Theine is the most important constituent of tea and coffee. It is a stimulant, but unlike alcohol, acts even more upon the central nervous system than upon the heart. It removes the sense of fatigue, and may, especially if taken in excessive doses, produce sleeplessness. Its stimulant action on the heart is followed by increased flow of urine, and it thus helps in the removal of waste products from the system. The effect on the tissue-changes of the body is somewhat doubtful. It has been stated to arrest or diminish the waste, i.e., the metabolism, constantly going on in the system, and so diminish the amount of food required to repair this waste. This is highly improbable; we cannot conceive the likelihood of the development of energy without a corresponding expenditure of material, and that is what would be the case if theine increased the activity of various organs while retarding their waste. The experiments of Conty and Guimarès on the action of coffee show that this (and tea has the same essential constituent) does not diminish tissue waste. It does not prolong life in starvation, though it may lessen the feeling of hunger. Hence tea and coffee, which owe their value mainly to the caffeine or theine contained in them, are in no sense foods.
(3) The amount of Tannin varies from 12·31 in Ceylon tea (broken leaf, Pekoe) to 11·76 in Moning, black leaf, and 9·9 per cent. in Natal Pekoe Souchong (Allen). The difference in tannin between Chinese and Indian teas is not therefore so great as is usually supposed. Tannin is a powerful astringent, and possesses a bitter styptic taste, and a constipating effect on the bowels. Its amount is increased by long “brewing,” as is shown by the following results (Hale White):—
| Three Minutes’ Infusion. | Fifteen Minutes’ Infusion. | |
| Finest Assam | 11·30 per cent. | 17·73 per cent. |
| Finest China | 7·77 per cent. | 7·97 per cent. |
| Common Congou | 9·37 per cent. | 11·15per cent. |
The Mode of Preparation of Tea is important. It is clear that the percentage of tannin to weight of leaf used in making the infusion increases with the protraction of the infusion. On the other hand caffeine is so soluble that it is nearly completely dissolved as soon as infusion has begun. Dittmann found that five minutes infusion of Indian tea extracted 3·63 and ten minutes infusion 3·73 per cent. of caffeine. The Chinese put the tea leaves in a cup, and having poured boiling water on them, drink the resulting infusion after a very short time, without adding anything. The Russians drink the infusion with a squeeze of lemon, and with or without sugar. We add cream or milk and generally sugar, and so render it more nutritious, though the delicate flavour is veiled. The Chinese plan of infusion for a short time is the best, as it ensures the extraction of the aromatic and stimulant principles of the tea with only a proportion of the tannin.
In making tea it is important to use a tea-pot which is quite dry, in order to avoid mustiness; to pour a small quantity of boiling water into the tea-pot and then out again, so that the infusion may be made at the temperature of boiling water; and to use water which has only freshly come to the boil, and so has not been rendered flat, and not to infuse longer than five minutes. For persons of weak digestion, the best kind of tea is that obtained by pouring boiling water on the leaves, and then immediately pouring the resulting infusion into another hot tea-pot. In all cases where tea has to be kept a considerable time, it should be poured into a second tea-pot, the leaves being left behind.
Indigestion is not an uncommon consequence of tea-drinking; caused by the excess of tannin in the tea, by the other constituents of the tea, or more commonly by the practice of drinking tea in small sips, with bread and butter. The tea infusion usurps the place of the saliva, the secretion of saliva remaining partially in abeyance. The presence of tannin in tea renders it an undesirable part of a substantial meal. Tannin coagulates albumin, and retards its solution by the digestive juices. Hence “high teas” and “tea-dinners,” unless the tea is very weak, are objectionable. The practice of drinking tea with every meal is inexcusable.
For quenching thirst during active exercise, and rendering possible prolonged exertions, tea is unsurpassed.
COFFEE.
Coffee is the seed of the berry of the Caffea Arabica. Each berry contains two seeds, or beans as they are sometimes incorrectly called. The coffee is prepared by roasting the seeds until they assume a reddish-brown colour, in which process they lose 15 per cent. in weight and gain 30 per cent. in bulk. During the process of roasting, a volatile oil having a powerful aromatic smell is developed. This is not produced in such large quantities from fresh seeds; the best time for roasting varying, however, for different varieties of coffee.
The amount of Volatile Oil in coffee is much less than in tea. As it is elicited during the process of roasting, this should be done with nicety and care. It is effected in an iron cylinder made to revolve over a fire. After the roasting, the sooner the seeds are ground the better the coffee. When it cannot be immediately used, it should be kept in closed canisters, and not in paper or open jars.