Anaerobic Coffee: What is Anaerobic Fermentation and Processing?

Anaerobic Coffee: What is Anaerobic Fermentation and Processing?
Anaerobic Coffee Tanks in Costa Rica / Ally Coffee

Anaerobic coffee is a unique coffee processing method that involves fermenting coffee cherries in an oxygen-free environment.

This technique results in a distinct taste and flavor profile that's more wine-like and boozy.

In this article, we'll explore what anaerobic coffee is and how it's processed.

What is Anaerobic Coffee?

Anaerobic coffee refers to coffee that has been fermented in an oxygen-free environment. Every coffee cherry undergoes fermentation when it’s transformed from a fruit into a bean, but anaerobic fermentation is a specific type of processing.

During the process, the coffee cherries are placed in a sealed container (for example, stainless steel tanks) with little to no oxygen, creating an environment that is ideal for the growth of microorganisms. The coffee cherry is sealed, and a valve or outbound tube allows carbon dioxide to escape.

This process creates an environment where the cherries go through a metabolic process, and introduces things like lactic acids, ethyl alcohol, and other compounds that shape the coffee's journey. Without oxygen, the microorganisms naturally present in the coffee cherries then ferment the sugars and organic acids, resulting in a striking flavor profile that tends to be intensely winey and an aroma profile that’s expressly fragrant.

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Anaerobic Coffee Taste and Flavor Profile

The anaerobic process tends to enhance the coffee's fruity notes and can include wine-like flavors. The different flavors from the distinct acids introduced to this coffee can change as the temperature of the coffee cools down, with bright and refreshing acidity and a syrupy body.

The flavor profile can also include fruity, floral notes, and a bright and refreshing acidity and a syrupy body.

This can change as the temperature of the coffee cools down. For example, Black & White Roasters describes a coffee from Benjamin Paz as follows:

When hot, this coffee has a delicate florality reminiscent of hibiscus, and the acidity is integrated and balanced. Red wine characteristics, like currants and baking spice, are predominant at this temperature. As the coffee approaches a pleasantly warm temperature, things start to get really interesting.
Those red wine notes give way to white wine characteristics, like vibrant acidity and tropical flavors that remind us of pineapple gummy bears. We found the most balance at this temperature and feel it reflects the nature of the coffee's processing most strikingly.
As the coffee becomes cool, flavors and acidity continue to intensify, resulting in a bright, tangy, slightly spicy cup profile that reminds us of a sparkling lambrusco wine. Here, the variety characteristics of the coffee become more apparent: blackberry joins the flavor party, and red currant returns for its encore.

Natural Process vs Anaerobic Coffee Processing

Anaerobic coffee processing is similar to natural coffee processing in that both fermentation processes promote prolonged contact between the seed and sugary mucilage and fruit layers of the cherry.

Anaerobic coffees have been compared to "natural coffees taken to an extreme". While natural coffees already express intense fruitiness, anaerobic coffees can further intensify flavors as fermentation is allowed to occur in a sealed environment, often for 96 hours or longer (washed coffees are usually fermented for fewer than 12 hours). In these sealed tanks, without oxygen, the fermentation process takes over.

What is Washed Anaerobic Coffee?

Washed anaerobic coffee is a variation of anaerobic coffee processing that involves washing the coffee cherries after they have been fermented in an anaerobic environment.

Similar to traditional washed processing, the washing process removes any remaining sugars and organic acids from the coffee cherries, resulting in a cleaner and more nuanced flavor profile. Washed anaerobic coffee typically has a brighter acidity and a lighter body than natural anaerobic coffee.

Anaerobic Processing for Farmers

Anaerobic coffee processing typically involves a sealed container to prevent oxygen inlet and has a valve or outbound tube that allows CO2 to escape. A popular and basic method of fermentation is through hermetically sealed GrainPro bags, but can get as advanced as sealed drums with pH and temperature monitors.

Because anaerobic fermentation runs the risk of ruining entire lots of coffee cherries, coffee producers embracing this style of fermentation have become more scientific and data-driven. Paired with the increasing demand for unique coffees, these producers are ushering in a new era of coffee processing and coffee consumption.

Trying Anaerobic Coffee

Interested, but not sure where to start? Here are some tips, if you're brand new to these different types of coffees.

  1. Find a reputable roaster: Look for a roaster that sources high-quality anaerobic coffees from trusted producers. A good roaster will be able to tell you about the specific coffee you're buying and how it was processed.
  2. Try different roasts: Anaerobic coffee can be roasted to different levels, so try different roasts to find the one that best suits your taste preferences. A lighter roast may accentuate the fruity and floral notes, while a darker roast may bring out the wine-like flavors.
  3. Experiment with brewing methods: Anaerobic coffee can be brewed using different methods, such as pour-over, French press, or espresso. Experiment with different brewing methods to find the one that best highlights the unique flavor profile of the coffee.
  4. Pay attention to temperature: As mentioned earlier, the flavor profile of anaerobic coffee can change as the temperature cools down. Pay attention to how the flavors evolve as the coffee cools and try to find the temperature that best suits your taste preferences.
  5. Enjoy with an open mind: Anaerobic coffee has a unique taste and flavor profile that may be different from what you're used to. Approach it with an open mind and be willing to explore new taste experiences!

We recommend coffees from Panama’s Creativa Coffee District, which is taking a committed, exploratory approach to creative processing methods including anaerobic fermentation and carbonic maceration.