25© CHEMICAL CONSTITUENTS. 



sometimes even to zero, after being roasted, and from 

 which, it would appear, that the description of sugar 

 contained in the raw coffee is destroyed by the roasting 

 process to which it is subjected previous to using. 



COMPARATIVE ANALYSIS OP RAW AND ROASTED 



COFFEES. 



Constituents. Raw. Roasted. 



Ash, 3.97 5.17 



Fat, 11.42 8.30 



Water, 8.26 0.36 



Sugar, 8.18 1.84 



Gluten, 10.68 12.03 



Caffeine, i.io 1.06 



Cellulose, 42.36 4496 



Extractive matter, . 14.03 26.28 



Total parts, 100 100 



In the operation of roasting, the saccharine matter is 

 converted into caramel, and a portion of the caffeine is 

 liberated from its combination with the caffeic acid, the 

 latter still retaining its astringent properties and develop- 

 ing into a bitter, soluble principle. A change in the fat of 

 coffee is also undergone in the roasting, as ether will 

 extract only from 4 to 5 per cent, of fat from the raw 

 bean, while it readily extracts double that quantity from 

 the roasted bean. So striking is this fact that Von Bibra 

 goes so far as to claim that the roasting process produces 

 fat, but most probably the process is only mechanical 

 and not chemical in its action in bursting the " fat cells," 

 and thereby rendering the fat accessible to the solvent 

 action of the ether. Roasted coffee is also tolerably rich 

 in nitrogen, containing from 2.5 to 3 per cent., but is 

 found to be quite devoid of starch. The operation of 

 roasting, in addition, tends to make coffee soluble in 

 boiling water, as, when raw coffee is perfectly exhausted 



