The most common
misperception is that the different types of tea come from different tea
plants. Black, Green and Oolong teas are all derived from the Camellia
sinensis evergreen plant. The difference comes from how the plant is
processed. Common processing terms are withering, rolling, oxidation, and
drying or firing.
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.
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.
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.
Drying or Firing:
In this stage the leaves are dried evenly and thoroughly without burning the leaves. Firing the leaves stops the oxidation process.
The Black tea process goes through the most stages. Once the leaves are picked, they are left to wither for several hours. After the leaves are rolled, oils from the leaves are brought to the surface. These aromatic oils aid in the oxidation process, which last for several hours. The last step consists of placing the leaves in an oven with temperatures reaching up to 200 degrees Fahrenheit. When the leaves are 80 percent dry, the leaves complete their drying over wood fires. The resulting product is brownish (sometimes black) in color and is sorted accordingly to size, the larger grade is considered "leaf grade," and smaller "broken grade" are usually used for tea bags.
Oolong goes through a similar process that black tea goes through. The first two steps are withering and rolling. Instead of rolling, sometimes shaking is done to bruise the outer edges of the leaves. The oxidation period for oolong is half that of black tea. Once the veins become clear and the edges of the leaves become reddish brown, while the center remains green, the oxidation process is stopped by firing. For oolong tea, the leaves are heated at a higher temperature so that they can be kept longer, due to the lower resulting water content.
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 fried 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.