On Fermentation


In Guatemala 95% of coffee is fully washed. This means the coffee beans are washed after de pulping to remove the mucilage completely. Before washing, fermentation might take place, to loosen up the mucilage or there might be a demucilager machine involved. There are many ways to ferment, it’s one of the most ancient way of changing or preserving natural ingredients. 

We are certain all of you have tasted the fruits of fermentation, be it in wine, yoghurt, sauerkraut, kombucha, cheese or more commonly, bread.  Even though humans have been fermenting for years, the coffee fermentation process can seem a Pandora's box. 

Fermentation is a metabolic (chemical) process that breakdown a substance (in this case sugars from the mucilage) by bacteria, yeast and other microorganism typically giving off heat. 

As many of you might be aware, fermentation happens not only in the fermentation tanks of washed coffees but also doing the drying of honey and natural processed coffees. Within the traditional washed coffees you can ferment in many ways, for example in aerobic and anaerobic environments - meaning with and without oxygen. Aerobic fermentations are the most common but some producers have experimented with anaerobic, in oxygen free tanks, or under water, which, we know still contains oxygen but it is disolved, making it a good stepping stone for experiments. 

Each producer in Guatemala has experimented and found a method that works for their coffee in their own, unique environment.Some like to ferment their coffees cherries in bags for up to 24 hours before de pulping, in other farms this would be impossible as the warmer climate would lead to immediate fermentation defect, so they have to de-pulp and wash straight away.  Our main take away is that it is crucial to understand the process and record key factors so that this process can easily be replicated. We recommend producers keep a log of time, temperature, relative humidity and if possible PH readings. 

Consistency is KEY! 
The reason for keeping measurements, is so that the process can be replicated if the results are favorable. This allows the producer to have more control over the quality of their coffee. At our Wet Mill we mostly do aerobic fermentations but have been experimenting with underwater fermentations - this year we processed some beautiful yellow catuais this way, which resulted in sweet and fruity flavors. We hope to replicate this process in the harvests to come. 

Natural and Honey Processing is something really special in Guatemala!  As water becomes scarce around the World; it is only responsible of us to take this into account when producing and processing coffee. Drying coffee with its skin, or taking it off and drying the beans without washing is a wonderful way to create interesting cup profiles while reducing water use. 

This all sounds skeptically easy - but over the last harvests, and after the Q-Processing course, we have learned that in order to make good tasting processes you have to be very careful, consistent and meticulous every step of the way. The importance of first submerging the coffees in water, to clean their dust, homogenize the temperature and lower the bacterial count; to the thin layers on raised beds that need to be moved frequently for even drying and mold prevention, requires a whole new team and training. 
With good processing and an excellent cup - all the efforts are worth it. 
It’s important to remember that every farm has its own micro-climate and  unique bacteria. What works at one farm, might not work for its neighbor, let alone someone in another region or country. It is important to be careful, only changing one variable at a time and always taking any (and all) advice with cautionary measures.  

The great thing is that every year, every harvest, there is something new to learn! 



Our first shipments from the 2019 harvest are landing this week! 
We have many amazing coffees on offer for you, from bigger lots to smaller micro-lots; from approachable flavor profiles to crazy fruit bombs. 
Have a look at our first list here and let us know if you would like to get roasted or green samples.