There is a misconception that the different types of tea come from different tea plant. Black, Green and Oolong teas are all derived from the camellia sinensis evergreen plant.
The difference comes from how the plant is processed. The common processing unit operations are:
a) WITHERING
b) ROLLING
c) OXIDATION
d) DRYING OR FIRING
a) Withering
Newly picked leaves are thinly spread to dry during this process. Heated air is forced over the leaves if the climate is not suitable. The main goal of this process is to reduce the water content. By the end of this process, the leaves should be pliable enough to be rolled.
b) Rolling
From the withering racks, the leaves are now twisted and rolled so that the leaf cells are
broken up. Sometimes shaking is done as well. Oils are released with this rolling process that give the tea its distinctive aroma. The leaves can be rolled with machinery or by hand. The juices that are released remain on the leaf; a chemical change will occur shortly.
broken up. Sometimes shaking is done as well. Oils are released with this rolling process that give the tea its distinctive aroma. The leaves can be rolled with machinery or by hand. The juices that are released remain on the leaf; a chemical change will occur shortly.
c) Oxidation
This is the chemical process where oxygen is absorbed. This process began once the leaf membranes were broken during the rolling process. Oxidation causes the leaves to turn bright copper in color. This process is the main deciding factor whether we have green, Oolong or Black tea.
d) Drying Or Firing
In this stage the leaves are dried evenly and thoroughly without burning the leaves. Firing the leaves stops the oxidation process.
For the purpose of this study Oolong tea is not considered. However, the processes of producing Black and Green tea are considered separately.
Black Tea Processing
The Black tea process goes through the most stages described above. Once the leaves are picked, they are left to wither for about a day. After this the leaves are soft enough to be rolled into balls; oils from the leaves are brought to the surface. These aromatic oils aid in the oxidation process, which last for a number of hours until proper smell and color are achieved.
Next is firing. This is the process of moving the leaves through hot air chambers to stabilize the leaves and lock in the flavour. The dry heat stops the fermentation process by killing the active enzymes. During this firing, the leaves turn dark and loose all but about 2% of their moisture. If the firing is not done correctly, and the leaves are too dark, the result cup of tea will taste weak. The tea is now ready for packing. It is then dispatched into local and export market.
Green Tea Processing
The process for making green tea is the shortest. Withering is done first, but this step might be omitted. Rolling the leaves to break the membranes for oxidation is skipped, hence the oxidation process is also skipped. After withering the leaves are pan fired or fired to prevent oxidation from occurring. The last step is to roll the leaves and dry them one last time for its final shape. The green tea leaves usually remain green. The tea is now ready for packing and market