Green tea, they first remove from the green leaf, imparts very little flavor or scent to its infusion. In some Oolong Black teas, and in some Ceylon Black teas, these oils are highly developed and are very fragrant. In the black Souchongs and Congous they have again been altered by treatment, but are no less perceptible, and to many, are quite as agreeable. Although constituting only one-half to one per cent. by weight of the dried leaf, these oils are all-important to the trademan and to the consumer.
These volatile oils are strongest in new teas, and are gradually wasted by exposure to the atmosphere. Robert Fortune and other travelers in China have stated that the Chinese will not use new teas, but allow them to pass through a sort of "ripening" process. Mr. Crole, speaking probably of the Indian teas with which he was so familiar as a planter and chemist, says that "tea should always be kept for a year before being drank. If the infusion of freshly manufactured tea is drank, it causes violent diarrhea; therefore it should be kept a year before it is consumed, in order to let it mellow."
There is no doubt that the more impervious the package containing tea is to the air, the more perfectly the finer qualities of the tea are preserved. If there is a necessity for ripening or mellowing by time, air should be rigidly excluded during that period.
As to the keeping qualities of fine teas, in tight packages, we know that they are not spoiled or injured by two years storage in this climate.
Tannin is the third important element of the tea leaf, and it varies greatly in percentage in different teas, and increases with the age of the growing leaf. It is the cause of the rasping, puckering, astringent effect upon the tongue and interior of the mouth.
Tannin in tea has been a great bugbear with the ill-informed, bit it is not nearly so deleterious as some careless or unscrupulous writers would have us believe. In the first place there is a very insignificant quantity of tannin in properly drawn teas, say in those drawn for not longer than five or eight minutes. The tannin present in a fine Black tea, steeped at a moderate temperature for fifteen or twenty minutes will not harm a delicate stomach. We take quite as much tannin in some fruits, and make no fuss about it. Secondly, if a strong solution of tannin is taken into the stomach and there comes in contact with albuminous or gelatinous foods, it will expend its coagulating power upon such substances. If there are no such substances present, it is the expressed opinion of Mr. Crole (in a discussion upon the chemistry of tea) that the tannin is converted into glucose and other harmless products by the digestive processes. The wild declarations that tea tannin "tans" the coating of the stomach into a leathery condition is without foundation. Even where too prolonged steeping has greatly increased the usual proportion of tannin in tea infusion, milk, when added, neutralizes the coagulating power of the tannin entirely or to such degree as to render it harmless.
Professor Johnston thinks it quite probable that tannin takes some part in the exhilarating effect of tea, and in that of the betel-nut of the East. While the astringent influence of strong tannin upon the bowels is regarded as unfavorable, hot tea infusion has with many persons a contrary effect, stimulating the peristaltic movements and antagonizing constipation.
If tannin is injurious, it should be observed that its proportion in the leaf of green teas is very much larger than in Black teas. An analysis by Mulder gave as the percentage of tannin in a Black tea, 12.85 per cent., and in a green tea as 17.80 per cent. But another analysis made by Y. Kazai, of the Imperial College of Agriculture of Japan, made the per centage of tannin (gallo- tannic acid) in a Green tea 10.64, and in a Black tea from the same leaf 4.89. In the green leaf from which these teas were derived he found 12.91 per cent. of tannin. This analysis indicates also that a portion of the tannin disappears in manufacturing Green tea, but a still larger, proportion is lost or changed in the manufacture of Black tea.
Tannic acid taken into the human stomach in large quantity produces, according to the U.S. Dispensatory, "only a mild gastro-intestinal irritation."
Passing over the phosphoric acid, the gluten, and other interesting constituents of the tea leaf, we proceed to the observed effects of tea upon the human system.