Anaerobic processing allows for several variations, all of which differ greatly from conventional processing methods.
As the name suggests (“An” – “aerobic” = “without” – “oxygen”), the fermentation process of the coffee cherries takes place without CO2. The term “anaerobic fermentation” as it is often used is misleading, however, because all fermentation is naturally anaerobic. In anaerobic processing, fermentation takes place in an anaerobic environment – with the exclusion of oxygen.
After harvesting, the coffee cherries are placed in a sack, tank or container, which is then sealed airtight. Some containers have a valve through which the oxygen that is still in the container and also created by the fermentation itself can escape. Another approach is to put the cherries in a container and add carbon dioxide (CO2) to displace the oxygen. Which cherries are placed in the containers and in which condition depends on the decision of the respective farmer: coffee cherries can be placed with or without pulp, as "naturals" or after "honey processing". Depending on the condition, the taste of the coffee can change significantly.
Anaerobic processing is also growing in popularity because it offers more control than other methods. Farmers can easily monitor the length of fermentation, temperature, pH and Brix (the unit of measurement for the amount of dissolved solids). In Ethiopia, for example, the fermented grains are stored in an airtight bag
The cherries are sometimes placed in a river for 48 hours to ensure efficient cooling. To measure the pH value, the lid of the container or the closure of the bag only needs to be opened briefly. The values determined can then also be used for processing the following harvest.
After fermentation, there are no limits to how farmers can process the beans. Some dry them in the sun afterwards, while others "pulp" them if they were not pulped before fermentation. The absence of oxygen creates certain acids that give the coffee a unique taste. Lactic acid in particular has a strong influence on the profile of the coffee. The extent to which it is influenced depends on the various factors mentioned above: time, temperature, pH value, Brix measurement and possible further processing measures.
