ADULTERATION AND DETECTION.
The Teas of commerce are subject to three principal forms of
adulteration, viz.: Facing or coloring with deleterious compounds in
order to enhance their appearance, mixing with spurious and spent or
once used leaves, with the object of increasing their bulk, and sanding
or adulterating with mineral matter to add to their weight. But it is
against the two first most commonly dangerous forms of adulteration
that the principal efforts of dealers and Tea inspectors should more
particularly be directed, the latter having received some attention
from analysts and chemists, but not to that extent which the importance
of the subject merits.
Of the various forms of adulteration practiced in China and Japan, the
facing or artificial coloring of low-grade Green Teas is perhaps the
most prevalent and glaring, the material used for the purpose being
usually composed of Prussian blue, China clay, gypsum, turmeric and
indigo.
The process of coloring Green Teas is performed by placing a portion of
the Prussian blue in a large bowl and crushing it into a fine powder, a
small quantity of gypsum is then added, and the two substances ground
and mixed together in the proportions of one part blue to four parts
of the gypsum, both making in combination a light blue preparation,
in which state it is applied to the leaves during the last process
of firing. One ounce of this coloring matter will face or color from
fifteen to twenty pounds of Tea leaves, imparting to them a dull
leaden-blue color and a greasy appearance readily detected in the hand.
When Green or Japan Teas are heavily coated in this manner it may be
readily recognized by their heavy leaden-blue color and oily or greasy
appearance in the hand; or, better still, by placing a small sample
of the leaves on a piece of glass and allowing them to rest there for
some minutes, then on removing them the coloring matter, if any, will
be found adhering to the glass, and its nature, whether Prussian blue,
indigo or soapstone, detected by the aid of a small microscope. But
when only lightly colored the best method is to put the leaves in a
cup or glass and pour boiling water on them, stirring them up well
meantime and then straining the infusion through a thin muslin cloth,
and the coloring matter will be found deposited in the cloth or forming
a sediment at the bottom or sides of the vessel into which they are
strained.
What are known to trade as “Made Teas,” that is, Teas artificially
manufactured from leaves once used, or tea dust, and a preparation
of gum or glue to hold them together, and then colored and glazed
to give them a pleasing appearance to the eye, are best detected by
crushing the so-called leaves between the fingers or hands upon which
they leave a yellowish stain, greasy in nature if spurious leaves.
Or again, by pulverizing a small quantity of the alleged Tea leaves,
and putting them in a cup or glass and pouring on boiling water, they
will immediately begin to disintegrate and form a thick, gluey deposit
at the bottom of the vessel, pasty in nature, the coloring matter
adhering to the bottom or sides of the cup or glass.
Another form of adulteration practiced principally in China is the
admixture of spurious or foreign leaves obtained from other plants,
such as the willow, plum, ash, and what is known in trade as Ankoi
Tea. Millions of pounds of such spurious Tea leaves are annually
picked, cured and colored in the same manner as Tea in some of the
Chinese Tea districts, and used for the purpose of increasing the bulk
and decreasing the cost of genuine Teas, this form of adulteration,
however, being only trivial when compared with the former one. Such
spurious or foreign leaves in a Tea are best detected by their
botanical character, that is, by the absence of the special structural
marks, which distinguish the genuine Tea leaf from that of the leaves
from all other plants in the vegetable kingdom, for while it is
admitted that the Tea leaf bears a strong resemblance to those of the
willow, plum and ash, it varies materially, however, in size, form
and structure from them, the border of the true Tea leaf being more
regularly serrated, the serrations stopping just short of the stalk,
and the venations are very characteristic in the genuine Tea leaf, the
veins running out from the mid-rib almost parallel with each other,
but altering their course before the border of the leaf is reached and
turning so as to leave a bare space just under it. So that in making
an examination of a sample of Tea for the purpose of ascertaining
whether these distinctive characteristics are present in the leaves,
it will be found best to pour boiling water on to soften and uncurl
them, and spread them out more easily on the glass as per the following
diagrams:--
[Illustration:
(True Chinese Tea-Leaf.)
(True Japanese Tea-Leaf.)
(True Ceylon Tea-Leaf.)
(True India Tea-Leaf.) ]
But in order to better detect the presence of spurious leaves in Tea, a
better knowledge of the botanical formation of the true Tea leaf will
be requisite, as Tea leaves in general bear a very strong resemblance
to those of the willow, plum and ash, but vary widely in size and
texture, being much smaller and more deeply serrated.
When infused and unfolded, the true or genuine Tea leaf is of a
lighter-green color, the looping of the principal veinings being
also very characteristic, while the spurious leaves are of a dark
greenish-yellow color and very irregular in form when examined under
the same conditions.
Sand and other mineral substances, such as iron and steel filings,
are also frequently introduced into Tea with the object of adding to
its weight, and are easiest detected by powdering a small quantity of
the leaves and spreading the powder out on a piece of glass and then
applying an ordinary magnet to the dust, so that if a quantity of the
particles gravitate and adhere to the magnet the Tea is undoubtedly
adulterated in this form.
All adulterations and fabrications in general, however, may be best
detected by the following simple but effectual method: By putting a
small sample of the Tea leaves in a wine-glass or thin goblet and
pouring in clear cold water on them, and then stirring up or shaking
well for a few minutes so that the Tea, if pure, will only slightly
color the water, but if adulterated in any form a dark, muddy-looking
liquor is quickly yielded, which, if next boiled and allowed to stand
until cold, will, if spurious leaves are contained, become very bitter
to the taste and almost transparent as it cools, while if the sample
is composed of pure Tea only, it will be dark in color and pleasing in
flavor under the same conditions.