Page:Popular Science Monthly Volume 20.djvu/379

Rh only slight fragrance. The African cola-nut is strongly aromatic as taken from the tree, and this seems to be the only one of the six chosen foods furnishing theine or theobromine that is not subjected to dry heat in its preparation.

Tracing, so far in our study, the common constituent of coffee and tea, in its occurrence in various vegetable products which have been appropriated, after similar methods of treatment, to the uses of adjunct food, it is full time to inquire what else is to be found in the tea-leaf, the coffee-berry, and the chocolate-nib, besides a certain stimulant, alkaloid. With entire justice to the remaining components they may be here classified in three groups—nutritious substances, astringents, and aromatics.

Tea yields from thirty to fifty per cent of its substance to solution by prolonged boiling in water; but, as the beverage is properly prepared, probably not over twenty to twenty-five per cent of the solids are dissolved. This soluble portion includes dextrine, glucose, gum, and potassium salts, besides tannin and the alkaloid. The nutrient portion of tea is comparatively small. In coffee we have ten to thirteen per cent of fixed oil, and about the same proportion of legumine, with gums and extractive matters, and two per cent of soluble potassium salts. The roasting reduces the glucose from six or seven to one or two per cent, liberates the oily matter, and so modifies the legumine as to render it measurably soluble. The beverage seldom contains over ten or twelve per cent of the roasted berry in absolute solution, so as to be retained in the liquid when perfectly clear, but some of the finer powder is likely to remain in suspension, and the oil is held with the liquid, while hot, to a still greater extent. In quantity, the food constituents of roasted coffee are generous enough, but in digestibility it is more than probable that they are deficient. As to the cacao-seed, its oil, constituting half its weight, is a substance well known in its separated state as cacao-butter, and is an agreeable and very wholesome form of oleaginous food. In quantity it ought not to be unduly diminished, either by removal with the press or by addition of farina, and it should constitute as much as twenty-five per cent of all of the cacao preparations. Besides the oil, a good portion of starch and about eighteen per cent of albuminoids are found in cacao-seeds, and all these are to a large extent obtained in chocolate beverages. The butter of these creamy liquids is less likely to cause disturbance of digestion than the roasted albuminoids they contain.

The astringents of tea and coffee are tannins, properly classified along with the numerous varieties of tannic acid, the astringent principles of plants. In tea the proportion is large, ranging, according to the lowest statements, from nine to twelve per cent, and placed by some authorities as high as thirty and forty per cent. Dragendorff reports green teas to bear a higher percentage of tannic acid than black, and this difference may be due to a decomposition of tannin