Hardcore coffee aficionados are always on the lookout for the next big twist on the world’s favorite caffeinated drink, and these days it’s fermented coffee that’s shaking and tickling the palate with its unique fruity notes. . Swiss scientists are conducting experiments on fermented coffee in hopes of identifying the specific chemical compounds behind the drink’s unique flavor.
“There are now flavors created by people that no one has associated with coffee before,” said Chahan Yeretzian, a scientist at the Coffee Excellence Center at the Zurich University of Applied Sciences, who presented the research at a new American Chemical. Society meeting in Indianapolis. “The flavors of fermented coffee, for example, are often more similar to fruit juices.”
Most coffee is lightly fermented as this occurs naturally as wet processed beans soak, break down enzymes and create sugar. It also facilitates the removal of skin and pulp. In this case, we are talking about green coffee beans that have already gone through the first processing. The beans are then soaked in water infused with carefully selected strains of yeast and bacteria and left to ferment for several days. Often fruit or other flavors are added at this stage or the beans are fermented in barrels previously used to store whiskey, rum, or other liquors. Then the seeds are washed and dried, and roasted as usual.
Yeretzian and research associate Samo Smrke used arabica beans and divided them into three batches. In the first batch, the seeds are washed, and the mucilage (the inner layer of pulp) is removed before drying. For the second batch, they removed the husk (husk) from the beans but left the mucilage. And for the third batch, they fermented the beans in stainless steel tanks using carbonic maceration, the same process used to make wine. This process involves infusing the tanks with carbon dioxide to create an anaerobic environment to lower the pH while the beans ferment.
For chemical analysis, Yeretzian and his colleagues used a combination of gas chromatography, which separates the volatile chemical compounds of a substance into their individual components, and mass spectrometry, which identifies such components. They also recruited a panel of human “sniffers” because taste and smell are closely related. And the human nose can sometimes detect odors at very low concentrations that may elude the mass spectrometer, although the perception of odors can be subjective.
“We use humans to detect smells, and everyone perceives flavors a little differently,” Smrke said. “But in this case, the panel was very consistent with the scents they described. So, what is traditionally considered a challenge is actually not an issue because the scents are so clear.”
Experiments have yielded six different compounds that contribute to the unique taste of fermented coffee. However, the team was only able to identify three: 2-methylpropanal, 3-methylbutanal and ethyl 3-methylbutanoate, all associated with unique “raspberry notes with a hint of rose water, ” per Yeretzian and Smrke. The other three compounds were detected by human sniffers but eluded the mass spectrometer.
Understanding how aromas are created will help producers master and perhaps standardize their fermentation processes, per Yeretzian, which are currently largely done by trial and error. Fermented coffees are expensive and not always available, but standardization could increase their availability. “We hope to bring these flavors to the average consumer so they can also experience these coffees with a unique, fruity, and delicious taste,” Smrke said.