Tczew

Tea Manufacture.

In the making of a good quality tea much depends upon the character of the plant and the circum stances of its growth and cultivation, but satisfactory methods of manufacture in dealing with the plucked leaf are also essential. Formerly, the processes were carried out by hand methods, but in the most modem practice machinery is employed in practically every operation. In the manufacture of tea the most important feature is the regulation of the fermentation (oxidation) process.

This fermentation is the cardinal feature in the making of black teas (which form by far the greater part of the teas entering com merce), but in preparing green teas the fermentation is prevented.

BLACK

TEA.—The following are the stages in the manufacture of black tea: (I) Withering. The plucked leaf is brought at once into the shady withering house and spread thinly in sterilised shallow trays made of hessian, bamboo or wire netting and arranged on racks; or, the leaf is commonly spread on clean withering floors. Withering is complete when the leaf has become soft and flaccid. The process usually occupies from 18 to 20 hours but must obviously depend upon varying conditions of temperature and moisture of the air. On this account special machines for withering the leaf under conditions which may be readily con trolled are now being widely used. The immediate object of withering is to obtain the leaf in a physical condition suitable for the subsequent rolling, but during the process the oxidising en zyme (ferment) present in the leaf, which brings about the im portant changes in the later fermentation process, greatly in creases in quantity, while other chemical changes also take place.

(2) Rolling. The withered leaf is fed into the "jackets" of rolling machines which operate by rubbing the leaf, under ad justable pressure, between two metal surfaces. The time occupied in the rolling varies from 15 to 6o minutes after which the rolled leaf is sifted and the older leaves treated again ; irregular balls of leaf are broken up by revolving beaters fitted to the sieves. Rolling imparts to the tea its characteristic "twist," but the operation is essentially subservient to the fermentation process which is an oxidation of the cell-contents of the leaf. The rolling ruptures the leaf-cells and the juice (sap) is pressed out on to the surface of the tissue where, under the influence of the oxidising enzyme (oxidase) present, its constituents combine with the oxygen of the air. This is the commencement of the fermentation.

(3) Fermentation. This process is designed to encourage the chemical action initiated during the rolling. The leaf removed from the rolling machines is transferred to the darkened ferment ing rooms where it is spread out in layers 1 or 2 inches thick to give full access to the air which is freely admitted. In large factories special fermenting floors made of cement, tiles or plate glass squares, which can be readily sterilised when necessary, are used. The atmosphere of the room is kept moist usually by sus pending wet cloths or by mechanical water sprays. During fer

mentation the leaf colour changes to a bright copper shade. The colourless "tannin" present becomes partly oxidised into reddish brown products, giving "body" and colour to the tea liquor., while the characteristic odour and flavour of tea are also devel oped. The oxidation, however, must not be allowed to proceed too far or the quality of the tea is affected as a result of an excess production of insoluble brown substances. Investigations have shown that a number of micro-organisms (chiefly yeasts and bac teria) are always present in fermenting tea leaf. The organisms are present on the fresh leaf and increase during the withering and fermentation. Improvement in the flavour and aroma of the tea appears to be associated with increased numbers of yeast cells. It is possible to improve the qualities of the tea by the use of cultures of "pure" selected yeasts.

(4) Firing or Drying. The action of the oxidising enzyme is arrested at the desired moment by means of heat. The ferment ing leaf is transformed to machines ("tea driers") where it passes automatically over a series of moving "tables" in the drying chamber through which hot air is passed. The firing is com pleted in about half an hour, though a second firing may be nec essary. The firing arrests fermentation by the destruction of the enzyme and also dries the tea.

(5) Grading. The fired tea is subsequently sifted into grades which in the main correspond to the size of the leaf. The four chief grades of black tea, arranged in descending order of quality are Orange Pekoe, Pekoe, Pekoe Souchong and Souchong, the first-named being the youngest leaf.

The graded tea is stored in air-tight receptacles until it is required for packing. Previous to the latter it is again dried by machinery (the final firing) and is then ready for packing in the familiar lead-lined chests which are now usually made of three-ply wood.

GREEN

TEA.—In making green tea the primary object is to prevent the occurrence of the chemical changes which take place in the withering and fermenting processes of black tea manu facture. The plucked leaf is therefore subjected to heat as the first process in the manufacture, with a view to the destruction of the oxidising enzyme in the leaf tissue. In China the method is by heating in cast-iron pans, but in India and Ceylon, where green tea is also made on a small scale, the plucked leaf is placed in a cylindrical steam heater for one or two minutes. Subse quently the moisture is removed in a centrifugal machine and the leaf subjected to a short and light rolling. The green tea is then fired (dried), graded and packed as in the case of black tea. The total tannin in green tea is higher than that in black tea made from similar leaf. This results from the fact that, during the fermentation of black tea, a proportion of tannin is converted (oxidised) into red and brown substances which are not extracted by hot water. (S. E. C.)