The fermentation of coffee

Fermentation? Coffee? Why? What does it do? What doesn't it do?

When it comes to coffee, fermentation is basically just a means to an end. While fermentation is significant for flavor development in foods as diverse as kimchi, cucumbers and chocolate, fermentation in coffee primarily serves a different but equally important purpose: releasing the coffee seed from the surrounding sticky pulp.

As long as coffee has existed as a beverage, farmers have fermented coffee cherries without even calling the process fermentation. They have placed cherries with their skins removed in tanks to ferment without water, or submerged the cherries in water to soak for an hour or days. In natural processing, farmers simply spread whole cherries out in the sun to dry. Rather than relying on scientific tools to monitor microbial activity, experienced farmers used sensory cues as indicators to tell when the process was complete. Microbial flora present on the cherry, in the air, or in fermentation tanks - bacteria, yeasts, and fungi - begin a process in which the microorganisms convert the insoluble pulp of pectins and sugars into a soluble material that can be washed away from the seed.

Until the advent of machines specifically built for this purpose, fermentation was the only way to separate the fruit from the seed. Whether coffee is wet, natural or honey processed, in either case, proper fermentation is the means by which the pulp separates from the coffee bean. When local farming practices dictate an exceptionally long immersion in water because of cool nights that slow the process of fermentation, or a post-fermentation immersion is required by law as in Kenya, this is done specifically by the farmers on each farm.

Technical progress is essential especially for those farms that do not have enough water for the washed process, but whose climatic conditions are also not suitable for drying whole cherries outdoors. Special separators enable even small washing stations located in very dry regions to produce coffee of the same clarity and quality. The secret here is a high overpressure used to separate the beans from the slimy environment.

A new direction gained from these findings is targeted fermentation with previously selected strains of bacteria that influence the fermentation in a specific way. This can then also lead to a change in taste. However, this work is still very much in its infancy and is being driven by a small number of coffee experts around the world. So it remains exciting to see how the already diverse world of coffee flavor will evolve through fermentation. Try our current single origin coffee assortment or enjoy the entire Advent season every morning a new top coffee with our coffee Advent calendar.


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