This section is from the book "Diet In Sickness And In Health", by Mrs. Ernest Hart. Also available from Amazon: Diet in Sickness and in Health.
The evil effects of tea have been attributed to the methods in vogue of making it. We have seen that the soluble theine is at once dissolved in the hot water, but that the tannin contained in the coarser teas generally used in England continues to be given off if the tea is left standing on the leaves. Now, this is what almost invariably happens; and the last cup of tea drawn from a pot long standing, and which is said to be " very strong," is strong, not so much in the restorative principle of the theine, but in the astringent tannin which inhibits or slows digestion, and also in the bitter principle which is finally extracted from the leaves. To the habit, customary among the poor, of slowly stewing the tea on the hob, and also to the practice at restaurants and railway stations of continuously boiling it in urns, much of the dyspepsia attributed to tea-drinking is probably due. The reason is, however, not clear. The professional tea-taster allows the boiling water to stand on the tea leaves five minutes and no more; the infusion is then poured off and drunk. If this custom were universally followed we should probably hear fewer complaints about the evil effects of tea-drinking. In order to prevent the tea standing on the tea leaves, various teapots have been invented, by means of which infusion for a certain definite time can be obtained, and the tea leaves are then withdrawn. The best and simplest method is, in my opinion, to have a fine wire basket, in which the measured amount of tea leaves is placed; it is then closed and dropped into the hot water in the teapot for five minutes, after which it is withdrawn. Another method is to have a china strainer under the lid of the teapot, in which the tea leaves are deposited, and the boiling water is poured through the strainer. These teapots are made in Japan, and are imported in large quantities into this country. I have also seen used in Germany a concave perforated metal measure, which is placed at the top of the cup; this is then filled with hot water. When the leaves are sufficiently infused the measure is withdrawn, and the tea leaves are thrown away.
 
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