132 MISC. PUBLICATION 54 0, IT. S. DEPT. OF AGRICULTURE 



15 percent above those permissible with vegetables, the high standard 

 of efficiency is not required. 



None of the membrane or laminated-membrane packages will pre- 

 vent the penetration of all insects, nor are they proof against the at- 

 tacks of rodents. But properly dehydrated vegetables are too dry 

 to support insect life. Eggs will live in the packages, however, and 

 will hatch if moisture becomes available. Dried fruits, on the other 

 hand, commonly contain sufficient moisture to maintain insect life 

 as well as microbial activity, and special sanitary precautions are re- 

 quired during packaging. 



Glaze Packaging for Compressed Dehydrated Foods 



Current investigations have shown that the packaging of compressed 

 dehydrated vegetables by the application of a glaze of moistureproof 

 thermoplastic material is entirely feasible. After the food is pressed 

 to the desired density, the dehyclrated product is tightly wrapped in 

 heat-sealable membrane, such as waxed paper or heat-sealing cello- 

 phane, and is then dipped into a molten mixture of thermoplastic 

 waxes, which upon cooling solidify to a firm continuous film that pro- 

 tects the food against absorption of moisture and contact with air. 



COMPRESSION TO HIGH DENSITY FOR PACKAGING 



In addition to the saving in shipping space that results when foods 

 are dehydrated, f uther saving can be achieved by compression. When 

 a ship is loaded with cargo at the rate of 1 ton per 40 cubic feet, the 

 holds are filled and at the same time the ship carries a full load. The 

 objective in the compression of dehydrated foods should therefore be 

 55 to 60 pounds per cubic foot as the minimum density. This calcu- 

 lated objective takes into account the fact that the finished package is 

 a little less dense than unpackaged cakes. Investigations have shown 

 that such densities can be attained without loss of quality in the recon- 

 stituted product. 



Even higher densities are to be preferred if an oxygen-sensitive 

 product is compressed and packaged in hemetically sealed containers. 

 Dehydrated cabbage, carrots, and tomato-juice cocktail are examples. 

 The denser the pack, the lower will be the ratio of oxygen in the can 

 to the dry fruit or vegetable. 



A further advantage of compression is the diminished tonnage of 

 steel and tin required when cans are used, since doubling the density 

 halves the metal required. The percentage of saving in cans result- 

 ing from compression is numerically equal to the percentage of re- 

 duction in bulk (table 13, column 9). 



In addition to increased density, rehydration to original size and 

 shape is an objective, with a low percentage of fines or small particles. 

 In tests, fines that pass through a 4-mesh screen after rehydration 

 have been kept under 5 percent. Weighed samples of blocks were 

 rehydrated and screen analyses made of the cooked product. The 

 low percentage of fines prevents a mushy texture and maintains 

 palatability equal to that of unpressed, rehydrated products. The 

 table shows the conditions under which fruits and vegetables have 

 been compressed with 5 percent or less of fines. The time required for 

 reconstitution is not increased over that required for unpressed foods. 



High densities in the pressed block require higher pressure when 



