Special Coffee Processing Methods: What's the Difference Between Anaerobic and Oxygen-Free Coffee Processing?

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Understanding Yeast in Coffee Processing

Yeast is essentially a facultative anaerobic organism. The term "facultative anaerobic organism" means it can survive in both aerobic and anaerobic environments. In oxygen-rich environments, it performs aerobic respiration, while in oxygen-poor environments, it carries out fermentation. Fermentation is not exclusive to yeast; lactic acid bacteria and acetic acid bacteria also undergo different fermentation chemical reactions.

Oxygen-Based and Anaerobic Fermentation

The so-called "oxygen-based fermentation" should more accurately be called respiration, as there is no actual fermentation process involved. In an oxygen-rich environment, it burns sugars, emits carbon dioxide, and produces energy.

Anaerobic fermentation (also known as the red wine processing method) has become a new trend following this year's WBC competition.

Anaerobic fermentation involves placing raw coffee beans in specialized containers filled with carbon dioxide or other gases to create a relatively oxygen-free or oxygen-deficient environment. The anaerobic environment produces lactic acid, making the coffee's acidity milder and the taste smoother.

The Red Wine Processing Method

FrontStreet Coffee is here today to share what the so-called "red wine processing method" actually is.

The red wine processing method for coffee beans, also called the wine-like processing method, draws inspiration from the winemaking process. Currently, only eight farms in Colombia have successfully brought coffee beans processed using this method to market. According to information from these eight farms, we can roughly categorize the types of red wine processing methods into: acetic acid fermentation (Aerobic fermentation), lactic acid fermentation (Anaerobic fermentation), and mixed fermentation (Mix Fermentation = Aerobic + Anaerobic).

Advantages Over Traditional Processing

Traditional processing methods struggle to control the varying degrees of fermentation in coffee beans. However, the red wine processing method can ensure coffee bean quality by controlling pH values, and even temperature and humidity. Furthermore, enclosed fermentation prevents aromatic substances from easily volatilizing.

The Fermentation Process

Next, let's discuss the specific fermentation process.

Selected coffee cherries are placed by farmers in specific containers (when Australian barista Sasa competed, the beans he used were processed in metal containers). Regardless of the container type, it should have a device similar to a red wine fermentation lock or a one-way exhaust valve. This allows carbon dioxide to escape through this device, controlling the air concentration inside the container. At this point, the coffee cherries in the container undergo acetic acid fermentation, resulting in beans with relatively bright, clean flavors and citric acid notes.

According to Sasa's description during the competition, processors inject carbon dioxide into the container to prevent the formation of volatile acids through oxidation. This process is lactic acid fermentation, which produces malic acid and tartaric acid. Since tartaric acid is relatively stable, beans produced through lactic acid fermentation have a richer acidity with cheesy, nutty, and creamy flavors.

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