THE PRESERVATION OF FISH BY SMOKING AND DRYING 395 



activated and most yeasts and molds and many bacteria that may be present are 

 killed. 



Removal of Moisture. The fundamental principle involved in the preservation 

 of most cured fishery products is dependent on the fact that moisture is highly 

 essential for both general types of spoilage— putrefaction and autolysis. As mois- 

 ture is gradually removed from fish flesh, decomposition due to bacteria and 

 enzymes is progressively retarded. If this dehydration is carried far enough, both 

 actions will be completely checked. 



Only in a few dried products is this stage reached. In the vast majority of cured 

 fish products the decomposition or breakdown of the protein material is only in- 

 hibited or retarded to a greater or lesser degree, depending on the amount of 

 moisture removed. The keeping qualities will therefore vary greatly. Lightly 

 smoked products, such as finnan haddie and smoked fillets, spoil almost as readily 

 as fresh fish, while thoroughly dried stockfish will keep for several years. As men- 

 tioned previously, the holding of prepared products in cold storage after curing 

 is essential. In fact without the use of refrigeration the market for many kinds of 

 cured fish would be strictly of a local nature. 



Antiseptics. The action of microorganisms and enzymes can be inhibited by the 

 use of certain antiseptics, the principal one used commercially being acetic acid 

 which is found in all vinegars. In order to stop decomposition completely the acid 

 content of the vinegar would have to be so great that the finished product 

 would become inedible. Even though spoilage of pickled fish proceeds slowly after 

 preparation, the use of low temperatures for storage is advisable at all times. 

 Benzoate of soda, sodium nitrate, sodium nitrite, and other preservatives have 

 limited use in a few fish-curing processes. Smoke also has antiseptic properties. 



Elimination of Air. While strictly speaking the elimination of air is not a basic 

 principle involved in the actual curing processes, it prevents certain physical and 

 chemical changes during storage which would spoil the finished product. In storing 

 many kinds of salt fish, especially those of an oily nature, it is most important to 

 keep the product covered with brine to prevent exposure to the air, which would 

 lead to the oxidation or "rusting" of the oil and subsequent spoilage. Artificially 

 dried fish also exhibit better keeping qualities when stored in the absence of air, 

 such as in a vacuum-sealed can. 



Methods of Removing Moisture 



Although in the preparation and storage of many varieties of cured-fish products 

 all 5 basic principles may be utilized, the fundamental one involved in the actual 

 curing processes is the removal of moisture, which is found in the flesh of all fish 

 and which constitutes 60 per cent or more of the total weight. The removal of 

 this water may be effected in one or more of the following ways: 



Exposure to Currents of Air. This may be done in the open air by utilizing the 

 natural wind currents; in ovens where drafts are created by the burning of wood 

 fires or other forms of heat; or in specially designed driers in which the air cur- 

 rents are created by artificial means. Typical of this application are the various 

 kinds of dried and dehydrated marine products. 



Osmosis. This is the term commonly applied to that natural phenomenon oc- 

 curring in all forms of plant and animal life, whereby nutrients in solution are 

 able to pass through the cell membranes into the body and at the same time cer- 



