Yeast Strain Inoculation in Coffee Wet Fermentation: Impact on Volatile Compound Formation

Starter cultures enhance coffee sensory quality by producing yeast-derived volatile organic compounds (VOCs). This study evaluated five native yeast strains—Hanseniaspora guilliermondii, Pichia membranifaciens, Schizosaccharomyces pombe, Torulaspora globosa, and Rhodotorula aurantiaca—for their VOC contributions in mucilage, green beans, and roasted coffee. A 2×2+1 factorial randomized complete block design assessed two consortia (c1, c2), two inoculation growth phases (lag, t1; exponential, t2), and a spontaneous fermentation control. VOCs were analyzed via HS-SPME-GC-MS, and sensory quality was evaluated per SCA protocols. Multivariate and univariate statistical analyses were conducted across matrices, demonstrating a shift from fermentation-derived alcohols and esters in mucilage and green beans to thermally generated pyrazines, furans, and aldehydes in roasted coffee. Treatment c2t2 exhibited higher metabolic activity in mucilage, with increased peak areas for acids, alcohols, and aldehydes, while c1t1 showed a greater chromatographic response for acids and ketones in green coffee. In roasted coffee, peak areas of compounds associated with enhanced aroma and body, such as 1-(2-furanyl)ethanone, 1-(2-furanyl)-1-propanone, and pyrazines, were significantly higher for c2, whereas 1-hydroxy-2-propanone, 1-hydroxy-2-butanone, and 1-acetyloxy-2-propanone were higher for t1. Although non-parametric sensory tests did not reveal statistically significant differences among treatments, c1t1 achieved the highest numerical overall cupping score (82.63 SCA points) due to improved flavor, acidity, and balance. Yeast inoculation obtained SCA total scores 2.6 to 3.5 points higher than that of spontaneous fermentation (79.13 points) without developing defective off-flavors. The evaluated yeasts show potential in modulating specific volatile profiles and sensory attributes in coffee effectively.