1. Is tea left overnight is harmful to human body?
Though it is fine to drink infusion of tea left overnight, it is not advisable to drink the tea left longer than that as there is a risk that microorganisms, particularly mildew, may reproduce because tea leaves contain protein, sugar, fat, etc., and as the polyphenol ingredient in tea leaves will show strong irritative property by being oxidized in the air with time and cause excessive secretion of gastric juice by stimulating the gastric mucosa. It is fine to store tea water in a refrigerator for about 5 days as the change in the composition will be little and the flavor and taste will be maintained in a refrigerator.