Scale-Up of Black Tea Batch Fermentation by Kombucha

Local domestic Kombucha (Acetobacter strains in symbiosis with Saccharomycodes ludwigii, Saccharomyces cerevisiae, Saccharomyces bisporus, Torulopsis sp. and Zygosaccharomyces sp.) was used for fermentation of 1.5 g L−1 of black tea (Indian tea, ‘Vitamin’, Horgoš, Serbia and Montenegro), sweetened with approximately 70 g L−1 of sucrose. Inoculation was performed both by 10% and 15% of fermentation broth from the previous process. This fermentation has been left to continue for 28 days, in geometrically similar vessels containing 0.4 L, 0.8 L, 4 L and 8 L of liquid phase, at 22 ± 1°C. The samples were analysed after 3, 4, 5, 6, 7, 10, 14 and 28 days. Their pH values, content of total acids, content of sugars (sucrose, glucose and fructose) as well as quantities of ethanol and vitamin C were measured. By processing the measured data, a response surface was defined. It expresses pH value of the product as a function (second order polynomial) of time, volume and inoculum concentration. The defined pH-response surface and the principle of similarity were used for estimation of both large-scale reactor geometry and large scale-process duration. The process duration was estimated so as to enable the achievement of the desired pH value of the product.