Growing hardier coffee plants

Whether it’s what you long for in the morning, or you can’t stand the taste, coffee is a global, multi billion dollar sector - coffee farming alone involves over 100 million people worldwide. And despite the fact there are over a hundred species of coffee plants that we know of, only 2 - arabica and robusta - make up the vast majority of what is drunk due to the fact that the others are simply disgusting to most consumers. But, arabica and robusta are sensitive to both temperature and rainfall. And with the changing climate there will be a smaller amount of land suitable for growing these valuable plants. One potential strategy is to find another coffee plant that is more hardy to warmer climates but still delicious, and this week Eva Higginbotham heard from Aaron Davis at the Royal Botanic Gardens at Kew about the rediscovered coffee species Stenophylla that so far ticks all the boxes…

Aaron - We found a coffee that will take much higher temperatures than Arabica coffee, and yet tastes very much like it: Coffea stenophylla, that's the Latin name; or just stenophylla coffee, or sometimes Sierra Leone coffee. It comes from upper West Africa - in Guinea, in Ivory Coast, and Sierra Leone - and it was cultivated in those countries up until the 1920s, and then pretty much disappeared. All the early historic reports tell us that it has an amazing flavour. And one report in particular tells us that it has a better flavour than arabica. So there's a lot of interest in this plant; the trouble is we just didn't have a sample to taste. And what we really wanted to do was find it in the wild, which we did in December 2018. It was sort of rediscovered, as it were, in Sierra Leone; it hadn't been seen there since 1954. Last year we were able to taste that, and were greatly surprised and relieved to find that it did taste excellent.

Eva - How did you go about finding it, if it had been lost for like 70 years?

Aaron - We're working in collaboration with partners in Sierra Leone. So we discussed this with Daniel, our Sierra Leonean partner, and he said, "look, let's make some posters, distribute them to farmers around Sierra Leone, to see if anybody's growing it still." So what Daniel did was to travel around the country on a motorbike, giving these 'wanted' posters out to farmers, and that generated... not a great response! We had two or three responses from that and we went out to those farms, and it wasn't there, it was robusta coffee. Plan B was to try and find it where it was last seen in the wild.

Eva - When you found it, how did you know that it was the same plant as had been written about in the books from before?

Aaron - My speciality is wild coffee species. My job was to actually, once we're in the forest, to identify it amongst all the other plants in the forest. And we're talking about a very dense forest: thousands of plants in front of you, they're all green, typically nothing's in flower or fruit, so we've got nothing to go on apart from leaves. And it was a matter of just looking each leaf to see whether this was the plant we were looking for. And I can't remember whether it was Daniel or Jeremy who said to me, "is this it?" And I said, "no." "Is this it?" "No." And then a little bit later, "is this it?" I said, "yeah, that's it!" I was quite confident, but nobody else was. So what we did was to take a DNA sample from a collection of stenophylla that was sent to Kew in 1873, extract the DNA from that old coffee bean, extract the DNA from the leaf in the forest, to be absolutely sure that this was stenophylla. So we knew we had the right thing, but we had to wait until May 2020 to actually get a small sample for the initial tasting.

Eva - And what does it taste like?

Aaron - Arabica coffee! And at first tasting, the panel leader - who's a very experienced coffee taster - said it actually tastes like a Rwandan arabica, which is a very specific flavour profile. And what we're hoping is that it actually has some different qualities to it that will make it desirable for those coffee connoisseurs who are willing to pay high prices for coffee.

Eva - Do you get tasting notes from it? Like, "this is a vanilla-y flavoured," or, "tastes a bit like wood," or anything?

Aaron - Absolutely! Fruitiness, like elderflower syrup, English candy. All those excite your palette and make the coffee something special.

Eva - What about the coffee bean itself makes it taste different from another species of coffee bean, in terms of the molecular chemistry?

Aaron - That's the key question. We're really still trying to understand the chemical basis of a good cup of coffee. Many others have done a lot of research on the taste of coffee and it's still elusive. There are over a thousand different chemicals involved in coffee flavour - it's not straightforward.

Eva - So what's your hope for this plant going forward?

Aaron - Our hope, initially, is really for countries like Sierra Leone who own the biological heritage of this plant - and for Sierra Leone, it's really part of their cultural heritage as well - so the hope is it's something that can be used to reinvigorate coffee farming in Sierra Leone. I think that's our first aim. And in the long term, because stenophylla has these features - this great taste, ability to withstand hot temperatures, and also the ability to resist some of the most severe diseases for coffee, and we think that it might have some drought tolerance - as a breeding resource it ticks lots of boxes. And for the long term, the hope is that it will be used in breeding work to generate the world's next generation of coffees.