The entire process of producing tea can be broken into the following steps: cultivation, pruning, plucking, withering, rolling, oxidization, firing/drying, sorting/grading, and packing. Of these, the first two steps are considered part of the growing process and the last seven steps are considered the manufacturing process. The key steps for determining the specific type of tea are withering, rolling/breaking, oxidation, and firing.
WITHERING THE TEA
All types of tea (black, oolong, green, white, puerh, and dark tea) go through this process. After the leaves are skillfully plucked from the tea plant, they are spread out onto trays or screens. Withering is often conducted in open sheds by utilizing the natural breeze. During this process the leaves lose 50-80% of their moisture and become limp and flaccid, which makes them suitable for rolling.
The aim of rolling is to twist the tea leaves, either by hand or through a mechanical process. This ruptures the cell walls of the tea leaves, releasing enzymatic juices. A wide range of machines and rolling techniques are used. After rolling, the tea goes through a roll-breaking machine, which separates the large clumps of rolled leaf into smaller, more consistent pieces.
Oxidation, which is sometimes incorrectly referred to as fermentation, is the process which makes black tea different from all other types of tea (green, oolong, white, etc.). The tea leaves are spread out, no more than 2-3 inches thick on large troughs with wire mesh bottoms, allowing for sufficient air flow. The leaves are left to sit out for a period of time, during which they will lose most of their remaining moisture and absorb extra O2 from the atmosphere.
Oxidizing the Leaves
Oxidation typically occurs in rooms with a temperature between 75 and 90 degrees Fahrenheit and a relative humidity of 90%. Oxidation times range from 45 minutes to 3 hours, depending on the temperature and the style of tea desired. White and green teas are not formally oxidized. Oolong tea is partially oxidized and black is fully oxidized.
FIRING AND SORTING
During this stage, a gentle heat is applied to the leaf to stop the oxidation process. Firing may be done by blowing hot air over the leaf or running the leaf through heat tunnels. The temperature for firing is between 140 and 170 degrees Fahrenheit and lasts from 10 minutes to no more than an hour. This heating, or "firing" processes destroys the specific shapes of the enzyme proteins in the leaf, killing the enzymes so the leaf is stable and does not mold or break down.
Chamber for firing teas
Once the tea is fired, the leaves are sorted into grades of different sizes. Sorting may be done by hand or with the use of sizing equipment. Often, tea leaves are sorted using mesh screens of various sizes. When the tea has completed its processing and is sorted, it is packaged and sold for consumption.