All true teas—as distinct from herbal and flower infusions, which afficiandos call tisanes, are made from the leaves of an evergreen tree with the botanical name of Camellia sinensis. Although reaching a height of 30 feet in the wild, on tea plantations (called gardens or estates), the plant is kept as a shrub, constantly pruned to a height of about 3 feet to encourage new growth and for convenient picking.
Tea plants grow only in warm climates but can flourish at altitudes ranging from sea level to 7,000 feet. The best teas, however, are produced by plants grown at higher altitudes where the leaves mature more slowly and yield a richer flavor. Depending upon the altitude, a new tea plant may take from 2-1/2 to 5 years to be ready for commercial picking, but once productive, it can provide tea leaves for close to a century.
Tea plants produce abundant foliage, a camellia-like flower, and a berry, but only the smallest and youngest leaves are picked for tea—the two leaves and bud at the top of each young shoot. The growth of new shoots, called a flush, can occur every week at lower altitudes but takes several weeks at higher ones. The new leaves are picked by hand by "tea pluckers," the best of whom can harvest 40 pounds per day, enough to make 10 pounds of tea.
All tea plants belong to the same speciesCamellia sinensis, but local growing conditions (altitude, climate, soils, etc.) vary, resulting in a multitude of distinctive leaves. The way the leaves are processed, however, is even more important in developing the individual characteristics of the three predominant types of tea: green, black and oolong.
Green tea is the least processed and thus provides the most antioxidant polyphenols, notably a catechin called epigallocatechin-3-gallate (EGCG), which is believed to be responsible for most of the health benefits linked to green tea. Green tea is made by briefly steaming the just harvested leaves, rendering them soft and pliable and preventing them from fermenting or changing color. After steaming, the leaves are rolled, then spread out and "fired" (dried with hot air or pan-fried in a wok) until they are crisp. The resulting greenish-yellow tea has a green, slightly astringent flavor close to the taste of the fresh leaf.
See more at:
http://www.whfoods.com/genpage.php?tname=foodspice&dbid=146
