Anatomy of a Coffee Bean

What’s inside a coffee bean?

Coffee beans are the seeds of the coffee plant, and they have a unique anatomy that is responsible for the flavour and aroma of the coffee that is brewed from it. Understanding the different internal and external elements of a coffee bean can help coffee roasters and blenders to better understand the how different elements of the bean react to the heat of the roaster.

The external elements of a coffee bean are the outer layers of the bean that are visible to the naked eye. The outermost layer is called the parchment, which is a protective layer that surrounds the bean. This layer is removed during the processing of the bean, leaving behind the green or brown coloured seed, the bean.

The internal elements of a coffee bean are the inner layers of the bean that are not visible to the naked eye. The first internal layer is called the endosperm,  a starchy layer that surrounds the embryo. The endosperm is responsible for providing the energy and nutrients for the growth of the seed.

The next internal layer is the embryo, the germ of the bean. The embryo is the core of the coffee bean, and it contains the genetic information for the growth of the plant.

The final internal layer is the silverskin, a thin layer surrounding the embryo. This layer is not visible when the bean is roasted, but it is important for protecting the embryo during the roasting process.

Coffee Bean Structure Cross Section
Cutaway mage of coffee bean raw and roasted.

Compounds in coffee beans

As well as these internal elements, coffee beans also contain various compounds that contribute to its flavour and aroma. These compounds include caffeine, chlorogenic acids, trigonelline, and melanoidins. Caffeine is a stimulant that gives us our daily pick-me-up, while chlorogenic acids are responsible for the acidity and bite in the coffee taste profile Trigonelline is a compound that releases the aroma of coffee and is responsible for the unique flavour of some coffee beans. Melanoidins are a group of compounds that are formed during the roasting process and are responsible for the colour and aroma of the coffee beans.

By Pat McArdle