Coffee processing is a unique and vital step in the journey from harvested fruit to freshly brewed cup. Just
as grapes must go through processing and fermentation before it becomes wine, the coffee bean must
be extracted and dried before it is ready to roast, and be consumed.
There are a variety of ways that coffee can be processed, and each method can impart or highlight different flavors
and characteristics in the final coffee. Certain processing techniques are more common depending on the region,
contributing to the distinctive flavor profile of coffees from said region.
Natural Process (Dry)
The oldest and most traditional method to process coffee, natural or dry processed coffee one that is still commonly used today. This process involves drying the entire coffee cherry with the seed still inside, which imparts deeper flavors and adds to the sweetness and body of the final cup. Usually seen in some Ethiopian and Brazilian coffees, this processing method favors dry and sunny areas without much water, as not requiring large amounts of water to wash and soak the coffee is an important factor in choosing this process. Some issues with the natural process is the inconsistant quality, as its hard to replicate same conditions as prior, and potential for spoilage, rot, and overfermentation.
Coffee cherries are sorted and then laid out on drying beds as is, with the seed still inside. The cherries are dried in the sun and raked and turned to prevent mold and rot. The process of drying the whole fruit together imparts stronger fruit (blueberry, strawberry etc.) flavors, sweetness, and produces a deeper heavier cup of coffee. It can also impart some unpleasant flavors as well (barnyard, ferment, manure) however if not done correctly, or some spoilage occurs.
After the fruit is completely dry, the seed is hulled which removes all the outer layers; the skin, dried fruit, mucilage, parchment husk, to reveal the green bean inside.
Washed Process (Wet)
Wet or washed processing involves removing all the flesh from the seed before drying. Instead of drying in the fruit, the coffee seed is depulped, often using a specialized machine, which detatches the skin and flesh from the seed. These then move to tanks of water, where the remaining fruit and mucilage are fermented and completely washed away. This process is more common in regions like Central America, where large plantations and water sources make it a consistent and viable option.
Unlike the natural process, coffee cherries in the washed process go through a de-pulping stage. The coffee cherries are sorted then run through a "de-pulper", a machine which removes the outer skin and the pulp. The coffee is then moved to remove the mucilage.
After de-pulping, the coffee seeds are moved to tanks for a short ferment. Done in either tanks filled with water or dry, this fermentation period helps to break down the mucilage, or sticky outer coating still present after de-pulping. After a day or so, the fermented seeds are rinsed and washed, removing any remaining mucilage before it is set to dry.
Washed coffee seeds are laid out into a thin layer to dry. They are usually raked several times a day, making sure that they dry out evenly. This is continued until the beans reach the optimal moisture level (about 11%) and usually takes 1 to 2 weeks. The seeds are then left in their parchment (thin layer around seed) and stored until it is ready to ship.
Once dried, the seed is hulled to remove the parchment layer.
Honey Process
Originating from Costa Rica, honey processing is seen increasingly in the specialty coffee market. Contrary to what the name might suggest, honey processing doesn't involve the use of honey at all, but instead refers to the mucilage within the coffee cherry thats kept on to impart flavor to the seed. Because of this there are various levels to honey processed coffee, reflecting the amount of mucilage that is left on:
- White Honey: close to wet processed, 80-100% of mucilage removed.
- Yellow Honey: 50-75% of mucliage removed.
- Red Honey: 25-50% of mucilage removed, getting close to natural process coffee.
- Black Honey: 0-25% of skin and mucilage removed.
Sorted coffee cherries are run through the de-pulper. Depending on the style and level of "honey" desired, the machine will be set to remove a small portion or much of the pulp and mucilage from the seed. The more mucilage left on will result in bolder, fruitier flavor.
Once de-pulped, the beans are moved to be dried with the mucilage still attached. As opposed to the washed process, keeping the mucilage on the fruit while it dries will fuse some of the flavor of the cherry into the seed. Spreading out under the sun, the seeds are raked and moved frequently to avoid mold and spoilage.
Washed coffee seeds are laid out into a thin layer to dry. They are usually raked several times a day, making sure that they dry out evenly. This is continued until the beans reach the optimal moisture level (about 11%) and usually takes 1 to 2 weeks. The seeds are then left in their parchment (thin layer around seed) and stored until it is ready to ship.
Wet Hulled Process (Semi-washed)
The wet hulled process, sometimes called semi-washed, is a method commonly used in Indonesia which allows for efficient and speedy processing in areas with a humid climate. This process goes through two drying stages, and removes the parchment layer before drying, which aids in speeding up the drying process. The combination of leaving the mucilage on before the first dry, then removing all the layers before the second dry, contribute to the unique earthy, smokey, woody, tobacco flavors and heavy body found in Indonesian coffees.
Much like with the other processes, the coffee cherries are first depulped to remove the outer layers. The seed is then left with mucilage in a tank and left for a short fermentation.
After a short fermentation, the seeds are moved to dry outside. This initial drying step is not to dry the seed completely but to prepare the seed for wet hulling. After the moisture reaches 30-35% in the coffee bean, it will bee moved to be hulled.
The seed goes through the hulling machine, and much like the de-pulping stage, the outer layers remaining will be removed. The main difference with the wet hull method is that the parchment layer, or the thin layer surrounding the green bean, is also removed at this stage. In other methods, the parchment is left on to dry until the product is ready to ship. The removal of parchment at this and exposing the green beans at this stage leads to them having a swampy green color, and affects the ultimate flavor of the coffee.
The bare green bean is taken outside to dry again and left to dry. Usually done layed out and raked as with other methods, drying the green bean without the parchment leads to shorter and easier drying in humid and cloudy environments.
Anaerobic Fermentation? Carbonic Maceration?
A process seen more in the specialty coffee field is anaerobic fermentation or carbonic maceration. All coffee goes through a fermentation
period, for instance, after being depulped to break down the mucilage around the seed and aid in additional processing. Anaerobic fermentation
and carbonic maceration are methods used to control the fermentation process and impart different flavors into the coffee.
Coffee is placed into sealed tanks, with a scarcity of oxygen. This encourages different communities of microorganisms to flourish than open
air fermentation. As the bacteria break down the sugars into carbon dioxide and alcohol, a pressure release valve is necessary to release the gas
without letting in oxygen. This increased pressure, along with the differing bacteria, produce aromas and flavors unique to coffees fermented
the traditional way.
Some producers will add the pulp from the coffee cherries, pulp from other cherries, spices, fruit etc. to impart more flavor into the coffee.
Overall, this fermentation process is more tedious and time consuming, and can take up to 3 months to complete.
Anaerobic Fermentation: mucilage covered seeds are placed into the sealed tanks. Some pulp, additional fruit, spices are occasionally
added to enhance flavor during fermentation.
Carbonic Maceration: adapted from wine-making, similar to anaerobic fermentation except that the whole fruit is
fermented in tanks rather than the depulped seeds.
Souces & References
- Coffee Processing Methods, https://beannbeancoffee.com/blogs/beansider/coffee-processing-methods?srsltid=AfmBOorAY650h4u2qiZpMjLUkXzne77hryE6gGAUjnFsAkjSRuetmQ8K
- DISCOVER THE UNIVERSE OF COFFEE PROCESSING: ESSENTIAL KNOWLEDGE FOR ALL COFFEE LOVERS!, https://rootsbkk.com/journal/basic-coffee-processing/
- Woodburn-Simmonds, M. (2023) Coffee Processing Methods 101: Washed vs Natural vs Honey, https://homecoffeeexpert.com/coffee-processing-methods/
- Anaerobic & Carbonic Maceration Coffee Processing, https://www.royalny.com/post-harvest-coffee-processing-anaerobic-fermentation-and-carbonic-maceration/?srsltid=AfmBOoq26NoTziqC0k9VyaO42PUalO0SgV12vbvaqX5EDMLNCXXDffu2
- Coffee Varietals Explained: Ethiopian Heirloom, Typica, Caturra & More, https://us.theroasterspack.com/pages/coffee-varietals-explained