Tea has an excitatory and a stimulating effect on human mental abilities. First of all it depends on the content of caffeine in tea. For the first time caffeine was isolated from coffee in 1820 by Ferdinand Runge Fridlibom. In 1827 the Frenchman Audrey discovered in tea leaves an unknown substance, originally called „theine”. In 1837 it was proven that theine was identical to caffeine.
In the process of tea brewing caffeine is relatively rapidly and almost completely extracted from tea leaves. After tea-drinking the concentration of caffeine in the blood increases, and doesn’t differ from concentration after drinking coffee. However, the stimulating effect of caffeine in the same amounts of coffee and tea is very different, due to differences of related substances: in tea - tannins, and in coffee - substances produced by roasted beans. On a percentage basis tea contains more caffeine than coffee, however from one pound of tea you can make much more cups of the drink, rather than from one pound of coffee. Thus, an average cup of tea contains 0.053 gr. of caffeine, and one cup of coffee – twice more - 0.1 gr.
In contradistinction from coffee caffeine, tea caffeine acts more slowly and longer. Tea caffeine affects the central nervous system, while the coffee caffeine affects mainly the vessels and heart. Thus, tea has a stimulating effect, but not nervous effect. Effect of tea, increasing woking efficiency, is proved scientifically.
So, what determines the content of caffeine in tea?
First of all, the content of caffeine is determined by the size of the leave. The smaller is the tea leaf, the more caffeine it contains. Besides, the temperature of the water, which is used for pouring the brew, is very important. The hotter is the water, the more caffeine is extracted.
Considering the fact that caffeine is a water-soluble substance, then, theoretically, the longer is the process of brewing, the more caffeine comes out. However, in practice the maximum caffeine with minimal damage to flavor and aroma may be received not more than after 5-6 minutes of brewing.
A significant effect on the content of caffeine in tea leave have the conditions of its drying in the manufacturing process. Thus at the great risk are black teas, which are dried in special ovens at high temperatures, as any occasional disturbance of (increase) temperature conditions destroys the caffeine.
The content of caffeine depends also on temperature and light conditions in the tea growing area. The colder are the conditions, the slower are growing the tea leaves, and the more caffeine it contains, that’s why all elite tea varieties (for example, Darjeeling) are grown in extreme conditions, on the northern border of tea area. At the same time, the greater is the solar activity, the greater is the concentration of caffeine in tea leave. These teas with the large content of caffeine are grown at the southern equatorial border of the tea area, for example, in Ceylon. However, such „southern” caffeine teas are generally second to „north” teas in the quality of taste and aroma.
And finally, the content of caffeine in tea leaves depends on the characteristics of the soil in the tea growing areas. Nowadays, almost in all major world’s tea plantations the tea is feeded with fertilizers or is not feeded intentionally.