h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I had always thought that green tree and black tea where one and the same plant - the only difference being that the latter was processed by fermenting the leaves. Since the health benefits are probably due to a chemical in the leaf and since fermentation only really changes the sugars/starches in the leaf, shouldn'y black tea have exactly the same heart attack/cancer preventing qualities?
Still - they're both much better than coffee.

Actually, there is a great deal of variance within both green tea and black tea themselves, not to mention the differences between the 2 categories. Take tea leaves, for example. Under the category of green tea includes a set of plants whereas a different set exists for black tea.

Different methods in brewing can also change the chemical composition of the tea leaves since chemicals react differently and interact differently under different temperature settings.