Equilibrium Moisture Content of Tea

Abstract

A method of measuring equilibrium moisture content relations for tea was investigated at temperatures from ambient up to 90°C used in drying. The method used a high-temperature chilled mirror dewpoint meter with the sample in a sealed chamber in a temperature-controlled oven. Computer control is essential for the system and made it possible to detect stable conditions and to move to the next set of measurements. As a consequence, the time needed for collecting data for sorption isotherms was significantly reduced in comparison to the saturated salt solution method. In this study, the equilibrium moisture content of Central African tea under drying conditions has been measured. No consistent rate of change with temperature could be determined. Several isotherm equations were fitted to the data, and the Guggenheim Anderson de Boer model was found to give the best fit. Validation measurements of the equilibrium moisture content of tea to compare the dewpoint meter method with the usual saturated salt method on ungraded black teas gave comparable results.