Tea professionals often spend years understanding a single style of tea production so we certainly won’t try to cover all nuances and varieties of tea on this page!
Mastery of the processes involved in tea cultivation and preparation is the deciding factor in a tea's taste. First, oxidation must take place following harvesting; a reason, why most plantations have their own processing plants on-site to process the leaves as soon as they arrive from the field.
Tea production falls into one of two styles: orthodox or non-orthodox (the latter usually being the CTC, or “Crush-Tear-Curl” method). All tea production involves five basic processing steps which are adjusted depending on the tea variety.
The leaves are harvested by hand, usually ranging between just the unopened bud to the top three leaves and the bud, depending on the tea being created. In order to make hand plucking possible, the tea "trees" are pruned into waist-high bushes. After plucking, the leaves are sorted for uniformity and any stems, twigs, broken leaves, etc. are removed.
The leaves are laid out to wilt and wither for several hours to prepare them for further processing. Tea leaves, even fresh tender ones, aren't very pliable. Without withering, they would shatter and crumble when rolled and shaped. During withering, the leaves are very gently fluffed, rotated and monitored to ensure even exposure to the air.
This is where thousands of varieties in tea appearance are created, and also where the process of developing flavor is started. The softened tea leaves are rolled, pressed or twisted to break the cell walls of the leaf, wringing out the juices inside. This exposes enzymes and essential oils in the leaf to oxygen in the air - the start of oxidation.
After rolling, the leaves are laid out to rest for several hours, allowing oxidation to take place. Oxidation is the process in which the oxygen in the air interacts with the now-exposed enzymes in the leaf, turning it a reddish-brown color and changing the chemical composition. This step also has the greatest impact in the creation of the many wonderful and complex flavors in tea. The length of this process depends on the style of tea being produced and the ambient conditions at the time. Depending on the type of tea, from here the leaves could be rolled again and oxidized further, or not.
The final step in the production process is to "fire" or heat the leaves quickly to dry them to below 3% moisture content and stop the oxidation process. A good, even drying with very low residual moisture also ensures the tea will keep well.