The black tea manufacturing process is quite an involved one, buy first, the tea has to be plucked. While in the industrialized country like Japan this activity is performed using a mechanical harvester, in India this is mostly done by hand. It is usually the ladies who are considered the better pickers. They tend to be vey deft at picking only the two leaves and a bud, and leave the more coarser leaf alone.
Once the leaf basket if full, the picker brings it to the central station where the basket is weighed and passed on to the factory floor. On the factory floor, the tea undergoes a withering process designed to remove as much moisture as possible from the tea, to prepare it for oxidation and drying. Usually, the tea leaves are spread out on a large tray of wire mesh, and hot air blowers are used to heat the leaf and drive the mositure out. At higher elevations, it is not unusual for the withering process to require 12-24 hours.
At this point, the leaf has become limp and turned into a darker shade of green. The next step in the process is Rolling wherein the leaf is put into roller machines which twist and turn the leaf and break it, giving it the wirey shape characteristic of Darjeeling orthodox leaf. This process of rolling releases the enzymes from the leaf as the leaf breaks, exposing the juices to natural process of oxidation.
In the next stage, the Oxidation stage, the leaf is allowed to oxidise by exposing it to air in large trays. As the leaf oxidizes, it generates heat, and slowly changes in color from green to red to brown to eventually black. Proper oxidation of the leaf is critical in the final flavor and color produced in the leaf. If the leaf is oxidised at too high a temperature, it would spoil the tea, and if it is oxidized at too low a temperature, the tea produced would be flavorless.
Finally, the tea is ready for drying. Once again, the leaf is exposed to hot air from air blowers, which drive the remaining moisture out of the leaf.
Once the leaf is dry, the tea is marked and tasted by an expert taster who describes the tea and issues the certificate of release. Often times, a blender blends various batches of tea to produce a characteristic flavor, however, most blending work is not done at the tea garden level. Rather, this happens at the blender and packers warehouse.
This is where the manufacturing process generally ends, and the tea arrives into the market place.