Modulating Coffee Fermentation Quality Using Microbial Inoculums from Coffee By-Products for Sustainable Practices in Smallholder Coffee Production

This study developed an inoculum culture for semi-controlled coffee fermentation using lactic acid bacteria (LAB) and yeast, with coffee production by-products as carbon sources. The viability of the inoculum was optimized by using a mixture design to vary the proportions of coffee pulp (CP) and wastewater (CWW) in 0.25 increments; as a process variable, fermentation time ranged from 36 to 48 h for LAB and 12 to 36 h for yeast. Soluble solids (SS), pH, and titratable acidity (TA) were monitored, and the response variable was the variation in microbial viability. The optimized inoculums were used for coffee fermentation alone and in combination, and fermentation parameters and sensory evaluation were measured. The optimal by-product combination for LAB inoculum was 100% CP, with a 48 h fermentation, reaching a maximum of 7.8 × 107 CFU/mL. The optimal formulation for yeast was 100% CWW for 36 h, achieving a maximum concentration of 8.3 × 108 CFU/mL. Experimental results for both inoculums were fit to a quadratic statistical model with R2 of 0.84 and 0.88 and Adj-R2 of 0.77 and 0.83 for LAB and yeast, respectively. The optimized inoculums produced high sensory scores, particularly in balance, fragrance, and acidity. Using mixed inoculums, we achieved the highest fragrance/aroma score (8.25) and an improved balance, attributed to higher TA and lower pH, which are linked to enhanced flavor complexity. This demonstrates that by-product-based inoculums can not only increase microbial viability but also improve the sensory quality of coffee, supporting sustainable practices in coffee processing.