Oolongs are a speciality of Fujian. They are known as blue-green teas among the Chinese due to the colour of the infused leaves, and have had their oxidation interrupted during processing. There are many Oolongs, which vary according to the growing region, species of tea plant and processing method.
These are teas for which oxidation has been interrupted mid-process. Oolong teas are a specialty of China's Fujian Province and Taiwan. These Oolong teas are generally divided into two categories: lightly oxidised teas (10%-15% oxidation) prepared in the so-called Chinese way, and teas for which the oxidation process is much greater (60%-70%) and which are processed according to a method more specifically developed in Taiwan. In practice, the preparation of semi-oxidised teas is not quite this clear-cut, as each plantation has its own recipes and produces teas with a degree of oxidation that does not necessarily correspond to these two categories.
ALL SEMI-OXIDISED TEAS MUST UNDERGO THE FOLLOWING PROCESSES:
The leaves are left to wilt outside for a few hours under slatted panels which filter the sunlight. Some of the moisture evaporates before the leaves are placed in a room with a high moisture content. Oxidation occurs during the sweating phase. To encourage this process, the leaves are stirred gently, in contrast to the more energetic rolling process used for black teas. Oxidation is the result of an enzyme which causes the leaves to turn red from the edges towards the centre and determines the aromatic profile of the tea.
Once the desired degree of oxidation has been reached, roasting allows the enzyme reaction to be stopped. This procedure is identical to that used to produce green teas.
As with green teas, the rolling process gives the tea leaves their twisted shape. Naturally, the leaves are often very large and are simply creased or sometimes rolled into large pearls, as is the case with Dong Ding teas.
This is the most important stage in the preparation of semi-oxidised teas.
The leaves are placed in a room kept at a constant temperature of between 72°F-77°F / 22°C and 25°C with a humidity level of roughly 85%, where they are continually stirred with ever-increasing force. This allows the aroma to be released and facilitates the evaporation of water. The final degree of sweating depends on the duration of this process: in the so-called Chinese method, oxidation is stopped as soon as the leaves have reached a 10%-12% degree of oxidation, which produces light teas with a leafy flavor. The so-called Taiwanese method involves a longer period of sweating allowing oxidation to progress to a level of up to 70% and producing darker, fruitier teas.