Coffee Processing - Washed, Honey, Natural, & Anaerobic
Exploring the Types of Processes and Effects on Coffee Flavor Profiles
Fermentation is an integral part of coffee’s post-harvest processing and plays a large role in the development of coffee flavor. Coffee fermentation is not widely understood even though it occurs in every style of coffee preparation.
Many variables are considered in coffee fermentation, such as: the ripeness of the fruit; the ambient temperature in the environment, as well as the temperature in the coffee as it is piled or soaking in fermentation tanks or spread on patios drying, the local population of microorganisms; the water activity and moisture content throughout the drying process; and even more.
Washed Process (Wet Process)
The most common processing method for specialty coffee is referred to as “washed”, or coffee that’s been wet processed. It’s the most reliable processing method, producing coffee with more brightness (acidity), cleaner flavors, and consistent characteristics.
The basic method begins with sending the just-picked coffee cherry through a pulping machine, which removes the outer skin while leaving the pulp (also called mucilage) clinging to the seeds inside. The pulp-covered seeds are then soaked in water and periodically agitated to encourage the pulp to fall off. Fermentation follows, where the seeds sit in water for anywhere between a few hours to a couple of days, depending on the climate, equipment used, and the producer’s preference.
Following fermentation, the beans are rinsed thoroughly and then dried, either outdoors on raised beds, or in a mechanical dryer.
Natural Process (Dry Process)
Natural processing is the oldest processing technique, where whole coffee cherries dry intact on raised beds, patios, or mats. Once the fruit is entirely dry, it’s either stored for a period of months or hulled right away to remove the outer skin and the inner parchment. All that remains are the two seeds—known more commonly as beans.
Natural processing originated in places without reliable access to water, like parts of Ethiopia and Yemen. The technique makes sense there, where temperatures are hot and the sun is powerful. In these conditions, the drying coffee cherries have little chance to mold, as compared to places like Guatemala, where perpetual mist falls throughout the harvest season.
When processed well, natural coffees articulate fruited flavors rarely experienced in washed coffees. Notes of intense blueberry and strawberry are very common, so that even those new to coffee tasting are able to pinpoint the exact flavors. This method allows the beans to actually absorb the flavors of the coffee fruit. That’s why natural coffees exhibit a wide range of vivid fruit and sometimes wine-like notes, along with greater body and less acidity.
Natural processing is not without risks. If the drying cherries are not frequently raked, the fruit can ferment or spoil, and the resulting coffee can taste sour or yeasty. Natural coffees are exciting, because they have the potential to show off a region’s terroir in a unique way—a result of the coffee beans' prolonged contact with the original fruit.
Honey Process (AKA Semi-Washed, Pulped Natural)
In many ways, this process is halfway between washed and natural processes. It gets its name from the sticky mucilage left on the coffee bean after it is depulped and laid out to dry.
The coffee cherry skin is removed, as in washed processing, but instead of soaking the cherry in water, they’re spread out to dry with the pulp still attached to the beans. The result is a coffee with increased body and low acidity, like a natural, but without the intense fruitiness. Specialty coffee producers like to experiment with the amount of fruit pulp left on the coffee in an effort to move the flavor profile towards or away from natural or washed characteristics. This flavor modulation can also be affected by the speed of the drying process and how often the coffee is turned and moved throughout that process.
The honey process is strongly associated with Costa Rica and, in recent years, subcategories have developed: yellow, red, golden, black, and white honey. This reflects the ability this process has to influence the taste and overall profile of a coffee. It can become a highly scientific process, as the level of mucilage – which influences the sweetness and depth of body of the coffee – is monitored and controlled. Typically, the more mucilage left on the bean, the fruitier the taste. The level of honey can also be dictated by how often the coffee is turned or the rate that it is allowed to dry. If the coffee is dried faster with frequent turning, it will result in a lighter honey profile and vice versa.
Anaerobic Fermentation
Anaerobic fermentation is not necessarily a processing method by itself, but a fermentation technique that can be used with any of the previously mentioned methods to greatly influence the flavor profile of the finished coffee.
In anaerobic processing, a producer has specifically deprived the coffee’s surrounding environment of oxygen during the fermentation stage. Deprivation of oxygen can happen within a bag, drum, or other container that limits oxygen’s ability to reach the coffee as it ferments. The oxygen can be released via a one-way valve, or specifically pushed out by forcing carbon dioxide into the container. This allows for a longer fermentation phase to occur without the risks of over-fermentation and unpleasant notes being added to the coffee, as could happen in an open environment (such as during the “natural” processing style).
These coffees usually have the most intense and unique flavor profiles you will find in the coffee world. Some producers have experimented with adding fruits to the fermentation or using the fermentation liquid from previous fermentations to jump start and manipulate the flavor creation.
