THE CHEMISTRY OF COFFEE AND TEA. 365 



ing 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, alka- 

 loid. 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 pre- 

 pared, 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 por- 

 tion 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 whole- 

 some 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 di- 

 gestion 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 prin- 

 ciples 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. Dragendorlf 

 reports green teas to bear a higher percentage of tannic acid than 

 black, and this difference may be due to a decomposition of tannin 



