What really happens when we ferment coffee

Article by Sasa Sestic

During the process of natural fermentation in coffee, there are several different bio-processes that occur.

In these processes, enzymes produced by the yeast and bacteria start breaking down sugars in the mucilage of the coffee. This causes the sugar to degrade its lipids, proteins and acids, converting them into alcoholic acids. This changes composition of smell, colour, pH and the composition of mucilage.

The yeast in these processes is called saccharomyces cerevisiae. This is a micro-organism and it is a natural, wild yeast that is also found on skin of grapes, cacao beans and other fruits. It is usually present in winemaking, but can also be found in coffee processing. 

The bacteria is called lacto bacillus. Coffee, unlike grapes, will adapt to more wild yeast and  bacterias during fermentation, depending on the terroir and microclimate .

Take, for example, in wine. Bacteria found on the shiraz grape will have same DNA of saccharomyces  cerevisiae, in different countries and in different weather.  However, in coffee, we can have the same bourbon varietal in Brazil and El Salvador, but the two different coffees and their respective bacteria will have different DNA.

The speed of fermentation depends of different factors that affect metabolism, such as external temperature, type of system, fermentation time, quality of coffee in mucilage, acidity of the mucilage, access to oxygen and of course, general hygiene and cleanliness.

All of these above can contribute to increase quality for coffee and also to change and add more flavour complexity.

There are different types of natural fermentations:

Dry fermentation
Wet fermentation
Closed fermentation

More to come in future posts.