Coffee Bean Anatomy: 101

Did you know that coffee beans are not actually beans? Instead, coffee beans are seeds inside a fruit called a coffee cherry. So, while money may not grow on trees, coffee sure does! Coffee trees grow flowers that become coffee cherries that grow in clusters on their branches. As their name suggests, the coffee cherries turn bright red when ripe and ready for picking.

For most people, when we think of coffee beans, we imagine they’re grown in the same form that we find them in-store before they become coffee grounds. However, the coffee beans we know and love are a small part of a beautiful fruit.

The Main Parts of a Coffee Bean

Before your favorite coffee grounds at your local coffee shop or grocery store make it to your shopping cart, they are just seeds in a fruit. The anatomy of a coffee cherry can be divided into two categories; those two categories can then be broken down further into the individual parts of the fruit.

Pericarp: The Outermost Layer of a Coffee Cherry

The pericarp consists of the three outermost layers of the coffee cherry fruit:

• Exocarp
• Mesocarp
• Endocarp 

Exocarp

The exocarp is the outermost skin layer of the coffee cherry. A single layer of parenchyma cells makes up this layer. Parenchyma cells have thin walls containing chloroplasts that allow them to take in water. The chloroplasts give the coffee cherry their green color. However, it will turn red as it ripens, with some variations turning yellow. 

Mesocarp

Underneath the exocarp is the mesocarp layer, which consists of a thin layer of sweet and edible pulp. Prior to ripening, while the coffee cherry is green, the pulp will be stiff but will begin to soften as the fruit ripens. 

Endocarp

The third layer of the coffee cherry flesh is the endocarp or parchment layer. It is the innermost layer that directly surrounds the coffee bean. The endocarp is made of up to seven layers of sclerenchyma cells. Sclerenchyma are fibrous cells that work as primary assistant cells in plants. While the pulp in the middle mesocarp layer softens during the ripening process, the cells in the endocarp layer harden as the coffee bean matures. The hardening of this layer restricts and controls the size of the coffee beans.

Coffee Seed: The Innermost Layer and Coffee Bean

The internal components of the coffee cherry, referred to as the coffee seed or the coffee bean, can be broken down into three layers. Each coffee cherry will contain two coffee beans. If a coffee cherry only produces one coffee bean, it is called a peaberry coffee.

These coffee seeds are harvested and roasted to become the coffee grounds you can buy at your local coffee shop. Coffee beans can vary in size; however, the average size is 10 millimeters long and 6 millimeters wide. 

The coffee bean is made up of 3 layers:

• Silver Skin
• Endosperm
• Embryo

Silver Skin

The silver skin is also referred to as the perisperm or spermoderm of the three layers; this is the outermost layer that covers the coffee beans. Oftentimes residue from the silver skin will remain on the coffee beans after harvesting and will not come off until the roasting process but before they become coffee grounds. Although many believe that an excessive amount of silver skin on the coffee beans indicates that the coffee beans were picked before they reached peak ripeness, some of these are considered flawed and are tossed out before they become coffee grounds. 

Endosperm

The majority of the coffee bean consists of the endosperm. The endosperm is tissue created at the time of fertilization. It surrounds the embryo and is responsible for providing nutrients to the embryo. The chemical makeup of the endosperm is what develops the aroma and flavor profile of the coffee beans, which then become coffee grounds that you can use to brew your morning coffee.

Embryo

A hypocotyl and two cotyledons are what come together to make the embryo. The embryo itself is between three and four millimeters long. Coffee beans develop by way of epigeous germination, which essentially means that, when planted, the coffee seed is pushed above ground by the hypocotyl instead of growing beneath the soil.

Life Cycle of Coffee Beans

The process of coffee beans becoming coffee grounds at your favorite coffee shop or for use to brew at home is not a quick or easy process. It takes patience, skill, and knowledge. The life cycle of coffee, from seedling to coffee grounds for your morning cup, can be explained in seven stages:

• Seedling
• Flowering
• Green Cherry
• Ripe Cherry
• Processing Coffee Beans
• Roasting Coffee Beans
• Grinding Coffee Beans 

Seedling: When a new coffee tree is planted, it can take between three and four years to bear fruit. Once the coffee tree begins to bear fruit, it can take between seven and eleven months for the coffee cherry to ripen fully. So, we are looking at five years before the coffee has been harvested, and it still has to make its way to becoming coffee grounds for you to use.

Flowering: Coffee trees are self-pollinating plants, meaning the pollen is transferred from flower to flower from the same plant. The flowers on coffee trees bloom for a few days; once the petals fall from the tree, a node is left in its place. These nodes will be where the coffee cherries grow.

Green Cherry: The green coffee cherries that develop from the nodes will grow and develop for up to eleven months. The length of time needed to ripen fully is dependent on the length of the location's rainy season. The more rain, the more nutrients the coffee cherries receive.

Ripe Coffee Cherry: Not all coffee beans will ripen at the same pace, so it is essential for those harvesting coffee cherries to pay close attention to the individual colors. The majority of coffee cherries will be red, while some variations will be yellow. The care and attention that goes into picking and harvesting coffee beans is a tedious skill to be appreciated.

Processing Coffee Beans: There are two coffee bean processing methods: wet process and dry process. The wet process requires specialized machinery. First, the skin and pulp are removed from the coffee bean before drying. Then, they are immersed in water, with unripe seeds floating to the top while ripe ones will sink to the bottom. The ripe seeds are then cleaned of the remaining pulp and dried outside in the sun.

With the dry process, the coffee cherry is cleaned first and then immediately dried in the sun. The coffee beans are circulated and raked in both processes to ensure the beans dry evenly and do not produce mildew.

Roasting Coffee Beans: Roasting coffee beans is an art, and each coffee roaster will have its own method for cultivating the most flavor and aroma out of their coffee beans. For some coffee beans, this will involve creating a blend to optimize the flavor profile before they become coffee grounds.

Grinding Coffee Beans: Once coffee beans have been roasted, they can either be sent to coffee distributors in coffee bean form or turned into coffee grounds. There are five degrees of coffee grounds:

1. Extra-Fine Coffee Grounds
2. Fine Coffee Grounds
3. Medium Coffee Grounds
4. Medium-Coarse Coffee Grounds
5. Coarse Coffee Grounds 

When choosing which type of coffee grounds are ideal for your morning brew, the brewing method plays a major role. The best way to remember which coffee grounds to use is; the shorter the extraction period, the finer the coffee grounds should be. Espresso will use fine coffee grounds, while cold brew uses coarse coffee grounds. 

What’s in a Coffee Bean?

From pericarp to seed and everything in between, the individual parts of the coffee cherry come together to create a magical bean. The process of growing coffee beans to create coffee grounds that then become your favorite espresso, cold brew, or pour-over is long, tedious, and absolutely worth the time and effort involved. When you are drinking your morning or afternoon cup, you can take comfort in the fact that from the very first planting of the coffee tree, your coffee was produced by talented growers, harvesters, and roasters.