What on earth is Anaerobic Fermentation?

19th October 2023

So, you’ve heard about this anaerobic fermentation process and want to hear more? Don’t worry, you’ve come to the right place.


Machine pulping coffee cherries

Strap yourself in for a little history lesson on the coffee bean and how we get it brew-ready, mainly the mechanics behind anaerobic fermentation. It all starts with a cherry, but not the one you typically think of – we are talking about a coffee plant cherry. Did you know a coffee bean comes from the cherry off a coffee plant? The seed from this fruit is the coffee bean itself – crazy, right! There are two established methods to extract this precious cargo: natural processing and washed processing. Let’s break them down.

What is natural processing?

Natural processing is the traditional method of using the sun to dry the cherries on raised beds. The dried pulp is then removed to extract the bean. This method is usually adopted by countries with fewer water sources, such as Ethiopia, who must retain their water for essential uses. With this process, the coffee tastes sweeter, fruity, and what we at Two Chimps call ‘funky’. This is because the beans absorb the natural sugars from the fruit while fermenting in the sun, tending to score higher due to these characteristics

What is washed processing?

Washed processing is a very different procedure. Instead, the bean is extracted from the cherry as soon as it is picked. It’s then washed to remove any sticky residue, and from there, it is then dried. Countries like Mexico, with easy access to natural water sources like rivers, tend to use this method. It creates a classic, clean, traditional coffee taste, which you would associate with coffee.


What is Anaerobic Fermentation?

Enough with the basics: what is anaerobic fermentation? You might have seen this buzzword on our website or social media, and it’s time to find out what it’s all about!

It is a new experimental method of preparing the coffee bean ready to be made into, you guessed it…. coffee! As its name implies, this fermentation process reduces the coffee bean’s exposure to air. The beans or whole cherries are put in an airtight container like a barrel or tank for several hours to days. These tanks have valves that stop oxygen from getting in and allow CO2 to be released as it builds up during fermentation.

Once removed, they are dried to the optimal moisture level of 11%. This method can be used for whole cherries or extracted beans; therefore, you may see two terms used: Anaerobic washed, which means the bean was removed from the fruit before it was fermented. Or Anaerobic natural, which means the bean was still inside the cherry when it was fermented. So why use this method? This gives the beans funky, fruity flavours as it’s had time to absorb some of the natural sugar and flavourings from the flesh of the cherry.

System map of Anaerobic Fermentation

The origin of this method is generally credited to the 2015 World Barista Champion Sasa Sestic. Inspired by a winemaker in Australia, Sestic wanted to mirror the technique for fermenting grapes for wine to coffee beans. Wine is created by fermenting grapes within enclosed containers, helping control temperature, oxygen levels, and other factors affecting the wine flavour (sounds familiar). A specific wine procedure called carbonic maceration, typically used for red wine, is when whole grapes (not crushed) are deposited into a barrel without oxygen. This variation is what inspired Sestic to give coffee cherries a go. He competed in 2015 with a variety of Colombian-grown coffee created with anaerobic fermentation. From his success, it has been adopted by many countries, farms, and roasteries. They elevate their coffee beans, creating new flavours, unique combinations, and original roasts.

Has this got your taste buds tingling? Desperate to try a cup of this exciting brew? Don’t worry, Two Chimps has you covered!


Our new speciality coffee, Raves, Sadden, Wildcats, is created with natural anaerobic fermentation! With the natural sweetness of strawberry, treacle, and black wine gums notes-  come on, doesn’t that sound good? Maybe Sestic was onto something…


Order now!

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