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Introduction to the Coffee Plant

Apr 17, 2020
Ripe coffee berries

When you drink your morning cup of coffee with its welcoming aroma and smooth taste, do you think about what’s in your cup and where it came from?

A glass of orange juice doesn’t fall far from the tree, and you know there’s a cow behind every glass of milk (older folks will remember that sometimes it’s even a “contented cow”1).

But you may be a little less certain about coffee. You know that the hot brown liquid in your coffee cup is made from “beans,” but what kind of beans are they and where do they come from?

The short answer: coffee “beans” are the seeds of the coffee plant. For a complete botanical treatise, you’ll need to look elsewhere. But here’s a little more information about the coffee plant and its seeds.

Coffee’s botanical family

Coffee is part of the botanical family Rubiaceae, one of the largest families in the plant kingdom. The Rubiaceae family comprises almost 500 genera and more than 6,500 species.

Species in this family include trees, shrubs, and herbs. They grow widely in tropical and sub-tropical regions throughout the world and are typically found in the lower story of forests.

Economically, the coffee plant (the Coffea genus) is by far the most important member of the Rubiaceae family, but other members of the family are also economically significant. In addition to beverage plants, the family also includes:

  • medicinal plants: the bark of Cinchona officinalis is the source of quinine, used to treat malarial fever

  • dye plants: the roots of Rubia tinctora (common madder) are one of the oldest sources of red dyes

  • timber plants: the wood of Adina cordifolia is used for furniture, flooring, and more

  • ornamental plants: Gardenia jasminoides (common gardenia, cape jasmine) is found in many gardens

Coffee plant characteristics

The coffee plant is indigenous to the Kaffa region of Ethiopia in Africa. According to legend, it was discovered by Kaldi, a young goatherd. Coffee plants are now cultivated in more than 70 countries, primarily in the equatorial regions of Central and South America, Africa, and Southeast Asia.

There are some 25 major species within the Coffea genus. The plants and seeds display significant variations, making precise classification difficult.

All coffee species are woody evergreens, but the plants range in size from small shrubs to trees more than 10 meters (30 feet) tall. Leaves vary in color from yellowish to dark green, with touches of bronze or purple. Leaf size and shape also vary, but most coffee leaves are oval or elliptical.

The plant produces white flowers and red berries or “cherries” that contain seeds. The seeds of the berries are the “beans” from which the coffee beverage is made. Most coffee berries contain two seeds. (About 5% of berries contain only one developed seed. These coffee beans are known as “peaberries”).

The anatomy of a coffee berry

Coffee bean structure

This illustration shows the berry and seed structure. The key: (1) center cut, (2) bean (endosperm), (3) silver skin (testa, epidermis), (4) parchment (hull, endocarp), (5) pectin layer, (6) pulp (mesocarp), (7) outer skin (pericarp, exocarp).

Once the coffee berries are harvested from the trees, they are processed to extract the beans, which can then be roasted to make the coffee beverage.

Coffee species

Of the 25 or so Coffea plant species, two species, Coffea arabica (Arabica coffee) and Coffea canephora (Robusta coffee), account for almost all commercial production. According to the International Coffee Organization, two other species, Coffea liberica (Liberica coffee) and Coffea dewevrei (Excelsa coffee) are also produced commercially, but in much smaller quantities unlikely to be available to most consumers.

Coffea arabica (Arabica coffee)

Arabica coffee accounts for over 60 percent of worldwide commercial coffee production. It is the primary species of coffee grown in South and Central America and in Central and East Africa and is widely grown in other regions along with Robusta.

Coffea arabica berries
Coffea arabica leaves and berries

Arabica grows best in shade, at higher elevations of 1,000–2,000 meters (about 3,300–6,000 feet). Arabica trees thrive in environments where annual rainfall averages 1,500–2,000 millimeters (59–79 inches) and temperatures average 15–24° C (59–75° F). The trees can tolerate lower temperatures, but not frost.

Coffea arabica is genetically different from the other coffee species: it has four sets of chromosomes rather than two. It is predominantly self-pollinating, so that Arabica seedlings usually vary little from their parents. The berries are oval, about 1 cm. in length, with flat seeds.

The two best-known varieties of Coffee arabica are ‘Typica’ and ‘Bourbon’. From these, numerous sub-varieties, cultivars, and hybrids have been developed.

Arabica beans are generally considered to produce higher quality, better tasting coffee than Robusta. Most gourmet coffees are made from Arabica beans. Well-known Arabica beans include Colombian Supremo, Ethiopian Sidamo, Jamaican Blue Mountain, Tarrazú, Costa Rica, and Guatemalan Antigua.

Coffea canephora (Robusta coffee)

Although ‘Robusta’ is actually one of the two primary varieties of the Coffea canephora species rather than the species itself, the name is often used to refer to the species.

Coffea canephora (robusta) berries
Robusta (Coffea canephora) berries

Robusta accounts for almost 40 percent of commercial coffee production — just about all coffee production that is not Arabica. Robusta is the predominant coffee grown in Southeast Asia and West Africa. The world’s leading producer is Vietnam, which recently surpassed Brazil, where the beans are often called ‘conilon’.

Optimal growing conditions for Robusta differ from those for Arabica: Robusta grows in lower elevations, from sea level to 700 meters (about 2,300 feet). It prefers higher temperatures: 24–30° C (75–86° F), and more rainfall: 2000–3000 millimeters (79 – 118 inches).

Robusta beans have a more bitter taste than Arabica, as well as 40–50 percent higher caffeine levels. But, as suggested by its name, Robusta is a robust plant: it is resistant to Hemileia vastatrix, coffee berry disease, and other diseases to which Arabica is susceptible. And Robusta trees yield significantly more coffee beans than Arabica.

Because Robusta has more body than Arabica, it is often used in traditional Italian espresso blends where a full-bodied taste is desired. But more often Robusta is used in coffee blends as a less expensive substitute for Arabica. That’s why most high-quality or gourmet coffees will tout the fact that they are “100% Arabica coffee.”

Arabica or Robusta — enjoy your coffee!

So now, although you may not be a coffee botanist, you should have a little more knowledge of the plant behind those coffee beans. And the next time you enjoy a cup of coffee out in the garden, pick some fresh gardenias for the table. They’re cousins, after all.