Abstract This study aims to optimize the quality of Indonesian coffee for export markets using roasting and in vitro fermentation as a two-step process. The Taguchi L9 (3³) orthogonal array method was employed to determine the dominant factors and their optimal level. Coffees, which were grown in Malang, East Java, and belong to Robusta, Arabica, and Luwak, were studied. The data were generated through controlled experiments by varying roasting temperature, roasting time, drum speed, microbial inoculum concentration, fermentation duration, and temperature. Sensory characterization was performed in the laboratory according to Specialty Coffee Association (SCA) cupping protocols and chemical composition (moisture, organic acids, pH, and amount of caffeine). SNR and ANOVA tests assessed the factors' robustness and statistical significance. The results showed that dry roasting at a temperature of 220°C within 12 min and a tumbling speed of 30 rpm achieved the highest sensory scores; fermentation at condition levels of microbial inoculum (5%), fermentation time (24 h), and fermentation temperature (25°C) was optimal for aroma, and lactic acid balance, respectively. Confirmation trials confirmed these results, reaching a final cupping score over 85, the minimum value for specialty coffee. This study demonstrates that roast temperature and microbial inocula levels are the most significant factors influencing quality (contributing>30%) in coffees tested. These results suggest that evidence-based process improvement can contribute positively to the competitiveness of Indonesia's premium quality coffee market. Optimized fermentation and roasting conditions can provide feasible strategies for producers, cooperatives, and exporters to achieve quality standardization, traceability, and compliance with international standards.
PRASETYO et al. (Tue,) studied this question.