Coffee basics: A guide to anaerobic fermentation

Kahwei Yoong
September 1, 2021
anaerobic fermentation

All coffees, whether washed, natural, or honey processed, undergo some degree of fermentation during the post-harvest processing phase.

Its primary purpose is to remove the mucilage from coffee seeds, but it can also have a considerable impact on the sensory profile of the coffee.

The two most common methods are washed and natural: in washed, the pulped cherries are fermented in a water tank before being washed and dried, while in natural the cherries are left out to dry in the sun.

However, one method that has become increasingly popular in recent years is anaerobic fermentation.

Defined as an experimental approach to processing that ferments the cherries in an oxygen-free environment, it can impart distinct characteristics on coffee that makes it popular among the growing cohort of specialty coffee consumers.

To understand more about anaerobic fermentation and its benefits for roasters, I spoke with the manager of Quality & Market Development at Daterra Coffee, Gabriel Agrelli Moreira.

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anaerobically fermented coffee
Anaerobic fermentation usually takes place in a custom-built, oxygen-free container

What is anaerobic fermentation?

Fermentation is a chemical process whereby carbohydrates, such as sugars are broken down into alcohols or acids by microbial activities in the absence of oxygen.

While fermentation is, by its nature, an anaerobic process, the term “anaerobic fermentation” refers specifically to fermentation that occurs in a custom-built, oxygen-free environment, such as a sealed container or tank.

Gabriel is manager of quality & market development at Daterra Coffee in Brazil. Daterra was one of the first farms in Brazil to use anaerobic fermentation after being introduced to the technique by one of their French clients, a winemaker from Beaujolais.

“Anaerobic fermentation provides producers with the flexibility to extend the fermentation timeline.”

He tells me that there are two different ways to ferment coffee anaerobically. “One way is by putting coffee in a tank and injecting carbon dioxide (CO2) to remove all oxygen,” he explains. “Since oxygen is absent from the very beginning, it is completely anaerobic.

“Or, you can put coffee in a tank with a valve on top. Initially, there is still oxygen present in the tank. But as fermentation starts taking place, CO2 is released as a by-product.

“CO2 is heavier than oxygen so it pushes oxygen to the upper part of the tank where oxygen leaves the system through the valve. At a certain point, where only CO2 is left in the tank, it becomes anaerobic – this is usually called semi-carbonic.”

This is in contrast to aerobic fermentation, a significantly quicker, more intense process in which cells metabolise sugars in the presence of oxygen. As a result, aerobic tends to require greater attention than anaerobic fermentation in order to avoid over-fermentation of the cherries.

Anaerobic fermentation also provides producers with the flexibility to extend the fermentation timeline, giving rise to the development of new and interesting flavours.

It is also more controlled as a sealed environment makes it easier to monitor different variables such as temperature and pH level.

pouring coffee using a v60 drip filter
For many, their first anaerobically fermented coffee is an eye-opening experience

Impact of anaerobic fermentation on the cup

Anaerobic fermentation has opened up possibilities for producers to unlock unique and exotic flavours that are not commonly found in natural, washed, or honey processed coffees. 

An article by coffee expert Kenneth Davis suggests that an anaerobic environment encourages the formation of lactic acid, which produces intensified flavours in coffee.

Indeed, a group of researchers have also suggested the potential of lactic acid fermentation in flavour modulation and the creation of novel aroma characteristics.

Gabriel tells me that, for him, trying anaerobically fermented coffee for the first was an eye-opening experience.

“I’d never tasted something like that, not from our farms or anywhere else in the world,” he says. “It was just super crazy flavours of tropical fruits like mango and papaya, super floral, with some alcoholic presence at the back – but all very pleasant.”

Further, Gabriel explains that anaerobic fermentation had allowed them to preserve the sweetness and body of Brazilian coffee, while adding layers of complexity.

“I’d never tasted something like that, not from our farms or anywhere else in the world.”

“This is what makes it so interesting when we ferment our coffee anaerobically,” he says. “It is coffee that ticks all the boxes: it has body, sweetness, acidity, fruitiness, and everything else.”

The complexity of anaerobically fermented coffee has allowed Daterra to stand out at some of the most prestigious coffee competitions around the world, including the World Barista Championship and World Brewers Cup.

In 2018, Swiss barista and café owner Emi Fukahori used Laurina, one of Daterra’s anaerobically fermented coffees, when she won the World Brewers Cup.

Gabriel tells me that the years of hard work Daterra poured into creating an exceptional anaerobically fermented coffee has helped elevate perceptions of Brazilian coffee. 

“We do think the varietal and processing method were great,” he says, “but all the years of research that we have done in fermentation and developing special recipes for anaerobic fermentation made it possible for us to create a coffee which broke the belief that Brazilian coffee could not be a coffee for World Brewers Cup.

“It gives us the opportunity to be seen as an origin that is producing quality, great quality.”

anaerobic fermentation
It’s important to know how to process the coffee cherries without taking away their intrinsic flavours

What does it all mean for the coffee industry?

Although anaerobic fermentation is still in its nascent stages, it presents exciting opportunities for the coffee industry.

On farms, it gives producers the opportunity to create coffees that have greater complexity and quality, which, in turn, command premium pricing.

However, Gabriel notes that this can only happen when the fermentation is done right, and best backed by robust scientific research and strong data collection.

When producers approach anaerobic fermentation as an experiment without a scientific basis, it can lead to inconsistency and difficulty in replicating outcomes due to the multitude of variables involved in the fermentation process, like coffee varietal, fermentation time, temperature, and pH, just to name a few.

“It starts a conversation, it shows people that coffee is not just coffee…”

Besides that, it is also important to know how to ferment coffee without taking away its intrinsic characteristics. In the case of Daterra, it took them years of research to fully understand the fermentation process and develop different recipes for their coffee.

“We have a lot of recipes and we try to keep certain attributes of the varietal when fermenting,” Gabriel says. “We want to develop more flavours, but also keep the differences between coffee lots so they don’t all taste the same.

“There are specific flavours in a varietal that are beautiful by themselves. For example, the aramosa varietal has very floral and honey notes, and it sometimes tastes like grapes. When it is fermented anaerobically, you can still find those flavours but they are boosted or become more intense.”

For coffee roasters or café owners, anaerobically fermented coffee creates a buzz and novelty for consumers.

Gabriel runs a coffee shop as his personal project and he tells me that he finds the average consumer willing to try and pay more for experimental coffees.

He says that having a wide selection of offerings sparks consumer’s curiosity in the different types of coffee and the price differences between those coffees.

“It starts a conversation, it shows people that coffee is not just coffee and you can have different experiences with coffee,” he adds.

compostable coffee bag
It’s important to use packaging to highlight unique qualities about the coffee

The buzz around anaerobically fermented coffees is showing little sign of abating. The intriguing cup profile it produces, as well as the story behind it, has captured the imagination of consumers the world over.

As such, it’s important for specialty roasters who offer anaerobically fermented coffee to promote it properly. This includes creating packaging with clear, coherent, and eye-catching designs.

The expert design team at MTPak Coffee can help you, all the way from concept to creation. Our range of recyclable, biodegradable, and compostable coffee bags are fully customisable, while you can also choose from a selection of additional features, including degassing valves and resealable zippers.

For information about our compostable coffee bags, contact our team.

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