By Harold McGee
Coffee beans are the seeds of two species of a tropical relative of the gardenia. Coffea arabica, a 15 ft/5 m tree that is native to the cool highlands of Ethiopia and the Sudan, produces what are known as “arabica” beans; and Coffea canephora, a larger tree native to hotter, more humid West Africa, produces “robusta” beans. About two-thirds of the beans in international trade are arabicas, which develop a more complex and balanced flavor than the robustas. They contain less caffeine (less than 1.5% by weight of the dry bean, vs. 2.5% for robustas), less phenolic material (6.5% vs. 10%), and more oil (16% vs. 10%) and sugar (7% vs. 3.5%). Robusta varieties didn’t become prominent until the end of the 19th century, when their disease resistance became important in Indonesia and elsewhere.