Page:Popular Science Monthly Volume 20.djvu/380

366 during the fermentation in the manufacture of black teas. But it is important to know that only a small part of this tannin is extracted from the leaf in the suitable preparation of the beverage. Some experiments with tea as it is prepared for the table gave, for a five fluid-ounce cup of the liquid, in ten instances an average content of a trifle over one grain of tannin. Other experiments with tea after five minutes' steeping gave in twelve instances an average of tannin equal to only per cent of the dry leaf; while the same teas, on thirty minutes' gentle steeping, yielded tannin amounting to an average of 2 per cent of the dry leaf. In another case, by thirty minutes' active boiling, so much tannin as 11 per cent of the tea-leaf was obtained in solution. Black teas are necessarily steeped longer than green, as they yield all their soluble matters more slowly. In coffee the proportion of tannin is not over one third, perhaps on an average not over one fourth or one fifth, of that in tea. The cacao-nib and its preparations are free from tannin. Guarana is heavily charged with a specific variety of tannic acid, and the mate is even more astringent than the tea-leaf.

The fragrant principle of tea, the essential oil, already referred to, has not been separated in notable quantities, but it is recognized as a diffusible stimulant, transient and harmless in its effect on the system, and certainly attracting no little favor to the tea-cup. The diffusible flavorous substance of coffee is a product of its roasting, and the same is true of the proper fragrance of cacao, to which other odors are often added. These vaporous bodies are so easily dissipated by a prolonged steeping, and especially by an active boiling, that brief infusions of tea and of coffee are likely always to be preferred.

In the quantity of the alkaloid, theine or caffeine, the tea-leaf is over twice as rich as the coffee-berry. The medium proportion is that of 2 to 2 per cent in tea, a little under 1 per cent in coffee, and about 1 per cent (theobromine) in the cacao-nib while the guarana preparation has 5 per cent, and the mate H per cent. Attfield found 2 per cent of alkaloid in the cola-nut. From a pound of tea, then, there can be obtained at least 140 grains, or over a quarter of an ounce, of the crystallized alkaloid, about enough to balance a silver quarter-dollar and a dime. The theine in a pound of tea is twenty-five or thirty times as much as could be taken at once without notable disturbance of the nervous system. A pound of coffee contains twelve or fifteen times as much theine as one ought to take at once.

The greater portion of the alkaloid enters into solution in making the common hot infusions of coffee and tea. Tea yields its alkaloid to hot water upon even brief application; coffee, especially when but lightly roasted, requires longer steeping for the extraction of the theine. It may be said, then, of long steeping of coffee and tea, that it is not required in obtaining the chief portion of the stimulant principle; that it only serves in the case of coffee to increase somewhat