134 MISC. PUBLICATION 5 40, U. S. DEPT. OF AGRICULTURE 



These machines use a worm screw to force the fruit paste through a 

 tapered nozzle. Determination of a suitable taper for a particular 

 product requires some experimentation. The bars are wrapped after 

 cutting. If they are to be pasteurized, a suitable wrapping consists 

 of a layer of greaseproof paper for use in handling, a cellophane bag 

 that is heat-sealed after insertion of the bar, and a light chipboard 

 box. A typical pasteurized fruit bar packaged in this manner has 

 a density of 80 pounds per cubic foot. 



The maximum attainable density of dried fruits and vegetables can 

 be estimated from (1) existing analytical data on their pulps and (2) 

 data on the densities of their constituents. For dried peaches the esti- 

 mated attainable density is about 75 pounds per cubic foot at 20 per- 

 cent moisture content, or 85 pounds if free from moisture. 



Presses and Processes 



Hydraulic presses have been used in Germany for the compression 

 of mixed vegetables, herbs, carrots, cabbage, and dried sauerkraut. 

 Continuous tile presses are reported to be in use, in which pressure 

 is imparted by two cams acting at different stations in the machine. 

 Knuckle-joint presses are used in the United States to compress hops, 

 and screw presses are in use for compressing dehydrated-egg powder. 

 Some free-flowing powdered soups have been smoothly handled in in- 

 dustrial tableting machines on an experimental basis. The latter are 

 not well suited for use in forming blocks of dehydrated vegetables 

 because: (1) The vegetables are not free-flowing, and therefore auto- 

 matic and uniform charging of the molds cannot be accomplished in 

 typical machines ; and (2) such tableting machines ordinarily operate 

 at compression ratios of 2 to 1, or less. The compression ratio is the 

 ratio of the volumes of the filled mold before and after compression. 

 It can be computed by dividing the density after compression by that 

 before compression. Column 7 in the table shows such ratios. Press 

 makers must know the compression ratio in order to determine the 

 length of stroke of the ram (fig. 65). 



The capacity of a press is usually stated in terms of the total safe 

 working pressure between the platens. Molds may have one cavity 

 or multiple cavities. Dried fruits and vegetables have been formed 

 into blocks 6x3x1 inches in size. Blocks 2% inches thick have been 

 formed and a brick approximately 6y 2 x 4y 2 x 2V4 inches with 1 edge 

 rounded has been proposed, since it lends itself well to packing in 

 standard 5-gallon cans at the rate of 16 blocks per can. Such a block 

 weighs 2 pounds and can be reconstituted into 50 servings of carrots 

 (fig. 66). Military recipes are in terms of 100 servings (43) for 

 companies, and probably the most suitable blocks should contain 

 weights corresponding to this number of servings. Blocks can also 

 be formed with indented scorings like those on milk-chocolate slabs 

 to facilitate breaking the blocks into smaller units of known weight. 



To reduce friction, the surfaces of molds must be very smooth, a 

 condition which can be produced by a surface grinder. It is fre- 

 quently the practice to follow this by nickel or chromium plating 

 and polishing. The surface of new dies must be lubricated with salt- 

 free, moisture-free, edible oils or fats such as commercial hardened 

 shortenings or special edible lubricants. Continuous use of lubricants 

 may be required to reduce the friction as the fruit or vegetable moves 



