Revolutionizing Coffee Fermentation: Beyond Sensory Performance in Yeast Starter Culture Design—A Review

Fermentation is now recognized as extending well beyond its traditional role in mucilage removal during coffee processing; rather it is a biochemically complex, microbially driven process that exerts a critical influence on coffee flavor, aroma, and cup quality. Yeasts, including Hanseniaspora, Pichia, Torulaspora, Candida, Meyerozyma, and Saccharomyces, form ecologically diverse communities whose composition is shaped by processing method, geographical origin, and environmental conditions, contributing not only to flavor development but also to mucilage degradation, microbial stability, and the suppression of undesirable microorganisms. Although starter cultures formulated from both Saccharomyces and non-Saccharomyces yeasts have frequently improved sensory quality and process control, fermentation outcomes remain highly strain-, dose-, and process-dependent, such that neither ecological dominance nor pectinolytic activity consistently predicts fermentation performance or cup quality. This review identifies environmental variability, microbial competition, the incompletely elucidated mechanisms underlying mucilage degradation, and the frequent disconnect between ecological dominance and technological functionality as principal constraints on the reliable implementation of starter cultures. Collectively, the evidence supports a shift from sensory-driven strain selection toward a multidimensional framework that integrates ecological fitness, stress tolerance, metabolic stability, persistence, mucilage-degrading capacity, and defect-mitigating potential under farm-representative, non-sterile conditions.