Guide to Lactic and Anaerobic Fermentation Methods
Fermentation occurs in all coffee processing to some degree, and recently some of the coffee producers we work with have been experimenting with different fermentation methods in order to create unique and interesting flavours.
These fermentation styles may be more common in other industries, such as wine, beer, cheese and bread making, but they are new in the world of coffee, and we’re really enjoying discovering the results in the cup!
What is fermentation?
Put very simply, fermentation happens when microbes like yeast and bacteria consume sugars and, in doing so, break down the starches to create acids or alcohol.
What is fermentation in coffee?
A coffee bean is the seed of a sweet red fruit that grows on a coffee tree. These fruits are commonly called coffee cherries. The fruit, or ‘mucilage’, inside a coffee cherry naturally begins fermenting the moment the cherry is picked, so most coffee cherries go through some kind of fermentation. This may simply be the few hours the cherries spend sitting in a bucket or barrel before they are processed, or it may involve a longer designated fermentation period.
The following are some of the more unusual fermentation styles being used by some of the producers we work with at Market Lane. It’s worth noting that the names of these methods are not internationally uniform, so these terms may sometimes mean different things to different producers or roasters.
As the name suggests, this fermentation process involves reducing the coffee’s exposure to air. The coffee is put in an enclosed container like a barrel or tank for anywhere from three hours to several days, and then it’s dried.
Anaerobic fermentation can be used for whole cherries or pulped beans. This is why you might see the term combined with other processing methods, such as ‘Anaerobic Washed’, which means the coffee was pulped (to remove the skin and fruit) before it was anaerobically fermented and then dried, or ‘Anaerobic Natural’, which means the coffee was fermented and dried with the cherry skin and fruit still intact.
What to expect: Anaerobic coffees can taste pretty wild! They often have a rich mouthfeel with concentrated notes of fruit, spices or herbs.
There are many different yeasts and cultures involved in coffee production, and the one that dominates – meaning, the one that eats all the available sugars and reproduces – depends on the environment created during the fermentation process. To encourage a lactic fermentation, producers aim to create an environment that is ideal for the growth of lactobacillus cultures; the kind used in dairy production that generate lactic acids.
For a lactic fermentation, a coffee producer will select perfectly ripe cherries with the highest possible sugar content, then place those cherries in an anaerobic environment like a tank or sealed barrel. Throughout the fermentation process that follows, the producer will carefully monitor and control temperature, pH levels and available oxygen to achieve the right conditions for lactobacillus to flourish and dominate the fermentation.
Lactic fermentation can be used for whole cherries or pulped beans, so you might see the term combined with other processing methods, such as ‘Lactic Washed’, which means the coffee was pulped (to remove the skin and fruit) before it was lactic fermented and then dried, or ‘Lactic Natural’, which means the coffee was lactic fermented and dried with the cherry skin and fruit still intact.
What to expect: Lactic processing often creates sweet, fruity and creamy flavours (like a mango lassi), but it can also produce a more complex, clean and fruit-forward cup without strong pulpy or winey notes.
Market Lane's lactic and anaerobic coffees
From time to time, we're lucky to feature beautiful coffees from Bolivia that were fermented using these special methods. These micro-lots are usually limited releases because these fermentation methods are very time and labour-intensive and risky for producers, so the coffee is only produced in small lots. Our long-time producing and exporting partners, the Rodriguez family, have invested a huge amount of time and effort into perfecting these processes, and they are producing some truly exotic, rare and distinct coffees.
In Bolivia, tanks are used for lactic and anaerobic fermentation