Mass transfer coefficient and mass diffusivity of O2 and CO2 during oxidation of macerated CTC and rolled orthodox leaves in black tea manufacturing

Abstract

AbstractOxidation of withered and macerated crush‐tear‐curl (CTC) and rolled orthodox tea leaves of TV25 clone was carried out in a closed chamber and oxygen and carbon dioxide concentration inside the chamber was measured at small time intervals. From the O2 consumption and CO2 production pattern during oxidation, mass transfer coefficient (ky′) and mass diffusivity (DAB) of O2 and CO2 was calculated considering equimolar counterdiffusion of the gases. Change in mass transfer coefficient and mass diffusivity of O2 and CO2 with duration of oxidation was fitted into exponential equation. Value of R2 for all the relationships were greater than .80 and reduced chi‐square values was less than 1. Values of ky′ and DAB at the initial stage of oxidation are higher for macerated CTC leaves and they reduce at a faster rate for oxidation of CTC tea than orthodox leaves.Practical applicationFermentation (oxidation) in black tea processing is the most important processing step responsible for characteristics tea quality in terms of color, flavor, and aroma. This step consists of several biochemical reactions which are associated with consumption of O2 and production of CO2 gas. Mass transfer coefficient and mass diffusivity of O2 and CO2 gas during oxidation in CTC granules and rolled orthodox leaves were estimated in this study. This would help with the control of air flow rate in designing continuous fermentation machines and also the number of changes in room air required for floor/gumlah/trough fermentation and thereby improved tea quality.