FREEZING AND COLD STORAGE 299 



mackerel, or herring; or in some cases, institutional five- and ten-pound 

 packages of fillets or steaks. Consumer-size packages of fish fillets undergo 

 bulging because of the absence of a method of controlling expansion during 

 freezing. 



Excessive handling of the product is another disadvantage in the use of 

 sharp freezers. As much as three hours are required for loading and three 

 hours for unloading 40,000 pounds of fish fillets. Infiltration of air and 

 accumulation of frost on the shelf coils during loading and unloading are 

 problems. In a New England plant, handling requirements and air infil- 

 tration have been reduced by utilizing conveyors to carry the product 

 from the processing room into the freezer and from the freezer to the 

 cold-storage room. Some labor is still required, however, to transport the 

 product from the conveyor to the freezer shelves and from the shelves to 

 the conveyor. 



Space requirements vary with the installation and with the type of 

 product being handled. However, about one square foot of shelf space 

 should be allotted for each 7J^2 pounds of round fish or for each 10 pounds 

 of packed fish in institutional cartons. 



The Air-blast Freezer. Air-blast freezers are generally small rooms or 

 tunnels in which cold air is circulated by one or more fans over an evapo- 

 rator, cooled by ammonia, brine, or Refrigerant 12 or 22, and around the 

 product to be frozen. The freezers are usually fully loaded at one time by 

 rolling or pulling a rack of shelves of fish into the insulated room. More 

 recently, conveyors have been used to move fishery products continu- 

 ously through the blast room or tunnel. Most freezers of this type operate 

 at air temperatures of — 30°F or lower. The velocity of the air moving 

 over the product generally varies between 500 and 1000 fpm to give the 

 most economical freezing. Lower air velocities result in slow product 

 freezing, whereas at higher velocities the freezing costs per pound of fish 

 frozen per hour increase considerably. 



Dehydration of product, or ''freezer burn," may occur in freezing un- 

 packaged whole or dressed fish in blast freezers unless the velocity of air 

 is kept to about 500 fpm and the period of exposure to the air is controlled. 

 Consumer-size packages of fish fillets or fish fillet blocks requiring close 

 dimensional tolerances undergo bulging and distortion during freezing. 

 In blast rooms or tunnels, where the product is frozen on trucks, the use 

 of specially designed freezer trucks enabling distribution of pressure on 

 the surfaces of the package will remedy this condition. 



The Contact-plate Freezer. The contact-plate freezer consists of hori- 

 zontal movable plates stacked vertically within an insulated cabinet or in 

 an insulated room. The refrigeration effect is furnished by cold brine, 

 ammonia, or Refrigerant 12 or 22 circulating in connected passageways 

 in the plates. This freezer was designed for freezing packaged food prod- 



