Oolong, also called “Blue Tea” in China because of the colour of their brewed leaves, are semi-oxidized teas.
Two categories of Oolong are commonly contrasted: slightly oxidized teas (10% -15% oxidation), prepared according to the “Chinese method”; and others, whose oxidation is much higher (60% -70%) being prepared according to a method developed in Taiwan.
In fact, the preparation of semi-oxidized teas is a much less compartmentalized field: each plantation has its own recipes and produces teas with degrees of oxidation which do not necessarily correspond to either of these two categories.