The washed process involves completely removing both the cherry and the mucilage from the outside of the parchment with the use of friction, fermentation and water.
The fruit of the coffee plant, known as the cherry, is picked once it ripens on the branch. Mature coffee cherries can manifest themselves in red, yellow and orange pigmentation. After being harvested, cherry is transported to washing stations where it is first weighed and then loaded into a depulping machine. The coffee cherry is then sliced open by either a metal or a sharp plastic blade. The two beans are pushed out of the cherry, which leaves the beans with mucilage as their outermost layer. Mucilage, composed of natural sugars and alcohols, plays a crucial role in developing the sweetness, acidity and overall flavor profile in the coffee beans. It is important in the washed process that all mucilage is removed from the bean which leaves only the flavor that developed in the cell structure of the bean prior to processing. In the washed process, the mucilage is removed either with fermentation or mechanically.
In fermentation tanks, naturally present bacteria and microbes break down the sugars and alcohols that make up the mucilage clinging to the outside of the parchment. Fermentation can take anywhere from 6 hours to 4 days depending on the desired flavor profile, amount of mucilage, weather, temperature, and humidity. The skill and craft of fermentation can have a dramatic impact on the overall quality and clarity of coffee. Fermentation can remove 100% of the mucilage.
Mechanical demucilagers (Penagos and INGASEC are popular brands) are a fairly new technology that removes the cherry and a specific amount of the mucilage with friction – typically with bristles. These machines cannot remove 100% of the mucilage like traditional fermentation, but very close. They use far less water and create less waste than the manual or traditional pulper/fermentation combo. A mechanical demucilager also has the advantage of calibration – one can control the amount of mucilage left clinging to the outside of the parchment according to flavor profile. Mechanical demucilagers can be used for the washed or semi-washed process. A number of the producers that we work with use mechanical demucliagers as the first step of the washed process, but then also use fermentation to remove any remaining mucilage from the parchment.
After mucilage removal the beans are fully washed of any remaining mucilage. The beans are then dried (on patios or drying beds) in the sun or mechanically in either drum or vertical driers. Coffee beans are then stored and left to rest with their innermost layer, the parchment or pergamino in Spanish, as the only remaining protective layer. Finally, the beans have the parchment removed (dry milled/hulled) and are prepared for shipment.
Washed coffees are generally characterized as being clean, bright and mild in flavor due to the process. They typically make up the majority of the Stumptown coffee menu.
Kenyan ’72 hour’ Washed Process
Kenya, famous for the clarity and complexity of its flavor profile, is a model example for coffee processing across the producing world. The coffee undergoes fermentation twice, is then washed, and finally soaked in water before being dried.
Farmers must resort their cherry on-site at the processing station (called a ‘factory’ in Kenya), before delivering to the syphon. Coffee is then depulped with McKinnon depulping units, which use water flotation as the initial density/quality separation of the process. This is ideal, because the most dense (highest quality) coffee beans will sink and be sent via canals to the fermentation tank. The less dense (lower quality) beans are processed separately.
The process begins with a primary fermentation of up to 24 hours, and then the coffee beans are carefully washed before being sent to the secondary fermentation tanks for another 12-24 hours.
Now that the fermentation process is complete, the coffee beans are sent to washing channels where they are meticulously washed clean of any remaining solids, mucilage, bacteria or yeast for as long as 6 hours using fresh spring water from nearby water sources. During this process ‘floaters’, or less dense/lower quality beans, are allowed to run off.
After double fermentation and an extensive washing process, the beans are sent to soaking tanks where they sit under water for as long as 24 hours. This process increases proteins and amino acids, which in turn heightens the complexity of the acidity.
After the soaking stage, the coffee beans are laid out to dry no more than an inch thick on pre-drying beds known as ‘skin beds’. With such a thin layer exposed to the elements, air flow and sunlight are able to quickly wick away the mass of moisture from the coffee beans. The skin drying process lasts 6 hours. Coffee is then mounded in thicker piles on raised drying beds to finish drying, which can take anywhere from 5 to 10 days depending on sunlight, cloud cover, etc.
In other countries, coffee parchment is often left to rest in plastic or jute bags, which doesn’t allow coffee the ability to breathe freely as it rests. These bags can cause the coffee parchment to sweat and develop off flavors that are not intrinsic to the bean. But in top-notch Kenyan processing the dried parchment coffee is taken to bodegas and piled lot by lot in wire cages, leaving it completely exposed, and able to breathe.
This complicated method of processing coffee is one of the most important factors (along with variety, terroir and plant care) in controlling the flavor profile of Kenyan coffees.