What Is Peaberry?

The elusive coffee cherry that continues to smoothly flow off the tongue of coffee professionals and coffee amateurs alike – peaberry. It’s catchy and sophisticated. So what exactly is a peaberry?  Why is it unique and what causes this anomaly in the coffee world? To better understand what a peaberry is, we’ll approach it from a coffee botany standpoint.

A peaberry is an underdeveloped coffee fruit that has only one seed inside of it as opposed to the typical two seeds that develop inside a coffee cherry and it inherently grows on all coffee species.  About 5-7 % of harvests are peaberries, and they are smaller in size.  To understand why they are smaller and have only one seed, we first need to understand how fruit develops in the plant world.

A fruit of any plant is nothing more than a ripened ovary. That ovary is the fleshy substance surrounding the seeds inside the plant (also called mucilage in coffee). How do those seeds come about? Fertilization is the simple answer. With regards to the Coffea arabica species, there are 2 floral organs that we will briefly talk about, the stamens and the pistils. The stamens are the male representation and the pistils are the female representation. When the pollen from the stamens reach the pistils, it fertilizes the ovules (contained within the ovary prior to fertilization) and those ovules form into two seeds. Within Coffea arabica, there are two ovules that must be fertilized to get a typical coffee cherry. If, for some reason, there is a malfunction in that fertilization process and only one of the ovules can be fertilized you get an anomaly called peaberry.

So, why does this happen? Much research is still going on about what exactly causes it, but when you distill it down it’s a fertilization issue. Coffea arabica is self-fertile meaning, although beneficial, pollinators are not necessary to fertilize coffee flowers. Both the stamens and pistils are in the same flower and are compatible with each other, but genetics are not always perfect. So, what exactly causes the incompatibility? Is it an issue in the uptake of pollen? Is it an ovary malfunction? Is it the pollen itself? Does it have to do with genetic diversity in Coffea arabica? It’s still an ongoing discussion and more research needs to be done to fully understand how it comes about, but it becomes a conversation of genetic diversity and maintaining good breeding practices. The farther away we get from true Coffea arabica genetics, the more genetic malfunctions we get. So, celebrate proper horticultural practices and celebrate quality cups. Tasting is knowing, so drink up!


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