Chapter VII. Chemistry and Physiological Aspects of Tea.
If the reader desires an example of imperfect and arrested knowledge in some of the common affairs of life, let him collate the statements of scientific experts concerning the physiological effects upon mankind, of tea. He will then admit that "in a multitude of counsellors there is confusion."
Without pretending to more than the rudiments of chemical or physiological science, we shall attempt to examine the nature of tea, and its effects upon the human system; taking as a basis for our remarks Professor Jas. F. Johnston's Chemistry of Common Life, from which work more recent writers draw most of their inspiration.
Chemists find in manufacturing tea leaves three principal constituents to which all the physiological effects of tea are attributed. These are, (1) Theine, (2) Essential or Volatile Oils, (3) Tannin.
Theine is present in the green leaf of tea, and is apparently unchanged in the manufactured leaf and in the infusion or beverage. We regard it as the one essential and the most valuable element of all teas, physiologically considered. Strangely enough theine is the one important constituent which is entirely neglected by the tea-tester and the trader. In testing and grading teas for purchase and sale, their appearance, odor and taste, their color and body when " drawn," determine their pecuniary value, without relation to their percentage of theine, or its effects upon the tester.
Theine has been found in nature in but a few plants, as in tea, in coffee, (then termed caffein), in Mat'e (Paraguay or Brazilian tea), and in the Kola nut of Africa. A very similar principle, having analogous properties, but containing more nitrogen, exists in cocoa, (theobroma).
Theine, when isolated by heat from the tea leaf or infusions, condenses in minute white needles or crystals, having no odor and but a faintly bitter taste. In manufactured tea leaves, theine constitutes from one to five percent. of their weight. According to Professor Johnston, three or four grains per day of this substance may be taken without injury by most persons; or such quantity as would be contained in half and ounce of Chinese black tea. Indian (Assam) tea and Ceylon tea, being stronger in theine, would suffice in lesser quantity.
Theine is soluble in about 100 parts of hat water. It vaporizes at 185 degrees C. or 365 degrees Fahr., hence it is not driven off by continued boiling of tea infusion.
W. Dittmar found by experiment that prolonged steeping of tea leaves up to ten minutes increased the proportion of theine in the infusion. His results are as follows:
STEEPED 5 MINUTES.
- Average of 8 samples Chinese tea:
- Theine, per cent infusion - 2.58
Tannin - 3.06
- Average of 6 samples Ceylon tea:
- Theine - 3.15
Tannin - 5.87
- Average 12 samples of Indian tea:
- Theine - 3.63
Tannin - 6.77
STEEPED 10 MINUTES.
- Average of 8 samples Chinese tea:
- Theine, per cent infusion - 2.79 - Increase about 10 per cent
Tannin - 3.78 - Increase about 25 per cent
- Average of 6 samples Ceylon tea:
- Theine - 3.29 - Increase about 5 per cent
Tannin - 7.30 - Increase about 25 per cent
- Average 12 samples of Indian tea:
- Theine - 3.73 - Increase about 3 per cent
Tannin - 8.09 - Increase about 20 per cent
W. M. Green reported that in prolonging the steeping of tea from 10 to 20 minutes, he observed the formation of a tannate of theine, which diminished the proportion of 1.30 per cent. of theine at 10 minutes to 1.16 per cent. after 20 minutes steeping, a loss of about 10 percent., unless the latter salt so formed is proved to yield up its theine constituent in the human stomach.
While theine is credited as the source of the most powerful and useful properties of tea, and without which no plant would be recognized as tea, yet some of the stimulating or exhilarating influences of this plant are attributed to the volatile oils which contribute so largely to the flavors and odors which characterize tea.
These Essential or Volatile Oils of manufactured tea are said to reside in the minute cells of the green leaf, but they are greatly changed by manipulation, for they are not manifest to the sense of taste or smell when expressed from the green leaf by bruising, nor does the green leaf yield their aromatic flavors to an infusion. Professor Johnston says that these precious oils are artificially developed by manufacture. David Crole declares that they are developed "to a certain extent during withering, and also during the first stage of firing, " which last process, if carelessly conducted, " oxidises it (the oil) into resin."
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.
Professor Johnston (before quoted) says that tea " exhilarates without sensibly intoxicating. It excites the brain to increased activity and produces wakefulness; hence its usefulness to hard students, to those who have vigils to keep, and to persons who labor much with the head. It soothes, on the contrary, and stills the vascular system, (arteries, veins, capillaries, etc.), and hence its use in inflammatory diseases, and as a cure for headaches. Green tea, when strong, acts very powerfully on some constitutions, producing nervous tremblings and other distressing symptoms, acting as a narcotic, and in inferior animals even producing paralysis. Its exciting effect upon the nerves makes it useful in counteracting the effects of fermented liquors, and the stupor sometimes induced by fever." And again, tea " lessens waste," and diminishes the quantity of food required; " saves food; stands to a certain extent in the place of food, while at the same time it soothes the body and enlivens the mind."
Professor A. H. Church, of Oxon, England, in one of his often quoted books on Food, says that " the infusion of tea has little nutritive value, but it increases respiratory action, and excites the brain to greater activity."
J.C. Hutchinson, M.D., (late President Medical Society of State of New York), remarks that caffein, which he regards as identical with theine, " is a gentle stimulant, without any injurious reaction. It produces a restful feeling after exhausting efforts of mind or body; it tranquilizes but does not disqualify for labor, and therefore it is highly esteemed by persons of literary pursuits. The excessive use of either tea or coffee will cause wakefulness."
Dr. Kane, the Artic Explorer, speaking of the diet of his men while sojourning in the Artic ice fields, said that his men preferred coffee in the mornings, but at night, " tea soothed them after a hard day's labor, and better enabled them to sleep."
Dr. Edward Smith, an English Physiologist, in an address before the Royal Medical and Chirurgical Society, remarked that " tea increased waste in the body, excited every function, and was well fitted to cases where there was a superfluity of material in the system; - but is injurious to the under-fed, or where there is greater waste than supply." Dr. Smith recommended tea as a preventive of heat-appoplexy, and in cases of suspended animation, as from partial drowning.
We have selected these expressions of opinion from among a large number of diverse character, for the purpose of illustrating the uncertainty of knowledge concerning tea. To recapitulate: -
Professor Johnston finds that tea exhilarates; excites to activity, produces wakefulness; yet it sooths, and it tranquilizes the vascular system; it lessens waste and saves food.
Dr. Smith found tea to increase waste, and to be injurious where food is deficient; says tea excites every function, - which must include the vascular system.
Dr. Hutchinson and Dr. Kane agree in the main.
What is the meaning of such radical differences of view? We think they arise from three causes: First, tea affects different persons very differently; secondly, the subject has not received that careful study which it merits, and thirdly, there is a careless confounding of at least three classes of effects, and a confusion of terms in describing them.
We feel an unaffected diffidence in criticising and endeavoring to improve upon the expressions of scientific men of honest purpose, but we may be pardoned for pointing the way to a more careful analysis of the merits and deficiencies of an article of diet used by so many millions of people.
We find among the ordinary effects of tea-drinking:
Exhilaration: - an elevation of feeling, a lightness of mood or spirits; a cheerfulness or even joy, which is compatible with rest. This effect may be entirely independent of pure stimulus, or of any disposition to mental or physical activity.
Stimulation: - a quickening or rousing to action of any faculty, but as usually employed, an urging to action of bodily or mental powers.
Sustaining: - enabling one to continue the expenditure of energy with less sense of fatigue, at the time, or afterwards.
Refreshing: - relieving or reviving after exertion of any kind; reanimating, invigorating; contributing to rest after fatigue.
Exciting: - in the sense of stimulation of brain and nervous system to higher tension, but not necessarily attended by disposition to labor or useful activity.
Now some tea-drinkers find in the beverage exhilaration only, a lightness of mood, but they are disposed to rest and to revery, to simply a passive meditation, or an indulgence of the imagination.
Others are stimulated to mental or to physical activity, and are sustained during such action. Afterwards they are refreshed when fatigued, by the same beverage.
Others again are nervously excited and cannot rest or sleep; but are too " nervous," as they express it, to set about any formal task, especially of a mental character.
We have known tea-drinkers, too, who after a hard day's toil, could drink two or three cups of strong tea and lie down to sleep for the night as quietly as babes are expected to - but do not.
It must be evident that each person should observe the effects of tea upon himself or herself and be governed accordingly. Tea is a poison to some temperaments, and so are strawberries. Tea will cure a headache or may produce one; will dispose to rest or excite to action. We will sum then by conceding that all our quoted authorities are right in their conclusions, if limited to a limited class of tea-drinkers, and all are wrong, in a very broad application.
Theine is the one constant agency in the effects of tea. It is present in teas that are devoid of essential oils - so far as the senses go - and it then still refreshes, stimulates, sustains, and even exhilarates, by actual experiment.
The feeling of "comfort," attributed by some writers to the hot water of the tea, may be also enjoyed by drinking cold tea, which is no less refreshing in hot weather. The high-flavored essential oils (strictly oils which evaporate at very moderate temperatures) of Formosa teas seem to take part in the superior exhilarating or almost intoxicating effects of the choice varieties, but we have no certain proof of the fact; while the more intoxicating and stimulating, as well as deleterious, green teas possess very little, if any, of these pleasant oils.
It seems to be an authodox opinion among physiologists that tea contributes nothing towards support of the human system; that it only rouses it into action, an effect which should, consistently, be followed by corresponding reaction and depression, which plainly is not the case. This hypothesis leaves the enquiring layman in a dilemma. Tea must either enable the system to draw more heavily or more economically upon the resources afforded by recognized food, or it is itself nutriment. Otherwise, an established principle of physics - that there can be no expenditure of energy without correlative cost - would be subverted. As tea is admitted upon experience to be most useful, and most craved by mankind, where the supply of food is insufficient; and as it is known to refresh and sustain in large degree in the absence of any food whatever, there is fair ground for the opinion, however heterodox, that tea directly affords nutriment to the human organism, and, possibly, to the brain and nerves in particular, as with phosphoric acid.
Animal gelatine has been placed in the same class with tea by Liebig, Dr. John W. Draper, and others, and it is asserted that it conserves waste without itself entering into the substance of human tissue. It is an accepted physiological law that nothing taken as food or drink can support expenditure of human energy in sensible motion, in heat, or in the nervous waste of mental or emotional exercise without first being built up into living tissue; the breaking down or chemical decomposition of which tissue, and subsequent oxidation of less complex compounds or their constituents, is the direct source of bodily energy of every description. This, at least, is our reading of modern authorities, like Foster. If tea and gelatine, and possibly alcohol, are to form exceptions to the law, the law no longer stands. But it would seem more reasonable to amend the hypothesis concerning exceptions, and bring them into line by admitting that they are nutritious in a manner not yet ascertained. All physiological laws are provisional, good until proved insufficient, and then to be amended in the light of accumulating facts.