The universally recognized coffee bean is actually the seed of the fruit produced by a flowering plant belonging to the genus Coffea, part of the Rubiaceae family. The term “coffee bean” is a misnomer, as botanically, a bean refers to the seed of a legume. The coffee bean is the seed of a small, berry-like fruit commonly called the coffee cherry. The plant is cultivated specifically for these seeds, which contain high levels of caffeine and other compounds that develop characteristic aromas and flavors through roasting.
The Coffee Plant
The Coffea genus encompasses over 120 species of evergreen shrubs or small trees, predominantly native to tropical and southern Africa and tropical Asia. These plants thrive best in the narrow equatorial band referred to as the “Bean Belt,” which provides the necessary warm temperatures and high rainfall. Coffee plants have glossy, dark green, elliptical leaves that grow in opposite pairs along the stems and often display a waxy texture.
The plant produces small, fragrant flowers, typically white or light pink, which often bloom after a dry period, sometimes lasting only a few days. These flowers then develop into the coffee fruit, which takes many months to ripen fully. Most commercial coffee plants are pruned to a manageable height of about 10 to 12 feet, allowing for easier harvesting of the fruit.
The preferred habitat for most Coffea species is the understory of tropical forests, providing the semi-shaded conditions many varieties favor. This requirement makes the climate of tropical and sub-tropical regions important for successful cultivation. The seeds harvested from this plant are the most valuable and widely traded commodity crop globally.
From Fruit to Seed
The fruit of the Coffea plant is known as the coffee cherry, which is botanically classified as a two-seeded drupe, or a stone fruit. The cherry consists of several distinct layers that enclose the seeds. The outermost layer is the exocarp, the skin that changes from green to a deep red, yellow, or purple color when ripe, depending on the species.
Beneath the exocarp is the mesocarp, a fleshy layer of pulp that contains natural sugars and moisture. This pulp is followed by a sticky, gelatinous layer called the mucilage, which also holds a high concentration of sugars. These sugary layers are influential in the development of the final coffee flavor profile during the processing stage.
The seeds are protected by the endocarp, a tough, paper-like layer referred to as parchment. This parchment acts as a protective shell, helping to maintain the seed’s quality during drying and storage. Within the parchment, the seeds are typically found in pairs, pressed flat against each other, giving them their characteristic flat side and convex back.
A thin membrane called the silverskin adheres tightly to the surface of the seed, which is mostly composed of the endosperm. The endosperm stores nutrients for the embryo and contains the chemical compounds that develop the coffee’s aroma and flavor during roasting. Approximately 5 to 10% of coffee cherries contain only a single, rounded seed, known as a peaberry.
Main Types of Cultivated Coffee
While the Coffea genus includes over 120 species, two species, Coffea arabica and Coffea canephora (commonly called Robusta), account for the vast majority of the world’s commercial production. Coffea arabica is the most widely cultivated, making up about 60 to 80% of global coffee production. Arabica plants are more delicate and require a cool, subtropical climate, typically grown at higher altitudes between 2,000 and 6,500 feet.
The Arabica plant is generally a smaller shrub, growing to about 10 to 12 feet tall, and is more susceptible to pests and diseases. This species is self-fertile, meaning it can self-pollinate, which contributes to its lower genetic variability. Its beans are known for being flatter and more elongated in shape.
In contrast, Coffea canephora is a hardier, more robust plant that can tolerate warmer temperatures and grow at lower altitudes, from sea level up to about 2,000 feet. This species often grows into a larger tree, reaching up to 30 feet tall, and has a greater crop yield. Robusta is significantly more resistant to pests and disease, which lowers its cultivation cost.
Robusta beans are typically smaller, more rounded, and more convex than Arabica beans. This species has a higher caffeine content, which contributes to its strong bitterness and provides a natural defense against insects. The botanical differences in hardiness, size, and growing requirements influence where and how these two primary coffee sources are farmed globally.