Green Coffee Processing Methods

• Fruit Removal: Typically depulped (skin removed) or demucilaged (skin and pulp removed) within24hours of harvest

• Fermentation: Depulped coffees are typically held in “fermentation tanks” for 12–72 hours; demucilaged coffees are not commonly held in tanks but moved to drying surfaces or equipment. Fermentation may occur from the moment of harvest until the seeds reach an inhospitable moisture content for them (11% moisture)

• Drying Time: On average, 18–36 hours mechanically; 7–15 days on patios, raised beds, or in parabolic dryers

• Profile: Clean, articulate flavors; caramel or sugary sweetness; a wide spectrum of fruit acidity depending on other factors; capable of bright, crisp notes    

     Washed or Wet process could be the quickest and most efficient of the post-harvest processing methods, but doesn’t always require water. This process is the primary method for preparing specialty-quality coffee in most of Africa, Central and South America (with the exception of Brazil, where it’s uncommon), and select parts of the Asia-Pacific growing region.

     Based on place, tradition, climate, and access to resources such as fresh water, your mileage may vary on the particular approach any number of producers will take, but “Washed” as a loose definition typically means that the coffee fruit has been removed from the coffee seed as quickly and as cleanly as possible. Some professionals and even some coffee markets and contracts differentiate between “Fully Washed,” which does use water, and other types of “Washed” coffees, such as those that have their mucilage mechanically removed.

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     This process is probably the one in which the use of the term “fermentation” is most often used incorrectly, as we often assume that fermentation happens only when the seeds are stored, contained, or held in an actual “fermentation tank.” On the contrary, fermentation begins the moment there is an access point in the fruit that allows microorganisms like yeast and bacteria to begin metabolizing sugars such as fructose and sucrose. Often, this access point is created at the time of picking, when the fruit and stem are separated and a small hole is typically created. Fermentation can take place in Washed coffees as long as there is either fruit material (mucilage) and/or a certain amount of water (11% moisture) available as a fuel source.

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      Generally, in the coffee industry, we describe the “length of fermentation” as being a period of time in which coffee is piled in tanks or held underwater, with the goal of either accelerating or retarding the ability and access that microorganisms have to the fruit material. “Open,” or “dry fermentation” are terms used to describe coffees that are depulped (have their skin removed) and are then placed in open-air tanks or buckets and allowed to sit in their mucilage, typically for 24 hours or less though occasionally for as long as 72 hours. “Underwater,” or “wet fermentation” can take longer, depending on the climate, water quality, and activated populations of microorganisms.

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• Fruit Removal: After drying

• Fermentation: Occurs inside the fruit mucilage surrounding the seed and under the pulp, will take place as long as there is fuel available to the microorganisms (e.g. sugar, moisture, acids, etc); the seeds typically become inhospitable to microorganisms when they reach 11% moisture

• Drying Time: Upto30daysonaverage, weather permitting

• Profile: Noticeably fruity or “pulpy” flavors, often described as “boozy” or “winey”; can also have strong nutty and/or chocolate characteristics, and typically has a heavier or syrupy body

While Washed coffees have their fruit removed relatively quickly after harvesting, Natural or “Dry” process coffees are something like the opposite. The fruit is picked when ripe and allowed to dry completely around the seed before being husked or hulled off.

Natural process coffees are most commonly found in Ethiopia, Yemen, Brazil, and Costa Rica, though producers around the world are also experimenting with this methodology.

As with all coffee preparation, there is fermentation occurring during the processing, from the moment the coffee is picked (or possibly earlier, whenever an access point is created in the fruit). Local or intentional populations of yeast and bacteria will enter the fruit at the access point and begin to metabolize the sugars and acids inside the coffee fruit immediately, a process that can continue until the coffee is dried to the standard of 11% moisture.

While the coffee itself is not held in “fermentation tanks,” its fermentation process can be altered by things like ambient temperature and exposure to full sun or shade; depth on the drying bed; rotation of the coffee during drying, etc.

Drying Natural coffees is considerably longer and the overall process is riskier than for Washed coffee, which hints at some reasons the Washed technique was developed:

Naturals take more space on drying surfaces, require more attention and labor (to prevent mold and infestation during drying, for example), and are constantly at potential risk for spoilage or “overfermentation,” as the fruit material that is intact on the seeds provides a long term and concentrated fuel source for yeast and bacteria to metabolize.

Natural processing is the oldest basic technique for preparing coffee, and in ancient times (as well as currently in some cultures and applications), it’s possible that the coffee fruit was allowed to dry completely while still on the branch, allowing it to be harvested only when needed. Modern Natural coffees are harvested ripe and intentionally dried, typically on patios, raised beds, or drying tables; they cannot be dried in mechanical dryers as Washed coffees can.

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Some of our very favorite foods and beverages are fermented: chocolate, wine, beer, bread, sauerkraut, kimchi, and… coffee?

    Well, yes and no: While fermentation is involved in the production of a majority of the world’s coffee, coffee itself isn’t a fermented beverage like spirits or kombucha are. Instead, when we talk about coffee fermentation, we’re referring to what the coffee fruit undergoes between the time that the cherries are harvested and the seeds are fully dried and ready for export.

     The word “fermentation” describes the process of metabolization of sugars and other compounds by microorganisms like yeasts and bacteria, which will consume those compounds and convert them into fuel for their own use, leaving behind useful by-products like ethanol and different acids. Those converted compounds are absorbed into the cellular structure of the seed and, when heat is applied to those seeds in the roaster, the compounds will be what transform into the flavors we love in coffee: Complex tastes, fruity acids, and other good, or at least interesting, stuff.

While it’s an integral part of coffee’s post-harvest processing and plays a large role in the development of coffee flavor, fermentation is not a very widely understood aspect of coffee’s production cycle, though fermentation does occur in almost every style of coffee preparation. We often use the words “fermentation” and “processing” interchangeably and incorrectly:

While they are related, they’re not identical.

     Fermentation is a natural occurrence that is undertaken by living microorganisms that are in search of energy sources; processing is a purely agricultural set of mechanical and technical steps designed to prepare a crop product for export. While fermentation can be used as part of processing, that distinction is important.

When we think about fermentation, we try to consider many variables, such as: the ripeness of the fruit; the ambient temperature in the environment as well as the temperature in the coffee as it is; say, 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. It is a very difficult process for producers to track, and so most of the ways we discuss fermentation are colloquial, anecdotal, or “layman’s terms.”

     The microorganisms that perform fermentation processes are found almost everywhere, and they will begin to consume fuel as soon as they have access to it, which means that fermentation can actually begin before the coffee cherry is even picked. The more fruit material that is exposed to the environment and to the population of microorganisms (when the skin is removed from the cherry, for instance), the faster this process can happen.

    Different types of bacteria and yeast populations—which will vary based on location, climate, and health of the local ecosystem—consume different compounds and, so, convert them into different by-products, but generally speaking they will continue to ferment whatever useful material is available to them until they are no longer able to survive.

     For instance, in a Natural process coffee, they will ferment the fruit material around the seed until either all of the fuel is metabolized or until the environment is too dry for them to live. In a Washed process, the fermentation might happen all the way through the drying process, depending on how much mucilage was left on the parchment after the washing was completed.

Anaerobic Fermentation

    As producers consider the effect of fermentation more and more on the quality and profile of their coffee, they are adopting different and interesting techniques to their repertoires in order to diversify their offerings. One method that’s becoming more popular is fermenting coffee in a controlled anaerobic environment, meaning that the coffee is held in a vessel without any presence of oxygen during some of all of the duration of fermentation.

    The fermentation process itself is already anaerobic, meaning that the yeast and bacteria that do the work of fermenting a coffee cherry’s sugar content do not need oxygen to be present in order to successful complete their mission or transform the organic material. (This is why we specify that it’s the environment that’s anaerobic in these cases.) One of the main benefits of holding the coffee in an oxygen-depleted environment, then, is to slow the fermentation process, which allows a totally different spectrum of flavors to express. Where in a Washed process the controlled fermentation might last 12–24 hours on average, anaerobic environment fermentation can take 96 hours or longer, depending on the thermal retention inside the tank.

    Different fermentation-tank materials will have different thermal retention, and producers choose wisely based on the desired effect. Stainless steel is a common material, as is thick plastic. The tanks will contain a one-way valve that allows the producer to remove oxygen from the vessel and release CO2 created during the fermentation process; careful monitoring of the coffee fruit’s pH as well as the temperature inside the tank is pivotal to ensuring the success of the process.

    After fermentation, the coffee’s processing can be completed in any number of ways: The fruit can be fully removed as in a Washed process, the pulp can be removed but the mucilage left on as in a Honey process, or the cherries can be dried whole as in a Natural. The length of drying time will vary based on this last step as well as the environment around the drying area.

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Wet-Hulled (aka Semi-Washed, Sumatra Process, Giling Basah)

• Fruit Removal: Coffee is generally depulped within 24–48 hours; mucilage remains on the seeds until it is purchased by a collector and/or delivered to a mill

• Fermentation: Occurs in the coffee from the moment it is picked, and is accelerated during the piled or sack phase, will continue until the coffee is completely dry to 11% moisture for export

• Drying Time: 12–15 days, on average

• Profile:  Earthy, savory, herbaceous, heavy body, dark chocolate, nutty

Areas of Indonesia—including Sumatra, where it is best-known—are famous for this rather specific and flavor-altering processing method, which is vastly different from other commonly used styles.

    The Wet-Hulled process is a result of a combination of environmental conditions, market access, and traditions found in Indonesia which sets these coffees apart from the rest of the world.

   The process can be simplified for description, but as with other processing methods, it may vary from region to region or mill to mill. After harvesting, the coffee is often depulped in small machines on-site at a farm or household, and then the depulped seeds are stored in plastic tanks or jute sacks to await delivery to a collection point.

(Sometimes cherry is delivered to the mill instead, depending on the producer’s available resources.)

    While in these containers, the mucilage is available for microorganisms to begin to metabolize the sugars, acids, moisture, and other compounds in the mucilage, which remains clinging to the seeds. The coffee is then delivered at high moisture to a market, collector, or receiving point, where it is purchased and then transported and/or sold to a mill for hulling.

     At this point, the coffee is typically between 35–50% moisture—quite a bit higher than the 10–12% moisture at which most coffees are hulled. The mucilage and parchment layers are removed simultaneously using specialized machines, and then the coffee is typically laid tarpaulins for drying.

    In some areas of Sumatra, the wet parchment coffee is held in tanks and fermented briefly (12 hours or so) before being washed clean of its mucilage. It’s then given a pre-dry of a few hours and Wet-Hulled.

    It is important to recognize that while it is parchment coffees that are typically spread to dry in other producing countries, it’s what we call “green coffee” that is dried in the Wet-Hulled process. Removing the protective parchment layer so comparably early in the process creates not only the very distinct flavor profile from these regions, but also adds a bit of risk, as the seeds themselves are more vulnerable to environmental factors (such as rising and falling relative humidity) and other interference or taints (animals, for instance, or dirt and debris).

    However, part of the effectiveness of Wet-Hulling, or Giling Basah, is the rapidity of drying after the coffee is hulled: The damp climate and cloud cover over Sumatra can render other drying methods difficult or inviable for commercial production. Wet-Hulling also allows producers and mills slightly more flexibility when it comes to selling and delivering their yield, which is especially significant to smallholder farmers in rural, remote areas.

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• Fruit Removal: Fruit skin is removed within 24 hours of harvest; all or some of the mucilage is left to dry on the seeds

• Fermentation: Occurs throughout the drying process (until seeds reach a moisture content of 11%)

• Drying Time: 18–25 days on average

• Profile: Can express some fruity/pulpy/jammy flavors or stewed-fruit-like characteristics; caramel or burnt-sugar sweetness; nuttiness

     Honey is a relatively recent processing style and has become prominent throughout Central American coffee-producing countries, perhaps most notably Costa Rica. In many respects, the Honey process is similar to the Brazilian post-harvest process known as Pulp or Pulped Natural. Similar to the Pulped Natural methodology.

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     Honey coffee is depulped to remove the skin of the cherry, and the coffee seed is allowed to dry with some or all of its sticky fruit mucilage intact. This process retains some of the desirable characteristics of a full Natural coffee (heavy body, sweet fruitiness with lower acidity, deep chocolate notes) while also speeding the drying process considerably, and reducing some of the risks of spoilage, mold, and other defects that can occur with fully intact coffee cherry on the drying patios or tables.

     In Costa Rica (and increasingly in El Salvador and Honduras, among other places worldwide), some producers will remove a particular amount of the mucilage material in order to manipulate the coffee’s finished profile. Others focus on modulating the drying process to achieve different Honey levels, assigning differentiating terms to correspond with the results, from Yellow/Golden Honey (the mildest, perhaps closest to Washed coffees), Red Honey, and Black Honey (which is arguably most comparable to the Brazilian Pulped Natural).

     The most obvious benefit to the Honey process over strict Naturals is the speed and efficiency of the drying process, as well as the various flavor characteristics that can emerge through fermentation and exposure. On the other hand, the exposed fruit material does create more risk for the producers, as it requires more labor in drying to prevent taints from developing. These coffees will also often have an uneven or inconsistent appearance in their green forms, which can be unappealing for roasters who are used to the more uniform cleanliness of a Washed coffee.

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• Fruit Removal: The fruit is not removed until after it is fully dry

• Fermentation: Microorganisms present both in the fruit and in the environment will create fermentation in the coffee until it is completely dried and/or until there is no longer useable fuel available for the microorganisms to metabolize (this occurs when the seeds are at about 11% moisture)

• Drying Time: 15–25 days on average, typically on patios

• Profile: Pulpy or boozy fruit, berries, dark chocolate, toasted nuts, toffee or caramel, citric acid, heavy mouthfeel

There are just a few distinct differences between Brazil Naturals and Natural processed coffees.

• Most of the coffee on large farms in Brazil are harvested mechanically, using strip-picking machines that can be calibrated to strip or vibrate ripe cherries off of branches.

• There are also manual strip-picking techniques that can be used to remove all of the cherry—of varying degrees of ripeness—from branches on a coffee tree.

    Generally speaking, there is less selective hand-picking in Brazil (though that continues to change with the increased focus on specialty coffee). Most Brazil Naturals are dried on patios, rather than on the raised beds that many other coffee-growing countries use.

    Due to the climate, varieties being grown, and picking and processing styles, Brazil Naturals also tend to express different flavors than Natural coffees from elsewhere in the world: While they often do show prominent fruit characteristics, the flavor is closer to a coffee-cherry pulp than the blueberry and strawberry notes we see from the finest Ethiopian Naturals. Brazil Naturals also tend to have lower acidity and heavier body or texture in the cup.

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Coffees of any process (Washed, Natural, Honey, etc) can also be processed for decaffeination. The decaffeination itself takes place after the coffee has been harvested, processed, and had its parchment layer removed; most of the time,

    Coffees need to be sent to specific facilities to be decaffeinated, rather than having the caffeine removed at the mill level.

    At present, there is no such thing as a genetically decaffeinated coffee, which means that decaf coffee needs to be created by physically removing the caffeine from green coffee seeds. Most of today’s decaf processing methods are sophisticated and thorough and can remove 99 percent of the caffeine naturally present in coffee.

Mountain Water Process (MWP)

Mountain water-processed decafs are done in a facility in Mexico called Descamex.

    Green coffee is soaked in a water solution, which removes both the caffeine as well as other solubles in the coffee (such as flavor compounds). The water is removed from the seeds and run through a special filter that captures caffeine molecules and allows them to be strained from the solution.

The solution—now containing flavor compounds but no caffeine—is then reintroduced to the green coffee seeds, which reabsorb the soluble materials. The coffee is then dried once more, and prepared for reexport.

Swiss Water Process

The Swiss water process is a chemical-free decaffeination process. Green coffee beans are first soaked in water and the resulting caffeine-and-flavor-rich solution is strained through activated carbon, which captures the larger caffeine molecules while letting the flavor stay intact

    The resulting solution, which is full of flavor and has no caffeine, has been termed Green Coffee Extract and can be used on an entirely new batch of green coffee beans to extract caffeine without losing any flavorings due to solubility and osmosis.

   This process can be repeated for up to ten batches with the same Green Coffee Extract before a new solution has to be created. Although this method doesn't use any chemicals, it may seem a bit wasteful since one batch of coffee beans is discarded for every ten batches of decaf coffee created. Also, some say that flavors may get mixed up among batches since the green coffee extract can carry a previous batch's flavor.

Carbon Dioxide Process

The carbon dioxide process also does not use any chemicals, but it does rely on carbon dioxide that is under extremely high pressure.

    Green coffee beans are initially soaked in water to increase their water content before being placed in a stainless-steel extraction vessel. The extraction vessel is then infused with liquid CO2 at 1,000 pounds of pressure per square inch and compressed to 200 times its normal atmospheric level.

    The CO2 solvent dissolves and removes the caffeine from the beans while leaving behind their flavor. Afterward, the caffeine-rich CO2 is moved to another container so that the CO2 can be used again after turning back into a gas and naturally separating from the caffeine.

Ethyl Acetate (E.A.)

This naturally occurring ester (present in bananas and also as a by-product of fermented sugars) can be isolated and used as a solvent to bond with and remove caffeine from green coffee.

     The coffee is sorted and steamed for 30 minutes under low pressure in order to open the coffee seeds’ pores and prepare them for decaffeination. The coffee is placed in a solution of both water and ethyl acetate, where the E.A. will begin to bond with the salts of chlorogenic acids inside the seeds. The tank will be drained and re-filled over the course of eight hours until caffeine is no longer detected.

    The seeds are steamed once more to remove the ethyl acetate traces,

Methylene Chloride (MC)

Methylene chloride is a solvent that is used to bond with and strip caffeine molecules from the green coffee seed.

    The KVW MC process first uses hot water to extract caffeine and other solubles from the coffee seeds, and then the seeds are removed from the water. Methylene chloride is then added to the water solution, and it bonds with the caffeine

    Because MC is not capable of being mixed with water, it is easily removed from the solution along with the bonded caffeine, and the coffee seeds are re-submerged in order to absorb their soluble compounds.

    The United States Food and Drug Administration has stated that MC is safe for use in decaffeination processes, and is harmless to humans in consumption of 10 parts per million (ppm) or less. Coffee decaffeinated using this method has been shown to contain a fraction of that safe amount.

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• Fruit Removal: The skin of the fruit is typically removed within 24 hours of harvest; mucilage is left intact on the seed

• Fermentation: After skin removal, the mucilage-covered coffee is moved to a drying surface, where it will ferment as it is exposed to air and microorganisms until it reaches an inhospitable moisture content for them (11% moisture)

• Drying Time: 10–15 days on average, typically on patios

• Profile: Pulpy fruit, nutty characteristics, citric acid, chocolate, syrupy or creamy body, medium-low acidity but often noticeably fruity flavor

In most respects, Pulped Natural is a similar process to Honey, where the coffee cherry’s skin is removed and the seed is allowed to dry in its mucilage layer. Though the steps are almost identical, one of the key differences

    The pulped natural process was developed in Brazil in order to speed the drying process, as the more traditional Natural process can take quite a bit longer to complete, putting the coffee’s quality at greater risk.

    Whereas, in Costa Rica and elsewhere, Honey processing is primarily used to affect the flavor characteristics of a lot. 

     As a result, the profile of most Pulped Natural lots from Brazil tends to be quite different from the majority of Honey lots, in that there tends to be less of an intense fruity flavor in these lots, which leans toward a toasted-nut or a chocolate characteristic with some pulpy or boozy notes underneath.

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