Unfortunately, once the tea has oxidized there’s no way to revert the process. But you can avoid it happening in the first place by following the tips from this article: 1. Remember that green tea is very delicate so it needs very short steep time at lower temperatures. In case of doubt, follow vendors instructions or cold steep it. 2. If your green tea leaves get old, you can make hojicha out of them by roasting them: they won’t be green anymore but they will still be delicious.