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Could the rediscovered coffee species Coffea stenophylla be the next arabica?

The rediscovered coffee species Coffea stenophylla, with a flavour quality that matches Arabica, could provide an important resource for the development of climate-resilient coffee crop plants.

Despite there being 124 identified coffee species in the world, Coffea arabica and Coffea canephora (Robusta) are the only two are cultivated at large scale.

While other species are experimented with or grown in smaller levels, like Coffea liberica and Coffea eugenioides, this makes up less than 1 per cent of production. Dr Aaron Davis, Head of Coffee Research the Royal Botanic Gardens, Kew (RBG Kew) says whilst the above two species have potential, most species struggle to match the quality of Arabica or productivity and resilience of Robusta.

“There was a lot of interest in several coffee species up until the beginning of 1900s. But that declined when Robusta came in as the ‘new kid on the block’ and was widely disseminated to counter the coffee leaf rust crisis,” Davis says.

“It was coffee leaf rust resistant, fast growing, and had a yield that could be much higher than the dominant Arabica. Robusta was almost unknown at the beginning of the 1900s, now it’s a multibillion-dollar crop species. It’s had a rapid ascendence from nothing to global commodity in less than 120 years.”

With climate change threatening coffee production, Davis and co-workers have suggested that other species or hybrids between species could provide a more sustainable alternative to the especially vulnerable Arabica.

By looking at the past, RBG Kew and partners at the University of Greenwich, French Agricultural Research Centre for International Development (CIRAD), and Sierra Leone may have found a species that offers considerable potential.

Credit: J. Haggar

Coffea stenophylla originates in West Africa, particularly the hills of Sierra Leone. In Sierra Leone, the species had not been seen in the wild since 1954, until Davis, Professor Jeremy Haggar of the University of Greenwich and Daniel Sarmu, Development Specialist from Sierra Leone, rediscovered it in late 2018.

Davis tells Global Coffee Report that C. stenophylla used to be grown commercially but was abandoned long ago, probably due to its low productivity compared to Robusta.

“In that era, the focus on flavour wasn’t as strong as it is now. People just wanted affordable coffee – they still want that to a degree, of course – but for species like C. stenophylla, Robusta was probably the death knell,” he says.

“When we went back to Sierra Leone in 2018, we couldn’t find a single farm growing Coffea stenophylla and none of the farmers, government officials, or agronomists were familiar with it outside of historical records.”

One such record, a report from J H Hart, the superintendent of the Royal Botanic Gardens, Trinidad, in 1898 described the flavour of C. stenophylla as “excellent, and equal to the finest Coffea arabica”. Scottish explorer and botanist, George Don, went one step further and commented that for some the flavour even surpassed Arabica. Such comments peaked Davis’ interest in the plant, as well as that of many other others in the coffee sector. 

Obtaining a small sample from partners in Sierra Leone, RBG Kew and University of Greenwich carried out an assessment of C. stenophylla with an expert tasting panel at Union Hand-Roasted Coffee in London in mid-2020. The panel awarded the coffee a cupping score of 80.25 out of 100, based on Specialty Coffee Association protocols and identified Arabica-like qualities in the coffee.

To reach ‘specialty’ status, a coffee needs a score of 80 points or higher. Jeremy Torz from Union Coffee told RGB Kew that “Arabica is currently our only specialty coffee species, and so this score, particularly from such a small sample, was surprising and remarkable”. Davis adds the C. stenophylla sample only underwent rudimentary processing, making the specialty grade all the more impressive.

Coffea stenophylla coffee cherries are black, which differentiates them from Arabica and Robusta.
Credit: © CRB Coffea, IRD-CIRAD

While C. stenophylla was not found on farms or in the wild for many decades, a few samples exist in coffee research collections, such as CIRAD’s Coffea Biological Resources Center on Reunion Island.

Not long after RBG Kew’s initial tasting, CIRAD carried out one of its own with a much more substantial sample of C. stenophylla in late-2020 and early 2021. This sample came from the Coffea Biological Resources Center but originated from forest in Ivory Coast.

A panel of judges and coffee experts from companies including Jacobs Douwe Egberts, Nespresso, and Belco evaluated the sample at CIRAD’s sensorial analysis laboratory in Montpellier, France, and at other locations. The 15-strong panel blind tested two Arabica samples (one high quality and one low grade), one high-quality Robusta sample, and the Ivory Coast C. stenophylla. 

The evaluation revealed that C. stenophylla has a complex flavour profile, with judges noting its “natural sweetness, medium-high acidity, fruitiness, and good body”. Desirable tasting notes included peach, blackcurrant, mandarin, honey, light black tea, jasmine, spice, floral, chocolate, caramel, nuts, and elderflower syrup, as found in high-quality Arabica.

When asked if the C. stenophylla sample was an Arabica, 81 per cent of the judges said ‘yes’, compared to 98 per cent and 44 per cent for the two Arabica samples, and 7 per cent for the Robusta sample). Despite the high ‘Arabica-like’ score for C. stenophylla, 47 per cent of the judges identified the sample as ‘something new’, suggesting a market niche for the rediscovered coffee.

“These results provide the first credible sensory evaluation for Coffea stenophylla coffee, from which we are able to corroborate historical reports of a superior taste,” said Dr Delphine Mieulet, the scientist at CIRAD who led the tasting, in a statement on the research. 

“The sensory analysis of Coffea stenophylla reveals a complex and unusual flavour profile that the judges unanimously found worthy of interest. For me, as a breeder, this new species is full of hope and allows us to imagine a bright future for quality coffee, despite climate change.”

CIRAD conducted a tasting panel of the rediscovered species with a panel of 15 coffee experts in early 2021.
Credit: CIRAD

The results of both tastings, as well as RBG Kew’s work on climate profiling, was published in a paper in Nature Plants in April 2021. Not only does the paper discuss the flavour and quality potential of C. stenophylla as a crop, it also reveals the results of the key climatic conditions the under which it grows.

“The ground rule for high quality coffee is that it’s Arabica grown at high elevation in good climatic conditions. This is a coffee that has an Arabica-like flavour, but originates from the other side of the African continent, some 5000 kilometres away from Arabica, and in a very different environment,” Davis says.

“Arabica is a cool tropical species whereas Coffea stenophylla is a hot tropical species. When you go to Sierra Leone, it’s very different to Ethiopia. It’s much hotter and you think, ‘are we really going to find a good quality coffee here?’”

Endemic to Guinea, Sierra Leone, and Ivory Coast, C. stenophylla grows wild in hot-tropical areas at low elevation, only 400 metres above sea level. The Nature Plants research paper states that C. stenophylla grows and crops under similar climatic conditions to Robusta, but with a higher mean annual temperature requirement of 24.9⁰C, which is 1.9⁰C higher than that of Robusta and a substantial 6.2⁰C to 6.8⁰C  higher than Arabica. 

“It is widely known that our beloved Arabica coffee is being impacted by climate change, and so the results of the study are extremely exciting,” says Dr Justin Moat, the RBG Kew scientist who led the climate analysis. “Our analysis shows that Coffea stenophylla coffee grows at substantially higher temperatures than Arabica, providing the sort of robust differences we need if we are to have any chance of a sustainable coffee sector under climate change.”

Davis says with these results, C. stenophylla has potential to help futureproof the coffee industry against climate change. 

“In terms of tackling climate change, it’s all very well going for incremental changes and small improvements, but what we really need is a step change, a robust difference in how we grow coffee crops,” he says.

Desirable tasting notes of Coffea stenophylla include peach, blackcurrant, and mandarin, among others.
Credit: CIRAD

“Even if we achieve net zero emissions by 2050, climate change will still have a substantial impact, particularly if we’re unable to keeping global warming under 1.5⁰C. We need new coffees that can, for example, survive many degrees of warmer temperatures, and much lower rainfall. We don’t know yet how Coffea stenophylla will pan out in terms of farming potential, but we know it can grow in places where Arabica can’t, like Sierra Leone.”

C. stenophylla coffee is also reported to be quite drought tolerant, although Davis says this attribute needs greater investigation. 

“So far, the data shows that Coffea stenophylla appears to have a tolerance of a broad range of rainfall patterns. It grows in quite dry environments in parts of the Ivory Coast as well as wetter environments in Sierra Leone,” Davis says. “I’ve seen reports in old coffee books that say it will grow in ‘desert like’ conditions. I doubt that very much, but drought tolerance and agronomic suitability certainly requires further research.”

While C. stenophylla may seem to many like a panacea for coffee production, the plant is not necessarily ready for cultivation and more work is needed to verify its climate and disease resilience, and to address its lower productivity. 

“Imagine if we were at the beginning of Arabica or Robusta cultivation; now think about the decades of dedicated research, and many thousands of research papers on those two species, since they were brought into widescale cultivation. We’re pretty much trying to restart a crop species from scratch and at this early stage, there are still a lot of unknowns, but the early indications are really positive,” Davis says.

“Since the release of the paper, we’ve received several hundred emails and other correspondence from coffee farmers and producer wanting to try C. stenophylla from across the tropical belt and even southern Europe. The majority are encountering issues with Arabica production, but want something of a higher quality than Robusta to replace it, so clearly there’s a demand for more coffee crop species.”

Dr Haggar of the University of Greenwich, and a co-author of the paper, suggests the coffee species could offer producers, particularly countries with lower production levels like Sierra Leone, a point of difference in the global market.

“On average, smallholder farmers in Sierra Leone earn less than £100 (about US$140) per year from coffee production, so the rediscovery of this native coffee species might finally offer an opportunity for some of the world’s poorest farmers to grow a crop that commands a decent price,” he says.

Daniel Sarmu, co-author of the paper, says with Sierra Leone tied to Stenohphylla’s history, it will serve as a fitting starting point to reintroduce the species.

“We hope that Coffea stenophylla coffee will become a flagship export crop for our beloved Sierra Leone, providing wealth creation for our country’s coffee farmers. It would be wonderful to see this coffee reinstated as part of our cultural heritage,” Sarmu says.

While C. stenophylla could be used as a crop in its own right, Davis and colleagues see great potential in using it to breed and develop new great tasting, climate resistant coffee.

“We can produce coffees that are disease resistant or drought tolerant, but if they don’t taste good, no one will buy them,” Davis says. “One of the issues so far with breeding rust resistant Arabica varieties has been that we do it using the Timor hybrid [of Arabica and Robusta], but those have struggled with marketing, because a lot of buyers don’t want the negative flavour notes that come from Robusta.

“You can backcross those cultivars with Arabica to bring the taste back, but in doing so, you risk losing the resistance those coffees were developed for in the first place. Imagine if you could bring C. stenophylla into that mix for the flavour rather than Arabica? Coffea stenophylla possesses the desired taste as well as the temperature resilience and resistances you’re looking for, so it’s exciting to think about how it could be used from a breeding perspective.”

For the next stage of their research, the institutes involved in the paper plan to plant C. stenophylla seedlings in Sierra Leone and with CIRAD at Reunion Island in France to start assessing its agronomic potential under a range of environmental conditions.

“Generally, there isn’t an immediate issue with production. There’s plenty of Arabica and Robusta on the market, probably too much, which is one of the drivers of low prices. However, there are already a lot of farmers experiencing the impacts of climate change, and in the longer term this will become a major issue for global supply,” Davis says.

“Even if we do something drastic to address greenhouse gas emissions, temperature rises won’t just stop immediately. We’ll still need to improve the variety of coffee crops we grow, with those that are much more climate resilient. We need to be thinking mid-century, and over the next few decades what the situation might be, and how to prepare for it.”

This article appeared in the July/August 2021 edition of Global Coffee Report, read more HERE

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