Investigation of different aeration strategies for the production of kombucha with defined co-cultures

Kombucha fermentation is a complex process influenced by many different process parameters and the dynamics of the microorganisms present. Since no universally established standards exist for large-scale production of kombucha, manufacturers still need to acquire the knowledge to establish controllable and reproducible processes. The aim of this study was to investigate the extent to which the kombucha fermentation process can be influenced by varying the oxygenation regime and the initial pH value. For this purpose, co-culture fermentations with the yeast Zygosaccharomyces bailii and the acetic acid bacterium Komagataeibacter hansenii were carried out under defined conditions, varying the type and intensity of aeration using various fixed aeration rates and controlled oxygen saturations. The pH values were varied in ranges between 4.1 and 7.5. The fermentations were comprehensively characterized via online and offline analytics, so that both the processes and the products could be chemically, microbiologically, and sensorially evaluated over time. By splitting the process into a sufficiently long anaerobic phase of 4 days followed by an active aeration phase at 0.1 vvm for three to four days, a sufficient oxygen supply was achieved under the given conditions to adequately convert the ethanol produced by the yeast into acetic acid by the bacteria. Sensory properties of the products were not negatively affected by oxidation reactions. Compared to reference processes conducted under traditional, static fermentation conditions, a process acceleration was achieved with equivalent sensory quality but significantly reduced alcohol concentrations (<0.08 %vol vs. 0.47 – 0.50 %vol. after 7 days). This study provides an example of how to produce a kombucha product under defined and accelerated conditions that includes an aerobic phase, and which can be used as basis for further production process developments.