422 MARINE PRODUCTS OF COMMERCE 



midity should be kept low, it may vary between 10 and 40 per cent, the optimum 

 being in the neighborhood of 20 per cent. A low relative humidity coupled with 

 high initial drying temperatures is instrumental in maintaining a high rate of dry- 

 ing. With conditions such as these dehydration may be accomplished in around 

 4 to 5 hours, and the moisture content should be reduced well below 5 per cent. 



Many species have been dehydrated, both in the United States and Canada, 

 to yield a palatable product. Among these are angler fish, raja fish, sea robins, 

 puffers, croakers, sea trout, whiting, Atlantic cod. Pacific gray cod, ling cod, 

 herring, red snapper, halibut, pilchard, dogfish. Pacific mackerel, petrale sole, 

 king salmon, coho salmon, chum salmon, and Pacific squid. 



Immediately after dehydration the quality of the product is high, but upon 

 subsequent storage certain changes occur which affect the texture, flavor, and 

 appearance. These changes are quickened when the humidity is high or when 

 storage is at high temperatures. Some investigators (Cutting and Reay, 1944) 

 recommend that all dehydrated products be hermetically sealed in an atmosphere 

 of nitrogen. Their research has indicated that storage time up to 2 years under 

 normal temperatures may be obtained when packed in this manner. If not stored 

 properly the product becomes rancid. Even the so-called non-oily varieties are 

 afi^ected; as moisture is removed, the percentage of oil to protein rises and the 

 product becomes oily. Moreover, exposure to ordinary atmospheric conditions re- 

 sults in other rapid changes: the flesh darkens, becomes tough, and has a burnt 

 flavor and odor. 



Nutritionally speaking, the product is very good and recent research (Martenik 

 and Jacobs, 1943) has indicated that on the species studied (cod, whiting, mullet, 

 carp) neither the nutritive value nor the digestibility of the proteins was adversely 

 affected. Most of the losses of vitamins Bi and B. were in the precook process and 

 could be recovered at least partially from the stickwater. 



Rehydration is accomplished rapidly. The use of cold water is recommended and 

 most species take less than 30 minutes to reconstitute. Four to 6 parts of water 

 are used to each part of dehydrated fish and the resultant product has the color 

 and texture of minced, cooked fish. The rehydrated fish is suitable for use in any 

 recipe calling for flaked fish (i.e., fish balls, fish salads, fish loaves, etc.). 



Pressjish. A recent innovation on dehydration is a method introduced in Norway 

 which produces from cod something known as "pressfisk." Hamm describes the 

 method as follows: 



"The fish are first cleaned and split, the bones and skin are removed, and the flesh 

 is laid flat on an aluminum sheet about 8 feet long by 4 feet wide. A second aluminum 

 sheet is placed over the fish on the first sheet. Several of these 'sandwiches' so obtained 

 are placed in the vacuum dehydrator. 



"The dehydrator has a series of hollow plates, similar to a 'Birdseye' freezer, and 

 one 'sandwich' is placed between eacli pair of opposing surfaces of the hollow plates. 

 The plates are then pressed together by a hydraulic jack, the dehydrator is shut and 

 evacuated to an internal pressure of about 25 millimeters of mercury, and hot water 

 at 194° F (90° C) is circulated through the hollow plates. The heat passes readily from 

 the hollow plates through the aluminum plates to the fish. After about 6 hours the 

 flattened fillets are sufficiently dehydrated. They are then removed from the aluminum 

 sheets and stacked in a dry room for a few days to allow equalization of the moisture 

 content. Then 1.5-inch squares are cut from the fillets and fitted in layers into a deep, 

 closely fitting receptacle of a hydraulic press. 



