What Is Anaerobic Fermentation in Specialty Coffee Processing?

The anaerobic fermentation of green coffee is a unique process that aims to create and control a flavor profile that enhances its original qualities. When coffee is described as anaerobically fermented, it has been left to ferment in a sealed tank equipped with a one-way valve, a crucial component that prevents the entry of oxygen.

How does it work?

The fermentation process begins as soon as the coffee cherries are harvested. Then, depending on the method used to separate the seed from the cherry (pulping), the fermentation process will be longer or shorter.

Fermentation is shorter in washed processes, where a bit of fermentation is purposely sought (pulping, fermenting, washing, and drying) than in a semi-washed process (pulping and drying). The entire process may be longer, but the fermentation process in washed coffee is shorter and more controlled.

An anaerobically fermented coffee is left, with pulp or just with mucilage, for 36 hours or more in a sealed tank to stop the oxygen flow. This process can be done with a tank, barrels, or grain-pro plastic bags. The important thing is that the coffee is sealed without access to air for some time. It can be done before the cherries are pulped or after they have been pulped. In both cases, the microorganisms will break down glucose molecules, a chemical reaction that generates CO2 and heat. This will displace the oxygen in the tank and expel it through the one-way valve. The bacteria naturally found in the coffee cherry and the mucilage produce enzymes during this process, which causes complex compounds, such as organic acids and alcohols, to be generated.

Why is anaerobic fermentation used, and how does it influence coffee?

All coffees undergo a fermentation process, which is generally brief once harvested. This fermentation process, which is deliberately extended in some types of coffee processing, such as honey or natural, is a characteristic part of each coffee's flavor profile.

Anaerobic fermentation allows for precise control of this process by managing the pH. Controlling and lengthening coffee fermentation alters its chemical composition and, therefore, its profile.

In other words, fermentation can enhance flavors or create different flavor profiles of the same coffee. For example, coffee with a 48-hour fermentation process will not taste the same as coffee with a 120-hour fermentation process.

Overall, anaerobic fermentation, through its unique process, inspires producers to experiment and create distinct coffee flavor profiles. Many producers have embraced this, leading to variations, such as extended fermentation, double fermentation, and hot anaerobic, each applying the same general method with slight differences.

Learn more and shop our specialty coffee offerings.