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 chemistry of tea.
Chemists find in manufacturing tea leaves three principa constituents
to which all the physiological effects of tea are attributed. These
are:
1. Theine (synonym for caffeine)
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 chemists, 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 hot water. It vaporizes at 185
degrees C (or 365 degrees Fahr.), hence it is not driven off by
continued boiling of tea infusion.
It is found by experiment that prolonged steeping of tea leaves up to
ten minutes increased the proportion of theine in
the infusion. The 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
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
It was reported that in prolonging the steeping of tea from 10 to 20
minutes, 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. These precious oils are
artificially developed by manufacture. They are developed to a certain
extent during withering, and also during the first stage of heating,
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. Many travelers in China have stated that
the Chinese will not use new teas, but allow them to pass through a
sort of "ripening" process.
According to many experienced tea consumers, 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, 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.
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.
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. 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.
The infusion of tea has little nutritive value, but it increases
respiratory action, and excites the brain to greater activity. Theine,
which is identical with caffein, when taken in moderation, 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 intelectual 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.
|
SPONSORED LINKS
RELATED 