Fermentation of tea in aqueous suspension

The fermentation of macerated tea leaf in aqueous suspension has been studied both manometrically and in a suitably controlled fermentation vessel. Oxygen consumption proceeded rapidly at a steady rate for an initial period, termed the primary fermentation, then decreased sharply as the availability of simple polyphenol substrates became rate limiting. Maximum reaction rates were observed at 20-35 mg ml^?1 total solids, as a result of substrate inhibition. At higher concentrations of solids reaction rates were also affected by diffusion effects within the leaf particles. At 50 mg ml^?1 total solids and 25°C the system approximated to Michaelis-Menton kinetics with K_m⁰² = 5 × 10^?5M and V_max corresponding to a primary fermentation time (PFT) of 10-15 min. The PFT corresponded with the attainment of maximum total colour and maximum level of theaflavins (TF) (often >30% of total colour). Beyond the PFT total colour remained constant, TFs decreased and non-dialysable pigments increased with time. At fixed levels of dissolved oxygen and solids concentration > 60 mg ml^?1 the proportion of TFs was inversely related to solids concentration. At 50 mg ml^?1 total solids TFs increased to ca 60% of total colour as the dissolved oxygen level was increased to 0.175 mM. As temperature was increased from 15-35°C the reaction rate increased, the proportion of TFs decreased slightly and thearubigins of intermediate molecular weight increased markedly.