Arabica and Robusta, and why we only buy one
There are well over a hundred species of coffee out there, but only two of them reach your cup in any quantity: Coffea arabica, and Coffea canephora, which almost everybody calls Robusta.
Arabica is the fussier plant. It needs higher ground and cooler air, it carries roughly half the caffeine, and it gives back a much wider range of aromatics1. Robusta is hardier, cheaper and far more heat tolerant, and it genuinely earns its place in traditional Italian espresso where it adds body and crema. But the floral, fruited flavors that specialty coffee is built on come almost entirely from Arabica grown slowly at altitude. So Arabica is all we buy.
What a variety actually is
Inside that one species there are dozens of documented varieties. World Coffee Research, which is the non-profit research body the industry funds together, catalogues 55 Arabica varieties across 15 producing countries2.
Some of them happened on their own, carried out of Ethiopia and Yemen by centuries of trade. Typica and Bourbon are the two great ancestors and most of what grows in the Americas descends from one or the other. Others were bred deliberately on research stations for shorter trees, bigger yields or resistance to disease.
A variety affects three things a farmer cares about. How much fruit the tree gives. How well it survives disease and weather. And how it tastes. Those three almost never line up, which is why the best tasting varieties tend to be the most fragile and the least productive. That is also why they cost what they cost.
The ones worth knowing
Castillo
Our Colombia Passion Fruit, grown by Jairo Arcila at Santa Monica Farm in Quindio. Castillo was bred in Colombia specifically to survive coffee leaf rust, a fungus called Hemileia vastatrix that strips the leaves clean off the tree and can wipe out harvests across entire regions3. For years everybody assumed that surviving rust meant giving up flavor. Producers like Arcila have spent a decade proving that wrong. One thing worth knowing though, because the research says it plainly: resistance does not last forever. A variety that resists rust today may not resist the next strain of it3.
Gesha
The opposite trade entirely. Tall, slow, temperamental, stingy with fruit, and capable of something genuinely extraordinary when it is grown high enough4. Our Mexico lot from Carlos Cadena at Finca Xilontla is Gesha. There is a caveat here that we would rather say out loud than skate past, and the research body says it too: the name now gets attached to coffees that do not share the genetics of the Panamanian Geisha that made the variety famous4.
SL28 and SL34
Selected in Nairobi in the 1930s at Scott Laboratories, which is where the SL comes from. Deep rooted, drought tolerant, and responsible for that blackcurrant intensity Kenya is known for.
Ethiopian landraces
Ethiopia is where Arabica comes from, and a huge amount of what grows there has never been formally catalogued. When you see heirloom on a bag, that is honest shorthand for a genetic diversity too vast to put a name to.
Is peaberry a variety?
No, even though it gets sold like one.
A coffee cherry normally holds two seeds, each one with a flat side, pressed up against each other. Sometimes only one of them develops, and it grows round instead of flat. That is a peaberry. It happens across every variety, in a small share of any harvest, and it has to be sorted out by hand or by machine.
Whether it tastes better is genuinely argued about. What is not argued about is that peaberries are smaller, denser and rounder, so they tumble and take heat differently in a roaster. That physical difference is the reason roasters treat them as their own lot instead of blending them back in.
Try this
Brew a Kenyan and an Ethiopian on two mornings in a row, same grind, same water, same ratio. Ignore the tasting notes on the bags completely. Just notice the shape of each cup. The Kenyan will feel sharper and more structured. The Ethiopian will feel softer and more perfumed, more like tea than juice. Once you have felt that difference you cannot unfeel it.