There are three species of coffee trees: Arabica trees do best at altitudes of 3,000 to 6,500 feet where the slower growing process concentrates their flavors. They have a much more refined flavor and contain about 1 percent caffeine by weight. Because of its delicate nature, an Arabica tree yields only 1 to 1.5 pounds of green coffee per year. This is the coffee that specialty roasters search for. It accounts for about 75% of the world production. Because the arabica tree is susceptible to disease, frost, and drought, it requires very careful cultivation with just the right climatic conditions. Robusta beans come from a high yield plant that is resistant to disease. It does best at lower elevations and has harsh flavors. It contains about 2 percent caffeine. It bears more coffee cherries than the arabica plant. It yields 2 to 3 pounds of green coffee a year. This plant is used for the lower grades of coffee that are sold in the market. Although generally not found in gourmet shops, robusta beans are often used in the processing of soluble - instant coffees and popular commercial blends.
Liberica is the third recognized commercial variety, it is also hardy and low-altitude. It is a minor crop of coffee from Africa and is similar to robusta. | 
