Abstract
This study investigated the impact of fermenting Yunnan Arabica coffee beans with a defined kombucha yeast consortium (Saccharomyces cerevisiae, Brettanomyces bruxellensis, Zygosaccharomyces bailii, Candida stellata, Pichia fermentans, Schizosaccharomyces pombe, Kloeckera apiculata) on flavor quality. Yeast-fermented coffee (YC) demonstrated superior sensory attributes, particularly aroma, aftertaste, and body, compared to naturally fermented (NC) and unfermented (NFC) controls. Physicochemical analysis revealed that YC beans possessed significantly higher acidity (26.43 mEq/L), amino acids (27.36 mg/g), flavonoids (13.68 mg/L), polyphenols (7.38 mg/L), but reduced caffeine content (10.62 mg/g). The increased levels of amino acids provided key precursors for Maillard and Strecker reactions during roasting. Yeast β-glucosidase activity liberated bound phenolics, enhancing their bioavailability. Network metabolomics confirmed the targeted upregulation of pyrazine precursors and phenolic compounds, while suppressing off-flavor alcohols. The consortium, dominated by Saccharomyces and Wickerhamomyces, modulated ester complexity. Overall, the yeast consortium systematically enhanced coffee quality through enzymatic and micro-environmental modification pathways. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10068-025-02056-x.