Most of the alkaloids in tea contain three parts, namely caffeine, theobromine and theophylline. These three substances are mainly composed of caffeine. Once they are absorbed by the body, they will produce obvious excitatory effects on the central nervous system and affect sleep. The green tea and oolong tea are typical examples. Green tea is non-fermented and oolong tea is semi-fermented. The content of caffeine in both is about 30mg per cup. It’s a good alternative for keeping you awake.  

      But not all teas are not suitable for drinking at night: black tea and Pu-erh tea are an exception. Both black tea and Pu-erh are of a higher degree of fermentation. The composition of tea polyphenols is less, and the irritation weakens after aging, as a result, the tea is very mild. It is recommended to wash Pu-erh tea more times before drinking in the evening, which will further reduce the caffeine content in the tea. A little milk can be added to black tea in drinking to warm the stomach. Good old Pu-erh is more effective in calming the nerves and promoting sleep.

       Finally, however, it is not recommended for some particular consumers, who has a weak stomach, mental instability, or poor sleep quality, to drink tea at night. For normal consumers, it is best to drink mild tea at night and try to avoid strong tea. Moreover, tea is best drunk in the evening or after dinner. It is not recommended to drink tea with an empty stomach.