ANAEROBIC FERMENTATION OF COFFEE
by David Muñoz on Apr 11, 2023
Once the coffee cherry is collected, it is taken to the mill, where it is processed to extract the grain. There are three basic processes to obtain green beans: Natural (sun-dried in patios), Washed (pulped, fermented and dried) and Semi-washed (pulped and dried). Due to the rise of specialty coffee and the demand for new flavors and sensations, these processes have been expanded by introducing new techniques. Hence, we hear about prosecutions such as Yellow Honey , Wet Hulled, etc.
In the processes that make use of fermentation, this can be done in different ways. The anaerobic that concerns us in this post, is a type of fermentation based on anaerobic processes, that is, those that are carried out without the intervention of air, more specifically oxygen.
WHAT DOES IT CONSIST OF
Fermentation is a chemical reaction. The combination of yeasts, bacteria and other microorganisms causes the matter to decompose. Normally, the substances that break down are sugars. In a simpler way, fermentation is a natural change that occurs when sugar and water come together, and coffee cherries contain these two substances.
In the case of anaerobic fermentation, as we have seen before, it must be carried out in the absence of oxygen.
HOW IT IS PERFORMED
First of all, wash the cherries very well to remove twigs and impurities. You can use the whole cherries with the shell or already pulped, depending on the character that you want to print to the coffee. Once clean, they are placed in sealed barrels isolated from oxygen, which allows the generation of bacteria that only develop in this type of environment. These microorganisms decompose and oxidize matter and return acids and elements derived from carbon to the medium. For this reason, a conduit equipped with a one-way valve must be enabled that allows the exit of these gases and prevents the entry of air.
Before closing the barrels, it is necessary to measure the Ph and take a Brix reading (indication of the sugar content) to deduce the time they must be fermenting, which is crucial for us to extract the best from the grains. The research to obtain good results can take years before obtaining an optimal result.
The process must be done very carefully, paying attention to all the details: cherry selection, cleaning, correct humidity, temperature inside and outside the barrels, etc. It is very important to control the time so that it does not extra-ferment, which would ruin the coffee.
WHAT IS INTENDED WITH THIS FERMENTATION?
What is sought with this type of anaerobic fermentation is to enhance the flavors and offer different profiles of the same coffee. Refine the sweetness, acidity, and body of these coffees, and also add distinguished sensory notes, such as fruit, caramel, chocolate, and more. It is true that it is a common characteristic of these coffees to be very clean and balanced in the cup.
Likewise, the complexity of these coffees also improves. The sensory description becomes richer and more complex.