FREEZING AND COLD STORAGE 



297 



of thumb, the freezing time may be assumed to be directly proportional 

 to the square of the product thickness. Therefore, if it takes 180 minutes 

 to freeze 2 inch thick packages of fillets, 281 minutes will be needed to 

 freeze a similar product 2J/2 inches thick, provided, of course, that all 

 other conditions are similar. 



The type of package and method of packing also govern the time of 

 freezing. For example, packaging materials having a low conductivity 



Table 23.3. Average Water Content and Specific and Latent Heats of 

 Various Fishery Products 



* Calculated by Siebel's formula; for values above freezing S = 0.008a + 0.20; for values below freez- 

 ing S = O.OOSo + 0.20. a = water content in per cent, 0.20 = specific heat of solid constituents of the 

 substance. 



t Values for latent heat (latent heat of fusion) in Btu per lb, calculated by multiplying the percentage 

 of water content by the latent heat of fusion of water, 143.4 Btu. 



retard the transfer of heat from the product. The ideal packaging material 

 should have a high thermal conductivity and be relatively thin to permit 

 rapid transfer of heat from the product's surfaces to the cooling medium. 

 The fit of the package is also very important; a loosely fitting package, 

 with insulating air pockets or voids, will greatly increase the time and 

 efficiency of freezing. 



Calculation of Freezing Time. Information on the average water con- 

 tent and specific and latent heats of various fishery products is shown in 

 Table 23.3. 



