DIFFERENT TYPES OF TEA
The teas of the world are roughly divided into fermented and unfermented teas. Black tea or English breakfast, for example is fermented tea. There are a number of varieties of tea commonly drunk in Japan, but all of which are green teas or unfermented teas, e.g. almost no black tea is consumed in Japan compared to green tea. These tea leaves are not simply picked, dried and packed. The ways of processing the leaves to make unfermented tea or fermented tea are completely different.
There are mainly three types of tea, categorized by the processing method:
Unfermented tea (e.g. Green Tea)
Semi-fermented tea (e.g. Oolong Tea)
Fully fermented tea (e.g. Black Tea)
Green tea leaves are being steamed
Taiwanese Oolong tea indoor wilting and dehydration process
The interesting part is that basically all common teas are made from the same type of tree (Camellia sinensis). However, varieties (cultivars) of the tea tree have different amounts of astringency, and the trees used are selected according to those characteristics. Each different kind of tea is made with a suitable cultivar. So one makes a good Sencha and another one makes a good black tea or Gyokuro. There are also types which can be used to make almost all kind of teas but no superior product.
The bottom line is:
The key difference between the teas is, black tea and Oolong are fermented teas and green tea is not.
To make black tea or Oolong tea, the leaves are first rolled and then exposed to air to trigger the fermentation and oxidation process. These reactions cause the leaves to turn dark brown and allow the flavors to heighten and intensify.
On the other hand, green tea is processed to prevent fermentation and oxidation and is thus much lighter in color than black tea or Oolong tea.