Green tea is unfermented tea and black tea is completely fermented tea. Fermentation is the enzymatic oxidation of tea polyphenols under the action of polyphenol oxidase. The vast majority of polyphenol oxidase in green tea and black tea lose their activity during drying and have no enzyme function.
Therefore, the way to turn green to red is to wet green tea with water and mix it with crushed fresh tea evenly, then pile it up to a certain thickness for fermentation, and then observe its fermentation changes and dry it in time to control the degree of fermentation.
It must be noted that the taste of black tea pointed out by this method is definitely not as good as that of fresh leaves.
If you say green tea refers to tea tree, you can check the processing technology of black tea. Of course, it should be considered comprehensively according to the leaf quality of the tea variety you choose.