14 FISHERY industries' OF THE UNITED STATES. 



scale. The sundry civil appropriation act of July 19, 1919, contains 

 provision for an additional assistant for the Fishery Products Labo- 

 ratory, but in the examination held before the end of the calendar 

 year no applicant qualified. 



DETERMINATION OF PRINCIPLES OF PRESERVATION OF FISH WITH SALT. 



Recent reports have contained reference to the technological inves- 

 tigations on the preservation of fish with salt, initiated for the 

 purpose of determining the basic principles governing this method of 

 preservation, to effect improvements in present practices, and to 

 develop satisfactory methods of salting fish at higher temperatures 

 and therefore in warm climates. The preliminary investigation has 

 been completed and the results published in Bureau of Fisheries 

 Document No. 884, "Some Considerations Concerning the Salting of 

 Fish," by D. K. Tressler. A brief summary of some of the results 

 follows : 



On the assumption that the more rapidly salt penetrates the flesh of fish the sooner 

 will decomposition be stopped, the first work aimed to determine the rate of penetra- 

 tion of salts of different qualities into the flesh, the squeteague being used. Small 

 amounts of calcium chloride or magnesium chloride retarded the rate of penetration 

 of pure salt (sodium chloride), but produced a firmer, whiter fish than the pure sodium 

 chloride. Other impurities, such as the sulphates, had a similar though less notice- 

 able effect. In this connection it may be of interest to note that analyses of com- 

 mercial salts reveal the fact that they vary greatly in purity. Solar salts are of 

 lesser purity than salts prepared by evaporation in open or vacuum pans, and most 

 domestic salts are of greater purity than foreign salts available in large quantities. 

 The purest brands obtainable at reasonable cost contain between 99.5 and 99.75 per 

 cent of sodium chloride. 



As the rate of penetration in itself was an insufficient index of the keeping qualities, 

 it was considered essential to provide some means of measiu-ing the amount and rate 

 of decomposition of protein in order to determine the amount of decomposition taking 

 place in the course of salting any lot of fish, and thus test the value of the various 

 methods. Having salted fish with prepared salts containing different amounts of 

 the common impurities (calcium, magnesium, and sulphates), the rate of protein 

 decomposition was estimated by determining the amounts of amino-acid nitrogen 

 formed. In this manner the preservative action of the various salts on the protein of 

 the fish was estimated . Calcium and magnesium salts and sidphates cause an increase 

 in decomposition and therefore produce a less perfect preservation of the fish dm'ing 

 salting. This reveals the importance of selecting brands of salt low in these impuri- 

 ties for salting fish in warm climates. For salting at temperatures below 50° F. it is 

 possible to exercise a measure of control in producing fish of the desired quality by 

 the use of salts having a high percentage of calcium and magnesium if a hard, white 

 fish is desired and pure salts if a soft, pliable fish is wanted. The degree of fineness of 

 the salt is considered of little importance save in a physical way. 



A comparison was made as to the relative efficiency of the two general methods of 

 salting fish, viz, by the use of dry salt or brine and salt, by determining the rate of 

 penetration of salt into the flesh of fish salted by each method and the rate of protein 

 decomposition. These experiments showed that the salt penetrates more rapidly in 

 the dry-salted fish than in the fish in pickle and that more amino acid was formed by 

 the brine method. The dry-salt method is apparently the more economical of both 

 salt and labor. 



In addition, experiments were made to determine the effects of a more thorough 

 cleaning of the fish before salting, the rate of formation of amino-acid nitrogen being 

 used to indicate the rate of protein decomposition. River herring cleaned by various 

 methods were salted at high temperatures. All except those from which all roe or 

 milt and blood had been removed spoiled, the thoroughly cleaned fish being success- 

 fully salted at 88° F. From these experiments it was concluded that the chief cause 

 of spoilage diu-ing salting is due to the decomposition of the blood remaining in the 

 flesh. 



The rate of penetration of salt into skinned fish was found to be about double that 

 in the unskinned fish, thus revealing the importance of splitting fish before salting. 



