Robusta is Coffea canephora, a separate species from arabica, and it accounts for roughly forty per cent of world production.
What differs
Caffeine: about double arabica’s, at 2.2 to 2.7 per cent by weight.
Hardiness: tolerates heat, lower altitude, and disease far better. Rust is largely not a problem for it.
Yield: substantially higher.
Cup: traditionally harsher, more bitter, woody or rubbery at low grades, with far less aromatic complexity. It also produces markedly more crema.
Where it is used deliberately
Traditional Italian espresso blends include 10 to 20 per cent robusta for crema and body — a craft choice rather than a cost saving. Vietnamese coffee is built on it entirely.
Fine robusta
A real movement. Carefully grown, washed, high-altitude robusta from India, Uganda and elsewhere is sweet and chocolatey rather than harsh, and it is worth trying.
The climate argument
As arabica’s viable range shrinks, robusta’s tolerance matters more each decade.
Brewing it
Espresso or a heavy immersion at medium-dark roast.