Modulation of Thai arabica coffee cupping profiles using Saccharomyces cerevisiae and Pichia spp. Fermentation

: This research investigated the impact of controlled submerged fermentation using local yeast starter cultures Saccharomyces cerevisiae and Pichia spp., on the physicochemical, microstructural, and aromatic profiles of Northern Thai Arabica coffee. Two thermal regimes (15°C and 25°C) were compared over 24, 48, 72, and 96 h to evaluate the metabolic transition from green to roasted beans. Microbial population dynamics revealed that S. cerevisiae demonstrated robust fermentative vigor, reaching 4.8×10 8 CFU/mL and outcompeting endogenous bacteria. S. cerevisiae inoculation stimulated synergistic proliferation of lactic acid bacteria (LAB) (reaching 3.07×10 8 CFU/mL at 15°C), essential for refined acidity development. Physicochemical analysis revealed that S. cerevisiae exhibited high glycolytic efficiency, significantly reducing mucilage pH, °Brix, and exhausting glucose within 48 h. Scanning electron microscopy (SEM) confirmed that yeast inoculation accelerated mucilage degradation by increasing cellular porosity and inducing cell wall loosening. Volatile organic compound profiling analyzed using solid-phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC-MS) identified a significant post–roasting expansion in chemical complexity, increasing from 10 chemical groups in the green stage to 14 in the roasted state. Pichia spp. primarily facilitated ester enrichment, maximizing floral precursors like benzyl benzoate, while S. cerevisiae promoted substantial accumulation of pyrroles and pyrazines, essential for nutty and toasted attributes. Sensory evaluation confirmed the 96 h fermentation space as critical for aromatic maturation. The S. cerevisiae treatment at 15°C achieved the highest specialty score (81.50±0.25 points). The fully washed control remained in the commercial category with flat sensory balances. Utilizing indigenous yeast strains under optimized thermal parameters highlights the unique terroir of Northern Thai coffee, providing a scalable, evidence-based protocol for sustainable value addition in the regional specialty coffee industry.