882 COFFEE 



Chenovix affirmed that by the roasting of coffee a certain quantity of tannin pos- 

 sessing the property of precipitating gelatine is generated. Cadet made the same 

 observation, and found moreover, that the tannin "was most abundant in the lightly 

 roasted coffee, and that there -was nearly none of it in coffee highly roasted. Passi 

 and Sehrader, on the contrary, state that solution of gelatine does not precipitate 

 either the decoction of roasted coffee or the alcoholic extract of this coffee. Kunge 

 likewise asserts that he could obtain no precipitate with gelatine ; but he says that 

 albumen precipitates from the decoction of roasted coffee the same kind of tannin as 

 is precipitated from raw coffee by the acetate of lead, and set free from the lead by 

 sulphuretted hydrogen. With these results Dr. Uro's experiments agreed. Gelatine 

 certainly does not disturb clear infusion of roasted coffee, but the salts of iron 

 blacken it. 



Schrader endeavoured to roast separately the different principles of coffee, but none 

 of them exhaled the aromatic odour of roasted coffee, except the horny fibrous matter. 

 He therefore concluded that this substance contributes mainly to the characteristic 

 taste of roasted coffee, which cannot be imitated by any other vegetable matter, and 

 which, as we have seen, should be ascribed chiefly to the altered caffeic acid. Accord- 

 ing to Garot, we may extract the caffeine without alteration from roasted coffee by 

 precipitating its decoction by subacetate of lead, treating the washed precipitate with 

 sulphuretted hydrogen, and evaporating the liquid product to dryness. 



To roast coffee rightly we should keep in view the proper objects of this process, 

 which are to develop its aroma, and destroy its toughness, so that it may be readily 

 ground to powder. Too much heat destroys those principles which we should wish to 

 preserve, and substitutes new ones which have nothing in common with the first, but 

 add a disagreeable empyreumatic taste and smell. If, on the other hand, the rawness 

 or greenness is not removed by an adequate heat, it masks the flavour of the bean, and 

 injures the beverage made with it. When well roasted in the sheet-iron cylinder set 

 to revolve over a fire, it should have a uniform chocolate colour, a point readily hit by 

 experienced roasters, who now manage the business for the principal coffee dealers 

 both of London and Paris. The development of the proper aroma is a criterion by 

 which coffee roasters frequently regulate their operations. When it loses more than 

 20 per cent, of its weight, coffee is sure to be injured. It should never be ground 

 till immediately before infusion, since the fine essential oil rapidly escapes from the 

 finely-divided coffee. 



Liebig's views of the process of nutrition have given fresh interest to every analysis 

 of articles of food. A watery infusion of coffee is used in almost every country as a 

 beverage, and yet it is uncertain whether it is an article of nutrition or merely a con- 

 diment. A minute examination of the raw seed, or coffee bean as it is called, must 

 precede the determination of that disputed point. Caffeine is the principle best known, 

 being most easily separated from the other substances, resisting most powerfully 

 chemical reagents, and by assuming a crystalline state is discoverable in very small 

 quantities. 



Boasted coffee affords a much richer infusion to hot watei- containing a minute 

 quantity of carbonate of soda, and improves the quality of the coffee on the stomach, 

 by neutralising the caffeic acids. 



Coffee, as sold in the shops in its roasted and ground state, is often adulterated with 

 a variety of substances, but chiefly with chicory. See CHICOET. 



If tannin exists in roasted coffee, as maintained long ago by Chenevix, and generally 

 admitted since, it must be very different from the tannin present in tea, catechu, kino, 

 oak-bark, willow-bark, and other astringent vegetables ; for it is not, like' them, pre- 

 cipitated by either gelatine, albumen, or sulphate of quinine. With regard to the 

 action upon the animal economy of coffee, tea, and cocoa, which contain one common 

 chemical principle called caffeine or theine, Liebig advanced some ingenious views, 

 and, in particular, endeavoured to show that, to persons of sedentary habits in the 

 present refined state of society they afford eminently useful beverages, which 

 contribute to the formation of the characteristic principle of bile. This impor- 

 tant secreted fluid, deemed by Liebig to bo subservient to the function of respiration, 

 requires for its formation much azotised matter, and that in a state of combination 

 analogous to what exists in caffeine. The quantity of this principle in tea and coffee 

 being only from 2 to 6 per cent., might lead one to suppose that it could have little 

 effect upon the system even of regular drinkers of these infusions ; but if the bile con- 

 tains only one-tenth of solid matter, called choleic acid, which contains less than 4 

 per cent, of azote, then it may be shown that 3 grains of caffeine would impart to 500 

 grains of bile the azoto which occurs in that crystalline precipitate of bile called 

 taurine, which is thrown down from it by mineral acids. 



One atom of caffeine, 9 atoms of oxygen, and 9 of water, being added together, 

 produce the composition of 2 atoms of taurine. Now this is a very simple combi- 



