What Is a Coffee Bean?
Where does your coffee come from? You may know that coffee is a plant and recognise that the beans came from a bright red coffee cherry. But what is inside that coffee cherry and what does it mean for your cup?
The different parts of the coffee cherry have an impact on processing method and on your coffee’s final profile. Let’s take a look at the basic anatomy of the coffee cherry to better understand our daily brew.
Understanding The Coffee Plant
The beans we roast, grind, and brew to make coffee are the seeds of a fruit. The coffee plant produces coffee cherries, and the beans are the seeds inside.
Coffee trees can naturally grow to over 30 ft/9 m. But producers prune and stump plants short to conserve the plants’ energy and to help harvesting. Smaller trees have better yield and quality in a limited space.
Each tree is covered with green, waxy leaves that grow in pairs and coffee cherries grow along its branches. Depending on the variety, it takes three to four years for a coffee plant to produce fruit. The National Coffee Association USA states that the average coffee tree produces 10 lbs of coffee cherry per year, which results in around 2 lbs of green beans.
But there are different varieties of coffee and their beans have many different characteristics. Size, flavor, and disease resistance vary, among other factors.
The Layers of A Coffee Cherry
A coffee cherry’s skin is called the exocarp. It is green until it ripens to a bright red, yellow, orange, or even pink, depending on variety. Green coffee cherries shouldn’t be confused with green coffee beans, which are the unroasted seeds from inside the ripe coffee cherry.
Beneath the cherry skin is a thin layer called the mesocarp, more commonly known as the pulp. Mucilage is the inner layer of the pulp. There’s also a layer of pectin underneath the mucilage.These layers are full of sugars, which are important during the fermentation process.
Then we reach the coffee seeds, which are technically called the endosperm but that we know better as beans. There are usually two beans in a coffee cherry, each of which is covered by a thin epidermis known as the silverskin and a papery hull that we call parchment (technically the endocarp).
The parchment is usually removed in hulling, which is the first step in the dry milling process. Machines or millstones are used to remove any remaining fruit and the dried parchment from the beans. But sometimes green beans are sold with this layer intact as parchment coffee.
The silverskin is a group of sclerenchyma cells that are strongly attached to the beans. These cells form to support and protect the seed. They come off during roasting, when they are known as chaff.
Sometimes there is just one seed inside a coffee cherry and it is rounder and larger that usual. This happens in about 5% of coffee cherries and the beans are known as peaberries.
Peaberries can be an anatomical variation of the plant or they can form when there is insufficient pollination and one ovule isn’t fertilized. Sometimes the seed simply fails to grow, whether due to genetic causes or environmental conditions. Peaberries usually occur in the parts of the coffee plant that are exposed to severe weather conditions.
There is some debate over whether peaberries have a sweeter and more desirable flavour and they are sometimes sold at a premium. Regardless of whether you think they taste different, their rounded shape allows for better rolling in the roasting drum. So it’s best to keep them apart from other beans to avoid an inconsistent roast.
How Anatomy Impacts Your Cup
Coffee cherry skin and fruit is usually discarded, but sometimes they are dried to make cascara for tea and other products.
It is difficult to remove skin and mucilage from coffee beans and different processing methods have developed to do so. Each method has an effect on the flavour and profile of the final coffee.
For example, washed coffee has all of the fruit flesh removed before drying. But in natural coffee the fruit flesh is removed after drying. In honey and pulped natural processing, the skin and sometimes part of the mucilage is removed before drying but the remaining mucilage and other layers are removed after.
Leaving the mucilage on results in sweeter coffee with more body. It’s easier to understand why if we compare both dry and wet post-harvest processes.
When coffee cherries are taken from the branch, they start to germinate. This uses the sugar in the seed. Germination stops when drying begins. Natural processed coffees go to the drying terrace earlier than pulped naturals or washed coffees. Because of this, more sugars remain in the naturals and you end up with a sweeter bean.
Washed coffees have clean, more consistent flavours that can show off a lot of acidity. Natural coffees have a lot more fruitiness, sweetness, and body.
The sugars of the mucilage also ferment during both dry and wet processing, and this has an impact on the final flavor. Without careful monitoring and consistent drying, the unpredictable process of fermentation can undesirable qualities.
Understanding the basics of the coffee cherry can help you better understand production, processing, and roasting. Next time you are choosing between a natural processed and washed coffee, you can have more confidence in knowing what that means and its impact on your cup.
Written by Verônica Belchior and Hazel Boydell.
Perfect Daily Grind