Changes in Microbial and Physicochemical Composition in Water Kefir over Repeated Sequential Culture Transfers and Prolonged Storage

Water kefir production requires the fermentation of sweetened water with polysaccharide starter culture embedded with bacteria and yeast, which determines the finished product’s sensory, microbial, and chemical profile. The culture self-propagates, producing a new culture biomass used to inoculate subsequent raw materials. This study evaluated the effect of sequential culture transfers (across batches) and prolonged storage (within batches) on the microbial and chemical composition of finished beverages. Six commercial cultures were used in 20 sequential fermentations. The beverages were analyzed immediately after fermentation and then were stored at 4 °C for analysis every 2 weeks for 12 weeks. Microbial populations, including aerobic plate count (APC), lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeast, were enumerated; major organic acids, sugars, and alcohols were quantified chromatographically. Sequential culture transfers and storage resulted in minimal microbial and chemical component changes. The initial microbial counts were similar across brewing cycles and culture systems with high counts of LAB. The culture transfers resulted in a decrease in initial ethanol levels to a negligible level. Microbial viability and sucrose content decreased with prolonged beverage storage. Overall, this study revealed that water kefir cultures were resistant to temporal changes and beverages’ microbial and chemical constituents were statistically stable (p > 0.05) during refrigeration.