We come from a genus called Homo, of which there are around 14 known species some of whom are pictured below. Our species is Homo sapiens.
The plants in the genus Coffea flower and bear fruit called cherries. Inside the the cherries are two seeds that sit together like the two halves of a peanut. They've been lying to us all this while: these seeds are what people call coffee 'beans'.
Within the genus Coffea there are 128 known species. The three that are most commonly consumed are arabica, canephora and liberica. The speciality industry only uses a small percentage of the arabica species. Within each of these coffee species are varietals, which are like the difference between Chinese and Japanese - there is a difference, but it's often difficult to pin-point what, especially when interbreeding is common. Varietals are like the 128 ‘races’ of coffee.
Farmers tend to select varietals with good yield and pest resistance and not for good taste. Most farmers are as interested in the flavours possible in the cup, as a rubber farmer is interested in the natural feel of your Durex Featherlight. The coffee farmer has got some land and he wants to make as much money out of that land as possible, which usually means as much fruit to come off that land as possible. If a low-yield plant produces great tasting coffee, the only point, financially, of growing it is if people will pay more for his entire harvest than if he grew the higher yielding plants. And that only works if there are enough consumers prepared to pay higher prices for less coffee. And if a pest doesn't wipe out half of his plantation.
There are many hundreds of varietals and cultivars of arabica. The distinction is that cultivars mate with human persuasion and varietals are naturally frisky. Most varietals are in Ethiopia, Southern Sudan and parts of Kenya. From these hundreds of varietals, planters took Typica and Bourbon that were growing in Yemen in the seventeenth century and spread them out across the colonial lands resulting in a remarkably small genetic variation across the globe.
How much difference do different varietals make to taste?
British were definitely more salty than Maori. But the taste of the Brits might have had more to do with a diet of ship biscuits and salted beef at the time (compared to the sweeter kumara and kereru diet of the Maori) rather than genetics. Perhaps Brits and Maori taste quite similar now. More research is required.
And coffee? It can be difficult to say. If we have two varietals taken from the same terroir and processed the same at the same time, there are many more variables that will affect the flavour of the coffee. For example, if two varietals have different sized beans, should the two varietals still be roasted with the same profile in order to minimise variables or should the profiles take into account the different sizes of the beans to minimise variables?
The cherries do taste different. Plant a plot of Coffea rubi and a plot of Coffea bourbon side-by-side, therefore sharing terroir, then taste the cherries from each. Cherries from different rubi trees all taste similar and there is a marked difference between these and bourbon cherries. Most varietals are fairly similar in flavour and yet others are strikingly different in flavour, such as geisha (one of the original coffees cultivated in Ethiopia and rediscovered only recently) and the pacamara (a cultivar selected from pacas and maragogype).
For most of the industrial era of coffee, most growing regions typically grew only a couple of varietals. This led to the widespread misunderstanding that coffees from a continent have specific cup qualities. This is true only to a very limited extent. Since the 1960s many farmers and enthusiasts have been smuggling cherries of weird and wonderful varietals out of Ethiopia and the resulting flavours lends credence to the trend of ordering your brew by estate and varietal rather than by country.
The ability to be able to buy green beans as single varietals is recent. There are still many farmers around the world who have no idea what varietal they grow or whether there are different varietals on their farm. Even if they did have one varietal, it mightn’t be possible to keep that varietal separate from varietals from other farmers during processing. Single origin doesn’t necessarily mean single varietal. The recent growth in speciality coffee and, more pertinently, higher prices, gave many farmers the incentive to separate zones of their farms for different varietals.
Most roasters develop a preference for a particular varietal from particular estates. Sometimes though, through some trick of the weather, they're wrong and this year’s Mundo Novo from an estate in Carmo de Minas might outperform the exceptional Bourbon of last year.
It seems that the SL28 cultivar, common in Kenya, picks up higher quantities of phosphoric acid from the soil than ruiri 11. It also seems that the the SL28 is the more pleasantly sweet of the two. Of course, for the coffee beans to have the phosphoric acid, the soil needs to have orthophosphates in it. Take the SL28 out of Kenya into a soil with low orthophosphates and the coffee loses its distinctive blueberry flavour. Location has a large part to play in the flavour of coffee, but not the generic location of Central America or Asia, rather specifically the East facing mountainside with minimum year round temperatures and the good rain early on this season.
This is the domain of terroir.