Educate the Curious: Anatomy of a coffee bean

🍒  As you may already know, coffee beans are the seeds of a fruit. The coffee plant produces fruit known as coffee cherries, and the coffee beans are the seeds inside. If you were to cut into a coffee cherry, what would you find?

Starting on the outside, a coffee fruit includes the outer skin (known as the exocarp or pericarp), the pulp (or mucilage), the pectin layer, the parchment (also called the hull or endocarp), the silverskin and finally the coffee bean (endosperm).

Photo from Sweet Maria's

“The “coffee bean” we roast is a food supply for the nascent embryo of the coffee plant. It’s not about us and our love of aroma, flavor and caffeine! Caffeine functions for the plant to ward off insects and fungus, and the seed is just a “food reserve” to support the embryonic plant since the embryo itself cannot store its own.

The “bean” of the arabica coffee cherry is a seed from this flowering tree, but given that we call a peanut a nut, and a tomato a vegetable, I suppose it’s par for the course. In fact, the coffee fruit was most often called a berry in early literature, and now it is most commonly called a cherry, which it is also not.” – Thompson Owen, Sweet Maria’s 

Photo from Balekola Coffee

Let's dive deeper into each part!  

Outer Skin (Exocarp)

The outer layer or skin of the cherry is also called the exocarp. At the beginning of fruit development the skin is green, and as the fruit matures it turns yellow, then orange. Color upon maturity is dependent on the type of coffee, but it is most typically red or sometimes yellow.

(You may have heard of Cascara, which is the dried coffee skins. It have some caffeine and can be used for lots of stuff like making delicious tea. Learn more about the process of Cascara here.)

Pulp (Mucilage)

Beneath the outer skin of the coffee cherry is the fruity pulp. This is the “flesh” of the coffee fruit during coffee cherry maturation. In unripe coffee fruit, the tissue is stiff. But once it ripens, this layer is rich in sugars and has a huge influence on the taste of the coffee bean. 

Different things can be done with the pulp when processing the ripe coffee cherry to get the bean out, and greatly affect the outcome of the coffee flavor. In the wet processing technique, this mucilage layer is eliminated through managed fermentation. In the dry processing technique, the mucilage is left undamaged throughout drying. 

Pectin Layer

This layer is responsible for protecting the coffee bean and is made up of a cellulose layer.

Parchment (Endocarp)

The parchment is a thick shell-like layer that surrounds the bean and is made up of 3-7 layers. The cells of the parchment harden throughout coffee fruit maturation, hence restricting the last size of the coffee seed, or bean.

Silver Skin

This is a very thin and fine layer of skin which covers and sticks tightly to the coffee bean (the seed of the fruit). After the coffee bean is roasted, this is the unique by-product discarded after the roasting process, also called chaff.

Coffee Bean (Endosperm) 

This is the part that you’ve seen before, the part that gets roasted and then ground to make your daily cup! Most of the coffee bean itself is composed of endosperm, which is the tissue that is created near the time of fertilization in most flowering plants. The endosperm surrounds the embryo and supplies nutrition (starch) but may also contain proteins and oils. In a coffee bean the endosperm caffeine content ranges from about .8 percent to 2.5%, leading to its popularity as a brewed beverage and thus a major cash crop cultivated around the world.

To learn more about the anatomy of the coffee bean, check out this article from Perfect Daily Grind.  

Note – Approximately 1-7 percent of every coffee crop are peaberry coffee beans which are one whole coffee bean rather than the typical two half-beans. Peaberry coffee beans are esteemed for their robust taste which is thought to be due to their higher density than regular beans. If roasted correctly, they will be sweeter and have more flavor than a typical coffee bean. 

What do you think? Do you have more appreciation for the heavenly coffee fruit that grows the beans that makes the coffee for your morning latte?