Fermentation is one of the most important steps in preparing coffee for the global market. It
happens after the coffee cherries are harvested, but before drying and packaging. Fermentation can
occur either with or without depulping. Only green beans are fermented — not roasted ones.
So why is fermentation so important?
In short: it enhances flavor clarity and consistency, allowing producers to deliver tasty,
expressive coffee of repeatable quality year after year.
What Is Fermentation?
Fermentation is a biological process in which yeast, bacteria, or other microorganisms
“consume” the natural sugars in a product, releasing acids, alcohols, and other byproducts. It’s a
fundamental process used to create coffee, chocolate, bread, beer, wine, cheese, yogurt, and more —
all would be impossible without fermentation.
In coffee production, fermentation serves several purposes:
1. Softens the cherry pulp, making it easier to remove the mucilage and parchment layer —
especially in cases where mechanical depulping didn’t clean the beans thoroughly.
2. Enhances desirable flavors, such as acidity, sweetness, fruitiness, and clarity.
3. Suppresses or eliminates undesirable flavors and aromas, leading to a cleaner cup.
4. Improves consistency from year to year, helping producers build reliable, long-term
relationships with buyers.
Types of Fermentation
There are several types of fermentation:
Dry vs. Wet Fermentation
Dry Fermentation: Unwashed (sometimes depulped) cherries are left to ferment in the sun or
in large containers with access to oxygen. Depulped beans are typically fermented for no
more than 48 hours, then washed and dried. Whole cherries may stay in the sun for days or
even weeks, depending on temperature, wind, humidity, and sunlight.
Wet Fermentation: A key part of washed coffee processing, where depulped cherries are
immersed in water for 8 to 48 hours, depending on ambient temperature. The lower the
temperature (ideally +10 to +15°C), the slower and more controlled the fermentation.
Aerobic vs. Anaerobic Fermentation
Aerobic Fermentation: Requires oxygen. All dry fermentation is aerobic by default. Some wet
fermentation can also be aerobic — for example, if the cherries are only partially submerged
in water.
Anaerobic Fermentation: Occurs without oxygen — cherries are either fully submerged or
sealed in airtight tanks (with or without a valve to release CO₂). This method often yields
unique, fruity, and exotic flavor profiles.
The Role of Yeast
One of the most important fermentation tools is yeast — especially strains of Saccharomyces
cerevisiae. There are hundreds of subspecies, each capable of emphasizing different flavor
compounds in coffee. Many are now commercially produced specifically for coffee fermentation.
Yeast is typically added during wet fermentation, while dry fermentation relies more on
naturally occurring bacteria, fungi, and wild yeast — which may come from the cherries themselves
or from the surrounding environment during harvest, sorting, and drying.
Fermentation Control = Quality Control
Today, wet processing is becoming more popular among producers worldwide because it:
Enables the use of controlled yeast cultures
Is faster, easier to standardize, and more replicable
Allows the farmer to kill unwanted microbes and maintain consistent quality
By controlling variables such as time, temperature, and microbial environment, farmers can
consistently produce coffee with a reliable flavor profile. In other words:
Controlled fermentation is a direct path to producing high-quality specialty coffee.
This is especially important because specialty-grade coffee can command a wide range of
premium prices per kilogram, making it one of the most valuable segments in the global coffee trade.
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