The term "processing" is quite vague; the more common English equivalent is "process," which is mostly understood as the actions performed on coffee from harvesting, usually in the producing country.
Here, we will exclude
roasting and extraction, which are, in a way, other coffee processes, but we must separate them for clarity.
Harvesting is also part of coffee processing, if you will, but we will quickly move past this step as this article is primarily dedicated to post-harvest processing. In summary, the coffee farmer has a choice between selective manual harvesting (picking) or mechanical or manual mass harvesting (stripping). Of course, picking is of higher quality as it allows for the selection of ripe cherries, but it is more expensive. It is therefore usually reserved for
specialty coffee, as are the various sorting methods. The processing methods we will discuss now take place a few hours after harvesting, and most are also reserved for specialty coffee due to their higher cost.
Note that not all of them are antagonistic and incompatible. Some coffees may have undergone several of these treatments simultaneously.
Classic Processes (Industry Foundation)
The vast majority of coffees will have gone through these steps, which yield radically different coffees in the cup, even for the same coffee cherry.
1. Washed Process (Wet Process)
(Already defined in the coffee vocabulary and sometimes called the wet method) After harvesting, the cherry is mechanically depulped to remove the skin and pulp. The bean, still covered in mucilage, is then fermented in tanks (with or without water) for 24 to 36 hours. This fermentation allows enzymes and microorganisms to break down the mucilage, which is then removed by washing. The coffee is finally dried until it reaches a stable moisture content.
Sensory-wise, this process limits excessive fermentation and enhances acidity, aromatic clarity, and terroir expression.
Example: Our Funambulus from Ethiopia.
2. Natural Process (Dry Process)
(Also defined in the coffee vocabulary and sometimes called the dry method) The cherries are dried whole, without depulping. During drying, which can last several weeks, slow fermentation occurs inside the fruit. The sugars from the pulp gradually migrate to the bean.
This process requires little infrastructure but a lot of monitoring, as high humidity can cause defects. It amplifies the sweetness and body of the coffee.
Example: Our Pyro from Brazil
3. Honey Process (Pulped Natural)
The cherry is depulped, but the mucilage is partially left on the bean during drying. The more mucilage, the more active the fermentation. The coffee is turned frequently to prevent mold.
This process creates a balance between the cleanliness of washed coffee and the richness of natural coffee, with more controlled fermentation than natural processing.
There is a distinction in honey coffees based on the percentage of mucilage retained after depulping:
- White honey when very little remains (close to washed coffee)
- Yellow honey when a little more mucilage is left
- Red honey when a significant part of the mucilage is left
- Black honey: when maximum mucilage is left, difficult to control
Example: Our Orion from Costa Rica, which combines a honey process with other experimental processes discussed later in the article
Subtle Fermentation Processes
As seen previously, the coffee we know is a fermented product by definition. It is possible to "enhance" this fermentation through numerous processes, sometimes inspired by the world of wine. Below are some processes specifically applied by certain countries, without necessarily being categorized as "fermented coffees," as the impact is delicate and integrated.
4. Double Fermentation (or Extended Fermentation)
Applied to washed coffees, here after depulping, the beans are fermented once in a dry tank for 12 to 24 hours, rinsed, then re-immersed in a second fermentation bath for the same duration. This repeated cycle gradually breaks down the mucilage while developing the amino acids and proteins of the bean, which explains the intense sweetness and very pronounced fruity signature of Kenyan coffees. The beans are then soaked in clear water for an additional 24 hours, before slow and controlled drying on raised beds until 11-12% moisture.
The downside of this method is that it is labor-intensive, water-intensive, and leaves little room for error: over-fermentation can compromise the entire batch.
This process adds more aromatic complexity while remaining relatively close to traditional washed profiles.
Example: Our Citrus from Kenya
5. Aerobic Fermentation
There are different ways to perform aerobic fermentations. It simply involves extending the fermentation over time while maintaining a certain microbiological balance.
This can be done, for example, in bags on raised beds during drying, which allows for a slow micro-fermentation. This process accentuates sweetness without excessive fermentation.
Example: Certain coffees from Rwanda or Burundi
6. Enzyme-Assisted Fermentation
Natural enzymes (mainly pectinases) are added to the mucilage after depulping to accelerate and precisely degrade it. Where spontaneous fermentation can take 12 to 72 hours, enzymes do the same job in 4 to 8 hours, limiting the risks of over-fermentation or microbial drift.
The resulting coffee is very clean, crisp, without any harsh fermented notes. It is a tool for transparency that highlights the bean itself, its variety and its terroir, rather than a tool for aromatic creation.
Examples: Colombia, Costa Rica
Innovative Fermentation Processes
7. Anaerobic Fermentation
The coffee (as cherry or depulped) is placed in an airtight tank without oxygen. Microbial activity changes: certain yeasts and bacteria are favored, producing more organic acids and aromatic esters. The absence of oxygen slows down some aggressive fermentations, but makes the process more susceptible to errors.
Anaerobic coffees potentially have maximum aromatic intensity (acidity, sweetness, bitterness), which can make them superb when expertly handled but sickening otherwise.
Example: Our Ursa Minor, although a constantly changing reference, almost always includes anaerobic fermentation.
8. Carbonic Maceration
Highly inspired by the world of wine (a fermentation typical of Beaujolais Gamays), here whole cherries are placed in a CO₂-saturated tank. Fermentation occurs primarily within the fruit's cells (intracellular fermentation), without immediate skin rupture.
This mechanism promotes the formation of highly aromatic esters, resulting in very fruity and sometimes atypical profiles.
Example: A natural carbonic maceration Geisha from Colombia
9. Lactic Fermentation
A type of fermentation commonly used in cooking, which has largely inspired coffee. Fermentation conditions (temperature, oxygen, duration) are adjusted to favor lactic acid bacteria (which are sometimes added for greater process control). These mainly produce lactic acid, which is milder than acetic acid.
The result is a creamy, smooth cup, with a round and not overly aggressive acidity. This process has the immense advantage of not overpowering the terroir.
Example: Our Pyxis from Indonesia
10. Thermal Shock
One of our favorite processes at Celsius, which is why we will elaborate on the subject.
There isn't a single "thermal shock" recipe. Producers who master this technique adapt it based on several parameters:
- The temperature of the shock, which varies depending on the desired effect. Moderate heat around 40-50°C promotes cell opening without overcooking the sugars. Higher heat around 70°C caramelizes more and gives richer, candied profiles.
- The duration of the hot phase also plays a big role. A few minutes are enough for a subtle effect; prolonged exposure results in a more pronounced profile.
Some producers alternate several hot/cold cycles to accentuate the osmotic effect on cell membranes. This is where the term "thermal shock" takes on its full meaning: it is the abrupt temperature variation, not just the heat, that creates the most pronounced effect on the bean's permeability.
- The fermentation phase that follows can be aerobic, anaerobic, lactic, or a combination. It is by playing with this variable that producers finely tune the final profile.
It's a process that doesn't forgive approximation.
Poorly controlled heat can degrade delicate aromas or create baked and woody notes that mask everything else. Fermentation that is too long after the thermal shock can tip into excessive fermentation, especially if the membranes are very open and microorganisms have easy access to the grain's sugars.
Reproducibility is also a real challenge: ambient temperature, altitude, variety, ripeness level of the cherries—all these factors cause the result to vary from batch to batch, and producers who master this process often invest in fairly precise thermal control equipment.
Thermal shock is currently associated with elite competition coffees, mainly in Colombia and Costa Rica. It is still not widespread because it requires dedicated equipment, real technical expertise, and excellent quality raw material for the process to reveal something rather than mask it.
It's not a process applied to just any coffee: on an ordinary batch, heat only amplifies defects. It's on varieties with high aromatic potential, harvested at full ripeness, that thermal shock truly expresses what it can do.
Examples: Our Ursa Minor often includes thermal shock in its production stages
11. Fermentation with yeast inoculation (inoculated yeast)
Specific yeast strains (Saccharomyces cerevisiae, Pichia kluyveri, etc.) from oenological or coffee research are inoculated into the fermentation tank to replace or guide the natural microbial flora. These yeasts consume the sugars in the mucilage and produce volatile compounds (esters, organic acids, alcohols) which migrate into the bean and directly modify its aromatic profile.
Unlike enzymes that clean, yeasts build: each strain has its own aromatic signature (tropical fruit, floral, spicy) that the producer chooses according to the desired result. Repeatability is excellent, but the question of terroir legitimacy remains open in the industry.
Example: Our Ursa Minor was fermented with inoculated wine yeasts
12. Double or triple sequential fermentation
The coffee is fermented several times at different stages: in the cherry, after pulping, or even during drying. Each phase brings a distinct transformation.
These coffees are very complex but require great expertise, they are generally coffees from the most renowned farms.
Examples: micro-lots from Granja Paraiso 92 in Colombia
13. Co-fermentation / Infusion
Fresh fruits, tropical fruit juices, spices, flowers, or alcohol are introduced directly into the fermentation tank alongside the coffee. During fermentation, the bean absorbs part of the aromatic compounds from these ingredients, which are added to the aromas produced by natural microbial activity.
The resulting profiles can be spectacular and very identifiable: passion fruit, hibiscus, cinnamon, pineapple. This process is one of the most visible in current competition circuits. However, it raises a legitimate debate in the industry: the line between a terroir coffee and a flavored preparation is very blurred here, and some professionals refuse to consider it as specialty coffee in the strict sense.
At Celsius, we believe that within these co-fermentations, some coffees are better made than others. When an infused flower or herb enhances the coffee while respecting its original taste, like our Ursa Major, we are convinced. However, when a very aromatic fruit like watermelon or mango completely masks the taste of the coffee to the point of completely ignoring its terroir, we are skeptical.
Examples: Many coffee farmers in Colombia have made it a specialty
Rare and Advanced Processes
These processes are quite rarely encountered in reality, but who knows, they might be the future of exceptional specialty coffee?
14. Cryo-fermentation
Fermentation takes place at very low temperatures, which greatly slows down unwanted microorganisms.
The coffees are very pure, with precise and crystalline acidity.
Examples: experimental micro-lots (Colombia)
15. Fermentative osmotic dehydration
A hypertonic medium causes water to migrate out of the fruit, concentrating the internal sugars and compounds.
The coffee becomes dense, very sweet, and textured.
Examples: R&D projects in Latin America
16. Vacuum fermentation
Fermentation is carried out under reduced pressure, which facilitates gas evacuation and limits certain undesirable reactions.
The final profile is clean, precise, and without fermentative heaviness.
Examples: competition lots
Endemic Processes
These processes share a common point: the transformation of the bean does not rely on human-controlled fermentation, but on an external agent, biological or climatic. To locate the geographical origins of each, see our article
Where does coffee come from.
17. Kopi Luwak (civet coffee)
The cherries are ingested by the Asian palm civet (Paradoxurus hermaphroditus), a small mammal from Southeast Asia. During intestinal transit, proteolytic enzymes modify the proteins of the bean, and a specific bacterial fermentation occurs. The beans are recovered from the feces, cleaned, and dried.
Sensorially, the profile is known to be less bitter and more textured. However, this process is more of a marketing gimmick than a serious specialty tool: almost all commercial production relies on captive civets in deplorable conditions. Wild Kopi Luwak exists but is extremely rare and very difficult to verify. It's something to know for industry culture, not for its cup value.
Origins: Indonesia, Philippines, Vietnam
18. Black Ivory Coffee (elephant coffee)
A Thai variant of the zoological principle. Arabica cherries are integrated into the diet of sanctuary elephants. Transit takes 15 to 70 hours, during which enzymes and intestinal flora act on the bean. The result is a very smooth, low-bitterness coffee with chocolate and floral notes.
The ethical approach is more serious than for Kopi Luwak (elephants are not captive for production purposes), but the project remains ultra-marginal and the cost per kilo is among the highest on the market.
Origins: Northern Thailand
19. Jacu Bird Coffee
The Jacu bird (a large forest bird of the Cracidae family) feeds on ripe cherries on certain certified organic Brazilian properties. The beans recovered after transit are processed like Kopi Luwak. This process originated accidentally on Henrique Sloper's Fazenda Camocim in Espírito Santo. It remained confidential and artisanal but inspired broader reflection on animal-derived enzymatic fermentations.
Origins: Brazil (Espírito Santo)
20. Monsooned Malabar Coffee
A historical Indian process, born by accident. Before the era of steamships, coffees from the port of Malabar took several months to reach Europe. In the holds of sailing ships, the beans were exposed to the humidity of monsoon winds, causing them to swell and undergo a profound chemical transformation. For the historical context of these major trade routes, see
Where coffee comes from.
Today, the process is deliberately recreated: green beans are exposed in open warehouses to the Indian monsoon winds (from June to October) for 12 to 16 weeks. The bean absorbs moisture, swells, loses its acidity, and develops a very particular profile: earthy, spicy, woody, with very low acidity and a full body. The color of the green bean changes from a characteristic blue-green to pale yellow. This is one of the few processes that intervenes on green coffee after the initial processing and before roasting.
It is also a process that we will never order.
Origins: India (Malabar Coast, Karnataka)
21. Aged Coffee
In a logic similar to monsooned coffee, some producers and traders age green coffees in warehouses for 2 to 10 years, sometimes in jute bags, sometimes in wooden barrels. Indonesian and Indian coffees are particularly well suited to this. The result is similar to monsooned coffee in its broad outlines: progressive disappearance of acidity, development of body, and woody, earthy, spicy notes.
The distinction from monsooned coffee is important: here, there is no active climatic exposure, only time and storage conditions. On the question of coffee preservation in general, see our article
How to store your coffee.
You will read in this article that this process is everything we try to avoid at Celsius.
Examples: Old Brown Java, India Aged Monsooned
22. Wet-hulled (Giling Basah)
A traditional process emblematic of Indonesia, particularly Sumatra, Sulawesi, and Flores. Unlike all other processes, the parchment is removed while the bean is still moist, at 40 to 50% humidity, well before reaching usual stability. The bare, still tender bean is then dried in this state, giving it a very particular porosity and cellular structure.
The profile is radically different from other processes: very dense body, very low acidity, earthy, woody, tobacco, cedar notes. This is not an experimental process; it is a tradition deeply rooted in the Indonesian industry for generations.
Examples: Sumatra Mandheling, Sulawesi Toraja
Decaffeination Processes
While decaffeinated coffee long suffered from a deserved reputation for being soulless and flavorless, technological advancements in recent decades have gradually rehabilitated it. Decaffeination remains a high-wire act: it involves selectively extracting caffeine from a green bean, one molecule among hundreds, without sweeping away the aromatic compounds that make up the value of quality coffee.
The common principle of all decaffeination methods: Regardless of the technique, decaffeination follows the same three-step logic. The green bean is first hydrated to open its cellular structure and make the caffeine mobile. A solvent is then brought into contact with the bean to capture the caffeine. Finally, the bean is rinsed or treated to eliminate any trace of solvent before drying. It is in the nature of the solvent that the methods diverge radically.
23. Chemical Solvent Decaffeination
The two most commonly used industrial solvents are dichloromethane (DCM) and synthetic ethyl acetate. In the direct process, the beans are brought into direct contact with the solvent. In the indirect process, the beans are soaked in water that extracts all compounds; the water is then treated with the solvent to extract only the caffeine, and then reintroduced into contact with the beans to restore their aromas.
These methods are effective and inexpensive, but they leave a noticeable sensory footprint: loss of aromatic complexity, slight artificial sweetness. They remain little used in serious specialty coffee.
Examples: Supermarket coffees
24. Sugar Cane Process (Naturally Sourced Ethyl Acetate)
This decaffeination method, once unpopular, has reconciled with specialty coffee. The principle relies on ethyl acetate, the same solvent used in industrial processes, but from a radically different source: here, it is produced by natural fermentation of sugarcane molasses, then distilled. This process has particularly developed in Colombia, benefiting from the local abundance of sugarcane.
The green beans are first steamed to open their pores, then brought into contact with this natural ethyl acetate which selectively binds to caffeine. After several cycles, the beans are steamed again to remove solvent residues before drying. The decaffeination rate reaches 97 to 99%.
The natural origin of the solvent changes everything on a sensory level: the Sugar Cane Process preserves the bean's sweetness and develops a subtle, slight fermentation note that particularly suits Colombian coffees. The body remains present, and the chocolate and caramel notes hold up well to the treatment. This is often the first method to convince specialty decaf skeptics, as the resulting coffee truly tastes like coffee.
It is also Celsius' preferred method, as it is capable of preserving the coffee's original aromas and balance.
Examples: Colombia (main country of origin), Central American micro-lots
25. Swiss Water Process (SWP)
Developed in the 1930s in Switzerland, and industrialized in Canada by the eponymous company, the SWP is based on an elegant concept: using water as the sole solvent. A first batch of beans is treated with hot water until all its compounds are completely extracted. This water is then filtered through activated carbon: larger caffeine molecules are retained, while aromatic compounds pass freely. This produces Green Coffee Extract (GCE), water rich in aromas but free of caffeine. Subsequent batches are immersed in this GCE: only caffeine migrates out of the bean to rebalance the concentrations. The method achieves 99.9% decaffeination, certified organic. It tends to slightly round off sharp acidity but is particularly suitable for sweet and fruity profiles.
Examples: Natural Ethiopians, Honey Brazilians
26. Supercritical CO2
This is the newest and probably the most expensive method. Supercritical CO2 is a particular state of carbon dioxide reached above 31.1°C and 73.8 bars: it possesses both the solvent properties of a liquid and the diffusivity of a gas. In this state, it exhibits a remarkably selective affinity for caffeine and very little for acids, sugars, and aromatic compounds. The caffeine is extracted and isolated in a separation chamber, and the CO2 is entirely recycled, leaving no residue on the bean.
Today, this method produces decaffeinated coffees that are quite true to their original taste, with sensory profiles that sometimes surprise tasters with their complexity and precision. Its main drawback remains its considerable investment cost, which is reflected in the price of the treated coffee.
Examples: Specialty micro-lots, mainly Europe and the United States
The rule is the same as in roasting: a bad raw material will not produce a good decaffeinated coffee. The bean determines the aromatic ceiling, the process determines the proportion preserved. Transparency regarding the method used is now a minimum standard of seriousness in the industry: simply indicating "decaffeinated" without specifying the process signals that the roaster probably hasn't looked too closely at what was in their bean before the caffeine was extracted.
