Moisture Contents and Water Activities in Chinese Tea

Abstract

Most of tea produced and consumed in Japan is steamed green tea. However, various tea types for domestic demand are needed to increase of tea consumption in Japan. Moisture contents and water activities are important for the maintenance of tea quality during storage. It has been shown that the optimum moisture content of Japanese green tea is 3-5%. On the other hand, the moisture content of black tea is about 7%, but the quality does not deteriorate during storage. It is thought that the optimum moisture contents of other types of tea are higher than that of Japanese green tea. Since there are many types of Chinese tea, useful information might be obtained from investigation of the moisture contents and water activities in Chinese tea. Difference between tea types was significant at the 1% level for moisture content in Chinese tea. The average moisture contents of white tea and dark tea were higher than those of blue tea, green tea and black tea. Difference between countries was significant at the 1% level for moisture contents in black tea. The moisture content of black tea from China was higher than the moisture contents of black tea from Nepal, Japan and India. The variance among moisture contents of blue tea was large. There were significant positive correlations between moisture contents and water activities in blue tea, green tea, black tea and dark tea. For teas with higher moisture contents, such as over 10%, the water activity in dark tea was lower than those in other types of tea. Since water activities in almost all of the Chinese teas were less than 0.65, it was assumed that no microorganisms can grow in Chinese tea.