Tea is generally divided into categories based on how it is processed. At least six different types are produced:
- White: Wilted and unoxidized
- Yellow: Unwilted and unoxidized, but allowed to yellow
- Green: Unwilted and unoxidized
- Oolong: Wilted, bruised, and partially oxidized
Black: Wilted, sometimes crushed, and fully oxidized (called ‘red tea’
- in China)
- Post-Fermented: Green tea that has been allowed to ferment/compost (‘black tea’ for the Chinese)
The most common are white, green, oolong, and black.
After picking, the leaves of C. sinensis soon begin to wilt and oxidize unless immediately dried. An enzymatic oxidation process triggered by the plant’s intracellular enzymes causes the leaves to turn progressively darker as their chlorophyll breaks down and tannins are released. This darkening is stopped at a predetermined stage by heating, which deactivates the enzymes responsible. In the production of black teas, halting by heating is carried out simultaneously with drying.
Tea harvest on the eastern shores of the Black Sea, Georgia, circa 1905–15
Without careful moisture and temperature control during manufacture and packaging, growth of undesired molds and bacteria may make tea unfit for consumption.