Introduction:Anaerobic fermentation processing has become a hot topic in the specialty coffee scene in recent years, not only adding more layers of flavor to coffee but also sparking deeper discussions on fermentation profiles. This article starts with the innovative techniques of 2015 WBC champion Sasa Sestic, explores the scientific principles and common types of anaerobic fermentation processes, and introduces real-world applications from renowned farms such as Santa Vini, helping you better understand how to choose and appreciate these specialty beans.
The global coffee consumption market continues to expand year by year, and consumer demand for diverse coffee flavors is also growing. To meet market needs, green bean processing technologies have been constantly innovated, giving rise to many techniques categorized as "specialty processing methods," such as anaerobic fermentation, enzyme washing, lactic acid fermentation, and wine barrel aging. These methods impart richer aromas and textures to coffee, making them a popular choice for many coffee enthusiasts looking to try something new.
Among various specialty processing methods, anaerobic fermentation has gradually risen to the forefront due to its unique flavor profile and scientific background. The widespread use of this technique can be traced back to the 2015 World Barista Championship (WBC), where the Australian champion Sasa Sestic stunned judges with anaerobically fermented coffee beans, also making "fermentation character" a hot topic of ongoing discussion among industry professionals and consumers alike.
Generally speaking, during the post-harvest processing of green coffee beans, some degree of fermentation is inevitable, and the fermentation environment is mainly divided into two types: aerobic and anaerobic. Traditional processing methods mostly rely on aerobic fermentation, but due to more variable environmental factors, the fermentation process is harder to control. In contrast, an anaerobic environment provides more stable and uniform fermentation conditions, allowing processors to adjust various parameters more precisely, thereby influencing the final flavor profile of the coffee.
Another common term for anaerobic fermentation is "carbonic maceration," which draws inspiration from red wine production techniques, hence it is often referred to as the "wine processing method" in the industry. In winemaking, grapes are placed in an oxygen-free, carbon dioxide-rich environment. Even without the involvement of yeast, the enzymes within the grapes themselves can convert some of the sugars into alcohol, resulting in a smoother aroma and more complex layers of taste in the wine.
The logic behind anaerobic coffee processing is similar: freshly harvested coffee cherries are placed in a sealed container, carbon dioxide is injected, and oxygen is removed to create an anaerobic fermentation environment. This approach not only slows down the rapid breakdown of sugars in the mucilage but also controls the rate of pH drop. Under strictly controlled anaerobic conditions, factors such as temperature, humidity, gas composition, and the types and quantities of microorganisms involved in the reaction can be more precisely regulated, helping the coffee beans accumulate higher sweetness and develop unique aromatic characteristics.
Most anaerobic fermentation processes available on the market today are extensions or adjustments based on this foundation. For example, in anaerobic natural processing, fresh coffee cherries are placed in a sealed tank and undergo anaerobic fermentation at a constant temperature of around 10–15°C for about three days, after which the beans are moved outdoors for sun drying until the moisture content reaches an appropriate level, then the pulp is removed to extract the coffee beans.
Anaerobic washed processing follows a different procedure: the harvested cherries first undergo 12 hours of dry fermentation, then the pulp is mechanically removed, and the naked beans are placed in a sealed tank for 24 to 48 hours of anaerobic fermentation, followed by conventional drying. As for double anaerobic washed processing, there are two anaerobic stages — first, anaerobic fermentation of the whole cherry, then after removing the skin and pulp, the mucilage is retained for a second round of anaerobic fermentation, and finally dried to around 11% moisture content to complete the entire process.
There are also coffee beans currently available that are processed using anaerobic fermentation techniques. For instance, a brand’s “Boundary Line Estate Geisha” beans from Colombia are processed using a double anaerobic natural method. When brewed with a V60 filter at a 1:15 coffee-to-water ratio, these beans often exhibit pronounced tropical fruit flavors such as grape, passionfruit, and citrus, accompanied by a slight fermentation note, and offer a smooth and rounded mouthfeel. Another highly regarded product is from Ethiopia’s Santa Vini processing plant, where the beans undergo 96 hours of long anaerobic natural processing. The flavor profile typically features intense fermented wine-like aromas, with bright acidity reminiscent of tropical fruits like pineapple and citrus, along with a rich and full-bodied texture.
The above content is compiled by CoffeeHunters, a coffee news website.
