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Fermentation is a key step in post-harvest coffee processing, and can have a significant impact on the cup’s flavor, depending on the microorganisms and methods used.
One out-there approach is co-fermentation: The process sees fruits or spices added to fermentation tanks alongside coffee cherries, which impart some of their flavor to the final coffee. Such practices are considered controversial among some coffee purists, although they have gained more widespread acceptance in recent years.
As well as its effect on flavor, researchers are also interested in how fermentation can improve coffee quality. A 2025 study from Brazil found that self-induced anaerobic fermentation was able to bring underripe cherries up to specialty standards. Earlier this year, trials in Colombia showed that CO2 fermentation could boost the quality of natural-processed coffees. And now, researchers in China have conducted a similar study, using a naturally occurring fungus found in coffee cherries.
As published in the journal Food Chemistry (and reported by Daily Coffee News), scientists from the Kunming Institute of Botany isolated more than 650 fungal strains from five arabica cultivars grown in Yunnan, China’s main coffee-producing region. Of these, six strains proved especially promising and one, Talaromyces funiculosus KQ2, stood out for its positive impact on coffee quality. When added to fermentation tanks, the fungus was able to increase commodity-grade coffee’s score by an average of 1.5 points, enabling it to reach specialty grade.
Additionally, the fungus produced distinctive cinnamon and vanilla notes in the coffee. Minghua Qiu, the study’s lead researcher, told China Daily that their findings could play a role in elevating Yunnan-grown coffee. “Yunnan coffee has long been relatively weak in floral and fruity notes,” Qiu said. “But endophytic fungi contain many aroma-producing microorganisms. By identifying strains with stronger flavor expression, we can enhance these characteristics.”
Read more on the fungal processing transformation here.
Photo by Nguyen Tong Hai Van on Unsplash
