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.
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.