Here I found this article on the web hope it helps
ref http://www.austinchronicle.com/gyrob...d=oid%3A208400


Tea and coffee both contain caffeine, a stimulant, but tea also has
tannin and theanine, which are calming. The presence of these chemical
compounds together in tea allows you to control its effect. When
boiling water is poured onto the tea leaves, in the first two minutes
all the caffeine is drawn out. At this point tea is most stimulating.
During the next few minutes, tannin and theanine are gradually brought
out of the tea leaves. After about five minutes this will tend to
cancel out the effects of the caffeine and will make a more relaxing,
calming tea. If you want only the calming effects from tea, discard
the liquid from the first two minutes of steeping and use only the
liquid from subsequent steeping, containing little caffeine and more
tannin and theanine