Coffee trees produce red fruit (cherry) which typically contain two seeds. These seeds are coffee beans. When harvesting coffee cherries, less than 10% of cherries will only contain one round bean, whereas all other cherries contain two semi spherical beans. Coffee cherries containing just one bean are referred to as Peaberries.
Peaberry Coffee beans are much smaller in size and twice as robust in flavor. Because the seed inside the cherry is much smaller, the acidity is also higher then in regular Arabica beans. In most coffee bean sorting facilities around the world, Peaberry coffee beans are separated from the larger cherries. In some cases Peaberries are bagged and sent to be roasted as ‘specialty peaberry coffee’.
A Peaberry is like the opposite of having twins, where twins are the norm and a single is rare and unusual. It is technically a defect, and occurs due to factors such as insect damage to a flower, tree stress from drought/nutrient imbalances, or with cherries that grow at the tip of branches. The majority of fruit from the coffee tree contain two halves of a bean in a single cherry, which is called Type I. Due to the vagaries of nature, some fruit mature with only a single fused bean. This oval (or pea-shaped), solo bean is known as Peaberry, or Type II.
Kona coffee is an example of coffee that is graded this way. In Kona, approximately 5% to 10% of beans come out as peaberry.
Some coffee drinkers feel that peaberry carries a more intense flavor. Because of its rarity it is sometimes known as the “caviar” of coffee and can be sold at a premium. Peaberry coffee usually runs out early in the coffee selling season.