The term treatment is quite vague, the more common English equivalent being "process" which is mostly understood as the actions carried out on coffee from harvesting onwards, generally in producing countries.
We will set aside roasting and extraction here, which are in a way other treatments of coffee, but which we must separate for the sake of understanding.
Harvesting is also part of coffee processing, but we'll move quickly through this step since this article focuses on post-harvest treatments. In short, coffee growers have the choice between selective hand-picking (picking) or mass mechanical or manual harvesting (stripping). Naturally, hand-picking is of higher quality because it allows for the selection of ripe cherries, but it is more expensive. It is therefore generally reserved for specialty coffee. The treatments we will discuss now take place a few hours after harvesting.
It should be noted that not all of these treatments are antagonistic and incompatible. Some coffees may have undergone several of these treatments simultaneously.
Traditional processes (foundation of the sector)
1. Washed/Wet Process
(Already defined in coffee terminology) After harvesting, the cherry is mechanically pulped to remove the skin and pulp. The bean, still covered in mucilage, is then fermented in vats (with or without water). This fermentation allows enzymes and microorganisms to break down the mucilage, which is then removed by washing. Finally, the coffee is dried until it reaches a stable moisture content.
From a sensory perspective, this process limits excessive fermentation and highlights acidity, aromatic clarity and the expression of terroir.
Example: A washed SL28 from Kenya
2. Natural process (Dry / Natural)
(Also defined in coffee terminology) The cherries are dried whole, without pulping. During drying, which can last several weeks, a slow fermentation occurs inside the fruit. The sugars from the pulp gradually migrate into the bean.
This process requires little infrastructure but a lot of monitoring, as high humidity can cause defects. It enhances the sweetness and body of the coffee.
Example: A natural Caturra from Brazil
3. Honey Process (Pulped Natural)
The cherry is pulped, but some of the mucilage remains on the bean during drying. The more mucilage there is, the more active the fermentation. The coffee is turned frequently to prevent mold.
This process creates a balance between the cleanliness of the washed and the richness of the natural, with a fermentation that is more controlled than natural fermentation.
Honey coffees are distinguished according to the percentage of mucilage retained after pulping:
- White honey when very little remains (similar to washed coffee)
- Yellow honey when a little more mucilage is left
- Red honey when a significant portion of the mucilage is left in place
- Black honey: when a maximum amount of mucilage is left, it is difficult to control.
Example: A Catuai red honey from Costa Rica
Controlled fermentation processes
4. Controlled extended fermentation
Traditional fermentation is intentionally prolonged (24 to 96 hours), with precise control of time, temperature, and sometimes pH. The goal is to allow for a deeper transformation of sugars and acids without microbial drift.
This process brings more aromatic complexity while remaining relatively close to traditional profiles.
Example: a natural Sidra with prolonged fermentation from Colombia
5. Anaerobic fermentation
The coffee (in cherry or pulped) is placed in an airtight, oxygen-free tank. 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 the aromatic profiles pushed to the maximum (acidity, sweetness, bitterness), which can make them superb when the process is mastered, but sickening otherwise.
Example: A washed anaerobic Pacamara from Colombia
Experimental and innovative processes
6. Carbonic Maceration
Heavily inspired by the world of wine (fermentation typical of Beaujolais Gamays), here whole cherries are placed in a vat saturated with CO₂. Fermentation occurs mainly inside the fruit 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 geisha in carbonic maceration from Panama
7. Lactic fermentation
A type of fermentation commonly used in cooking, which has largely inspired coffee. The fermentation conditions (temperature, oxygen, duration) are adjusted to favor lactic acid bacteria (which are sometimes added for greater control of the process). These bacteria primarily produce lactic acid, which is milder than acetic acid.
The result is a creamy, smooth cup of wine with a rounded, gently acidic character. This process has the immense advantage of not overpowering the terroir.
Examples: A Colombian Caturra honey in anaerobic lactic fermentation
10. Thermal shock
After initial fermentation, the coffee undergoes a thermal shock (hot water followed by rapid cooling). This variation alters the permeability of the bean's cell membranes.
Aromatic compounds are extracted or transformed more quickly, resulting in very expressive profiles.
Examples:
Colombia (Finca El Paraíso)
11. Enzyme-assisted fermentation
Natural enzymes (such as pectinases) are added to quickly break down the mucilage. This reduces fermentation time and the risk of defects.
The resulting coffee is very clean and homogeneous, sometimes with less of a terroir signature.
Examples:
Colombia, Costa Rica
12. Double or triple sequential fermentation
Coffee is fermented several times at different stages: as a cherry, after pulping, and even during drying. Each phase brings about a distinct transformation.
These coffees are very complex but require a great deal of expertise.
Examples:
Colombia, Brazil (micro-lots)
IV. Drying-related processes
13. Anaerobic dry fermentation
Fermentation takes place without free water, in a closed environment. Microbial activity is slower and more consistent.
The profile is often elegant, floral, and well-defined.
Examples:
Colombia, modern-day Ethiopia
14. Bag fermentation on raised beds
The coffee is placed in airtight bags during drying, which creates a slow micro-fermentation.
This process enhances the sweetness without excessive fermentation.
Examples:
Rwanda, Burundi
15. Slow drying in the shade (Shade Drying)
The coffee is dried in the shade to slow down water evaporation. The enzymes continue to act in the bean for longer.
The profiles are slim, elegant and very easy to read.
Examples:
Panama Geisha, Ethiopia high altitude
V. Rare and Advanced Processes
16. Cryo-fermentation
Fermentation takes place at very low temperatures, which greatly slows down undesirable microorganisms.
The coffees are very pure, with a precise and crystalline acidity.
Examples:
Experimental micro-batches (Colombia)
17. Fermentative osmotic dehydration
A hypertonic environment causes water to migrate out of the fruit, concentrating the sugars and internal compounds.
The coffee becomes dense, very sweet and textured.
Examples:
R&D projects in Latin America
18. Vacuum Fermentation
Fermentation is carried out under reduced pressure, which facilitates the evacuation of gases and limits certain undesirable reactions.
The final profile is clean, precise and without fermentation heaviness.
Examples:
Competition prizes
Pedagogical conclusion
Each process acts as a lever on:
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fermentation,
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sweetness,
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acidity,
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the texture,
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and aromatic readability.
The more we move towards experimental processes, the greater the aromatic potential , but also the technical risk .