On Black and Green Teas.—Though the distinct preparation of green
and black tea from the respective plants, the Thea viridis and the Thea
Bohea, has been warmly advocated by many botanists, yet it is now
generally admitted by all parties, that green and black teas can be and
are made, indiscriminately from the same parcel of leaves, taken from
the same species of plant. It is nevertheless, well known to all persons,
that the infusions from these teas have marked differences in color and
flavour, and that the effects produced in certain constitutions by green
tea, such as nervous irritability, sleeplessness, &c. are very different
from those arising from the use of black tea. Their characteristic
physical differences are well known; but they possess peculiar chemical
properties to be noticed immediately, and which have always been
ascribed by chemists to the effect of high temperature in the process of
manufacture.
To explain these peculiarities, Mr. Warrington directs attention to
certain changes which take place in herbs and vegetable substances
dried in different modes. From observations made upon various sub-
stances of this kind, in the routine work of the establishment, to which
Mr. Warrington is attached, especially the exsiccation of medicinal
herbs, he had been led to form certain inferences as to changes taking
places in these articles. These herbs are for the most part nitrogenous
plants, as Atropa belladonna, Hyoscyamus niger, Comum maculatum,
and others. The plants are brought to the establishment by the growers
or collectors from the country, tied up in bundles, and when they arrive
fresh and cool, they dry of a good bright green color; but on the con-
trary, it is found, that if they are delayed in their transit, or remain in
a confined state for too long a period, they become heated, from a
species of spontaneous fermentation, and when loosened and spread open,
they emit vapors and are sensibly warm to the hand. When such
plants are dried, the whole of the green color is found to have been
destroyed; and a red-brown and sometimes a blackish-brown tint is the
result. Mr. Warrington also noticed, that a clear infusion of such
leaves, evaporated carefully to dryness, was not all undissolved by water,
but left a quantity of brown oxidized extractive matter, to which the
denomination of Apothene has been applied by some chemists. A similar
result is obtained by the evaporation of an infusion of black tea.
The same action takes place upon the exposure of the infusions of
many vegetable substances to the oxidizing influence of the atmosphere.
They become darkened on the surface; and this gradually spreads
through the solution, and on evaporation, the same oxidized extractive
matter will remain insoluble in water.
Mr. Warrington further found that the green teas when wetted and
re-dried, with exposure to the air, were nearly as dark in color as the
ordinary black teas. From these observations, therefore, Mr. Warrington
was led to form the conclusion, that the peculiar characters and chemical
differences which distinguish black tea from green, were to be attributed
to a species of heating and fermentation accompanied with oxidation by
exposure to the air, and not to its being submitted to a high temperature
in the process of drying, as has been generally believed. This opinion
received some confirmation by ascertaining from parties conversant with
the Chinese manufacture, that the leaves for the black teas were always
allowed to remain exposed to the air, in mass, for some time before they
were roasted.
Mr. Ball, in his work on the manufacture of tea, has described in
detail the whole series of these processes, fully confirming the opinion
previously formed by Mr. Warrington. Some of these facts had been
published in Batavia in 1844, by Mr. Jacobson in the Dutch language.
In the preface to his work Mr. Ball says: “ It will be seen by dates in-
cidentally adverted to, that the facts and most of the materials of this
work, were established and collected thirty years ago.”—“ These facts,
as well as other materials, were derived from conversation with growers
and manipulators from the tea districts; from written documents fur-
nished by Chinese; from published works in the same language
diligently sought out; and also from correspondence with a Spanish
missionary long resident in the province of Fokin. These were all
put into their present form full twenty years ago, and were read to one
or two friends during my residence in China.”—“ They were not, how-
ever, so arranged, with any view to immediate publication.7’—“They
were thus disposed as the best mode of recording and keeping together
the facts and materials I had collected.”—“ But it was not till the year
1844, when I received Mr. Jacobson’s Handbook on the Cultivation of
Tea in Java, that I found my own views so far confirmed, and my in-
formation such, as to justify me in bringing my labors to a close.”
Of these facts the following is a summary.
The processes peculiar to the preparation of black tea, are styled
Leang-Ching, To-Ching, annd Oc-Ching, and these all consist in care-
fully watched and regulated processes of spontaneous heating or slow
fermentation of the leaves until a certain degree of fragrance is developed.
The leaves are said to wither and give, and become soft and placid.
The utmost care, practical skill, and experience is required in the
properly conducting these operations; and as soon as the proper
point is arrived at, the leaves are to be immediately removed to the Kuo
or roasting-pan. After being roasted and rolled two or three times, they
are then to be dried, and this is effected in the Poey-long, which con-
sists of a cylinder of basket-work, open at both ends, and covered on the
outside with paper; it is about 2J feet in height and 1J in diameter,
which diameter is diminished in the centre like an ordinary dice-box to
one foot and a quarter. This stands over and round a small charcoal
fire, and is supplied with cross-bars about fourteen inches above the fire,
on which an open sieve containing the tea is placed; and a small aper-
ture about an inch and a half in diameter is made in the centre of the
tea with the hand, so that an ascending current of air and the products
of the combustion pass through and over the tea contained in the sieve.
A circular, flat bamboo tray is passed partially over the mouth of this
cylinder, and most probably s'erves to regulate the rapidity of the
ascending current; prevent the admission of the cold air to the leaves,
and at the same time allow a sufficient outlet for the generated watery
vapors and the products of combustion. At the commencement of this
operation, the moist leaves are still green and retain their vegetable ap-
pearance ; after the drying has continued about half an hour, the leaves
are turned, and again submitted to the heat for another half hour ; they
are then taken out, rubbed and twisted, and after sifting away the small
dust, again returned to the sieve and drying tube. This operation of
sifting is very necessary, to remove any of the small tea or dust which
might otherwise fall through the meshes of the sieve on to the fire, and
the products of their combustion would deteriorate and spoil the flavor
of the tea. The leaves have now begun to assume their black color; the
fire is diminished or deadened by ashes; and the operation of rolling,
twisting, and sifting, is repeated once or twice until they have become
quite black in color, well twisted, perfectly dry and crisp. They are
then picked, winnowed and placed in large quantities over a very slow
fire for about two hours, the cylinder being closed.
Now, that this black color is not owing to the fire is evident; for in
cases mentioned by Mr. Ball, where the leaves have been dried in the
sun, the same color is obtained ; and on the other side, if roasted first,
without the process of fermentation or withering, and then finished in
the Poey-long, a kind of green tea is produced.
In the operations for the manufacture of green tea, on the contrary,
the freshly-picked leaves are roasted in the Kuo at once, without delay,
at a high temperature; rolled and roasted again and again, assisted
sometimes with a fanning operation to drive off the moisture; and always
with brisk agitation until the drying is completed.
The marked differences in the mode of manufacture of black and
green tea, will, after what has been stated, fully account for all the va-
riation of physical and chemical properties already mentioned.— Quar-
terly Journ. Chem. Society.