Coffee Processing Methods: What is Anaerobic Fermentation? Do Anaerobically Fermented Beans Taste Good?

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What is Anaerobic Fermentation? Introduction by FrontStreet Coffee

Anaerobic fermentation is not a new concept in fermented foods. The fermentation processes of kimchi and wine both involve anaerobic bacteria. Since we know that the post-processing of coffee beans is a fermentation process, the remaining aspect is simply the principle of fermentation.

Traditional natural, washed, and honey processing methods mostly involve exposure to open environments. Therefore, the bacteria that interact with them are typically aerobic species, such as photosynthetic bacteria and yeast colonies (yeast is facultative and can also function anaerobically). Anaerobic fermentation, naturally, utilizes the operational mechanisms of anaerobic bacteria, such as lactobacillus, filamentous fungi, and yeast.

To produce anaerobic fermentation, it's not about adding specific bacterial strains to coffee beans, but rather creating an environment that allows the coffee beans to ferment. This typically requires:

1. Airtight Enclosed Space

If you don't want to incorporate other flavors, you should use easy-to-clean storage spaces like tin or stainless steel. However, tin is too expensive... (hopefully, no one uses gasoline barrels).

2. Temperature Control and Proper Timing

Accurate temperature control and timing are crucial for successful fermentation.

3. High-Quality Coffee Beans

The beans must have a certain level of sweetness to begin with.

As for whether to remove the fruit pulp, or whether to use dry or wet processing methods, these are each plantation owner's trade secrets, with no unified standards.

Logically, this makes sense because during the anaerobic fermentation process, microorganisms play a significant role. Under anaerobic conditions, lactobacillus converts glucose to produce the sweet and sour sensation of lactic acid.

Chemical Reaction of Lactobacillus with Sugar:

C6H12O6 (glucose, etc.) + 2 ADP + 2 phosphate → 2 lactic acid + 2 ATP

However, in anaerobic environments, yeast undergoes anaerobic fermentation, converting glucose into alcohol (ethanol):

Yeast Anaerobic Fermentation:

C6H12O6 → 2C2H5OH (ethanol) + 2CO2 + 2ATP

The alcohol then reacts with other organic acids (such as the lactic acid mentioned earlier) to form esters, which are important sources of fruity flavor notes in coffee. Therefore, anaerobically fermented coffee beans have higher body thickness, with a wine-like richness, but the sweetness or fruity notes are superior to honey-processed coffee.

Some processors retain the fruit pulp of coffee beans for anaerobic treatment, but this carries risks: yeast will convert glucose into alcohol. With too much fruit pulp, the glucose content is certainly high. If there aren't enough organic acids to completely convert the alcohol, this can result in an overly strong fermented wine flavor, which can be unpleasantly dominant.

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