You can’t move in the world of speciality coffee right now without bumping into the term ‘fermentation” again and again whether it be “extended”, “anaerobic”, “anoxic” or “yeast” fermentation, “carbonic maceration”, “co-fermentation” or even the “river submerged” fermentation I spotted recently on a coffee available from Ethiopia (if you’re asking it’s an anaerobically processed coffee that was sealed in a bag and submerged in cold stream water for four days!). These experimental fermentation techniques, many of which have been adapted from the winemaking world, have recently become super popular in coffee as a way to enhance flavours and help specific lots stand out.
We’re no stranger to roasting a delicious funky anaerobically fermented coffee or two here at Glen Lyon (our natural anaerobic ‘Firecracker’ from Nicaragua’s Isacio Javier Albir being one of our most popular in recent months) so we thought it might be a good idea to talk a little bit more about what we actually mean by fermentation in coffee.
Like kefir or kombucha, coffee is indeed a naturally fermented drink. Every coffee bean that we roast has been fermented to a certain degree. All coffee ferments during the processing period including the traditional washed and natural processed coffees that make up most of the world's market — fermentation begins as soon as the coffee cherry is picked from the tree when microorganisms like yeasts and bacteria start to break down the sugars in the picked coffee cherries’ sticky sweet mucilage to create a coffee’s acidity and fruit-forward notes. But producers actively encouraging, prolonging, and controlling the process is a relatively recent phenomenon. Manipulating the fermentation process— such as removing oxygen, extending the fermentation time or even adding extra ingredients into the coffee fermentation tanks—can give the final cup noticeably different and unique flavours.
Anaerobic Fermentation vs Carbonic Maceration
Anaerobic fermentation is one of the most popular of these experimental methods. The farmer seals the freshly-harvested and depulped cherries in an oxygen-deprived chamber like a bag, barrel or vat, for a specific period of time. Oxygen is forced out through a one-way valve or sometimes by introducing CO2 (what’s known as carbonic maceration). In East Africa I even heard an example of producers achieving anaerobic conditions by placing lighted candles inside sealed coffee fermentation containers to remove the oxygen - technology at its simplest yet most brilliant form! After the specified time has passed the coffee is removed and is washed and dried in the traditional ways. Coffees processed in this way will sometimes be noticeably fruitier or the coffee’s already-present flavours will be accentuated. Either way, be prepared for a delightful sensory experience.
Washed Remonta Process
If you were signed up to our single origin subscription this last May then you might remember a delicious Colombian coffee we had from producer Alfredo Castaño. Castaño had processed this particular lot using a ten day ‘washed remonta’ process. Similar to anaerobic fermentation the coffee was sealed and fermented in a long rectangular can-like vessels which were turned at certain intervals to ensure that the coffee was fermented consistently across the batch and the fermentation juice homogenised with the beans equally. In this case the method was implemented over 10 days before the coffee was washed. Such coffees tend to achieve a profile similar to washed coffee but with an elevated acidity.
Yeast Fermentation
Yeast Fermentation in coffee is when producers add specific cultivated yeast strains to the fermentation tanks. The yeast breaks down the sugars in the coffee’s sticky mucilage typically over 24-48 hours creating esters, organic acids and other volatile compounds that enhance the coffee’s flavour. Using this process, producers are able to carefully control the environment to replicate desired flavour profiles across different batches and limit the growth of undesirable off flavours. Yeast fermentation can produce some very desirable cup profiles including enhanced tropical fruit, berry, floral or chocolate notes..
Yeast vs. Co-fermentation
In yeast fermentation and more traditional anaerobic fermentations it is only the natural sugars present in the coffee fruit that are broken down. In a co-ferment however, producers add an extra ingredient to the sealed fermentation tanks - often fruit like pineapples, oranges or strawberries, spices such as cinnamon or even milk which ferments alongside the coffee imbuing it with some very distinct aromatic flavours.
Sometimes the results can be very subtle creating a slightly fruitier coffee and sometimes, as was the case of a crazy strawberry co ferment from Colombia that we cupped recently, an in-your-face-strawberry-bubblegum-explosion. A word of warning though. With these co fermented coffees fetching super high prices some more unscrupulous players are suspected of possibly adding concentrated extracts or even artificial flavourings into the fermentation tanks to get the desired funky results. Here at Glen Lyon we are slightly on the fence about co-ferments. They’re certainly piquing our interest but with coffee itself having such incredible aromas and flavours it almost seems sacreligious to mess with it. We would love it if you let us know your thoughts?
The Fermentation Project
If experimental fermentation is a rabbit hole you're keen to go down then stay tuned. Later this year we are very excited to be taking part in James Hoffman's Fermentation Project with a live global tasting event in early September. Along with a selected handful of roasters we will be receiving 4 differently fermented lots from a single farm in Guatemala - a 'mechanical demucilaged', a 'wild fermentation' a 'Lactobacillus Inoculated' and a 'Yeast Inoculated' which we will roast and have available to pre-order from mid July so that you can take part in the project!
