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What is Anaerobic Fermentation?

Just as in wine, fermentation is a pivotal part of post-harvest coffee processing which could improve a coffee’s flavour or ruin it entirely. While its main purpose is to remove the mucilage layer of the cherries, the process also facilitates chemical transformation within the coffee beans. Careful management of the fermentation stage can have a positive impact on the coffee's quality attributes.

Credit: Montenegro Farms
Measuring pH and temperature during fermentation

There are, in general, two types of coffee bean fermentation: Aerobic and Anaerobic, both metabolize organic compounds in the cherries, leaving behind substances such as alcohol, acid, esters, etc. Aerobic fermentation is the most traditional method, whereas anaerobic processing, a relatively new approach, has been receiving growing interest as it offers exotic flavors to the coffee profile. For anaerobic fermentation, cherries are inserted into fully sealed tanks with one-way valves to keep them oxygen-deprived while releasing carbon dioxide build-ups. The sugars and acids in the coffee’s mucilage are converted into various acids, ethyl alcohol, carbon dioxide and other compounds, that give rise to the striking exotic flavours. As opposed to aerobic fermentation, this setting slows down the yeast and bacterial activity hence expresses a completely different spectrum of flavours of the coffee beans.

Producers control and modulate the fermentation rate by using different vessels and equipment. Careful monitoring of the coffee fruit’s pH and temperature is the key to success.

You may see coffee that features spices, molasses, tropical fruit, and other flavours on the market. Producers have applied additives during the fermentation process of these coffee beans to introduce diversified flavours to the coffee profile.

Recently, innovative producers have been experimenting with double fermentation. First in cherry, then again in mucilage after being depulped, followed by washing and drying. Results have shown that double fermentation can potentially enhance the coffee’s flavour and fragrance. In the case of our featured coffee this season, Brazil Fazenda Guariroba, it has undergone double anaerobic fermentation induced with microorganisms from the farm, giving it flavours of fennel, yellow fruit, as well as honey .

Coffee is ever-evolving.

Credit: O’Coffee
Fermentation tanks at Fazenda Nossa Senhora Aparecida, Pedregulho, São Paulo, Brazil

Credit: Capricornio Coffees
Pulped natural coffees dry stage under the sun

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