How a Forgotten Bean Could Save Coffee From Extinction
One leading botanist is scouring remote corners of the earth to find new species that could keep our mugs full
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Stenophylla is a coffee plant, not a criminal, and yet it can still lay claim to its very own “Wanted” poster. In 2018, Aaron Davis, head of coffee research at the Royal Botanic Gardens, Kew, in London, was desperate to track down the rare species, which hadn’t been seen in the wild since 1954. The data he’d found in historical records suggested that stenophylla might be resistant to drought and heat—increasingly valuable traits in a warming and drying world. So he created a “Have you seen this plant?” flyer with pictures of stenophylla’s leaves, whose pointed tips resemble snake fangs. A colleague of his based in Sierra Leone, Daniel Sarmu, jumped on a motorbike and rode across the country’s rust-colored dirt roads, handing out copies to farmers. Most shook their heads: They had never seen a plant like that. This went on for days: more roads, more farms, nothing. “It was clearly not working,” Davis says. He had no choice but to start searching Sierra Leone’s forests himself.
Every day, the world’s population consumes about two billion cups of coffee. It’s more popular in some places than in others. The average American drinks as many as three cups a day. People drink even more in some European countries, such as Finland and Luxembourg. Ethiopia has a coffee culture, but in other African coffee-growing nations, relatively few drink it. Brazilians drink twice as much per capita as Colombians, but most of Latin America barely touches the stuff, opting instead for less expensive bottled soft drinks. In Asia and Australia, people tend to prefer tea. Coffee is beloved as an energy booster and a mood enhancer. It’s also a social and cultural ritual, and, above all, a habit. Many coffee drinkers are quite particular about what’s in their cup, whether it’s a flat white or a venti iced caramel macchiato.
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When it comes to taste, coffee is amazingly complex. A single cup may contain up to 1,200 volatile compounds. Yet what you perceive in a cup depends on many things besides the plant’s genome: the environment in which it grew, the weather, the roast, the water used for brewing. Even the color of the cup matters. White makes coffee seem more intense, while clear glass makes it seem sweeter.
As of now, almost all of humanity’s coffee needs are supplied by just two species: Coffea arabica and Coffea canephora, widely known as robusta. Arabica has plenty of varieties, such as geisha or bourbon, but these are like types of apples you can find in a supermarket—whether it’s a Granny Smith or a Gala, it’s still an apple. Arabica is appreciated for its wide, complex range of flavors, including notes described as floral and fruity. The crop itself is delicate. It doesn’t like high temperatures, it doesn’t deal well with droughts, and it’s vulnerable to pests. It needs to grow at high altitudes, too, preferably more than 3,200 feet above sea level. Robusta entered the scene much later than arabica, described by a Belgian botanist only in 1898, when a fungal disease called leaf rust decimated plantations of arabica at the turn of the 20th century. Disease-resistant robusta quickly gained ground over its fragile cousin. Bitter, harsh and cheap, it’s more of a workhorse, often made into instant coffee. But in today’s changing climate, even robusta crops are failing.
Both arabica and robusta love water, and the places where they grow are getting less and less of it. Arabica likes at least 59 inches per year—as much as the annual rainfall in one of America’s wettest states, Louisiana. While robusta can do with less, it’s not just about the quantities of water. The timing matters, too. “The producers really want to know one thing: When does it start to rain?” says Christian Bunn, a coffee researcher at the International Center for Tropical Agriculture, in Colombia. When the rains come, the plants begin to flower, and the growing cycle begins. “Now, suddenly, these rains come later, they come early, they disrupt the dry season, or a dry spell disrupts the rainy season,” Bunn says.
Bunn was the lead author on a 2014 study showing that climate change could slash the global area suitable for coffee production in half by 2050. At the time, people were skeptical. “This attitude has changed,” he says. Coffee crops around the world have recently fallen short—the world’s second-largest coffee-producing country, Vietnam, had a 20 percent production drop in 2023. Now, companies are worried. “They don’t know where the coffee of the future will come from,” Bunn says. Due to habitat loss and climate change, 60 percent of wild coffee species are now threatened with extinction.
That’s why Davis is so interested in rediscovering lost coffee species. It’s not that any single species will provide a magical solution to the many challenges facing global coffee production—not even a mythical heat-and-drought-resistant coffee plant like stenophylla. But certain rare species could be used both to partly replace crops in areas that are becoming too hot for them and to crossbreed new, sturdier strains. To make this happen, though, scientists will need genetic resources from which to choose the best traits—and not only those that make them unusually resilient, but also those that impart a great taste, too. That last part is crucial. No species, however resilient, can become the coffee of the future if people don’t find it delicious.
Davis was a teenager in the 1980s when his mother’s green thumb got him interested in botany. He earned his PhD at England’s University of Reading in 1994 and went on his first coffee-finding mission later that decade, when his colleagues drafted him for a trip to Madagascar to look for new species. But his obsession with stenophylla only began about 15 years ago with one antique book, he tells me as he scans the shelves of his cramped office at Kew’s Herbarium. The place smells of old wood, dried leaves and coffee. Through large windows, I see the ocean of green that is Kew: a UNESCO World Heritage Site that harbors one of the most extensive botanic collections in the world. The gardens look calm compared with Davis’ office, which is a chaos of files, centuries-old botany books, coffee grinders, pots and filters, as well as bags, boxes and jars filled with rare coffee beans. No one has discovered more Coffea species than Davis has. He alone has found about a third of all the ones known to science. And he is far from finished.
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Davis finally locates the book he was hunting for, a 1925 monograph on coffee by American biologist Ralph Holt Cheney. He flips it open to read me a passage that describes stenophylla beans as “superior to those of all other species.” Other old books Davis found similarly praised stenophylla as “exquisite” and more delicious than the best arabica. Old documents also claimed that this species could grow in lowlands, survive high temperatures and withstand droughts. “I thought, ‘Oh, God, it’s just so interesting. I’d really like to try it,’” Davis says.
He now has two jars of stenophylla beans stashed in one of his office’s cupboards. They’re yellowed with age, which is hardly surprising, considering that they’re from 1856 and 1873. Davis unearthed them from Kew’s Herbarium. At one point, he was tempted to roast a few of the beans, but a colleague warned him that he might poison himself—the beans were likely laced with ancient preservatives.
Scientists first described stenophylla in 1834, when it was still being actively farmed in Sierra Leone. Yet by the mid-20th century, for no apparent reason, the species disappeared from coffeehouses and plantations. “We presume that it was because the British introduced robusta, which is more productive,” says Jeremy Haggar, an agroecologist at the University of Greenwich in England who has collaborated with Davis on several projects. “But why did it disappear totally when there is a clear quality difference? It still seems a bit strange.”
Not much is known about how people first started drinking coffee in the first place. According to Ethiopian folklore, it all began around the mid-ninth century, with a young Ethiopian goatherd named Kaldi. As the story goes, one day Kaldi’s goats discovered a new snack: red berries hiding among the glossy, dark-green leaves of a small tree. After they finished eating, the animals became agitated. Curious, Kaldi decided to try the berries himself, and he soon felt so energized that he started dancing around the field. When Kaldi shared the berries with an abbot of a local monastery, the monk ended up wide awake during the evening prayers. He liked the feeling and decided to turn the berries into an infusion. A global tradition was born.
Science hasn’t confirmed this story, but there is good evidence that Coffea arabica originated in Ethiopia and South Sudan and was most likely domesticated and cultivated in Yemen. From there, via the Yemeni port of Mocha, arabica conquered the world: first India, then, in the 17th century, Europe, and a few decades later, the United States. By 1668, coffee sweetened with honey and spiced with cinnamon was already being savored in New York. Yet it was the Civil War that made coffee into America’s favored hot beverage. Union generals believed that men fought better when dosed with arabica, and the troops were awash in it, their daily rations enough to brew more than two cups per person per day. As Jonathan Morris writes in his book, Coffee: A Global History, the drink was such an important part of battlefield life that the word “coffee” appeared in the diaries of Union soldiers more often than either “bullet” or “rifle.”
The genus Coffea, to which arabica, robusta and stenophylla all belong, has a wealth of diverse species. There are some with hairy fruits and some whose fruits look like pears with a brain-shaped seed inside. Some are high in caffeine, while others are naturally caffeine-free. Some taste like dark caramel, some like sausage rolls.
At first, Davis says, his work was pure botany, just filling out the Coffea family tree. Madagascar has a secluded ecosystem brimming with endemic species. “I went there not realizing how difficult it is to find coffee in the wild. It was really, really tricky,” he says. A local botanist named Franck Rakotonasolo showed Davis how it’s done. You don’t scan the greenery for the characteristic fruits (most often the plants don’t have any), nor for leaves (there are too many look-alike plants). Instead, you seek out the distinctive architecture of the Coffea genus. Davis draws the shape in the air with his hands: straight up, that’s the trunk, and then slash, slash to the sides, that’s the branches. “The branches are always held in a certain way,” he says.
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Yet even knowing what to look for, the two botanists often had to trek for days through rainforests, sometimes knee-deep in water. They got caught in a cyclone; Davis almost died of hookworm. One day, he recalls, “when I took my shoes off, my feet were white. It was just insane.” Davis went on to name one of the species he discovered in honor of his mentor: Coffea rakotonasoloi.
As a taxonomist, Davis had made it his main goal to discover and describe new species of coffee, to understand the genetic diversity of the genus more fully. But around 2009, Davis started thinking seriously about how to help coffee farmers adapt to the warming planet. He hands me a photo taken in Uganda by a member of his research team. It shows rows of robusta plants, all wilted, sticking out from cracked, dry soil. “Without lots of water, this robusta will be dead,” he says.
Haggar, the University of Greenwich professor, noticed signs of this worrying trend in the mid-aughts in Nicaragua. “That was the first time I saw a coffee production system just start to collapse,” he says. That year, the usual dry season of five to six months extended into seven. At first, the plants were doing fine, but then, “suddenly, in the space of one or two weeks, it was just like finally the system ran out of water, and everything started dropping leaves and dying back,” Haggar says. “It was quite incredible to see that tipping point.”
This concern is driving the effort to bring new species to market. Along with stenophylla, Davis is hopeful about Coffea zanguebariae, an East African species that prospers in hot weather. Coffea excelsa, native to Central Africa, survives without water long after robusta gives up. And Coffea racemosa, whose beans are as tiny as lentils, is resistant to most pests.
Once Davis’ “Wanted” poster had failed, he decided it was time to search the forests the way Rakotonasolo had taught him. But by 2018, many of the forests were gone, chopped down for fuel and farms. One place he and his team could still look was the Kasewe Forest Reserve, a hilly area in central Sierra Leone. It took the scientists all morning to find their way to the remote reserve. “We got there, walked up this steep hill for about an hour, looked around, and everyone was like, ‘Is this it?’ And I said, ‘No.’ ‘This is it, definitely!’ ‘No.’”
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When they finally found the plant, it ended up being measly, with no fruits or flowers. To an untrained eye, it looked like any other shrub in the forest. But Davis knew right away—he saw that distinctive architecture. “After all these years of wanting to find it, it felt fantastic,” he says. Bizarrely, though, his team couldn’t find any more specimens. There was just the single, scrawny plant. To protect it, the scientists cleared the undergrowth around the stenophylla and marked the location with stones. Then it was time to head back. Haggar, who was part of the expedition, remembers the group’s feeling: “It was kind of bittersweet, because we had found it, but with one plant, there’s not so much you can do.” Because the plant had not yet flowered, there were no seeds to gather and cultivate in a research plot.
Still, the scientists now knew the type of ecosystem where stenophylla might be found. Over the coming months, they managed to locate several more of the plants in Sierra Leone’s forests and gather beans. By 2020, Davis’ team had finally collected enough stenophylla in the wild to roast nine grams—a tiny amount, but enough for him to finally have his first long-awaited taste.
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The whole process was far from standard. To begin with, the beans were dried on a plastic chair on someone’s patio in Sierra Leone. Still, the first sip took Davis by surprise. Stenophylla resembled Rwandan bourbon coffee, a premium arabica of exceptional quality. “I was just, like, oh, my God, this is amazing,” he says. In a later panel tasting of stenophylla, Davis’ impressions were confirmed: The tasters agreed that it rose to the level of high-quality arabica. It was sweet, with undertones of peach, jasmine, chocolate and elderflower syrup.
As we walk among the rows of aged shelves and drawers that make up the archives of Kew Gardens’ Herbarium, Davis tells me that there are more than seven million dried specimens here. Collected around the world over the past 170 years, they include 450 picked by Charles Darwin during his trip aboard HMS Beagle. Expecting my visit, Davis has pulled out several dried coffee specimens to show me. One is a large leaf of Coffea liberica, collected by an explorer named J.D. Snowden in 1930 in what is now South Sudan. It’s paled with age and glued to a well-worn card. It looks brittle.
Yet Davis says such leaves are an invaluable source of high-quality DNA. “You might be looking through the specimens, saying: ‘I know what that is.’ ‘I know what that is.’ ‘Oh, this looks a bit different!’ And then you do DNA tests, chemical tests, micromorphology with an electron microscope—and you realize, it is different,” he says. Some of the specimens in the Herbarium are unnamed, awaiting a label; others have been miscataloged as a known species, while DNA data clearly shows they are something else. The liberica specimen Davis shows me is, in fact, an excelsa coffee—a species that he has recently proved to be separate from liberica. (The paper awaits publication.)
The clear cup Davis hands me is filled with freshly brewed racemosa, the pest-resistant coffee with minuscule beans. “You’re probably one of only 50 people who’ve drunk this,” he says as he takes a second cup for himself. It smells nothing like coffee—minty, with a hint of rosemary. “Some of the major compounds you find in arabica are not in this coffee. And some compounds that are in this coffee are not in arabica,” he adds. As with the smell, the first flavors I taste are not very coffee-like. There is some black currant, some anise. The aftertaste, though, is very much coffee. It’s unusual, I tell Davis, but delicious nevertheless.
The next coffee we taste is liberica. To my untrained taste buds, this one is even more bizarre, with hints of wild mushrooms. It’s still nothing compared to some Madagascar coffees Davis has tasted, he tells me. One was “a bit meaty” and “super, super acidic,” he says. The poor taste is also the reason why naturally caffeine-free coffees likely won’t hit your supermarket shelves anytime soon. “They’re not producing caffeine, they’re producing other acids,” Davis says. And those acids often translate into odd flavors.
While stenophylla has an amazing taste and climate-sturdy traits, it also likely won’t conquer the world in the near future. A major issue is low yield, Davis says, especially compared to robusta. This might be one reason stenophylla disappeared in the 20th century. But Davis hopes stenophylla could be bred together with other coffee varieties. He and his colleagues in Africa are already engaged in studies using traditional crossbreeding methods. According to Benoît Bertrand, a plant geneticist at CIRAD, a French agricultural research organization, the racemosa could also be crossed with another wild species, such as Coffea sessiliflora, to produce something that’s drought-resistant but with bigger beans. “The wild species are reservoirs of genes. That can be very interesting for the future of breeding,” he says. “Biodiversity is not just for fun; it’s a gene pool,” Bunn, of the International Center for Tropical Agriculture, agrees. “We’re losing these resources, and we need them.”
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In the meantime, scientists are advising coffee growers and consumers to think about the industry’s effects on climate change. One big issue is fertilizers, which are applied in large quantities to coffees grown in open fields. These fertilizers release nitrous oxide, a potent greenhouse gas. That’s why Haggar advises environmentally conscious consumers to choose shade-grown coffee, which requires less fertilizer. Coffee pods and capsules are problematic, too. A 2021 study showed they have the largest carbon footprint of all common coffee preparation methods. “If you are just taking ground coffee out of a bag and putting it into a French press, then you are avoiding a lot of these sorts of emissions,” Haggar says.
Regarding the future of stenophylla, Haggar says, he and Davis are now just “sitting around and waiting.” They oversee a plot with about 8,000 stenophylla plants in Sierra Leone, which, if things go well, should bear fruit this year. Yet Davis believes that for the near future stenophylla will be just a niche coffee, something for a small group of connoisseurs. He is not ready to promote stenophylla to farmers. “We don’t know what the yields are going to be,” he says. “We don’t know how resistant it’s going to be to pests and diseases. We don’t know how it will work for farmers from a profitability standpoint. There’s so many unknowns.”
But farmers urgently need solutions. If they can get better breeds, better varieties, maybe their farms can survive. That’s where Davis comes in: cataloging more and more types of coffee, searching for new genotypes, looking for resilient species that could be both used for crossbreeding sturdier hybrids and planted directly on farms as high-profit specialty coffees. “We need people like him to understand coffee diversity and put ideas out there,” says Tania Humphrey, director of research and development at World Coffee Research, a nonprofit formed by the global coffee industry. “Maybe he can narrow it down to the top three or five that are interesting, and eventually that material can flow into a breeding pipeline.”
As for Davis, he is already preparing his next trip to Africa. New species of coffee are still waiting to be found—to help farmers thrive and keep the world wide awake.