Coffee belongs to the botanical family Rubiaceae, which has some 500 genera and over 6,000 species. Most are tropical trees and shrubs that grow in the lower storey of forests. Other members of the family include gardenias and plants that yield quinine and other useful substances, but Coffea is by far the most important member of the family economically.
Since Coffea was first correctly described, by Linnaeus in the mid 18th century, botanists have failed to agree on a precise classification system. There are probably at least 25 major species, all indigenous to tropical Africa and certain islands in the Indian Ocean, notably Madagascar. Difficulties in classification and even in designation of a plant as a true member of the Coffea genus arise because of the great variation in the plants and seeds. All species of Coffea are woody, but they range from small shrubs to large trees over 10 metres tall; the leaves can be yellowish, dark green, bronze or tinged with purple.
The two most important species of coffee economically are Coffea arabica (Arabica coffee) – which accounts for over 60 percent of world production – and Coffea canephora (Robusta coffee). Two other species which are grown on a much smaller scale are Coffea liberica (Liberica coffee) and Coffea dewevrei (Excelsa coffee).
Some differences between Arabica and Robusta coffee
|Date species described||1753||1895|
|Time from flower to ripe cherry||9 months||10-11 months|
|Yield (kg beans/ha)||1500-3000||2300-4000|
|Optimum temperature (yearly average)||15-24� C||24-30� C|
|Optimal rainfall||1500-2000 mm||2000-3000 mm|
|Optimum altitude||1000-2000 m||0-700 m|
|Coffee berry disease||susceptible||resistant|
|Caffeine content of beans||0.8-1.4%||1.7-4.0%|
|Shape of bean||flat||oval|
|Typical brew characteristics||acidity||bitterness, full|
|Body||average 1.2%||average 2.0%|
Coffea arabica – Arabica coffee
Coffea arabica was first described by Linnaeus in 1753. The best known varieties are ‘Typica’ and ‘Bourbon’ but from these many different strains and cultivars have been developed, such as Caturra (Brazil, Colombia), Mundo Novo (Brazil), Tico (Central America), the dwarf San Ramon and the Jamaican Blue Mountain. The average Arabica plant is a large bush with dark-green oval leaves. It is genetically different from other coffee species, having four sets of chromosomes rather than two. The fruits are oval and mature in 7 to 9 months; they usually contain two flat seeds (the coffee beans) – when only one bean develops it is called a peaberry. Since Arabica coffee is often susceptible to attack by pests and diseases, resistance is a major goal of plant breeding programmes. Arabica coffee is grown throughout Latin America, in Central and East Africa, in India and to some extent in Indonesia.
Coffea canephora – Robusta coffee
The term ‘Robusta’ is actually the name of a widely grown variety of this species. It is a robust shrub or small tree growing up to 10 metres in height, but with a shallow root system. The fruits are rounded and take up to 11 months to mature; the seeds are oval in shape and smaller than those of C. arabica. Robusta coffee is grown in West and Central Africa, throughout South-East Asia and to some extent in Brazil, where it is known as Conillon.
Coffea liberica – Liberica coffee
Liberica coffee grows as a large strong tree, up to 18 metres in height, with large leathery leaves. The fruits and seeds (beans) are also large. Liberica coffee is grown in Malaysia and in West Africa, but since demand for its flavour characteristics is low, only very small quantities are traded.