Coffee plants belong to the botanical genus Coffea in the family Rubiaceae, which has 500 genera and over 6,000 species. Although there is some disagreement, the number of species belonging to Coffea ranges from 25 to 100. Most commercial green coffee is either the C. arabica or C. canephora species, which is referred to commercially as Arabica and Robusta, respectively. Coffea arabica is an allotetraploid inbreeder (2n = 44). Forty to fifty cultivars (infraspecific taxa) are known, and are suspected to be derived from two cultivars of C. arabica being var. arabica (including var. typica) and var. bourbon.

Arabica coffee is grown at altitudes over 2,000 (usually 4,000-6,000) feet above sea level and is typically harvested by hand when the cherries are perfectly ripe. Robusta has continued its share in the market due to its disease resistance and ability to grow below 2,000 feet. Robusta beans are inferior to Arabica beans in flavor, and they are often used in inexpensive instant coffee blends. Robusta coffee has almost twice the caffeine of Arabica coffee. Italians often will use a very small amount of Robusta coffee to increase crema and to tone down the acidity of the Arabica coffees.

A coffee cherry consist of four layers which are removed sequentially. The coffee bean is the seed of the coffee cherry and is covered with silverskin, parchment, pulp, and then an outer skin layer. The method of removal of these layers dramatically alters the flavor.

Coffee Plant Growth and Development

Three to four years after the coffee is planted, sweetly smelling flowers grow in clusters in the axils of the coffee leaves. Fruit is produced only in the new tissue. The Coffea Arabica coffee plant is self-pollinating, whereas the Robusta coffee plant depends on cross pollination. About 6-8 weeks after each coffee flower is fertilized, cell division occurs and the coffee fruit remains as a pin head for a period that is dependent upon the climate. The ovaries will then develop into drupes in a rapid growth period that takes about 15 weeks after flowering. During this time the integument takes on the shape of the final coffee bean. After the rapid growth period the integument and parchment are fully grown and will not increase in size. The endosperm remains small until about 12 weeks after flowering. At this time it will suppress, consume, and replace the integument. The remnants of the integument are what make up the silverskin. The endosperm will have completely filled the cavity made by the integument nineteen weeks after flowing. The endosperm is now white and moist, but will gain dry matter during the next several months. During this time the endosperm attracts more than seventy percent of the total photsynthesates produced by the tree. The mesocarps will expand to form the sweet pulp that surrounds the coffee bean. The coffee cherry will change color from green to red about thirty to thirty-five weeks after flowing.