Coffee processing is the fermentation of sugars in the coffee fruit and the drying of the coffee seed to a stable level of humidity and water activity. All coffee in the world must be processed before it can be milled, sorted and exported.
There are several common methods of processing coffee, and each method can result in a very different final taste. The method of fermenting and drying the coffee ultimately comes down to a decision by the coffee grower, producer or processor – whoever is handling the coffee cherries after picking.
Methods of processing
There are several common processing methods that are implemented by coffee growers worldwide, but first let's explore the layers of the coffee cherry.
Layers of a coffee cherry
Coffee beans are seeds inside of the fruit which grows on the coffee plant. The coffee fruit is typically referred to as a “coffee cherry.”
The skin of the coffee cherry is the outmost layer of the fruit. After removing the skin from the seed inside, the skin can be dried to brew as a fruit-tea often called cáscara (meaning “husk” in Spanish).
Inside the coffee cherry skin is a pectin layer often referred to as “mucilage.” The mucilage is where most of the sugars in a coffee fruit are stored. We have seen sugar contents up to 22-26 brix, depending on the coffee. The mucilage in the coffee cherry can be very sweet, sticky and oozy.
Underneath the mucilage is the parchment layer. Parchment is somewhat like a thin peanut shell in look and feel, and gives the green seed inside some protection against elements and oxygen.
Encapsulated within the parchment layer is the coffee seed. This seed will need to be dried, separated and sorted from the other layers, shipped, roasted, ground and brewed before we can enjoy all of its nuance trapped inside!
Natural processed coffee, also known as “fruit dried” or “dry process”, is the oldest and most traditional method of processing coffee.
During natural processing, whole coffee cherries are allowed to dry intact. Ideally this is done in thin layers of coffee on an elevated mesh material to allow even airflow over and under the coffee fruit. Lots of attention is critical during this process as the fruit can develop mold if not properly agitated. As the coffee is drying, there is fermentation happening within the fruit from indigenous yeasts and bacteria converting sugars into desirable building blocks of flavor. In our experience, the best tasting fruit-dried coffees take about 20-30 days to dry. Coffee is stored in the dried cherry (looks like a raisin) until hulling, grading and sorting for export.
Natural processed coffees typically have a much fruitier taste to them. They often have a heavier body and syrupy mouthfeel to back up those fruity notes.
Sometimes referred to as “parchment dried” or “wet processed” coffee, washed coffees involve removing the outer skin and some mucilage by running coffee cherries through a depulper machine. The removed skin is separated and often used to make organic compost while the parchment coffee, still covered in a layer of mucilage, is directed into a washing tank. Once inside of the washing tank, the coffee is submerged in clean water and allowed to ferment for about 12 to 24 hours, depending on a range of conditions. During this time fermenting in water, yeasts and bacteria consume the sugars in the mucilage and produce acids and other compounds that are desirable in the final cup. This process also loosens the mucilage from the parchment coffee, allowing it to be fully washed from the surface.
After fermenting in water, the coffee is agitated to remove any remaining mucilage from the parchment coffee. The fully washed parchment coffee is often rinsed a final time and then laid out on patios or raised beds to dry. We have found that the best tasting fully washed coffees spend roughly 10 to 14 days drying. Coffee is stored in parchment until hulling, grading and sorting for export.
Fully washed coffees often have more clarity in the cup with brighter acidity, thin to medium body, and balanced sweetness. Origin character and terroir can be tasted with more transparency.
Sometimes referred to as “mucilage dried” or “pulped natural”, honey processed coffees are similar to washed coffees in that the outer skin is removed through a depulper machine. However, after the skin is removed, honey processed coffees are not introduced to water, and instead are laid to dry on an elevated mesh material to allow even drying over and under the mucilage-covered coffee. Native yeasts and bacteria in the air convert sugars in the mucilage. Although there is no honey involved, bees love to snack on the sugary mucilage that coats the coffee as it begins to dry. Coffee is stored in parchment until hulling, grading and sorting for export.
Honey processed coffees can taste more like washed coffees or more like natural processed coffees, depending on how they are executed. A coffee processor may calibrate depulpers to remove more or less mucilage from the parchment, affecting the end flavor of the coffee.
Generally speaking, honey processed coffees tend to have a lot of sweetness, more mild fruit notes and a mild acidity.
Browse honey processed coffees.
Most common in Indonesia, specifically Sumatra, wet-hulled coffee undergoes the same initial steps as fully washed processing. When the parchment coffee has dried about half way (~35% humidity), the parchment is removed in the wet-hulling process. This opens up the green seed inside to the surrounding environment and can create a false aged taste that can be desirable.
Wet-hulled coffees tend to taste more earthy or herbal with a very heavy body and low acidity.
Experimental and innovative processing
Coffee fermentation is currently experiencing and explosion of research-driven innovation and investments. These range from the wildest multi-step procedures to adding other fruits into fermentation tanks along with the coffee. Technique and equipment for these types of fermentations is often being borrowed from wine makers. The results can be absolutely amazing!
We will dive deeper into some innovative and experimental processing methods in a later write up.
It should be noted that none of these unique processing methods are inherently better than another, but as coffee lovers we do tend to find that certain people gravitate towards different processing.
We encourage you to try a variety of coffees that have all gone through the same processing method and note how you like each one!