A recent article in the Journal of Food Science reports that the quantity of catechins, components in green tea that are thought to have antioxidant and other health benefits, declines as tea sits in storage. Researchers tested 8 commercial bagged green teas (of unknown history) available in the U.S., Korea, and Japan. The samples were stored in the dark in their original packaging at 20 degrees C (68 degrees F) for six months. Samples were tested at 1 week and 1, 2, 4, and 6 months. The average loss of catechins at the end of 6 months was 32%. All 8 teas showed a similar decrease in catechins over time, although 2 of the teas were quite low to start with. The authors speculated that the teas were probably of different ages, but noted that catechin content could also vary among the tea plants themselves due to soil conditions, weather, harvesting practices, etc.
It’s good to see studies like this being done. The results really aren’t all that surprising. All food has a higher nutritional value when it is fresher, so this is not unique to tea. But it is a good reminder to encourage everyone to only buy what they can use in a reasonable amount of time and also to store tea properly to minimize effects from controllable elements such as light and air. Be assured that we always order reasonable quantities of tea so that it is not sitting in our warehouse for extended periods. Also remember that loose leaf tea is less processed than tea bags are, so your chances are better of getting the freshest tea possible.