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Coffee fermentation: what is it and how can it improve the quality of coffee?

Some people hate fermented coffee. Some love it. But one thing is for sure: this is a new trend in coffee processing.

So what is fermentation? How can coffee quality be improved? And is it even possible to avoid fermentation during coffee processing?

To answer these questions, we spoke with Carlos Giraldelli, Harvest Coordinator at O’Coffee , a Brazilian farm that supplies direct roasting coffee. He heads an experimental program that examines how fermentation can affect coffee quality.

Coffee is dried on raised beds in Fazenda Nossa Senora-Aparecida, Pedregul, São Paulo, Brazil. Photo by  O’Coffee

What is Fermentation?

Remember school: fermentation is a chemical reaction. The combination of yeast, bacteria and other microorganisms causes the substance to decompose into other simpler substances. As a rule, the decomposing substance is sugar. And during the decay process, thermal energy is produced. This process can catalyze different types of enzymes.

So, to put it simply, fermentation is a natural change that happens when sugar is combined with water – and enough coffee in both coffee berries. The fermentation process begins as soon as the berry harvest is complete (and sometimes earlier, depending on the humidity).

The fact is that fermentation can both improve the taste of coffee and destroy. The result will depend on your actions.

Workers overcook coffee while drying at Fazenda Nossa Señora-Aparecida, Pedregul, São Paulo, Brazil. Photo by  O’Coffee

What does fermentation have to do with coffee?

Fermentation is a key step in the processing of coffee after harvesting. It can happen in one of two ways:

  • Aerobic: Occurs  when oxygen is present. This fermentation method is simple: put the recently harvested berries in a container and leave the microorganisms for further work. Keep track of time and temperature to keep the process under control.
  • Anaerobic:  In this case, the coffee berries (before or after pulp cleaning) are placed in a container and filled with water. This triggers various microorganisms.

So what’s the difference? Carlos explains: “Anaerobic processes are more homogeneous and easier to control, aerobic processes more heterogeneous and more difficult to track.” But you don’t have to choose one method. Carlos says that in O’Coffee they experiment with both aerobic and anaerobic treatment, and sometimes even “start with an aerobic process and end with an anaerobic process.”

There are many approaches to fermentation and the more we experiment, the more we learn about coffee quality.

 The coffee is dried under the sun in Fazenda Nossa Senora-Aparecida, Pedregul, São Paulo, Brazil. O’Coffee

How Does Fermentation Affect Coffee Quality?

Since fermentation is a complex process, there are many potential results. Poor, uncontrolled fermentation can lead to mold or even a chemical taste in coffee – which is why it’s so important for the manufacturer to understand the process, control it, and work to standards.

Then the fermentation will be successful and enhance the best quality coffee.

Carlos shares that O’Coffee is experimenting with fermentation to “enhance coffee and be able to offer customers exotic grains with a distinct profile. The sweetness and acidity become more pronounced, the body appears, and bright sensory notes such as fruits, caramel, chocolate and more are added. ”

Dr Britta Folmer in Craft and Science of Coffee writes: “[Pulp removal] by fermentation in water is known to emphasize acidity and aroma and eliminate some tartness. Semi-dry coffee and khani is a combination of washed and dry. The flesh is not harvested, or only partially, so that the fermentation begins little by little during drying. This can give the coffee a sweet taste similar to what we get during the dry process. ”

But manufacturers have to be careful. As Carlos says: “Prolonged fermentation can lead to a significant drop in sensory qualities … acidity, body and sweetness can be greatly reduced.”

Fermentation containers at Fazenda Nossa Señora-Aparecida, Pedregul, São Paulo, Brazil. O’Coffee

How exactly is fermentation in coffee?

Manufacturers can choose different ways to ferment coffee. The topic is still fairly new and unexplored, with plenty of room for quality experimentation.

In O’Coffee, according to Carlos, they act as follows:

  • “When the coffee is dry-processed … it goes to a 5,000-liter tile-covered fermentation tank.” Aerobic fermentation takes place inside.
  • “Semi -dry coffee passes through environmental depulpators that do not have water to maintain the maximum amount of pulp. The coffee is then placed in the tanks where it stays for a while, which depends on the ambient temperature. ”

So, berries inside, what’s next?

Carlos explains, “Regardless of the fermentation selected, aerobic, anaerobic or mixed, the time can vary from 16 to 25 hours, the process is stopped when the brix [probable sugar content] reaches 8 ° Bx (8 grams of sucrose per 100 grams of sample), and the pH is drops to 4.5, not lower. “

And of course, every difference in the fermentation process has a different result. “In general, the results are better in dry coffee compared to semi-dry. During coffee, the average mark for such coffee rises to three, ”says Carlos.

“It is important to emphasize that it is not only about grade, fermentation enhances the complexity of flavors. The sensory description of such coffee becomes richer and more detailed. ”

Anaerobic Fermentation at Fazenda Nossa Senora-Aparecida, Pedregul, São Paulo, Brazil. Photo by  O’Coffee

Stability and Fermentation – Friends or Enemies?

When it comes to excellent coffee, the issue is not only about high quality, but also about consistency. It serves as a guarantor for coffee buyers, roasters and of course the producers themselves.

Carlos admits that it is not always possible to predict the results of the experiments. However, there are ways to improve repeatability.

Manufacturers need to understand the fermentation process so that they can make informed decisions. They need to know how to analyze the quality, for example, during a copy to fully evaluate the impact of their experiments on grain – and make the necessary changes.

It is necessary to know well how all stages of the process go and follow the algorithm; this guarantees both quality and stability. Make sure the equipment is clean. Be sure to record data both during and after fermentation to be able to understand, control and repeat your actions.

Carlos emphasizes the importance of knowing brix, pH, fermentation time, temperature, and more – and finally, the ability to cap. The more information you have, the easier it is to get consistently high quality coffee.

Poor fermentation can have devastating effects on producers. But if you do it best, you can get delicious, expressive coffee that consumers fall in love with.

After all, fermentation is not avoided. So you have to decide whether to restrain it or to use it to the full.

Author: Ivan Petrich.

Note: This article was sponsored by O’Coffee .

Translation: Anna Polstiankina.