So what actually is fermentation? How can it be used to improve coffee quality? And is it even possible to process coffee without it?
What Is Fermentation?
Let’s take a trip back to our high school science class: fermentation is a chemical reaction. The combination of yeast, bacteria and other microorganisms causes a substance to break down into other simpler substances. Normally the substances that get broken down are sugars. As this happens they tend to release heat. Also, different kinds of enzymes can catalyze this event. Or to put it more simply, fermentation is a natural change that happens 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.
The thing is, fermentation can improve a coffee’s flavor or ruin it. It’s just a matter of how a grower deals with it.
What Does Fermentation Have to Do With Coffee?
Fermentation is a key part of post-harvest coffee processing. It can happen in one of two 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 and let the microorganisms work. The time and temperature are monitored.
- 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 homogenous and easier to monitor while the aerobics are more heterogeneous and more complex to monitor.
But growers don’t have to pick one or the other. Many experiments with both and sometimes they might start with the aerobic process and finish with the anaerobic process.
How Does Fermentation Affect Coffee Quality?
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).
When fermentation is successful it can enhance a coffee’s best attributes. But producers have to be very careful, as an over-extended fermentation time can be linked to a substantial loss of sensory qualities (notes like fruits, caramel, chocolate). Attributes like acidity, body, and sweetness can also be significantly diminished.
Consistency & Fermentation: Friends or Enemies?
Great coffee isn’t just high quality, it’s also consistently high quality. This adds security for coffee buyers and roasters as well as for producers.
Producers need to understand the process behind fermentation, so they can make informed decisions when experimenting. Quality analysis is important so a producer can evaluate the impact on their beans, and change them if they need to.
Producers must know their processes and follow them precisely. This helps to ensure both quality and consistency. Equipment must be clean and data must be recorded during and after fermentation so that a producer can repeat a successful process. After all, fermentation is inevitable. But if done badly it spells disaster for producers. Done well it can lead to delicious, distinctive coffee that consumers love.
Understanding the basics of the coffee cherry and fermentation can help you better understand production and processing. Next time you are choosing between a natural processed and a washed coffee, you can have more confidence in knowing what that means and its impact on your cup.