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Anaerobic Fermentation In Coffee Processing
Learn all about one of the most popular coffee processing methods today–anaerobic fermentation.
Published October 1, 2021
Joachim Estal
Coffee experts@The Coffee Lab
Processing is one of the essential factors that contribute to a coffee’s quality and flavor. And as coffee culture continues to evolve, new styles of processing are introduced through innovation and adaptation of existing principles.
Today, one of the most popular new processing methods is anaerobic fermentation. In fact, it’s been present in the coffee-farming industry for a long time now. In this article, let’s find out what makes this style different from the others.
What Is Fermentation?
In the simplest terms, fermentation is a chemical and metabolic process wherein complex molecules are transformed into simpler ones without oxygen.
Typically, bacteria and other microorganisms depend on carbohydrates and sugar for energy. These molecules are then converted to pyruvic acid through glycolysis. However, because no oxygen is present during fermentation, other organic molecules are produced instead. And since microbes can take any of the two different energy-producing processes, organisms are able to continue living and developing anaerobically.
What Is Anaerobic Fermentation?
Considering the scientific definition of fermentation, speaking of “anaerobic fermentation” in coffee is actually redundant because fermentation is technically anaerobic. When people talk about this, they usually refer to the method where coffee is placed in sealed environments for much longer periods than average, thus deploying more extended exposure to fermentation.
In this process, coffee cherries are de-pulped as usual and then transferred inside airtight tanks thereafter. These vessels are often made with stainless steel, and a valve is present for off-gassing. When coffee is added into the tanks, oxygen will be removed and continually seeped out of the vessels while allowing the release of carbon dioxide during the fermentation. The whole method can take forty up to sixty hours.
The surviving microbes in anaerobic fermentation are more limited as compared to when coffee is fermented within the usual timeframes. In addition, sugar content and temperature can be more easily monitored, altering its chemical composition. As a result, this will substantially affect the organoleptic profile of the coffee.
How Anaerobic Fermentation Influences Coffee
Regular fermentation generally offers bright acidity and flavors. On the other hand, anaerobically-fermented coffee offers more unique but precise fruity notes. Most coffee experts prefer light-roasting anaerobically-fermented coffees, as it highlights more of its fruity characteristics.
The slow fermentation leads to a more developed natural flavor, which is also sweeter and complex. And it’s consistently fruit–the time it’s still inside the burlap bags and up until you serve it in the brewed version. Citrus flavors like orange, pear, and pineapple are general terms attributed to this type of processing. Sometimes, more unique flavors such as licorice, bubble gum, and gingerbread can also be perceived from the cup.
What Is Carbonic Maceration?
Anaerobic fermentation and carbonic maceration are usually interrelated to each other. However, the most significant difference is that coffee cherries remain intact when they are placed inside sealed, carbon dioxide-rich fermentation tanks. This means that the cherries do not undergo the de-pulping stage in washed processing. This method is derived from the wine industry, wherein grapes are fermented whole without juicing in order to produce a fresher and fruitier taste.
Firstly, the harvested coffee cherries are siphoned to detect and take out low-density ones. After which, the cherries that passed this inspection will be entering airtight tanks with existing one-way valves. These valves allow fluids to pass in one direction but close to stop possible backward motion.
Since carbonic maceration retains the cherry’s skin, fermentation may take much longer. Also, the tank deploys varying pressure levels, creating pectins and sugars for the microbes to ferment. The end product has an uncommon flavor profile with nuances of berry, sage, maple, and dried dates.
The Future Of Coffee Processing
We have learned about interesting innovations occurring in coffee processing. The existence of these creative methods will help inspire more progressive practices in the coffee industry, which is usually reliant on tradition.
And although it is given that not all experimentation will give out positive results, the evolution of coffee processing continues to thrive. These will translate to more exciting sensory adventures that will take us to different places around the coffee world. For sure, we are bound to enjoy more thrilling coffee experiences in the future.
About the author
Joachim Estal
8-year barista for a world-class coffee chain from the Philippines. Passionate writer and coffee champion. "Coffee has always been one of my biggest love interests in life. And I am here to share it with all of you through this platform."
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