When it comes to top-quality coffee, only one type of coffee currently has a relevant market share: Coffea arabica. Thanks to its excellent taste, it is currently the most economically important type of coffee in the world. But climate change continues to limit their cultivation. Unlike less tasty varieties such as Robusta coffee, Arabica plants only tolerate medium temperatures. If it gets too warm, the harvests collapse. But a rare type of coffee from West Africa could possibly offer an alternative in the future.
The coffee industry is an important economic factor for many tropical countries and forms the basis of life for more than 100 million coffee farmers. The currently most important type of coffee is the high-quality Arabica coffee, which made up around 56 percent of global coffee production in 2019/20. But climate change poses increasing problems for coffee farmers. The species Coffea arabica comes from the cool, tropical highlands of Ethiopia and Sudan and prefers temperatures between 18 and 22 degrees Celsius. In view of the rising average temperatures, however, fewer and fewer growing areas are suitable for them, and fluctuating rainfall and extreme weather events put the harvests at additional risk. Robusta coffee (Coffea canephora) grows at higher average temperatures, but does not meet the taste requirements for high-quality specialty coffee.
Blind test against top-quality coffee
A team led by Aaron Davis from the Royal Botanic Gardens in Kew near London has now reported on a possible alternative: the wild coffee type Coffea stenophylla, which is native to Sierra Leone, Guinea and the Ivory Coast. “Several historical references from 1834 to 1929 indicate that this variety has excellent taste, possibly better than any other coffee, including arabica,” the researchers write. However, the variety has not been grown since the 1920s, possibly because it had lower yields than the Robusta coffee that was emerging at the time. In the wild, the plants are threatened with extinction and have long been thought to have disappeared.
Coffea stenophylla was only rediscovered in Sierra Leone at the end of 2018. In 2020, Davis’ team managed to get samples from beans collected in the wild. To review the historical reports regarding the superior taste, the researchers invited 15 independent coffee testers to blindly taste and rate the coffee brewed from these beans. A high-quality Ethiopian Arabica coffee, a Brazilian Arabica coffee of medium quality and a good Robusta coffee from Indonesia were used as a comparison. The judges did not know what types of coffee it was, nor that there was a new type.
Aromas of peach and honey
“The evaluation showed that Stenophylla has a complex taste profile with natural sweetness, medium-high acidity, fruitiness and a good body, as with higher-quality Arabica”, summarize the researchers. The testers described nuances of peach, honey, jasmine, nuts, caramel and chocolate as taste notes. 81 percent of the testers thought Stenophylla was Arabica coffee, compared with 98 percent for the high-quality Arabica and 44 percent for the medium-quality Arabica. When asked directly whether the Stenophylla sample was, in their opinion, a new type of coffee, 47 percent of the experts answered in the affirmative. “With this sensory rating for Stenophylla coffee, we are able to confirm historical reports of superior taste and demonstrate that Stenophylla has a desirable aroma analogous to high quality arabica coffee,” said Davis and colleagues.
The similarity in taste to Arabica coffee is particularly surprising because the varieties are not closely related, grow spatially far apart in different habitats and the coffee beans have different chemical compositions, say the scientists. However, both varieties have certain flavor-giving compounds in common. Both Arabica and Stenophylla contain a high proportion of so-called trigonellins, which become vitamin B3 when the coffee is roasted. The sugar content in Stenophylla beans is slightly lower than in Arabica, but higher than in Robusta.
New breeding material
In order to test the possible commercial applicability of Stenophylla, Davis and colleagues analyzed the climatic conditions in the range of the variety. On the other hand, they simulated growth under various influences of heat and precipitation. According to this, Stenophylla can grow at an average annual temperature of around 25 to 26 ° C – at least six degrees more than Arabica. The rainfall in the natural range of Stenophylla is higher than that of Arabica, but the simulations indicate that the variety is also likely to tolerate fluctuations in rainfall. There is also evidence that it has a certain resistance to the plant disease coffee rust, which is dangerous for Arabica.
It remains to be seen which yields can be achieved with Stenophylla. But even if the variety is not productive enough in its wild form, it offers promising material for breeding thanks to its good taste and climatic resistance. So far, Arabica plants have often been crossed in newly bred, climate-resistant varieties, which are supposed to provide good taste, but at the same time worsen the climatic properties. Stenophylla could offer a way out here. “The task now is to secure the future of the species in the wild and outside of its original habitat and to evaluate its full potential as a climate-resistant, high-quality crop species and breeding resource,” said the researchers.
Source: Aaron Davis (Royal Botanic Gardens, Kew, Richmond, UK) et al., Nature Plants, doi: 10.1038 / s41477-021-00891-4