Frozen Storage of Tea Leaves after Withering for Use in Black Tea Processing

Abstract

Tea leaves that have been frozen and stored after steaming are generally used for processing of hand-rolled Japanese green tea (Temomi). However, there has not been a useful method for long-term storage of tea leaves for black tea processing. We stored withered tea leaves for period up to 5 months at -20℃. Tea shoots of the cultivar Benifuki grown in a field of Kanaya Branch Station, NARO Institute of Fruit Tree and Tea Science, were used for materials. They were plucked by a riding-type plucking machine in the first crop season and second crop season. They were withered in a fresh tea leaf container. Fresh leaf weights were reduced by forty and thirty percent at the end of the withering process in first crop season and second crop season, respectively. The withered tea leaves were packed in 5-layered laminated film pouches. The pouches were vacuumed, filled with nitrogen, frozen quickly at -30℃, and preserved at -20℃. The frozen tea leaves were defrosted in a refrigerator overnight before rolling. Rolling and subsequent processes were carried out just after finishing the withering process and after frozen storage for 1 month, 3 months, and 5 months. Since there were no water drops on the unfrozen tea leaves, there was no inconvenience in the following processes. The quality of the tea was evaluated by a sensory test with 9 panels. There was no difference between the score for the tea produced just after withering and the scores for the tea produced with tea leaves that had been frozen for 1, 3 and 5 months. We won the silver award at Owari-Asahi Black Tea Competition for tea made with tea leaves that were plucked in the first flush season and frozen for 3 months. It was clarified that it is possible to produce a good-quality black tea with tea leaves that are frozen after withering.