracle of what coffee can taste like,” says George Howell, owner of an eponymous roasting company and small chain of coffee shops in Boston. Howell is a legend in the industry—and decidedly old-school. In his view, co-fermentation represents “a new age of flavored coffee,” a means of sneaking non-coffee flavors in through the back door after years of exile from the specialty realm.

Co-fermentation can even get coffees kicked out of formal competitions. At this year’s Best of Panama tasting, where the top-scoring microlot sold for an astonishing price of more than $4,500 a pound, four other submissions were disqualified for being “altered from their natural DNA expression, likely with the intent to score higher and win by using foreign additives,” according to an official statement. Though the exact details of the disqualified coffees were not made public, the clear message was that co-ferments are a no-go. In the high-stakes milieu of competition, some view co-fermentation as the equivalent of doping in sports, a means of gaining unfair advantage.

Yet other roasters and producers are positively excited about co-fermentation, embracing it over the past few years as a cutting-edge method for making wildly unique and flavorful coffees. Though still a niche fraction of the market, coffee consumers are increasingly likely to come across bags of beans advertising the influence of ingredients like passionfruit, lychee, and cinnamon.

These beans stretch the boundaries of what coffee can taste like. They also challenge the traditional paradigm of specialty coffee, which for decades has emphasized the pure expression of provenance and varietal. Are co-fermented coffees an exciting new direction, or a step backward after years of progress? And will coffee lovers pay extra for a morning brew that’s redolent with tropical fruit? These are the questions at the core of coffee’s brewing identity crisis. To explore them, I spent a few weeks speaking with experts in the industry and sampling some of the strangest coffees of my life.

Beans don’t fall from trees roasted and ready to brew in your morning cup. They start out as a fruit called a coffee cherry. The first step for most coffee is separating the hard inner seed, which we eventually purchase as a coffee bean, from the fruit that surrounds it. The seed is then rested (and typically ferments just a little bit), rinsed, and dried. This is known as the “washed” process, and it’s the standard method for most of the coffee we drink. The dried beans, known as “green coffee,” are then sold down the supply chain to roasters, who roast and package them for retail sale.

An alternative to the washed process is the “natural” process. In this method, whole coffee cherries are left to dry in the sun for several days or weeks before the fruit is removed from the seed. This more rustic method is useful in some environments because it’s less water-intensive than washing. It also allows for a very long period of fermentation within the fruit, leading to some truly wild flavors in the cup. When it goes well, natural fermentation produces deep, fruity, and winey notes that are prized by many coffee tasters.

Since it’s still just coffee cherries involved in the process, natural processing is distinct from co-fermentation with other fruits or spices. Natural coffees have nonetheless inspired their own periods of division in the industry. Howell, for example, used to be firmly in the washed-process camp, but has come around to appreciating some natural coffees. By now they are routine in specialty coffee, scoring highly in tastings and featuring prominently in barista competitions.

The rising popularity of natural coffees over the past couple of decades led to what coffee scientist Mario Fernández of the Specialty Coffee Association calls the “processing revolution.” At a recent coffee symposium, he described this as “an innovation jungle where every producer is trying to stand out through differentiation from their neighbors.”

Producers are suddenly experimenting with a vast variety of processing methods. These range from the honey process (a sort of hybrid between washed and natural) to fermentation techniques borrowed from the wine industry. Anaerobic fermentation, carbonic maceration, and thermal shock are a few of the obscure terms you may encounter on a bag of fancy coffee these days. You don’t have to know precisely what they mean. Suffice it to say that they are all techniques for developing flavors via the interaction of microbes with the coffee bean, often producing more boldly assertive fruit notes than you’d find in a typical washed coffee.

In Portland, Push x Pull is the roaster to visit if you want to experience these kinds of coffees. I met with owner Christopher Hall over a cup of “Black Sheep,” which is a “double anaerobic natural” coffee from Yunnan, China. It’s a coffee that would have blown my mind as a barista in the early 2000s. Beans from China? We didn’t have those. Double anaerobic? I wouldn’t have known what the phrase meant. (In brief: It means coffee that has undergone two periods of fermentation while sealed off from fresh oxygen.)

Push x Pull features 10–15 different coffees at any given time, offering new beans every week. Often there’s not a single washed coffee among them. “When we opened, we figured we’d play it safe; we’ll do half washed coffees,” says Hall. “And really quickly, we were having people that were not educated on the processes coming back and being like, ‘Whatever that was, that’s the one I like.’ ”

Black Sheep was relatively normal compared to other coffees we sampled. While at Push x Pull, we put several of their co-ferments through the evaluative process known by coffee pros as “cupping”: brewing the coffee in bowls of hot water, scooping the grounds off the surface while inhaling the aroma, and slurping from a tasting spoon. The co-ferments we tried ranged from coconut lemonade and lychee to the evocatively described “sangria.” As the names suggest, these were dramatic flavor profiles, often tasting markedly like the fruits they were processed with.

Stylistically, Hall’s coffees are far removed from what you’d find at a shop like Howell’s, where the focus is on washed coffees and an occasional natural. Yet both roasters see their role as showcasing the work of farmers who grow the coffee cherries in the first place, who, even in co-ferments, provide the foundation of what the coffee tastes like. “If we don’t mess it up, we’ve done our job,” says Hall. It’s just that with co-fermenting, the impact of processing is way more evident (in fact, unavoidably evident). “Are these coffees a diversion from what they could have been? Yeah,” says Hall, who notes that co-fermentation can make what might have been a mid-tier coffee more flavorful and interesting; “you’re getting the farmers’ handiwork and experimentation in the seed.”

Cupping these coffees side by side was an illuminating experience, showcasing the wide range of co-ferments. The sangria, my favorite of the bunch, was grapey, fruity, and complex. The lychee was delicately tropical. The coconut lemonade was, to my palate at least, a bit discordant. But they were all intriguing, unlike any coffees I’d tried before. I was curious to learn more about how these flavors made their way into the beans.

In theory, co-fermentation works like this: You take some coffee cherries, you toss them in a tank with a bunch of strawberries to ferment, and you end up with coffee that tastes like strawberries.

The reality, according to experts I spoke with, is a bit more mysterious.

“The coffee bean is designed to absorb water because it’s a seed,” explains Peter Giuliano, executive director of the Coffee Science Foundation. “But it’s also designed to keep things out that are going to prevent it from germinating.” That means that the coffee beans in that vat wouldn’t absorb the strawberry flavor so easily. And even if they did, then there’s the high-heat roasting environment, which kicks off a cascade of incredibly complex Maillard reactions, the chemical process that creates distinct tastes in browned foods like a seared steak, a crusty loaf of bread, or, of course, coffee. For a volatile flavor molecule to make it out of a fruit and into the coffee bean, survive the heat of roasting, and then express itself in your cup would be a minor miracle.

So, where do the flavors in a co-fermented coffee come from? Theories abound—and the process can vary from producer to producer. One answer is that fermentation really does produce wildly fruity flavors that persist to the cup. Adding fruit to a fermentation tank can certainly impact that process, though not necessarily in the sense of directly transferring flavor to the bean such that your cup of coffee is exploding with strawberry flavor. Another possibility touted by some producers is that the beans are soaked not in a vat of whole fruit, but rather a sugar-rich environment of concentrated fruit juice. In that scenario, water flows out of the bean as flavor soaks in, a process called “osmotic dehydration.”

An honest discussion of co-fermented coffees must also raise the possibility that some producers are discreetly adding less natural sources of flavor to their beans, such as flavor extracts or dehydrated fruit powders. As a consumer, it’s difficult to know exactly what goes into making co-fermented coffees. Even roasters don’t always know for sure.

Kyle Ramage of Black and White Coffee Roasters in Raleigh, North Carolina, acknowledges there is sometimes an air of mystery about co-ferments. “I can be OK with this as long as producers are truthful with what they’re doing, and to a degree, I have to take what they say and believe it until it can be proven wrong,” he says. When he asks for more details, he sometimes finds that producers are also adding fruit powders. Another recently admitted adding a vial of artificial flavoring, a practice the producer suspected others of quietly doing too.

But Ramage is wary of pushing back too aggressively, noting that producers have a genuine interest in protecting their trade secrets. “I can’t in good conscience say, ‘Tell me everything you’re doing or I’ll never buy coffee from you again,’ ” he says. “That feels pretty colonial.”

Perhaps we need to use better language to describe these coffees. “Anyone can do whatever they want and say whatever they want and call it whatever they want because there’s no standard or regulatory body,” says Lucia Solis, a coffee processing specialist who also hosts a podcast about coffee production. She suggests differentiating between unique fermentation processes and “infusions,” the latter referring to any technique aimed at producing a one-to-one addition of external flavors to coffee beans.

In Solis’ experience, most producers who experiment with co-fermentation are using real fruit, and producing coffees that are fruity, but may not taste overwhelmingly like the fruits they are fermented with. She advises that consumers should trust their palates if a flavor seems too singular and pronounced. “I think we can trust ourselves to say this was an artificial addition. It was an essential oil, a crystallized powder, or some other method.”

The “co-fermented” label is winning the marketing battle for now, but regardless of the terminology, producers and roasters will only make such coffees if consumers ultimately want to buy them. With that in mind, I was curious to see how coffee drinkers who don’t work in the industry would respond to tasting coffee that falls under the umbrella of co-ferments.

On a recent Saturday morning, I gathered a group of coffee-loving friends for a tasting of five coffees co-fermented with different ingredients: coconut and citrus, mango, hops, watermelon, and cinnamon. The group knew that these were co-ferments, but I kept the specific details under wraps. I wanted to find out if they would recognize the additions by taste alone, as well as whether they would like them.

Interestingly, the panel identified only two of the coffees spot-on. Two of five tasters nailed the watermelon and called out its candy-like aroma. Two also correctly noted the distinct flavor of cinnamon.

More often, tasters picked up related notes but didn’t perfectly correlate them to the actual ingredients. Hops came across as bitter, herbaceous, or junipery. One taster picked up hints of dill from the coconut and citrus co-ferment. The watermelon flavor that I found so overwhelming was not quite as obvious when tasted blind, prompting one taster to guess it was cucumber. The mango confounded everyone.

Tasters were also divided on whether they liked the coffees. Several thought the watermelon was too weird; another picked it as her favorite. Everyone agreed the co-ferments made for a fascinating tasting, though, as one tester summed up the experience, “I’m glad I got to try these, but I wouldn’t buy a whole bag.”

Through my own tasting, I’ve come to think of co-ferments in three different groupings. The first are coffees that are noticeably wild and fruit-forward, but that don’t taste specifically of a certain fruit. The second group tastes more like typical coffee but with a little something extra layered on top, like the cinnamon or hop notes that were unmistakably present if you knew to look for them.

In the last group are the co-ferments that taste a little too much like the fruit on the label and not enough like, well, coffee. Tasting these was like listening to music with the treble turned way up and no bass; the high notes were there but the depth was absent.

In a way, coffee is going through what has happened with alcoholic beverages, a bombastic phase with creators trying to outdo each other in pushing the boundaries. Like a cinnamon-roll imperial stout or a six-ingredient cocktail made with banana foam, these wild coffees were fun to taste, but I probably won’t make a habit of drinking them, especially since all of the co-fermented coffees I tried sell for more than $25 a bag. I’ll always come back, again and again, to a simple pilsner or Manhattan—and a more classic cup of coffee. Still, I certainly wouldn’t discourage anyone from giving co-ferments a try if only to experience how out there the flavors of coffee can be.

It would be easy to condemn co-fermented coffee for lacking purity or to hype it up as the next big trend. It’s fairer to say that it’s simply interesting. Coffee is a slippery bean; as soon as you think you have a grip on it, you realize you have so much more to learn. As Howell laughingly said to me, acknowledging his own evolution learning to appreciate some natural-process coffees, “I always have a hat that’s made of chocolate in case I have to eat it.”

One might also take this wild experimentation as a sign that the cultural status of specialty coffee has become secure enough to be less serious and have a little fun. I doubt that co-ferments will substantially displace more conventional coffees, but they can nonetheless have a role to play in coffee-drinking.

“We’ve embraced the concept that coffee doesn’t have to have the flavors that we stereotypically think that it has to have,” says Ramage. “What I love about [co-ferments] is that people go absolutely crazy for them and it’s an interesting little gateway drug for a lot of people. Sometimes they stay with those kinds of coffees forever, sometimes they move into other styles.” He also points out that co-ferments can play a promising role in blends, allowing their standout notes to play in concert with more traditional beans.

One can also argue that it’s hypocritical to insist that coffee growers and processors abstain from fermenting with fruits and spices while coffee shops serve all kinds of signature drinks. “You’ve got baristas making lavender lattes and matcha lattes and all these interesting, multicultural flavors,” says Giuliano. “It’s only natural that processors want to get in on the act.” A successful co-ferment can transform an unremarkable coffee into one that roasters will pay a premium to source.

Ultimately, whether co-ferments are a lasting part of the coffee world or more of a fad might depend on whether the financials behind them can work. Sampling a co-ferment may be a fun experience for us, but for financially precarious producers, making them can be a risky investment. A handful of producers, mostly from Colombia, are clearly finding success with co-ferments, and if you shop around, you’ll see their names pop up again and again. But Solis points out that for most producers, growing reliably good coffee with a more classic flavor profile is a better bet than chasing a potential fad. “People are gonna buy it one year, one time,” she says. “And then they’re going to want to go back to the regular stuff.”

Her appraisal matched my own experience. There were a few co-fermented coffees that I would gladly try again someday, but after weeks of drinking them, I was eager to get back to beans that were a little more traditional, the kind Howell might describe as “coffee coffee.” My girlfriend and I began tasting through a coffee advent calendar from Scandinavian roasters, trying new brews every morning. One in particular stood out for its remarkable depth, rich flavor, and incredible berry notes. Looking up the details, we learned that its character didn’t derive from any exotic process of fermentation or additions of fruit. It was a simple washed coffee from Kenya featuring a varietal known as SL-28.

Coincidentally, Howell had mentioned SL-28 in our conversation weeks before as an example of an exceptional coffee at risk of being forgotten if we lose sight of varietal and provenance. Out of all the coffees that I’ve tried in recent memory, it was one of the best.

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