The chief difference between the black and green tea lies in this fermentation process. By this means, some of the tannic acid in the leaves is changed so that it becomes less soluble. The black tea is thus less astringent than the green. Common varieties of green tea are hyson, corresponding to the pekoe or souchong, and gunpowder, corresponding to congou.
Aside from the varieties given by the stage of growth at which the leaf is plucked and by the method of preparation, teas are named from the different countries or the special district that produces them, or even from the gardens where they are grown.
Japan, Chinese, Indian and Ceylon teas each have their own marked characteristics, while the different districts of China give various kinds, as the oolongs from Formosa or the monings from north China.
The quality is dependent on the cultivation of the plant, the age of the leaf, and the care in manufacture. Some of the finest tea of China is so high priced that it can be purchased there only by the very rich, while the lowest grades are often made into bricks (brick tea) and sent into the interior. The choicest Japan tea is raised under protection from direct sunlight and is prepared without rolling. It is said to be untouched with the hand after it is put upon the steaming apparatus. Most of the teas sent to the United States might be classed as low middling, with some superior grades. The choice varieties are rarely received.
The most important constituents of tea are theine, or caffeine, tannic acid and the volatile oil that gives the flavor. Black and green tea contain practically the same amount of oil and caffeine, but black tea has only about half as much tannic acid as green.
The method of making tea has an important influence on the constituents of the beverage. Methods vary all the way from one Japanese fashion of stirring the finely ground tea into warm water and drinking the whole infusion, to the Russian method of bringing the water just to a boil and making a delicate infusion.
The boiling of tea and the practice of keeping the teapot on the stove all day that the brew may be ready at any moment, each results in extracting the largest possible amount of tannic acid from the tea. If tea must stand after making, it should be poured off the leaves immediately. The difference in extract can be easily seen if equal amounts of tea be in one case boiled four or five minutes, in another allowed to stand in cold water, and in a third infused in hot water for the same length of time. If these three results be put into glasses, the depth of color will indicate the difference in material extracted. If a solution of ordinary copperas be made, and a few drops of this added to each, a black, inky substance, a tannate of iron, will form, the amount varying with the tannic acid extracted.
Adulterations of tea are much less common than formerly. The chief fraud practiced is that of substituting an inferior grade for a better. One method of doing this is by facing the tea. This is practiced especially on green teas, giving them a brighter color.
Occasionally spent or exhausted leaves are mixed with fresh ones, thus constituting an adulteration.
Tea tablets are sometimes prepared for the use of travelers by pressing finely ground tea of varying quality into tablets to be dissolved in hot water.