Professor Yoriyuki Nakamura of the University of Shizuoka wrote the original article in Japanese, which CHAMART translated into English.

Caffeine is a type of alkaloid that has pharmacological effects, such as stimulating the central nervous system, but no narcotic effect. It is believed that caffeine is the most important component of tea which has made tea a popular favorite beverage all over the world since ancient times.  Caffeine is a silky white crystal with a bitter taste and is thought to have a considerable influence on the taste of tea.

There are more than 60 plants that contain caffeine. Other favorite beverages that contain caffeine other than tea (2.5-5.5%) are coffee (1-2%), cocoa (0.3%, theobromine 1%), cola (1-2%) and yerba mate (0.2-2%).
*The number of % in ( ) is the percentage of caffeine in each beverage.

The younger the tea buds are, and the closer the leaves are to the bud, the more caffeine they contain. Therefore, the younger and more tender the buds are, the higher the caffeine content in tea.  Also, caffeine levels increase if tea leaves are cultivated by blocking sunlight.  The tea garden of gyokuro is covered with mats for 2 or 3 weeks to block sunlight before picking the tea leaves and the tea leaves are very soft.  As a result, gyokuro contains a lot of caffeine.

Water-brewed gyokuro

Caffeine has a stimulating effect, cardiac intensifying effect, cerebral stimulation and diuretic effect, so drinking Gyokuro or high-quality Sencha may make you excited and unable to sleep.
Therefore, recently low-caffeine tea has developed taking advantage of the characteristic that caffeine dissolves more easily in hot water than other components.