Coffee is the world’s most widely consumed beverage, but the common term “coffee bean” is botanically misleading. It is not a true bean or legume. The item we grind for brewing is actually the seed, or pit, of a small, bright red or yellow berry called the coffee cherry. This fruit develops on a specific plant that requires precise environmental conditions to thrive. Understanding the plant’s structure and the fruit’s anatomy reveals the complex journey from a tropical seed to the finished product.
The Coffee Shrub and Tree
Coffee originates from the Coffea genus, though only two species dominate global trade: Coffea arabica and Coffea canephora (Robusta). The plant is typically an evergreen shrub or small tree, often pruned to 6 to 15 feet to facilitate harvesting. Arabica accounts for the majority of global production and is prized for its complex, aromatic flavor profile.
Arabica plants are delicate, requiring specific, cooler temperatures and higher altitudes. Robusta is a hardier, larger plant, tolerating warmer climates and reaching up to 33 feet in the wild. It is more resistant to pests and disease and produces a bean with a stronger, earthier taste and nearly twice the caffeine content. Both species feature glossy, dark green leaves and produce small, fragrant white flowers before fruiting.
Inside the Coffee Cherry
The coffee cherry is a complex fruit with several distinct layers protecting the seeds within. The outermost layer is the exocarp, a tough skin that turns vibrant red, yellow, or purple when ripe. Beneath this skin lies the mesocarp, a fleshy, sugary pulp that contributes to the initial fermentation process.
Adhering tightly to the seed is the mucilage, a sticky, honey-like layer rich in pectins and sugars. Encasing the seed is the endocarp, a brittle, protective shell known as parchment.
Inside the parchment are typically two seeds, or “beans,” nestled face-to-face, each covered by a thin layer called the silverskin. Occasionally, a cherry produces only a single, rounded seed, known as a peaberry.
Where Coffee Thrives Globally
Coffee cultivation is limited to a narrow, tropical band encircling the equator, famously known as the Coffee Belt. This region stretches between the Tropics of Cancer and Capricorn, encompassing parts of Central/South America, Africa, and Asia.
Arabica coffee demands a cooler, stable temperature (64°F to 72°F) and thrives at higher elevations, generally 2,000 to 6,000 feet above sea level. High altitude slows fruit maturation, allowing complex sugars and acids to develop within the seed.
The plant requires substantial, well-distributed rainfall (60 to 80 inches per year). Prime growing areas often feature rich, well-draining volcanic soil. Robusta tolerates warmer temperatures (72°F to 80°F) and is typically grown in lower-lying areas, up to about 2,600 feet.
Preparing the Bean for Roasting
After harvest, cherries undergo processing to remove the fruit layers and expose the green seed, which is then ready for export and roasting. The two primary methods, Natural and Washed, determine the final flavor profile.
The Natural Process
The Dry, or Natural, Process is the oldest method, where the entire cherry is spread out to dry in the sun for several weeks. During this period, the fruit pulp ferments, allowing the sugars and flavors of the cherry to seep directly into the seed. This results in a coffee with a heavier body and pronounced fruity, sweet, or wine-like notes.
The Washed Process
The Wet, or Washed, Process removes the skin and pulp almost immediately after harvest using a pulper. The seeds, still covered in mucilage, are fermented in water tanks to break down the sticky layer. After fermentation, the beans are thoroughly washed to remove all remaining fruit residue before being dried.
The Washed Process produces a cleaner, brighter cup with vibrant acidity, allowing the inherent flavors of the bean to shine through. Once the moisture content is reduced to 10–12%, the parchment is removed in a final step called hulling, yielding the green coffee bean.