The early history of tea is probably contemporary with that of China, although, in that country, the first authentic mention of the plant was as late as A.D. 350; while, in European literature, its earliest notice occurs in the year 1550. The first important consignment of tea into England took place in 1657. Chinese tea made its appearance in the United States in 1711; in 1858, the importation of Japan tea began. During the season of 1883-1884, the importation of tea into this country[4] was—from China, 30½ millions of pounds; from Japan, 32½ millions of pounds. Recently, numerous shipments of Indian tea have been placed upon our markets, the quality of which compares very favourably with the older and better known varieties. During the past four years the consumption of tea in this country has materially decreased; whilst that of coffee has undergone an almost corresponding increase. The per capita consumption of tea and coffee in the United States as compared with that of Great Britain is as follows:—United States, tea, 1·16; coffee, 9·50; Great Britain, tea, 4·62; coffee, 0·89. In the year 1885 our importation of tea approximated 82 millions of pounds, that of coffee being nearly 455 millions of pounds.

Genuine tea is the prepared leaf of Thea sinensis. The growth of the tea shrub is usually restricted by artificial means to a height of from three to five feet. It is ready for picking at the end of the third year, the average life of the plant being about ten years. The first picking is made in the middle of April, the second on the 1st of May, the third in the middle of July, and occasionally a fourth during the month of August. The first pickings, which obviously consist of the young and more tender leaves, furnish the finer grades of tea. After sorting, the natural moisture of the leaves is partially removed by pressing and rolling; they are next more thoroughly dried by gently roasting in iron pans for a few minutes. The leaves are then rolled on bamboo tables and again roasted, occasionally re-rolled and re-fired, and finally separated into the various kinds, such as twankay, hyson, young hyson, gunpowder, etc., by passing through sieves. The difference between green and black tea is mainly due to the fact that the former is dried shortly after gathering, and then rolled and carefully fired, whereas black tea is first made up into heaps, which are exposed to the air for some time before firing and allowed to undergo a species of fermentation, resulting in the conversion of its original olive-green into a black colour. The methods employed in the preparation of the tea are somewhat modified in their details in the different tea districts of China and Japan. In Japan two varieties of the leaf are used, which are termed “otoko” (male), and “ona” (female), the former being larger and coarser than the latter. After picking, the leaves are steamed by placing them in a wooden tray suspended over boiling water, in which they are allowed to remain for about half a minute. They are next thrown upon a tough paper membrane attached to the top of an oven, which is heated by burning charcoal covered with ashes, where they are constantly manipulated by the hand until the light-green colour turns to a dark olive, and the leaves have become spirally twisted. After this “firing,” the tea is dried at a low temperature for from four to eight hours; it is next sorted by passing through sieves, and is then turned over to the “go-downs,” or warehouses of the foreigners, where the facing process is carried on by placing the tea in large metallic bowls, heated by means of a furnace, and gradually adding the various pigments used, the mixture being continually stirred. The tea is finally again sorted by means of large fans, and is now ready for packing and shipment.

The sophistications to which tea is exposed have received the careful attention of chemists, but not to a greater extent than the importance of the subject merits; indeed, it is safe to assert that no article among alimentary substances has been, at least in past years, more subjected to adulteration. The falsifications which are practised to no inconsiderable extent may be conveniently divided into three classes.

1st. Additions made for the purpose of giving increased weight and bulk, which include foreign leaves and spent tea leaves, and also certain mineral substances, such as metallic iron, sand, brick-dust, etc.

2nd. Substances added in order to produce an artificial appearance of strength to the tea decoction, catechu and other bodies rich in tannin being mainly resorted to for this purpose.

3rd. The imparting of a bright and shining appearance to an inferior tea by means of various colouring mixtures or “facings,” which operation, while sometimes practised upon black tea, is far more common with the green variety. This adulteration involves the use of soap-stone, gypsum, China clay, Prussian blue, indigo, turmeric, and graphite. The author lately received from Japan several samples of the preparations employed for facing the tea in that country, the composition of which was shown by analysis to be essentially as follows:—

1. Magnesium silicate (soap-stone).
2. Calcium sulphate (gypsum).
3. Turmeric.
4. Indigo.
5. Ferric ferrocyanide (Prussian blue).
6. Soap-stone, 47·5 per cent.; gypsum, 47·5 per cent.; Prussian blue, 5 per cent.
7. Soap-stone, 45 per cent.; gypsum, 45 per cent.; Prussian blue, 10 per cent.
8. Soap-stone, 75 per cent.; indigo, 25 per cent.
9. Soap-stone, 60 per cent.; indigo, 40 per cent.

The “facing” or “blooming” of tea is often accomplished by simply placing it in an iron pan, heated by a fire, and rapidly incorporating with it one of the preceding mixtures (Nos. 6, 7, 8, or 9), in the proportion of about half a dram to seven or eight pounds of the tea, a brisk stirring being maintained until the desired shade of colour is produced.

Some of the above forms of sophistication usually go together;—thus exhausted tea is restored by facing. The collection of the spent leaves takes place in China. Much of the facing was, until about three years since, done in New York city, and constituted a regular branch of business, which included among its operations such metamorphoses as the conversion of a green tea into a black, and vice versÂ.

According to James Bell,[5] the composition of genuine tea is as follows:—

The ash of samples of uncoloured and unfaced tea, and of spent tea analysed by the author, had the following composition:—

Composition.

“Tea dust” affords a high proportion of ash, sometimes amounting to 20 per cent., the composition of which is usually strikingly different from that of the ash of ordinary tea. It is deficient in potassa and phosphoric acid, and the amount of ash insoluble in water and acids is very excessive, as is shown by the following analysis, made by the author:—

Ash of Tea Dust.

The portion of ash insoluble in acids consisted of silica, clay, and soapstone, indicating that the ash of tea dust is largely composed of the mineral substances employed for “facing” purposes.

The characteristics of the ash of unspent tea are the presence of manganic oxide, the large proportion of potassium salts present, and the solubility of the ash in water. The amount of ash in genuine tea ranges from five to six per cent. In the absence of exhausted leaves, it has been found that the finer sorts of tea afford a smaller proportion of ash than the inferior grades. It will be noticed that spent tea ash exhibits a marked increase in the proportion of insoluble compounds (silica, alumina, and ferric oxide), as well as a total absence of potassium salts.

The presence of foreign leaves, and, in some instances, of mineral adulterants in tea is best detected by means of a microscopical examination of the suspected sample. The genuine tea-leaf is characterised by its peculiar serrations and venations. Its border exhibits serrations which stop a little short of the stalk, while the venations extend from the central rib, nearly parallel to one another, but turn just before reaching the border of the leaf.

Plate I. (Frontispiece) is a photogravure of a twig of the tea plant, in possession of the author. The leaves are of natural size, but the majority are of a greater maturity than those used in the preparation of tea, which more resemble in size the few upper leaves.

Plate II. shows more distinctly the serrations and venations of the tea-leaf. The Chinese are said to occasionally employ ash, camelia, and dog-rose leaves for admixture with tea, and the product is stated to have formerly been subjected in England to the addition of sloe, willow, beech, hawthorn, oak, etc. For scenting purposes, chulan flowers, rose, jasmine, and orange leaves, have been employed. The writer has lately received from Japan specimens of willow, wisteria, te-mo-ki, and other leaves which at one time were used in that country as admixtures.

Plate III. exhibits some of these leaves, two genuine Japan tea-leaves being included for purpose of comparison. The leaves represented in this plate are: 1, beech; 2, hawthorn; 3, rose; 4, Japan tea; 5, willow; 6, te-mo-ki; 7, elm; 8, wisteria; 9, poplar. From very recent reports of the American consuls in Japan and China, it would appear that the addition of foreign leaves to tea is at present but seldom resorted to, and this accords with the author’s experience in the testing of the teas imported into this country.

In 1884, the Japanese Government made it a criminal offence to adulterate tea, and instituted “tea guilds,” which are governed by very stringent laws, and of which most dealers of repute are members. The facing of tea does not appear, however, to have been considered an adulteration, its continued practice being justified by the plea that otherwise Japan teas would not suit the taste of American consumers.

In the microscopic examination of tea, the sample should be moistened with hot water and spread out on a glass plate, and then submitted to a careful inspection, especial attention being directed to the general outline of the leaf and its serrations and venations. The presence of exhausted tea-leaves may often be detected by their soft texture and generally disintegrated appearance. If a considerable quantity of the tea be placed in a long glass cylinder and agitated with cold water, the colouring and other abnormal substances frequently become detached, and either rise to the surface of the liquid as a sort of scum, or fall to the bottom as a sediment. In this way Prussian blue, indigo, soapstone, gypsum, sand, and turmeric can often be separated, and subsequently recognised by their characteristic appearance under the microscope. The separated substances should also be subjected to a chemical examination. Prussian blue is detected by heating with a solution of sodium hydroxide, filtering, acidulating the filtrate with acetic acid, and then adding ferric chloride, when, in its presence, a blue colour will be produced. Indigo is best recognised by the microscopic examination. It is not decolorised by caustic alkali, but it dissolves in sulphuric acid to a blue liquid. Soapstone, gypsum, sand, and metallic iron, are identified by means of the usual chemical reactions. A compound very aptly termed “Lie-tea,” is sometimes met with. It forms little pellets, consisting of tea-dust mixed with foreign leaves, sand, etc., and held together by means of gum or starch. This falls to powder if treated with boiling water. In the presence of catechu, the tea infusion usually assumes a muddy appearance upon standing. In case iron salts have been employed to deepen the colour of the infusion, they can be detected by treating the ground tea-leaves with acetic acid, and testing the filtered solution with potassium ferrocyanide. Tea should not turn black upon immersion in hydrosulphuric acid water, nor should it impart a blue colour to ammonia water. The infusion should be amber-coloured, and not become reddened by the addition of an acid.

The United States Tea Adulteration Act was passed by Congress in 1883. The enactment of this law was largely due to the exertions of prominent tea merchants, whose business interests were seriously affected by the sale (principally in trade auctions) of the debased or spurious article. It is stated in the official report of the United States Tea Examiner at New York City, that from March 1883 to December of the same year, 856,281 packages (about four millions of pounds) of tea were inspected, of which 7000 packages (325,000 pounds) were rejected as unfit for consumption. Since the enforcement in New York City of the Tea Adulteration Act, nearly 2000 samples of tea have been chemically tested under the direction of the author. The proportion grossly adulterated has been a little over nine per cent. But this does not apply to the total amount imported, since only those samples which were somewhat suspicious in appearance were submitted for analysis. As the result of the past two years’ experience in the chemical examination of tea, the prevailing adulterations were found to be of two kinds—the admixture of spent tea-leaves, and the application to the tea of a facing preparation. A natural green tea possesses a dull hue, and is but seldom met with in the trade; some Moyunes and uncoloured Japans (which latter, properly speaking, is not a green tea) being almost the only varieties not exhibiting the bright metallic lustre due to the facing process. The addition of foreign leaves was detected only in a few instances; the presence of sand and gravel occurred far more frequently. Apropos of the practical utility of Governmental sanitary legislation, it can be stated that, since the enforcement of the Adulteration Act, the tea imported into the city of New York has very perceptibly improved in quality.

Attempts in tea culture are being made in the United States of Columbia, S.A. A specimen of the prepared plant received by the writer, differed greatly in appearance from the Chinese and Japanese products. The leaves, which had not been rolled but were quite flat, possessed a light pea-green colour and a fine but rather faint aroma. An examination indicated that the tea, although very delicate in quality, was seriously deficient in body.

The analysis showed:—

The following Tea Assay, while not including the determinations of all the proximate constituents of the plant, will, it is believed, in most instances suffice to indicate to the analyst the presence of spent leaves, mineral colouring matters, and other inorganic adulterations.

Theine (Caffeine), C8H10N4O2.—Contrary to the once general belief, there does not always exist a direct relation between the quality of tea (at least so far as this is indicated by its market price) and the proportion of theine contained, although the physiological value of the plant is doubtless due to the presence of this alkaloid.

The commercial tea-taster is almost entirely guided in his judgment in regard to the value of a sample of tea by the age of the leaf, and by the flavour or bouquet produced upon “drawing,” and this latter quality is to be mainly ascribed to the volatile oil.

The following process will serve for the estimation of theine:—A weighed quantity of the tea is boiled with distilled water until the filtered infusion ceases to exhibit any colour. The filtrate is evaporated on a water bath to the consistence of a syrup; it is next mixed with calcined magnesia to alkaline reaction, and carefully evaporated to dryness.

The residue obtained is then finely powdered, digested for a day or so with ether (or chloroform) and filtered, the remaining undissolved matter being again digested with a fresh quantity of ether, so long as any further solution of theine takes place. The ether is now removed from the united filtrates by distillation, whereupon the theine will be obtained in a fairly pure condition.

Theine contains a very large proportion of nitrogen (almost 29 per cent.), and Wanklyn[6] has suggested the application of his ammonia process (see p. 205) to the analysis of tea. Genuine tea is stated to yield from 0·7 to 0·8 per cent. of total ammonia, when tested in this manner.

Volatile Oil.—Ten grammes of the tea are distilled with water; the distillate is filtered, saturated with calcium chloride, then well agitated with ether, and allowed to remain at rest for some time. The ethereal solution is subsequently drawn off, and spontaneously evaporated in a weighed capsule. The increase in weight gives approximately the amount of oil present. A sample of good black tea yielded by this method 0·87 per cent. of volatile oil.

Tannin.—Two grammes of the well-averaged sample are boiled with 100 c.c. of water, for about an hour, and the infusion filtered, the undissolved matter remaining upon the filter being thoroughly washed with hot water, and the washings added to the solution first obtained. If necessary, the liquid is next reduced to a volume of 100 c.c. by evaporation over a water-bath. It is then heated to boiling, and 25 c.c. of a solution of cupric acetate added. The copper solution is prepared by dissolving five grammes of the salt in 100 c.c. of water, and filtering. The precipitate formed is separated by filtration, well washed, dried, and ignited in a porcelain crucible. A little nitric acid is then added and the ignition repeated. One gramme of the cupric oxide thus obtained represents 1·305 grammes of tannin. For the estimation of spent leaves (especially in black tea), Mr. Allen suggests the following formula, in which E represents the percentage of spent tea, and T the percentage of tannin found:—

E = (10 - T) 100 8.

The Ash.—a. Total Ash.—Five grammes of the sample are placed in a platinum dish and ignited over a Bunsen burner until complete incineration is accomplished. The vessel is allowed to cool in a desiccator, and is then quickly weighed. In genuine tea the total ash should not be much below 5 per cent., nor much above 6 per cent., and it should not be magnetic. In faced teas the proportion of total ash is sometimes 10 per cent.; in “lie-tea” it may reach 30 per cent.; while in spent tea it frequently falls below 3 per cent., the ash in this case being abnormally rich in lime salts, and poor in potassium salts.

b. Ash insoluble in water.—The total ash obtained in a is washed into a beaker, and boiled with water for a considerable time. It is then brought upon a filter, washed, dried, ignited, and weighed. In unadulterated tea it rarely exceeds 3 per cent. of the sample taken.

c. Ash soluble in water.—This proportion is obtained by deducting the ash insoluble in water from the total ash. Genuine tea contains from 3 per cent. to 3·5 per cent. of soluble ash, or at least 50 per cent. of the total ash, whereas in exhausted tea the amount is often but 0·5 per cent. The following formula has been proposed for the calculation of the percentage of spent tea E, where S is the percentage of soluble ash obtained:—

E = (6 - 2S) 20.

A sample prepared by averaging several good grades of black tea, was mixed with an equal quantity of exhausted tea-leaves. The proportion of soluble ash in the mixture was found to be 1·8 per cent. According to the above formula, the spent tea present would be 48 per cent., or within 2 per cent. of the actual amount.

d. Ash insoluble in acid.—The ash insoluble in water is boiled with dilute hydrochloric acid, and the residue separated by filtration, washed, ignited, and weighed. In pure tea, the remaining ash ranges between 0·3 and 0·8 per cent.; in faced tea, or in tea adulterated by the addition of sand, etc., it may reach the proportion of 2 to 5 per cent. Fragments of silica and brickdust are occasionally found in the ash insoluble in acid.

The Extract.—Two grammes of the carefully sampled tea are boiled with water until all soluble matter is dissolved, more water being added from time to time to prevent the solution becoming too concentrated. The operation may also be conducted in a flask connected with an ascending Liebig’s condenser. In either case, the infusion obtained is poured upon a tared filter, and the remaining insoluble leaf repeatedly washed with hot water so long as the filtered liquor shows a colour. The filtrate is now diluted to a volume of 200 c.c., and of this 50 c.c. are taken and evaporated in a weighed dish until the weight of the extract remains constant. Genuine tea affords from 32 to 50 per cent. of extract, according to its age and quality; in spent tea the proportion of extract will naturally be greatly reduced. Mr. Allen employs the formula below for determining the percentage of spent tea E in a sample, R representing the percentage of extract found.

E = (32 - R) 100 30.

In order to test the practical value of this equation, a sample of black tea was mixed with 50 per cent. of spent tea-leaves, and a determination made of the extract afforded. The calculated proportion of spent tea was 44 per cent., instead of 50 per cent. It should be added, however, that the tea taken subsequently proved to be of a very superior quality, yielding an extract of 40 per cent.

Gum (Dextrine).—The proportion of gum contained in genuine tea is usually inconsiderable. Its separation is effected by treating the concentrated extract with alcohol, allowing the mixture to stand at rest for a few hours, and collecting the precipitated gum upon a tared filter, and carefully drying and weighing it. As a certain amount of mineral matter is generally present in the precipitate, this should afterwards be incinerated and a deduction made for the ash thus obtained. A more satisfactory method is to treat the separated dextrine with very dilute sulphuric acid, and estimate the amount of glucose formed by means of Fehling’s solution (see p. 37); 100 parts of glucose are equivalent to 90 parts of dextrine.

Insoluble Leaf.—The insoluble leaf as obtained in the determination of the extract, together with the weighed filter, is placed in an air-bath, and dried for at least eight hours at a temperature of 100°,[7] and then weighed. In genuine tea the amount of insoluble leaf ranges from 47 to 54 per cent.; in exhausted tea it may reach a proportion of 75 per cent. or more. It should be noted that in the foregoing estimations the tea is taken in its ordinary air-dried condition. If it be desired to reduce the results obtained to a dry basis, an allowance for the moisture present in the sample (an average of 6 to 8 per cent.), or a direct determination of the same must be made.

The following tabulation gives the constituents of genuine tea, so far as the ash, extract, and insoluble leaf are involved:—

Total ash ranges between 4·7 and 6·2 per cent.

Ash soluble in water ranges between 3 and 3·5 per cent.; should equal 50 per cent. of total ash.

Ash insoluble in water, not over 3 per cent.

Ash insoluble in acid ranges between 0·3 and 0·8 per cent.

Extract[8] ranges between 32 and 50 per cent.

Insoluble leaf ranges between 43 and 58 per cent.

The table below may prove useful as indicating the requirements to be exacted when the chemist is asked to give an opinion concerning the presence of facing admixtures, or of exhausted or foreign leaves in a sample of tea.

Total ash should not be under 4·5 per cent. or above 7 per cent.

Ash soluble in water should not be under 40 per cent. of total ash.

Ash insoluble in water should not be over 3·25 per cent.

Ash insoluble in acid should not be over 1 per cent.

Extract (excepting in poor varieties of Congou tea) should not be under 30 per cent.

Insoluble Leaf should not be over 60 per cent.

The British Society of Public Analysts adopt:—

Total ash (dry basis), not over 8 per cent. (at least 3 per cent. should be soluble in water).

Extract (tea as sold), not under 30 per cent.

Below are the proportions of total ash, ash soluble in water, and extract found in 850 samples of tea (mostly inferior and faced), examined under the direction of the author in the U.S. Laboratory:—

Total Ash.

Ash Soluble in Water.

Extract.

The following tabulation exhibits the results obtained by the examination of various grades of Formosa, Congou, Young Hyson, Gunpowder, and Japan tea, made, under the supervision of the writer, by Dr. J. F. Davis.

It will be noticed, if the same varieties of tea be compared, that, with some exceptions, their commercial value is directly proportional to the percentages of soluble ash, extract, tannin, and theine contained.

The following analyses of several kinds of spurious tea, received from the U.S. Consuls at Canton and Nagasaki (Japan), have been made by the author:—

1. Partially exhausted and refired tea-leaves, known as “Ching Suey” (clear water), which name doubtless has reference to the weakness of a beverage prepared from this article.

2. “Lie tea,” made from Wampan leaves.

3. A mixture of 10 per cent. green tea and 90 per cent. “lie tea.” It is sometimes sold as “Imperial” or “Gunpowder” tea, and is stated to be extensively consumed in France and Spain.

4. “Scented caper tea,” consisting of tea-dust made up into little shot-like pellets by means of “Congou paste” (i. e. boiled rice), and said to be chiefly used in the English coal-mining districts.

The following are the results of the analysis by American chemists of samples representing 2414 packages of Indian tea.