Beverages may be classed into the following two groups: -

1. Those whose stimulant qualities depend on an alkaloid, e.g., tea, coffee, cocoa, kola, coca. 2. Those whose stimulant qualities depend on alcohol, e.g., spirits, wine, beer.

These will be in turn considered.

Tea is a preparation made from the leaves of the young shoots of an evergreen plant, "Thea." It is grown chiefly in China, India, and Ceylon. There are two varieties, black and green tea. In the former the leaves are allowed partly to decompose, and the black colour is due to their incipient decay due to fermentation. As in the process of fermentation the tannic acid becomes less soluble, black tea contains much less tannic acid than green tea, with the result that black tea has now the market practically to itself. The chief ingredients of tea are caffeine, tannin, and traces of volatile oils. The average composition of tea may be given as follows: -

Extractives and gummy substances are present in small amount. As a general rule, we may say that China teas have a delicate flavour, with little astringency; Indian teas have more body and astringency; Ceylon teas are also rich in caffeine, but not so strong as Indian teas. Most ordinary teas are blends.

Composition Of An Infusion

As caffeine is very soluble, all the caffeine present is dissolved at once on the addition of hot water. Tannin is much less soluble, the result being that prolonged boiling increases the amount of tannin present in the solution. This is specially true of all the cheaper teas. In some high-class China teas, costing 5s. per lb., the proportion of tannin extracted may not be appreciably greater after ten or fifteen minutes' infusion. On an average, it may be said that a teacupful of tea, after a few minutes' infusion, contains about 1 gr. of caffeine to rather more than 2 grs. of tannic acid. Tea should be prepared with water that has just come to the boil, and is best after from three to five minutes' infusion. If extracted too long, it contains more tannin, and a greater proportion of bitter principles. It is important that the water used should not be too hard or too soft. Excessive hardness may be neutralised by adding a pinch of soda to the teapot. A very soft water extracts more fully the bitter principle from the leaves.

Tea is not a food, but a pleasant beverage which has a stimulating effect on the nervous system. If made with boiling milk it possesses nutritive properties. When taken to excess it deranges the digestive, the cardio-vascular, and the central nervous systems. Various symptoms of indigestion, excitability, sleeplessness, anemia, constipation, and rapid, feeble pulse are the chief symptoms induced by excessive indulgence.