Coffee fermentation is the new trend in coffee processing.
It results is a unique taste, many cuppers been wondering about the secret behind it.
Fermentation is a natural change that can happen when you put sugar and water together. and coffee cherries are full of both. And so, just after the cherries are picked (or sometimes before, depending on the humidity), the fermentation process will start.
Fermentation can improve a coffee’s flavor or ruin it. It’s just a matter of how you deal with it.
It is also a key part of most coffee processing and it can happen in 2 ways:
Aerobic: This is what happens when oxygen is available. Engineering this kind of fermentation is simple: just leave the recently picked cherries in a tank or a container and let the microorganisms work. Monitor the time and temperature to help you control and analyze it.
Anaerobic: In this case, coffee cherries are laid in a tank (before or after pulping) and covered in water. That allows different microorganisms to work.
So, what’s the difference? The anaerobic processes are more homogeneous and easier to monitor, and the aerobics are more heterogeneous and more complex to monitor. Sometimes growers will use both processes for the same cherries.
Since fermentation is so complex, there are many different potential outcomes. Poor, uncontrolled fermentation can lead to moldy or even chemical flavors in coffee – which is why it’s so important that the producer understands the process, monitors it, and works according to best practices.
Because when fermentation is successful, it can enhance a coffee’s best attributes. It can refine the sweetness, acidity, and body of these coffees, and also adding distinguished notes, like fruits, caramel, chocolate, and others.
But producers have to be careful. An over-extended fermentation time can be linked to a substantial loss of sensory quality… attributes like acidity, body and sweetness can be significantly diminished.
With anaerobic fermentation, the coffee is placed into hermetically-sealed, stainless steel containers. Aside from yielding new, unexpected flavors, the anaerobic process provides a high level of control of the sugars, temperature, pressure, pH and time.
First the coffee is depulped and the seeds are placed inside the fermentation tanks. The separated mucilage is then tightly packed into a gel-like consistency and added to the fermentation tank until it covers the entire parchment. As the fermentation begins the levels of O2 diminish and the CO2 increase, creating pressure in the fermentation tank. The process lasts between 18 to 23 hours – long enough for the mucilage to be consumed, but not so long that alcohol is produced. After 15 hours the pH needs to be constantly controlled to determine how the fermentation is progressing.
The pressure created by the CO2 allows the flavors of the coffee juices to be injected into the parchment. Once the fermentation has concluded the tanks are opened (carefully!!! Due to the high pressure). The coffee is then sun dried for at least 4 hours otherwise the fermentation might continue and the flavors would change.
With our newest Microlot, the Colombia Caturra Gilberto Rojas - cherries were strictly picked with the same level of ripeness, exposed to a dry and anaerobic fermentation of 24 hours before pulped, later pulped and shadow-dried in parabolic beds to ideal moisture content. This has added fruity sweetness and enhanced the aromatics.