Deterioration of Steamed Tea Leaves during Frozen Storage

Abstract

In frozen storage of steamed tea leaves, it is necessary to maintain the storage temperature at about -20°C or lower. Above this temperature the steamed tea leaves cannot keep freshness for long time of 30-90 days.
Tea, manufactured with stored leaves for 90 days at -20°C, had no evident difference in the qualities compared with standard one, manufactured with fresh leaves.
But, some damages were found on their tissues in these frozen leaves and these damages seemed to occur with slow freezing of air flow at -20°C.
These damages occurred usualy in parenchyma of stem of shoots, rarely in main nerve and none in leaf blade tissue.
The occurrence of these damages was avoided with rapid freezing by immersing the leaves into 50% gricerin water solution at -20°C or liquid nitrogen.