l86 ILOASTING AND GLAZING. 



their substance, their weight decreasing, but volume 

 increasing in proportion to the extent to which the opera- 

 tion is carried, developing the aromatic oil and liberating 

 at the same time a portion of the caffeine from its 

 combinaticii with the caffeic or tannic acid. The 

 amount of this aromatic oil contained in coffee varies 

 from 8 to 1 3 per cent, at least, one-half of which is lost 

 by evaporation during the roasting process, so that it 

 may prove a paying experiment to attempt to collect it, 

 especially in large establishments where large quantities 

 of coffee are roasted and several pounds of this valuable 

 oil are dissipated daily, which would no doubt find a 

 ready market at a good profit for the making of liqueurs, 

 or medicinal use. 



Before being roasted coffee also contains fron 6 to 8 

 per cent, of sugar, which after roasting is reduced to as 

 low as I per cent, and sometimes even to zero, from 

 which it would appear that the description of sugar (cane) 

 present in the raw coffee suffers destruction during roast- 

 ing, which, however, is not the case, as in the process of 

 roasting the saccharine matter in the raw bean is con- 

 verted into caramel. A change in the fat of the raw coffee 

 is also brought about by the roasting, for where ether 

 extracts only some four to five parts of fat from the raw 

 coffee beans, it readily extracts double that quantity from 

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

 has even credited the roasting process with the produc- 

 tion of fat, whereas the action is only mechanical in 

 bursting the fat-cells of the raw bean, thereby rendering 

 the fat accessible to the solvent action of the ether. 



The operation of roasting also tends to make coffee 

 soluble in boiling water, as when raw coffee is perfectly 

 exhausted by means of boiling water, it yields up only 25 

 per cent, which passes into solution, while roasted coffee, 



