The term “coffee bean” is widely used for the roasted product that is ground and brewed, but this common name creates botanical confusion. The coffee bean is not a true bean, which is a seed from a leguminous plant. Botanically, the coffee bean is classified as the seed of the Coffea plant, a member of the Rubiaceae family. This reproductive unit is contained within the fruit, which is often called a coffee cherry. The continued use of the word “bean” stems from the seed’s physical resemblance to actual beans in shape and size.
The Botanical Source: The Coffee Cherry
The coffee plant, belonging to the genus Coffea, produces a small fruit that is classified as a berry but is universally known as the coffee cherry. This fruit requires approximately nine months to mature after the fragrant white flowers are pollinated. As the cherry ripens, its color changes from green to a deep red, yellow, or sometimes orange, depending on the specific variety.
The fruit’s structure consists of several distinct layers surrounding the seeds. The outermost skin is the exocarp, which protects the entire fruit. Beneath this skin lies the fleshy mesocarp, or pulp, a sweet layer rich in natural sugars and water.
A sticky, gelatinous layer called mucilage covers the seed itself. Under the mucilage is the parchment, a thin, papery layer known as the endocarp. This hard endocarp fully encases the seeds, protecting them during the drying and processing stages.
Inside the parchment, most coffee cherries contain two seeds, which are the “beans,” lying flat against each other. These seeds are the reproductive units of the plant and are covered by a final, delicate membrane called the silverskin. In rare cases, only a single, rounded seed develops, which is known as a peaberry.
Classification: Seed, Not Bean
The coffee bean is classified by botanists as a seed, not a bean. A true bean is defined as the seed of a plant belonging to the Leguminosae, or Fabaceae, family, which includes common legumes like kidney beans, soybeans, and peas. The Coffea plant is part of the Rubiaceae family, which also contains plants like gardenias.
A seed is the fertilized, ripened ovule of a plant that contains an embryo and stored food reserves. The coffee seed is the biological unit designed to germinate and grow a new coffee tree. Its primary function is reproductive, carrying the genetic code for the future plant.
The misnomer “bean” has persisted across cultures because of the coffee seed’s visual similarity to true beans in both shape and size. These seeds possess a characteristic oval shape with a distinctive groove down the center, resembling the appearance of many legume seeds. This visual resemblance led early users to adopt the common name that remains in use today.
The coffee seed consists mostly of endosperm, which is the tissue that stores food reserves for the developing embryo. This stored material contains the chemical compounds, such as caffeine and various acids, that contribute to the final flavor and aroma once the seed is roasted.
Major Species and Varieties
The vast majority of the world’s coffee production comes from two species within the Coffea genus. The first and most dominant species is Coffea arabica, which accounts for approximately 60% of global production. Coffea arabica features complex notes, greater acidity, and a smoother finish.
Coffea arabica plants are delicate and require specific growing conditions, typically thriving at higher altitudes and cooler, more consistent temperatures. The second major species is Coffea canephora, which is commonly known by its variety, Robusta. Robusta makes up most of the remaining global coffee market and is characterized by a hardier nature.
Robusta plants are easier to grow, tolerating hotter climates, lower altitudes, and greater pest resistance. In the cup, the seeds of Coffea canephora contain significantly more caffeine, ranging from 1.7% to 4.0%, nearly double the amount found in Arabica seeds. The flavor of Robusta is typically bolder and more bitter, leading to its frequent use in instant coffee and espresso blends where a stronger intensity is desired.