ROASTING AND GLAZING. 187 



on the other hand, when completely exhausted by means 

 of boiling water yields readily upwards of 40 per cent. 

 of soluble matter, proving that in actually using coffee 

 as a beverage, we are not in the habit of making any- 

 thing like a complete extraction, as only some 10 to 12 

 per cent, of the active principles of the coffee passes into 

 the liquid. 



The modern appliances for the roasting of coffee are 

 numerous and labor-saving to a great extent, many of 

 them are, however, calculated only to enhance the ap- 

 pearance of the bean, while others enable the roaster to 

 obtain almost to perfection the full development of the 

 aromatic properties of the coffee. Coffee is roasted for 

 commercial purposes and domestic use in a large sheet- 

 steel or malleable-iron cylinder mounted on a hollow 

 axle, so as to revolve over a brisk fire and allow the gases 

 generated during the torrefaction to escape. The surface 

 of the cylinder is perforated with a number of small holes 

 for the purpose of allowing the vapor arising from the 

 coffee in the process of roasting to pass off readily, and 

 through the interior runs laterally four ridges, the object 

 of which is to toss it about in all directions, causing it 

 to pass from end to end, and diffuse a uniform heat to 

 every part of the coffee in order to make the "roast" 

 even and regular in appearance. This cylinder is again 

 encased in a frame brick-work at the bottom of which is 

 built a coal fire well distributed so as to heat all portions 

 of the cylinder at the same time during the operation. 

 On the outer head it has a small opening through which 

 the operator occasionally inserts a " tryer " to enable 

 him to note the progress made as the process advances, 

 the cylinder being also so arranged that it can be drawn 

 from over the fire when it is required to either fill or 

 empty it through a slide or hopper in the centre. It is 



