Besides theine and certain aromatic substances, tea contains a substance called tannin. It is an astringent acid that can dry up the digestive juices and cause indigestion. Tannin is present in strong tea and tea that has been standing for a long time. After pouring boiling water on the tea leaves or tea bags, three minutes is enough to extract most of the flavour and aromatic substances. That is when the tea should be poured into the cup for drinking, for, it will not contain harmful amounts of tannin. The longer the tea infuses, the more tannin will be present.
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