Everyone recognizes a roasted coffee bean but unless you have lived or traveled in a coffee growing country, you might not recognize an actual coffee tree. Pruned short in cultivation, but capable of growing more than 30 feet high, a coffee tree is covered with dark-green, waxy leaves growing opposite each other in pairs. Coffee cherries grow along the tree’s branches. It takes nearly a year for a cherry to mature after the flowering of the fragrant, white blossoms. Because it grows in a continuous cycle, it is not unusual to see flowers, green fruit and ripe fruit simultaneously on a single tree. The trees can live as long as 20 – 30 years and are capable of growing in a wide range of climates, as long as there is no harsh fluctuation in temperature. Optimally, they prefer a rich soil and mild temperatures, with frequent rain and shaded sun.
Botanical Classification
Coffee traces its biological heritage to a genus of plants known as Coffea. Within the genus there are over 500 genera and 6,000 species of tropical trees and shrubs. The genus was first described in the 18th century by the Swedish botanist, Carolus Linneaus, who also described Coffea arabica in his Species Plantarum in 1753. Botanists have disagreed ever since on the exact classification. This is understandable considering that coffee plants can range from small shrubs to tall trees, with leaves from 1 to 40 centimeters in size, and from purple or yellow, to the predominant dark green, in color. It has been estimated that there are anywhere from 25 to 100 species of coffee plants.
In the commercial coffee industry, there are two important coffee species — arabica and canephora, more commonly called robusta.
coffeeplantCoffea arabica — C. arabica
Varieties: Bourbon, Typica, Caturra, Mundo Novo, Tico, San Ramon, Jamaican Blue Mountain
Coffea arabica is descended from the original coffee trees discovered in Ethiopia. These trees produce a fine, mild, aromatic coffee and represent approximately 70 percent of the world’s coffee production. On the world market, arabica coffees bring the highest prices. The better arabicas are high grown coffees — generally grown between 2,000 to 6,000 feet above sea level — though optimal altitude varies with proximity to the equator. The important factor is that temperatures must remain mild, neither too hot nor too cold, ideally between 59 – 75 degrees, with about 60 inches of rainfall a year. The trees are hearty but a heavy frost will kill them. Arabica trees are costly to cultivate because the terrain tends to be steep and access difficult. Also, because the trees are more disease prone than robusta, they require additional care and attention. Arabica trees are self pollinating. The beans are flatter and more elongated than robusta and lower in caffeine.
oldplantCoffea canephora — C. canephora var. robusta
Variety: Robusta
Most of the world’s robusta is grown in Central and Western Africa, parts of Southeast Asia, including Indonesia and Vietnam, and in Brazil. Production of robusta is increasing, though it accounts for only about 30 percent of the world market. Genetically, robusta carries fewer chromosomes than arabica and the bean itself tends to be slightly rounder and smaller than an arabica bean. The robusta tree is heartier, more disease and parasite resistant, which makes it easier and cheaper to cultivate. It also has the advantage of being able to withstand warmer climates, preferring constant temperatures between 75 and 85 degrees, which enables it to grow at far lower altitudes than arabica. It requires about 60 inches of rainfall a year and cannot withstand a frost. Compared with arabica, robusta beans produce a coffee which has a distinctive taste and about 50-60% more caffeine. Robusta is primarily used in blends and for instant coffees.
The Anatomy of a Coffee Cherry
The coffee cherry’s outer skin is called the exocarp. Beneath it is the mesocarp, a thin layer of pulp, followed by a slimy layer called the parenchyma. The beans themselves are covered in a parchment-like envelope named the endocarp, more commonly referred to as ‘the parchment.’ Inside the parchment, side-by-side lie two beans, each covered separately by yet another layer of thin membrane. The biological name for this membrane or seed skin is the spermoderm, but it is generally referred to in the coffee trade as the ‘silver skin.’