What is anaerobic fermentation?

Education Posted on February 18, 2021

Interview with: 
Rolando Ramirez
Country Manager Mercon Honduras

Ever wondered what “anaerobic fermentation” is? Curious about the science behind it, or how this type of processing method affects the roast process? We have you covered! We recently sat down with Rolando Ramirez, Country Manager of Mercon Honduras to learn more about Anaerobic fermentation and why we started using this new technique.

What is anaerobic fermentation?

Simply put, anaerobic fermentation of coffee is a process to create and control a flavor profile that enriches its original qualities. When we use the term anaerobic fermentation for a coffee, we mean that it has been left to ferment in a sealed tank with a one-way valve to stop the in-flow of oxygen.

How does it work?

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

Fermentation is longer in washed processes, where a bit of fermentation is purposely sought (pulping, fermenting, washing, and drying), than it is in a semi-washed process (pulping and drying).

An anaerobically fermented coffee is left, with pulp or just with mucilage, for up to 36 hours in a sealed tank to stop the flow of oxygen. This process can be done with a tank, with barrels, even with 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 begin to break down glucose molecules, a chemical reaction that generates CO2 and heat. This will displace the oxygen in the tank to be expelled through the one-way valve. The bacteria naturally found in the coffee cherry and the mucilage produce enzymes during this process, which causes fewer complex compounds, such as organic acids and alcohols, to be generated.

Why is anaerobic fermentation used and how influences coffee?

All coffees undergo a fermentation process, generally brief, once they are harvested. This fermentation process, which is deliberately extended in some types of coffee processing, such as honey or natural, is a characteristic part of the flavor profile of each coffee. The anaerobic fermentation allows for better control of this process by managing the ph. Controlling and lengthening the fermentation of coffee results in the alteration of its chemical composition, and therefore its profile too.

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

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