THE PRESERVATION OF FISH BY SMOKING AND DRYING 399 



Heavy brining is used in the development of special cures, as, for example, in 

 the mild-curing of salmon and for preserving fish until the smoke-curing process 

 can be applied. In this type of cure the salt concentration of the fish reaches 

 8 to 10 per cent. However, this concentration of salt, in itself, is not sufficient to 

 preserve the fish indefinitely, and the product must be held at low temperatures, 

 preferably about 32 to 34" F (0 to 1.1° C). Most of this salt must be removed 

 from the fish prior to smoking. This is accomplished by soaking the fish in cold 

 running water. The efficiency of the soaking will, of course, depend upon the 

 volume of water, temperature, and length of time. The control of these factors is 

 also important. 



Drying. After suitable brining (and soaking, if necessary) the fish are sub- 

 jected to a drying process. This is necessary to remove additional moisture, thus 

 aiding in the preservation of the product and the formation of the "pellicle." Under 

 similar conditions of time, temperature, air flow, and humidity the more moisture 

 removed from the fish the greater the keeping quahty. The moisture content of 

 most smoked products averages 60 to 75 per cent which is much above the critical 

 moisture content necessary for the growth of microorganisms. The beneficial effect 

 of drying is confined to the surface of the product. Drying is usually accomplished 

 in the smoking chamber and the maintenance of the proper humidity is quite 

 important. It has been found that in an atmosphere of relative humidity above 75 

 per cent very little drying of the fish will occur (Cutting, 1942). 



Drying aids in and is partially responsible for "pellicle" formation. The "pellicle" 

 is the glossy firm surface imparted to the fish which gives it the required desirable 

 appearance and allows for the development and absorption of the delicate smoke 

 flavor. Formation of this "pellicle" is quite important in securing a smoked product 

 of good quality. 



Heat Treatment. Fish may be smoked in a cold or hot atmosphere, depending 

 upon the type of product desired. Cold-smoking, which produces a product which 

 is generally referred to by the trade as smoked, is accomplished in an atmosphere 

 below 85 to 90° F (29.4 to 32.2° C). In this case there can be no preservative 

 effect attributed to the heat treatment. The amount of fat present in the flesh and 

 the method of preliminary cure affects the temperatures which may be tolerated 

 without cooking. A fatty fish with a cure such as that of mild-cured salmon may 

 tolerate temperatures in the neighborhood of only 80 to 85° F (26.7 to 29.4° C); 

 while lean, lightly brined haddock, used in the preparation of finnan haddie, is 

 best produced at temperatures around 90° F (32.2° C). These products are highly 

 perishable and must be kept under refrigeration, preferably at 32° (0° C) below, 

 at all times. 



Hot smoking produces the well-known kippered or barbecued items. These 

 fish are actually cooked or barbecued, and temperatures range from 120 to 180° F 

 (48.9 to 82.2° C), with some fish being smoked at even higher temperatures. The 

 heat destroys the enzymes producing autolytic changes and also coagulates the 

 proteins throughout the entire product. Molds are destroyed and most bacteria are 

 killed. In addition the removal of moisture is aided by this heat treatment since 

 the more the temperature is increased above atmospheric, the greater the rate of 

 diffusion of moisture through the fish to the surface, from which it escapes to the 

 air. As barbecued fish are cooked as well as smoked, they do not require any 

 further preparation before eating. 



