Processing and classification
Tea leaf processing methods
A tea's type is determined by the processing which it undergoes. Leaves of Camellia sinensis soon begin to wilt and oxidize, if not dried quickly after picking. The leaves turn progressively darker as their chlorophyll breaks down and tannins are released. This process, enzymatic oxidation, is called fermentation in the tea industry, although it is not a true fermentation. It is not caused by micro-organisms, and is not an anaerobic process. The next step in processing is to stop oxidation at a predetermined stage by heating, which deactivates the enzymes responsible. With black tea, this step is executed simultaneously with drying.
Tea harvest on the eastern shores of the Black Sea, ca. 1905-15.
Without careful moisture and temperature control during manufacture and packaging, the tea will grow fungi. The fungus causes real fermentation that will contaminate the tea with toxic and sometimes carcinogenic substances, as well as off-flavors, rendering the tea unfit for consumption.
Tea is traditionally classified based on the techniques with which it is produced and processed.[16]
* White tea: Wilted and unoxidized
* Yellow tea: Unwilted and unoxidized, but allowed to yellow
* Green tea: Unwilted and unoxidized
* Oolong: Wilted, bruised, and partially oxidized
* Black tea: Wilted, sometimes crushed, and fully oxidized
* Post-fermented tea: Green tea that has been allowed to ferment/compost