Tea is a product of the leaves, leaf buds, and internodes of various cultivars and different varieties of the Camellia sinensis plant. "Tea" also refers to the aromatic beverage prepared from cured leaves by combination of hot or boiling water. After water, tea is the most widely consumed beverage in the world. It has a cooling, slightly bitter, astringent flavour which many people enjoy.
Herbal Tea
: usually refers to infusions of fruit or herbs containing no actual tea, such as chamomile tea. Alternative terms for this are tisane or herbal infusion, both bearing an implied contrast with tea. In this post I'll focus exclusively with preparations and uses of the actual tea plant or better stated as Camellia sinensis, the Minnan word for which is the etymological origin of the English word tea.
There are at least six varieties of tea:
white, yellow, green, oolong, black, and what would be considered post-fermented tea. The most commonly found on the market are white, green, oolong, and black. Some varieties, such as traditional
oolong tea 
and Pu-erh tea, a post-fermented tea, can be used medicinally.
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 enzymatic oxidation process, known as fermentation in the tea industry, is caused by the plant's intracellular enzymes and causes the tea to darken. In tea processing, the darkening is stopped at a predetermined stage by heating, which deactivates the enzymes responsible. In the production of black teas, the halting of oxidization by heating is carried out simultaneously with drying.
Without careful moisture and temperature control during manufacture and packaging, the tea may become unfit for consumption, due to the growth of undesired molds and bacteria. At minimum it may alter the taste and make it undesirable.
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
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