The Coffee Cherry and Coffee Processing
The Coffee Cherry
The Coffee Cherry. Have you ever thought about how that delicious, roasted coffee bean starts out?
The coffee beans we brew and drink every day are the seeds of a small berry, referred to as the coffee cherry. Two seeds lie inside each cherry (unless it is a pea berry: a cherry where the seeds did not separate and so you have one, round one).
Native to subtropical Africa and southern Asia, botanically the coffee plant is classified as an evergreen shrub, but it is mostly referred to as a bush or tree. Coffee bushes have glossy, dark green oval leaves and small, fragrant white flowers that bloom simultaneously in clusters lasting only a few days, signalling the start of the coffee cherry growth! The views and sweet fragrances across the coffee hills when the flowers are in bloom are gorgeous. And in the Hawaiian Kona region, it is referred to as Kona Snow.
The coffee cherry begins as a green, unripe berry, that gradually ripens to yellow, turning to an orange colour, before finally turning a beautiful deep red. This is when it is harvested for the famous beans! Though some varietals ripen to yellow.
The whole growing and ripening of the coffee cherry takes about eight months but can vary due to factors like climate, soil, other foliage (e.g shade-grown), varietal and altitude. Though the ripeness is determined primarily by colour a more precise method is to squeeze the cherry, and if the seed (bean) comes out easily, then the cherry is ripe for harvest.
After harvesting, the next step is to remove the seeds, or beans, from the cherry. Looking at the coffee cherry you may just think it is like a cherry - fruit and seed, just remove the fruit! But it is not so clear cut, and this is where it starts to get interesting.
Each coffee fruit is made up of several layers: the outer skin (pulp) or exocarp; the mucilage or mesocarp, a silky, sticky layer, this sticky mucilage is composed of natural sugars and alcohols and contributes massively to the sweetness, acidity, and overall flavour profile of the coffee; a papery layer or endocarp called parchment; and the silver skin, a membrane which covers the two seeds.
Coffee processing is the removal of these layers of fruit. There are several ways to do it, removing all layers, some layers, drying in the sun, or washing in water to mention but some; with each method impacting the flavour of the coffee differently.
There are two main methods of coffee processing; natural or washed. Another method, pulped natural or honey processed, is less common, but we will have a brief look into all three.
Natural processing. This is the oldest and original form of coffee processing. Favoured in certain areas with limited access to water resources, or due to the lower costs involved.
Once the cherries are harvested, they are sorted using flotation and winnowing techniques. The first step is to put all the cherries in water to soften and remove any floaters (now now, stop giggling!). Defective cherries have poorly formed seeds, creating air gaps so they float, denser cherries that sink are considered a higher quality so the two lots of cherries are separated and sold at different prices and to different markets.
The coffee cherries are then taken to a drying area out in the sun, often large, raised beds or concrete patios, where they are laid out to dry.
The natural sugars in the coffee cherry’s mucilage begin to ferment and the bean takes on the flavour. What makes natural processing challenging is not only the risk of over fermentation, where the fruit is left to dry for too long, but also the development of mould. These moulds, at best, diminish the coffee flavours and at most cause defective flavours. The coffee is turned frequently to avoid this, ensuring the maximum surface area is exposed to the air to facilitate an even drying.
Once dry, the cherries resemble raisins, and the coffee is hulled to remove the outer layers. All the outer layers of the dried cherry are removed in one step by a hulling machine. The dried cherries are “cracked”, and the layers come clean away. Often with washed coffees, even after roasting, there can be a trace of the silverskin wherein natural coffees there is nothing, have a look at your beans next time and see if you can see any silverskin.
The whole Natural Process can take 3 – 6 weeks.
Naturally processed coffees can have an incredible cup profile. They tend to create a very bright, vibrant, and intense cup. Often with higher sweetness, with a heavy body and notes of berries being common.
Washed or Wet processed coffee. Wet processing is the most common, and popular, processing method in the coffee industry.
After the coffee cherries are picked, like in naturally processed coffee, the cherries need to be sorted to remove any unripe or defective cherries.
The next stage is to remove the pulp. The cherries are passed through a machine, these can be either manual or electrical, called a depulper. Some machines work by creating friction, causing the outer skin to come away, however, if the cherry isn’t ripe enough the skin may not be removed. Unripe cherries are separated and often used elsewhere for natural processing, sold for lower prices to local markets or used internally for the workers to drink.
What happens next depends on the farmer. Some beans are washed immediately, removing all the mucilage, leaving just the parchment, and put out to dry. Other farmers ferment the beans in large tanks or channels of water, during which the enzymes break down the mucilage. The length of time that the beans are left to ferment varies from around 12 to 72 hours depending on factors such as altitude and temperature. However, the fermentation will affect the flavour of the bean so it must be balanced. The beans are then washed again in fresh water to remove any remaining flesh, leaving just the parchment, and put out to dry.
Drying either takes place out in the open sun on large patios or raised beds to sit for a period of around 10-22 days where they are gently turned over. Or the beans are dried in large, heated mechanical dryers. Sun drying is preferred in climates with predictable sun and weather patterns, as it requires no investment in mechanical equipment. It is widely accepted that a slower drying time contributes to greater balance and complexity in the cup. However, if space is an issue, then mechanical driers are used. With mechanical driers a bean can be washed and dried in 3 days!
One of the biggest criticisms of washed processing is its high-water usage.
The washed process is often thought of as focusing on the coffee bean itself, allowing you taste all the flavours of the origin, variety, and terroir, without the influence of the processing method.
Washed beans can result in clean, sparkling acidity, lively, fruity characteristics with perhaps just a hint of sweetness.
Honey Processed Coffee/ Pulped Natural.
Honey or pulped natural coffee processing, are terms that are sometimes used interchangeably. The country of origin and producer traditions often dictate whether the coffee is described as a honey or pulped natural.
Honey processing is somewhere in the middle of washed and natural processing. You remove the cherry skin but leave some mucilage on the bean as it dries. How much mucilage is removed is determined by using a demucilager, a machine that allows a custom amount to be removed. The amount of mucilage left on the bean will give you not only the intensity of the character but will also determine whether the coffee is a Yellow, Gold, Red or Black Honey. The term honey refers to the sweet, sugar rich mucilage, but also references the sweet profile of the coffees, though they do not tend to be as sweet as naturals.
The more mucilage left after being washed, the darker the colour of the beans when dried and the greater sweetness and body you can experience. White and gold honeys have very little mucilage left; red and black have significantly more. However, humidity, heat, and the oxidation of sugar all affect honey processing – and there is no exact formula.
“Pulped Natural” coffees will often resemble a Yellow Honey. With “Yellow Honey” beans, since more mucilage has been removed from the bean than from black and red honeys, a yellow honey coffee tends to be more balanced with a little acidity, and less body and sweetness.
Gold, Red, & Black Honey coffees, what differentiates these three is the amount of light and drying time the beans are exposed for. More humidity and a slower drying lead to black honey. Slightly less humidity leads to red, and even less to gold.
Gold honey will be dried during warm, sunny times with little humidity. This helps it to dry quickly.
Red honey, is processed under more shade to slow down the drying time. This will increase the amount of humidity the beans are exposed to. Red Honey processing should result in a sweeter cup profile compared to yellow honey, with a medium body and high acidity.
Black Honey, you leave all the mucilage on the beans during drying. And the beans are dried under lots of shade increasing drying time and humidity. This makes it the most complex and risky of all the honeys. The beans dry surrounded by lots of sugar and microorganisms. It is important to dry these coffees in the shade to control the heat and so stabilise fermentation.
For producers with the ability to control fermentation, black honeys can be worth the risk. They tend to have a sweet cup, a heavy body, and a good amount of acidity.
Wet hulling or Gilling Basah.
Wet hulling, or Gilling Basah, is a type of coffee processing that is unique to Indonesia and most often used in Sulawesi and Sumatra. It does sound like wet processing, and may even begin similarly but it is quite different. The wet climate of Indonesia, the rain and humidity, makes it difficult for coffee to dry for long periods of time outside so the farmers had to come up with another way to process their coffee. Another factor is the desire to get their coffee to the market as fast as possible. Spending extensive time on drying out coffee means they must wait longer to sell it, so they prefer using a faster method.
In Indonesia it is mainly small holder farmers picking their coffee and pulping it, they run it through a hand-crank drum that has a surface like a cheese grater that peels off the skin of the fruit but leaving most of the fruit, or mucilage, still on the coffee bean.
They then ferment the beans overnight, using tubs, tanks, or whatever method they have access to. The fermentation makes it much easier to wash off the mucilage in the morning. Once the mucilage has been removed, the parchment remains. In wet processing the beans would now be dried to 11% moisture and the beans shrink away from the parchment, but in Indonesia, the farmer doesn’t want to wait for all this to happen. They leave the parchment coffee out until it has dried to 50% moisture and sell it to their local market.
Once sold at market the buyers will keep the parchment coffee in bags for a while, which allows the beans to ferment further. The speedy process of wet hulling makes it possible to sell coffee within a month of its first being picked.
Wet-hulled coffee often has earthy flavours, low acidity and brightness due to the fermentation it undergoes during processing.
Whichever processing method is used, before the raw or green beans are ready for export, they need to be hulled to remove the parchment (above). The hulling is done mechanically in a dry mill. After hulling, the beans are graded and sorted often by using large sieves with varying hole sizes. Once the beans have been sorted and graded, they are packed into 60kg or 69kg hessian sacks, depending on the country of origin. The hessian sacks full of raw coffee beans are then packed into a shipping container and they then begin their journey to a roastery!
