630 U. S. BUREAU OF FISHERIES 



be many hours or even days in chilling completely because of the 

 thickness of the can. A few degrees makes a great difference in the 

 keeping of these fillets. 



INSULATED PACKAGES FOR SHIPPING CHILLED FRESH FISH 



Several inventors have designed insulated packages for shipping 

 chilled fresh fish. The aim of all these inventions has been to chill 

 fish to 32° F. or thereabouts and to insulate it in a package so that 

 it will carry to destination in fresh condition. One of the earliest 

 of these inventions used ice but provided sawdust to absorb the water 

 from the melting ice. Later inventors, attempting to avoid the use 

 of ice, made use of double-wall containers, with sawdust, eelgrass, 

 corrugated paper, or other cheap insulating material between. The 

 containers are generally of corrugated paper. Balsa-wood boxes also 

 have been used for this purpose. The ideal at which these inventions 

 aim is excellent but is difficult to attain because of the poor insulating 

 quality of even the best insulators. If fish once chilled to 32° F. 

 could be kept at this temperature, they would carry several days with- 

 out spoiling, though even at this temperature deterioration occurs. 

 Unfrozen water, however, requires a relatively small amount of heat 

 in order to be warmed. Compare, for example, 10 pounds of frozen 

 haddock at 28° with unfrozen haddock at 32° — only 4° difference. 

 The haddock contains, say, 80 per cent water, and at 28° 62 per cent 

 of this is frozen ; that is, 4.96 pounds of ice in the 10 pounds. This is 

 to be compared with 8 pounds of water at 32° in the unfrozen lot. 

 To raise the 8 pounds of water in the unfrozen fish from 32° to 40° 

 at 1 B. t. u. per pound would require 8X8=64 B. t. u. To melt the 

 4.96 pounds of ice in the frozen fish, at 144 B. t. u. per pound, would 

 require 144X4.96— 714.24 B. t. u. To raise all the 8 pounds of 

 water from 28 to 40° would require 12X8=96 B. t. u. The total 

 B. t. u. would thus be 714.24-f-96=:810.24 B. t. u., as compared with 

 only 64 B. t. u. required to warm the unfrozen fish to the same tem- 

 perature. If the external dimensions of the container are 1 foot 

 cube, or 6 square feet, and the insulation is sufficient to pass 0.15 B. 

 t. u. per square foot per hour, per degree difference in temperature 

 between inside and outside (36° average for the frozen and 34° for 

 the unfrozen), and the outside temperature is 70°, then 25 hours 

 would be required to warm the frozen to 40°, and 2.1 hours 

 would be required to warm the unfrozen to the same temperature. 

 The time is not actually so short as this, nor the actual problem so 

 simple, because the heat must penetrate the fish itself, but the differ- 

 ence will be relatively large. The prospects for an insulated package 

 to keep fish fresh without ice in the fish or around it, therefore, do 

 not seem bright. 



TEMPORARY STORAGE OF FISH IN CHILL ROOMS 



Most fish cold-storage plants have chill rooms where fish may be 

 stored temporarily. The temperature of such rooms varies from 30° 

 to 40° F., and a time limit is usually set to the storage of fish in this 

 way. Barrels and boxes containing the fish are simply put in the 

 rooms. 



