REFRIGERATION OF FISH 527 



The air of a cold-storage room is stagnant. No ventilation is pro- 

 vided, except that which is occasioned by opening the doors. Being 

 in contact with fish continuously, it doubtless becomes charged with 

 volatile substances from fish. If fish are stale when frozen, they have 

 small quantities of ammonia, amines, hydrogen sulphide, and the like, 

 which are volatile. Oxidation of fats produces aldehydes and other 

 offensive substances, some of which are volatile. Smoked fish have a 

 decided odor, which arises from the volatile constituents of smoke. 



When large quantities and numerous varieties of fishes are stored 

 together in an unventilated room the air may, and probably does, 

 become charged with these volatile substances. Fish may absorb 

 them to some extent. Round fish, well glazed, may not be appre- 

 ciably affected, but fish without these protections, and especially those 

 of slight flavor of their own, like haddock fillets and cod steaks, may 

 be distinctly tainted with these odors. Protective wrappings for 

 these products are necessary, therefore, not only to prevent drying 

 out, but to prevent taint from foreign substances in the air. Low 

 temperatures reduce the tendency to taint from the air, because the 

 lower the temperature, the lower the tendency of volatile substances 

 to evaporate, and the more completely they are condensed on the cold 

 pipes along with the water. Smoked fish should be stored apart from 

 other fish as far as possible. 



This subject is of much practical importance, and has not been 

 sufficiently studied. Steamship or railroad companies hesitate or 

 refuse to forward fish in refrigerated compartments with meat, eggs, 

 butter, and poultry. General cold storage warehouses either do not 

 accept fish, or else store them in separate rooms, or, as in the case of 

 the cold-storage warehouse of the Harbour Commissioners of Quebec, 

 in an entirely separate building. Retailers usually avoid putting fish 

 in their refrigerators along with other food products because of pos- 

 sible taint with fishy odors. Scarcely enough of this subject is 

 definitely known to justify any broad generalizations. The writer 

 has done some investigating and found that if an impervious cover- 

 ing is used, such as the various moisture-proof papers, and tight boxes, 

 with low temperatures, taint may be reduced to a negligible amount. 



CHANGES THAT DEPEND ON THE TEMPERATURE AT WHICH FISH ARE 



FROZEN 



Generally, the colder the freezing medium the faster the fish 

 freeze, and it has been shown already that the rapidity of freezing 

 has much to do with the frozen product. Rapidity of freezing, 

 however, can be had without excessively low temperatures by having 

 good contact between fish and, say brine, and having the brine in 

 rapid circulation. It has been shown that temperatures at which fish 

 are frozen have an effect independent of the rate of freezing. The 

 lower the temperature the more of the water is frozen out. The 

 more water frozen out the more concentrated the remaining solu- 

 tion. At 104° F. below zero all the water is frozen out of the fish 

 and the fish substance is completely dehydrated. It does not return 

 to its original condition when defrosted. The implication of this 



