All About Coffee by William H. Ukers (interesting novels in english TXT) π
- Author: William H. Ukers
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Cooling and Stoning
"Coffee which leaves the roaster beautifully uniform in appearance", says A.L. Burns, "may lose all uniformity by delayed or inadequate cooling. Separated beans of coffee will cool off by themselves; but when heaped together, the inner part of the mass will get hotter and even take fire.... Coffee must be spread over a considerable surface, or all kept moving, and have at the same time a lot of air forced through it. Otherwise, there will be some darkening and over-development of part of the coffee, and a loss of the uniformity which is the first requirement of good roasting."
The cooling apparatus consists of a movable, box-like metal car which can be brought up to the front of the roaster to the revolving cylinders. The car has a perforated false bottom, to which is attached a powerful exhaust-fan system that sucks the heat out of the coffee. In large plants, utilizing two or more floors, the tilting-type cooling car is favored. This car permits instant discharge through an opening in the floor into a receiving tank suspended from the ceiling below and connected with the stoning apparatus. Recently, a flexible-arm cooler has been invented that provides full fan suction to a cooler car at all points in its track travel from the roaster to the emptying position.
The roasted coffee is being turned into the cooling car, equipped with a swinging "flexarm" that keeps it always in connection with a suspended header pipe; the cooling being started as soon as the coffee leaves the roaster. The cooled coffee, by tipping the box, goes into a floor hopper
The stoner, an essential part of the modern roasting plant, has for its function the removal of stones and other foreign matter of which the green-coffee operations have failed to get rid. The stoner is usually built in direct combination with the cooling equipment, and does its work by means of a gravity separation in an upward-moving column of air. The coffee passes into the suction boot of the stoner, either directly from the cooler box or from a floor hopper into which the cooler dumps, and is carried up the stoner pipe, or "riser", by an air current of ample power which can be accurately regulated. This insures the carrying up of coffee only, the stones remaining at the bottom of the machine and being dumped at intervals into a pan underneath. The coffee, passing up the riser pipe, is delivered into a large "stoner hopper" which is usually hung to the ceiling of the roasting room. The correct construction of this hopper is of great importance, as the coffee must be deposited completely without breakage, and the air must pass on through the suction fan carrying nothing except bits of loose chaff.
A different type of cooler is in the form of an upright cylinder, consisting of two metal perforated drums, one set within the other. The inner drum is sufficiently small to allow the coffee to move freely between the drums. Inside the smaller one is an exhaust pipe which draws the heat and chaff out of the coffee. This device is recommended for use only in connection with wet roasted coffee.
Still another type consists of a single perforated cylinder set horizontal with the floor, and revolving alongside of an exhaust box which sucks out the heat and chaff as the coffee is tumbled about in the cylinder. A rocking type, that is not generally employed, is constructed on the principle of the screen used by housebuilders to separate coarse sand from the fine, and is pivoted at the middle so that it can be rocked end to end.
Finishing or Glazing
Finishing whole-bean roasted coffee, by giving it a friction polish while it is still moist, using a glaze solution or water only, is a practise not harmful if the proper solutions are employed. Roasted coffee dulls in ordinary handling, and it is claimed that coating not only improves its appearance, but serves also to preserve the natural flavor and aroma of the bean. A machine having flat-sided wooden cylinders with ventilated heads, and operated two-thirds full of coffee so as to get an effective rolling motion, is generally employed. Coatings composed of sugar and eggs are
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