Only Sweets
Die-hard coffee lovers are always looking for the next big twist on the world’s favorite caffeinated beverage, and these days it’s fermented coffee that’s turning heads and tickling taste buds with its distinctive fruity notes. Scientists in Switzerland conducted experiments with fermented coffee in hopes of identifying the specific chemical compounds behind the drink’s unusual flavor profile.
“Now there are flavors that people have created that no one in the past associated with coffee.” Chahan Yeretzyan saidScientist at the Center for Coffee Excellence at the Zurich University of Applied Sciences presented his research During a recent meeting of the American Chemical Society in Indianapolis. “For example, fermented coffee tastes more like fruit juices.”
Most coffee is slightly fermented because naturally wet processed beans are soaked, breaking down the enzymes and producing sugar. It also makes removing the peel and pulp easier. In this case, we are talking about green coffee beans that have already undergone primary processing. The beans are then soaked in water with carefully selected strains of yeast and bacteria and left to ferment for several days. Fruit or other flavors are often added at this stage, or the beans are fermented in barrels previously used to store whiskey, rum, or other liquors. The beans are then washed and dried and roasted as usual.
Yeretzian and research associate Samo Smrke split them into three batches using arabica beans. In the first batch, the beans are washed and the mucilage layer (the inner layer of the pulp) is removed before drying. For the second batch, they removed the husk (husk) from the beans, but left the mucilage. For the third batch, they fermented the beans in stainless steel tanks carbon maceration, the same process for making wine. This process involves pouring carbon dioxide into the tanks 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 volatile chemical compounds in a given substance into individual components, and mass spectrometry, which identifies those components. Because taste and smell are closely related, they also recruited a panel of human “sniffers.” The human nose can sometimes detect odors at very low concentrations that may escape a mass spectrometer, although the perception of odors can be highly subjective.
“We use humans to detect smells, and everyone perceives tastes a little differently,” Smrke said. “But in this case, the panel was very consistent in the odors they described. So what was traditionally considered a problem was not really a problem because the aromas were so clear.
Experiments yielded six different compounds that contribute to the unique taste of fermented coffee. However, the team was only able to definitively identify three: 2-methylpropanal, 3-methylbutanal, and ethyl 3-methylbutanoate, all of which are associated with distinct “raspberry notes with rose water” for Yeretzian and Smrke. Three other compounds were detected by human sniffers but escaped the mass spectrometer.
Understanding how aromas are produced will help producers master and perhaps standardize fermentation processes. Fermented coffees are quite expensive and not always available, but standardization could expand their availability. “We hope to bring these flavors to the average consumer so they can enjoy these coffees with very unique, fruity and delicious flavors,” Smrke said.