VI. 



E undergoes essential chemical changes in 

 the process of roasting. In the raw or natural 

 state the coffee-bean is tough and horny in struc- 

 ture and entirely devoid of the appearance, character 

 and peculiar aroma that so distinguishes it in the 

 roasted condition, and by which it is best known to 

 the public. The testa or investing membrane of the 

 raw bean has a layer of long cells with a peculiar pitted 

 structure, containing a crystaline substance chemically 

 termed Caffeine, and another known as Caffeic, or tannic 

 acid, while the inner substance consists of an assem- 

 blage of vesicles of an angular form, the cavities of 

 which include in the form of little drops a considerable 

 quantity of a highly aromatic oil technically termed 

 Caffeone, on the presence and amount of which the 

 fragrance and active principles of the coffee depends, 

 and by which its commercial value in the roasted state is 

 estimated. The existence of this " coffee oil " makes itself 

 known in a striking manner by roasting; being driven out 

 of the beans by the intense heat, it is partially volatilized 

 and, togetherwith other products of the roasting, produces 

 the characteristic aroma peculiar to roasted coffee, 

 an odor possessed by no other known substance. 

 In the operation of roasting the beans swell up and 

 open at the furrow by the liberation of the gases within 



