Chen, Yo Ren (the former chief of TRES) pointed out that the caffeine content in tea is related to the tea varieties, the tenderness of tea leaves, and the tea processing. For example, the caffeine content in Bergamot cultivar and Wuyi cultivar is less, while in Assam cultivar, Qingxing Oolong cultivar and Qingxing Dapon cultivar is slightly higher; in addition, the tender the tea leaves are, the more the caffeine contained.
On the contrary, while the raw materials are the same, the degree of fermentation has little effect on the content of caffeine in tea. The most critical factor affecting caffeine is whether the tea processing has undergone a "baking/roasting" phase.
Hsu, Wei Ting (Professor at Nanhua University) looked back the reports of high-performance liquid chromatography (HPLC) analysis of caffeine content in different teas in international journals. It is found that the caffeine content in most of the teas including black tea (Pu'er tea), green tea, and red tea is similar, with a subtle difference. Oolong tea is the only one has less caffeine content than the other teas. He explained that the main reason is that the production of oolong tea was going through the "baking/roasting" processing phase.
The baking processing is mainly conducted to reduce the water content in tea. The natural sweetness of the tea often detected is produced by the "Maillard reaction" in the baking processing as well. Usually, some semi-fermented teas such as oolongs and Tieguanyin are to emphasize this phase, and caffeine is sublimated and reduced due to long-time high-temperature baking processing accordingly.
Therefore, after the high level of baking processing, the teas such as Dong Ding Oolong tea and traditional Roasted Tieguanyin, the caffeine contained in which is obviously removed. If people who are craving drinking tea but worry about caffeine disturbing the physiological clock, try the heavy baked oolong teas!
Translated and edited by Adm./Fong Mong Tea Corp, all rights reserved.