Arabica and Maragogype
The oldest-known species of coffee tree, arabica is the high-grown species, cultivated on mountainous plateaux or volcanic slopes at optimum altitudes of 1000-2000 meters where the annual rainfall ranges from 150-200 cm and where mild days alternate with cool nights in a yearly average temperature range of about 15-24oC. Arabica trees flower after a rainy season, and then require up to nine months for the fruit to mature. In one year a typical arabica tree may produce less than 5 kg of fruit, which processes down to about 1 kg of actual coffee beans. Much of the arabica harvest around the world is "washed", or wet-processed, and the beans, which are generally larger, longer and flatter than those of robusta, and which contain less caffeine, produce a more delicate, acidic flavor.
Arabica coffee accounts for about 70 percent of the world's coffee, but it is more difficult to grow, being more susceptible to disease, pests and frost, and is, not surprisingly, more expensive. Of the many varieties of arabica, the typica and bourbon are the most distinct and the best known, and from these have come other strains, such as tico, Kent, mokka, Blue Mountain, the Brazilian hybrid mondo nuevo (or mundo novo), garnica, and mibirizi, to name only a few. Cultivars from the mondo nuevo variety include villa Sarchi, Geisha and Villalobos, and catuai is a hybrid of mondo nuevo and caturra (a large-bean bourbon mutant). Catuai's fruit may be yellow (amarelo) or red (vermeoho). San Romon is another large-bean typica mutant.
The most famous typica mutation was first discovered in the Maragogype region of Brazil's state of Bahia. Maragogype trees produce the world's largest coffee beans, sometimes called "elephant'" beans (not to be confused with a certain bean defect, called an "elephant ear"). Maragogype beans are grown in several countries and are a sought-after coffee for their smooth flavor as well as attractive appearance. Unfortunately, because their yield is low, maragogype trees are expensive to maintain, and at the end of their productive lives, many of the trees are being replaced with more "normal" growths.
Canephora or Robusta
The canephora species of coffee is very different from the arabica; it is as robust in taste as it is in its resistance to diseases and pests; unfortunately, in this case strong is not the best, and its flavor is not as desirable as that of arabica. Consequently, robusta accounts for less than 30 percent of world coffee production, in spite of being cheaper in price. Robusta's commercial use is primarily in blends, where its full body is appreciated, and in soluble, or instant coffee, where the processing reduces its more obtrusive flavor. Although robusta trees must be pollinated or grown from cuttings, they are far easier to grow, and when many arabica plantations were destroyed by rust disease in the second half of the 19th century, many estates were replanted with robusta trees. It is now grown throughout the tropical zone, but most of the world's robusta comes from the West and Central Africa, South-East Asia, and Brazil, where it grows in altitudes from sea-level up to 700 meters.
Robusta can withstand heavier tropical rainfalls of 300 cm or more, although, as with all coffee, the trees should never stand in water. Conversely, the shallow roots of robusta enable it to live successfully where rainfall is unpredictable or even scanty. Similarly, it survives when equatorial temperatures sour, although its happiest at an average temperature somewhere between 24-30oC.
Robusta trees flower rather irregularly, and take 10-11 months to go from blossom to mature cherry. The ripe cherries are generally picked by hand, except in Brazil where the flat terrain and vast spaces allow machine harvesting. Robusta is processed mostly by the "unwashed", or dry method, and the beans are smaller and more hump-backed than those of arabica; they are also often distinguished by small points at either end of the central "crack" on the bean.
Robusta trees produce a slightly higher yield per hectare than do arabica trees. The most common varieties of robusta are conilon from Brazil, the Java-Ineac, Nana, Kouilou and congensis.
Hybridization has produced other cultivars which are propagated from cuttings rather than seeds, such as the more successful arabusta, developed by the French Coffee and Cocoa Institute in the 1960s and exported to many parts of the world from the Ivory Coast.
The goal of most hybridization is to combine the best qualities of arabica, robusta, and perhaps of some of the better natural mutants, with the hope of possibly improving all. The natural hibrido de Timor, the dwarf Ruiru Eleven from Kenya, the rust-resistance catimor, and the icatu hybrids are names of some strains involved in, or resulting from, experiments in hybridization.
There are many reasons why the development of new coffee hybrids is the object of so much activity around the globe. In various cases, these efforts have pursued higher crop yields, larger beans or uniformity in bean size, better cup flavors, drought-resistant trees, adaptability to specific soil, and variants in caffeine content, to name but a few sought-after results.
Almost no factors, however, present a greater challenge to coffee researchers than the two biggest enemies of the coffee plant: insects and diseases.