Enhancing coffee quality under humid subtropical conditions through ecological modulation of wet fermentation with an indigenous yeast starter.

Post-harvest fermentation plays a critical role in shaping the chemical composition and sensory quality of coffee. However, spontaneous fermentation conducted in humid subtropical regions often exhibit limited yeast activity and reduced metabolic efficiency. This study investigated the potential of an indigenous yeast starter culture to modulate microbial succession, metabolic pathways, and sensory quality during wet coffee fermentation. Yeasts were isolated from spontaneous fermentations, genotyped using (GTG)5-PCR and ITS sequencing, and screened for volatile compound production by HS-SPME/GC-MS. Among 24 isolates, Pichia kluyveri LBP UFSC L24 was selected based on its potential for production of aroma-active esters, particularly isopentyl acetate and 2-phenylethyl acetate. The selected strain was applied as a starter culture in field-scale fermentations and compared with the spontaneous process. Amplicon sequencing revealed rapid establishment of the starter culture, with P. kluyveri representing more than 96% of fungal reads throughout the fermentation, whereas spontaneous fermentation displayed higher fungal diversity during early stages. The inoculated fermentation showed accelerated carbohydrate metabolism and significantly higher ethanol production. Volatile compound analysis demonstrated enhanced accumulation of key esters. These metabolic shifts were associated with improved sensory performance, with cup scores increasing from 84.0 to 86.25 points, accompanied by greater aromatic complexity and intensified chocolate, fruity, nutty, and sweet descriptors. Overall, the use of the indigenous yeast P. kluyveri LBP UFSC L24 showed potential to modulate the coffee fermentation process under the evaluated conditions. These findings highlight the potential of targeted microbial bioprospecting and improved fermentation to enable high-quality coffee production in emerging regions.