What Is Anaerobic Fermentation?

The anaerobic fermentation process, also known as carbonic maceration, is inspired by winemaking. It is based on the principle that carbon dioxide levels gradually increase during grape fermentation, creating an oxygen-free environment that allows the grapes’ natural sugars to convert into alcohol, resulting in wine with rich flavors, soft aromas, and unique scents. Similarly, the anaerobic coffee processing method mimics this approach by placing whole coffee cherries into a sealed metal container and injecting carbon dioxide while expelling oxygen, fermenting and breaking down the cherries in an anaerobic environment. By effectively controlling factors such as pH, temperature, humidity, fermentation time, and bacterial strains, a more balanced flavor profile is developed, and the consistency of the coffee beans is improved, ensuring final quality.

In addition to the inherent flavors of the coffee beans themselves, anaerobic beans also possess relatively unique aromas. So, are they the so-called “flavored beans”? Clearly not, as no external chemical flavoring agents are used to enhance their aroma.

To achieve anaerobic fermentation, it’s not about adding any specific strains to the coffee beans, but rather creating an environment that facilitates such fermentation. Therefore, the following are usually required:

1. A sealed, enclosed space: If no additional flavors are desired, easy-to-clean storage spaces such as galvanized steel or stainless steel are typically used, although galvanized steel can be expensive.

2. Temperature control and precise timing

3. High-quality coffee beans (with a certain level of sweetness)

In traditionalnatural (sun-dried) processing, washed processing, and honey processing methods, fermentation in an oxygen-rich environment can lead to over-fermentation, which affects the direction of the coffee’s flavor profile. In contrast, anaerobic fermentation, which does not require oxygen, effectively monitors and reduces uncontrollable factors in the fermentation environment. The extended fermentation period results in a balanced flavor across the coffee’s front, middle, and back notes, making it smooth on the palate while also allowing for the appreciation of creamy, buttery, and even refreshing wine-like aromas.

| Characteristics of the Anaerobic Fermentation Process

Using metal containers (to avoid absorbing residual coffee bean flavors) to hold the coffee cherries results in purer flavors.

Fermenting in a sealed environment makes it easier to control various factors, leading to more consistent quality across batches of processed beans and preventing the easy dissipation of aromas.

Long-term fermentation in an oxygen-free environment yields richer, rounder flavors, along with cheesy and dairy-like aromas.

Coffee beans processed using this method often exhibit bright wine-like aromas, better sweetness, and reduced excessive astringency and acidity.

As the coffee industry has evolved, post-harvest processing methods for coffee beans have continued to innovate, with new techniques, concepts, and models. Each change can produce coffee with distinct flavor profiles. In addition to the “anaerobic fermentation process” mentioned in this article, emerging methods such as double anaerobic and anaerobic natural processing have recently appeared. These methods, still in the “developmental stage,” lack absolute standards, and processing methods vary from one facility to another. Coffee enthusiasts can thus explore a wider variety of coffee flavors through these innovations.

Of course, due to their intense aromas, anaerobic beans may be considered unfair competitors in some green bean competitions that emphasize the intrinsic aroma of the beans. This is also why some competitions explicitly prohibit the participation of anaerobic coffees.