Interested in what fermented coffee is? You're in the right place.
We'll look at what fermentation is, how fermented coffee is made, and what the benefits are.
Let's get started.
What Is Fermentation?
Fermentation is the process by which bacteria and yeast break down sugars and starches into simpler substances like ethanol and various acids.
Fermentation is used in the production of coffee beans, cocoa beans, tea, wine, and more.
The most prominent example of fermentation is washed coffee processing. During this process, the skin is removed from the coffee berries and the berries are left until bacteria break down the mucilage/pectin layer and pulp. Then this can be easily washed off the surface of the beans before the beans are dried. Fermentation occurs during any method of processing coffee—washed, honey, or natural.
The original purpose of fermentation was to speed up the process of extracting beans from coffee berries. But over time, manufacturers realized that as a result of fermentation, decomposition products of sugars are formed, which change the taste and aroma of coffee beans during roasting and can significantly improve the taste of coffee.
How Is Coffee Fermented?
Coffee fermentation can be divided into two types: aerobic and anaerobic. Aerobic fermentation involves oxygen, while anaerobic fermentation does not.
Fermentation is often confused with processing methods: aerobic with natural processing, and anaerobic with washed processing. In reality, fermentation and processing method are two different things, although they are closely related: fermentation is one of the stages of coffee processing.
You can ferment coffee beans in different ways, regardless of the processing method. Coffee can also be fermented using aerobic and anaerobic fermentation at the same time.
Aerobic Fermentation
The aerobic fermentation process can begin even before the coffee cherries are harvested because bacteria and yeast only need a suitable level of moisture inside the fruit and access to oxygen.
Aerobic fermentation occurs during natural processing, where coffee cherries are dried after harvest. This fermenting process can last up to 30 days or until the moisture level in the cherries drops to 11-12%.
Aerobic fermentation is difficult to control because it is influenced by external factors such as ambient temperature and humidity. You can only control the conditions for drying the coffee: dry it on patios or African beds and adjust the thickness of the layer of coffee cherries, the frequency of stirring, and the amount of time the coffee spends in the shade. This will allow you to control the intensity and overall fermentation time.
Dry fermentation with washed coffee processing is another example of aerobic fermentation. During this process, the cherries are peeled so coffee beans with pulp and gluten remain. Then the beans are placed in fermentation tanks without water and left for 18 to 48 hours. After this, the remaining pulp is washed off the beans, which are then dried.
Honey processing is also an aerobic fermentation process. It differs from the previous method in that the coffee, after being washed, is immediately sent to dry in the sun for a week to two. The pulp dries directly on the surface of the beans, and the bacteria are less active during this fermentation method, but they last longer.
Although the process of aerobic fermentation may seem simple, in reality it is quite time consuming and dependent on weather conditions.
Anaerobic Fermentation
As a rule, anaerobic fermentation works like this: the coffee cherries are loaded into large water-filled fermentation tanks and left there for 12 to 72 hours. This stage is called "wet fermentation" and is one of the stages of wet coffee processing.
Anaerobic fermentation is easier to control than aerobic fermentation and is also more uniform. Because access to oxygen is limited, alcoholic acidity is formed more slowly, and that which is formed dissolves in water. This allows for a longer fermentation time, which is better for unleashing the potential of coffee. If the temperature inside the vat is low (39.2 to 46.4°F), the coffee will be more acidic. If the temperature is higher (64.4 to 68°F), the coffee will be more sweet.
During anaerobic fermentation, it is important to monitor the temperature inside the vat, the pH of the water, the sugar content, and the duration of fermentation. Monitoring these indicators and analyzing the results allows coffee producers to carry out an unlimited number of experiments and find the process that gives the best-tasting coffee. For example, a coffee producer could compare coffee that's been fermented with carbon dioxide to coffee that's been fermented with the addition of various types of bacteria and yeast.
Due to its predictability and controllability, anaerobic fermentation is the most popular method among coffee producers. However, it's not ideal for all cases because each crop has its own potential, for which the fermentation process needs to be adjusted.
Benefits of Fermented Coffee
Fermentation is a tool that helps coffee producers create a range of flavor notes.
For example, a producer may use fermentation to improve the taste of Brazilian coffee, which, because it grows at low elevations, is inferior in taste to coffee from Colombia or Guatemala.
There are millions of bacteria and yeast in the environment that are involved in the fermentation processes. They all have their own habitat preferences. By changing temperature, pH, oxygen content, access to sunlight, and other environmental factors, we can slow down the activity of some bacteria and accelerate the activity of others.
A fermentation experiment can either raise or lower a coffee's overall SCA flavor score during cupping. Correct fermentation can increase the coffee's score up to 80 points out of 100 possible. Considering that specialty coffee is a category only awarded to coffees that score above 80 points, fermentation experiments can play a decisive role in the fate of a coffee farm.
Sources
- Alcoholic Fermentation - ScienceDirect
- The Role of Yeasts in Fermentation Processes - US National Library of Medicine National Institutes of Health
- Difference Between Aerobic and Anaerobic Fermentation - Pediaa.com
