The tea plant, which grows naturally in the wild throughout much of Asia, is cultivated in a variety of settings from small family gardens to giant estates covering thousands of acres. The best tea is usually grown at elevation, and often, on steep slopes. The terrain requires these premium teas to be hand-plucked, and it takes around 2,000 tiny leaves to make just one pound of finished tea! If that sounds crazy, keep in mind these methods have been around for several millennia. Many of the teas produced for large scale commercial production are grown on flat, lowland areas to allow for machine harvesting. However, it should be noted that some of the finest, hand-plucked teas in the world come from flat fields and lower altitude. So, how the tea is grown is just one of many factors to be considered. And in India, we take this very seriously!
Teas which are processed in the traditional fashion are called orthodox teas. Orthodox teas generally contain only the top two tender leaves and an unopened leaf bud, which are plucked carefully by hand and then processed using five basic steps, creating the thousands of varieties of tea we know and love today. (Note: While tea plants do have small flowers, the "buds" tea people refer to are the young, unopened leaves, not flowers) Most orthodox tea production these days involves a unique combination of age-old methods, such as bamboo trays to allow the leaves to wither on, and modern, innovative machinery, like leaf rollers carefully calibrated to mimic motions originally done by hand. A true art form, the tea is handled by artisans with years (often, generations) of training from the moment of plucking to when the tea is finished. For some teas, one batch can take several days of work.
The other way of making tea is the unorthodox method, of which the most common type is CTC (crush-tear-curl). This much faster style of production was specifically created for black tea. These teas may or may not be plucked by hand. For commercial production, large machine harvesters are used to "mow" the top of the bushes to get the new leaves, rather than hand-pluck. CTC production uses a leaf shredder which macerates the leaves (crushing, tearing and curling them, hence the name) into fine pieces, then rolls them into little balls. The result looks quite a bit like Grape Nuts cereal, actually. These teas will brew very quickly and produce and a bold, powerful cup of tea. CTC is usually used primarily in the tea bag industry, as well as in India to create Masala Chai blends (due to their strength and color).
Tea processing is five basic steps; some teas don't utilize all of these steps, while other teas repeat them several times. Basic processing is Plucking, Withering (allowing the leaves to wilt and soften), Rolling (to shape the leaves and wring out the juices), Oxidizing and Firing (i.e.: Drying).
The most crucial part, what defines the categories of tea, is Oxidizing. Oxidation occurs when the enzymes in the tea leaf interact with oxygen, after the cell walls are broken apart. This can happen quickly, through rolling, cutting or crushing, or more slowly through the natural decomposition of the leaf. Actually, you see the same process in a piece of fruit. Left to sit, an apple will slowly turn brown. Cut or bruise the apple, and it will brown much more quickly. Now, interestingly, if you bake the apple, it not brown. The lovely, golden-white apple slices inside a pie are just fresh looking as when you first put them in the oven. This is because heat (at 130 degrees) stops enzymatic activity and oxidation.
"Oxidation" is still referred to by some in the tea industry as "fermentation." This stems from an earlier belief that what was happening to the tea leaves was similar to fermentation of grapes into wine. Everyone now knows this is actually oxidation, but because of its long history, fermentation is still used. This is actually quite common to hear from very expert tea professionals in India, for example. (it would be considered quite rude to correct someone from a tea-growing country otherwise)