A peaberry is the result of the coffee cherry producing a single coffee bean instead of the normal two. Under normal conditions, a coffee blossom has two ovules which after fertilization develop into two distinct coffee seeds, or beans, within the cherry. In the case of a peaberry, one of these two beans does not develop and thus the ripe coffee cherry contains only one bean; our peaberry. Since there is more space within the cherry for the peaberry to grow, it takes on its rounded (or “pea”) shape. In English, a peaberry is also called a peabean. In Spanish, it is a caracol. In Portuguese, a peaberry is familiarly called a moka. While peaberries are technically defects, they are often coveted because of their flavor and because their round shape facilitates movement in the roaster and therefore results in an even roast. In Arabica coffee, peaberries typically account for 10% of total beans, though this varies by coffee variety.
Why Only One?
The ultimate cause of a peaberry is that either the ovule fails to be fertilized, or there is failure in the growth of the endosperm. Several factors are thought to cause these two conditions: Insufficient pollination, environmental conditions, and genetic defects. Peaberries are much more common in the extremities of the plant, where weather conditions are more severe, the journey of the nutrients is much longer, and the agents of pollination, gravity and wind (it is estimated that insects account for only 5-10% of pollination), have a harder time reaching the stigma of the blossoms for fertilization.
Do They Taste Different?
It is generally accepted that peaberries taste different, though not necessarily better or worse than normal beans. Some argue that since there is only one bean in the cherry, it absorbs more nutrients and is thus more flavorful. However, there is no scientific evidence I know of that supports this. The rounded shape of the peaberry does allow for better rolling in the drum and thus a more homogeneous transfer of heat. It is best to separate the peaberries and roast them separately since they roast differently than standard flat beans.