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caffeine and tannin in tea

How strong is a cup of tea? Some people drink a cup of tea to go to sleep, others to keep awake. Some drink tea to calm their nerves, others for a lift. How can the same beverage possess such opposing qualities? Precisely because tea -- unlike coffee -- can produce both these effects upon the body, it is viewed as a wonder drink.
Tea and coffee both contain the stimulating substance caffeine, but only tea contains both caffeine and tannin. The presence of these chemical compounds together in tea leaves allows tea to act as a calming or exciting agent.

Here is how it works. Once boiling water is poured onto tea leaves, in the first two minutes all the caffeine in the leaves is drawn out. At this point tea is at its most stimulating. Only during the next minute win tannin gradually be drawn out of the tea leaves. This will not only cancel out the effects of the caffeine but after five minutes will actually make a relaxing, calming tea. Graphically it can be shown thus:


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