The answer to the coffee industry's climate problem may lie in the forests of Sierra Leone, where there exists a newly rediscovered species of bean that researchers have now proven to grow at high temperatures and make a great cup.

Before 2018, coffea stenophylla had last been seen in the wild in 1954. The researchers who rediscovered this species believed it could help coffee growers develop newer, more climate-resilient beans, but there was one problem: They didn't know what it tasted like. Yet eventually the plant they found bore fruit, and in a study published April 19 in Nature Plants, many of those same researchers revealed that stenophylla grows at a mean annual temperature 6 degrees Celsius higher than common arabica beans — and tastes just as good.

Of the 124 known coffee species, 60% are at risk of extinction due to climate change, and only arabica and robusta are drunk. Coffee connoisseurs tend to choose arabica because, by most palates, it tastes much better than robusta, which is cheaper and mostly used for instant coffee. Some say a cup of robusta has a "burnt-rubber" quality. 

Both species, however, possess qualities desired by coffee growers.

"Robusta will grow in warmer conditions, but it just doesn't have that taste," said lead author Aaron Davis, head of coffee research at Royal Botanic Gardens, Kew, in England. "So to find something that was on a par with arabica, or could be, was really exciting."

Coffea stenophylla isn't easy to come by. The sample studied by Davis and his colleagues was only 10 grams. Co-author Daniel Sarmu sent these unroasted beans to England after he had found fruit on the stenophylla plant he and Davis initially discovered in 2018. With this meager sample, Davis and his colleagues still managed to hold a "cupping" of this rare coffee, where tasters assessed its flavors and aromas.

Davis didn't have high expectations. His previous 20 tastings of wild coffee were "sort of OK" at best, and "quite dreadful" at worst. But as he approached the cupping table this time, the aroma of stenophylla entered his nostrils, and he quickly converted. 

"Immediately I thought, 'Wow, this is, this could be good,'" Davis said in an interview with The Academic Times, likening his taste of stenophylla to a fine cup from Rwandan bourbon beans. "When we started to proceed through the cupping procedure, it was clear that this was a really good coffee."

While the 10-gram sample showed promise, it wasn't enough to gain traction in the scientific community. In October, the Coffea Biological Resources Center on Réunion island sent a 1-kilogram sample to Centre de Coopération Internationale en Recherche Agronomique pour le Développement, or CIRAD, in Montpellier, France for a thorough assessment by four panels and 15 judges. 

After a blind tasting, these judges awarded a high quality standard to coffea stenophylla, with 81% of them reporting it tasted "arabica-like," with notes "popular or desirable in high-quality Arabica: stone fruit (peach), soft fruits (blackcurrant, mandarin), honey, light black tea, jasmine, spice, floral, chocolate, caramel, nuts, English candy and elderflower syrup," according to the study.

Coffea stenophylla isn't notable only because it tastes like quality arabica coffee; it also shatters the expectations of where good coffee is supposed to be grown. 

Typical arabica coffee is not a hot tropical plant. Ethiopia, for example, is a plateau country whose economy is driven by coffee. On average, Ethiopia is much colder than Sierra Leone, and can provide higher altitudes where high-quality coffee is usually grown.

In theory, stenophylla shouldn't taste anything like arabica coffee. It grows in a relatively sultry environment, and at low altitudes. Drawing on climate data and the incidence of various coffee plants, including arabica and stenophylla, Davis and his colleagues found that stenophylla grows at an annual mean temperature of 24.9 degrees Celsius, about 6 degrees higher than arabica.

While some in the coffee industry have expressed skepticism about crossbreeding coffee plants to improve growth, calling the idea "science fiction," Davis believes it can be done with stenophylla to create a coffee as hardy as robusta and as tasty as arabica. It won't be easy, but he points to the success of Brazilian coffee-growers who managed to create a pest-resistant arabica through crossbreeding. 

According to Davis, coffea stenophylla was popular as late as the early 1900s. But thanks to the rise of cheap, easy-to-grow robusta, it fell out of fashion. Deforestation, too, has helped hasten the decline of stenophylla. 

"Coffee doesn't like to be disturbed," Davis said. "If the forest is disturbed to a certain extent then the coffee just dies out; it doesn't like it."

During the next rainy season, Davis and his colleagues intend to plant a small crop of 1,000 seedlings in western Sierra Leone, near the Liberia border. Eventually, they hope farmers can sell the coffee for around $10 per pound, which is not much for high-quality coffee; some beans can reach up to $1,320 per pound. But they believe the relatively low price will be sustainable for up to 10 years because of stenophylla's novelty factor. 

"The aspiration is to kind of re-establish part of Sierra Leone's cultural and biological heritage, and use it hopefully as a high-value coffee that farmers can benefit from," Davis said. 

The study, "Arabica-like flavour in a heat-tolerant wild coffee species," published April 19 in Nature Plants, was authored by Aaron P. Davis and Justin Moat, Royal Botanic Gardens, Kew; Delphine Mieulet, CIRAD and University of Montpellier; Daniel Sarmu, Welthungerhilfe; and Jeremy Haggar, University of Greenwich.