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Coffee Tree

Image credit: USDA via Wikimedia Commons

What is Coffee?

Everyone recognizes a roasted coffee bean, but unless you’ve lived or traveled in a coffee-growing country, you might not recognize an actual coffee tree.

White flowers on coffee tree

Pruned short for production but able to grow more than 30 feet (9 meters) 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’s not unusual to see flowers, green fruit and ripe fruit simultaneously on a single tree. The trees can live as long as 20 to 30 years, and are capable of growing in a wide range of climates, as long as there is no harsh fluctuation in temperature.  The trees grow best in rich soil, with mild temperatures, frequent rain and shaded sun.

Botanical classification

Coffee traces its origin 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.

Botanical illustration of Coffea Arabica circa 1887The 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, since coffee plants can range widely. They can be small shrubs to tall trees, with leaves from one to 16 inches in size, and in colors from purple or yellow to the predominant dark green. 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).

Coffea 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% of the world's coffee production. The beans are flatter and more elongated than Robusta and lower in caffeine.

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 (610 to 1830 meters) above sea level — though optimal altitude varies with proximity to the equator. 

The most important factor is that temperatures must remain mild, ideally between 59 - 75 degrees Fahrenheit, 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 ideal terrain tends to be steep and access is difficult. Also, because the trees are more disease-prone than Robusta, they require additional care and attention. 

Coffea 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% of the world market. 

Robusta is primarily used in blends and for instant coffees. The Robusta bean itself tends to be slightly rounder and smaller than an Arabica bean.  

The Robusta tree is heartier and more resistant to disease and parasites, 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 Fahrenheit, which enables it to grow at far lower altitudes than Arabica.  

It requires about 60 inches of rainfall a year, and cannot withstand frost. Compared with Arabica, Robusta beans produce a coffee which has a distinctive taste and about 50-60% more caffeine.  

The Anatomy of a Coffee Cherry

Coffee CherryThe 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 paper-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 thin membrane. The biological name for this seed skin is the spermoderm, but it is generally referred to in the coffee trade as the silver skin.

The coffee bean follows an amazing process to reach your mug -- check out the entire process of Coffee Production: 10 Steps from Seed to Cup.

Image credit: Lilibeth Serrano - USFWS via Wikimedia Commons, Wikimedia Commons, Michael C. Wright via Wikimedia Commons



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