requirements. The growth and expansion of 

 the fishery in the late 20's and early 30's forced 

 the rapid development of the brine system we 

 have today, which is in some ways one of the 

 most efficient systems yet devised for freezing 

 fish at sea. It consists essentially of a chilled 

 sea water storage accumulation, followed by 

 brine freezing, frozen holding (wet or dry) and 

 thawing, all in the same well. Ideally operated, 

 this system delivers fish to the cannery in good 

 condition. However, in the variable operating 

 circumstances encountered, a number of prob- 

 lems can arise which lead to loss and lowering 

 of quality of all or parts of the load. These 

 problems have been the subject of some study. 



The experiments we have carried out so far 

 have been exploratory in nature and aimed at 

 locating which of the operating variables have 

 the most influence on quality so that work might 

 be concentrated in these areas. It has not been 

 possible to carry out confirmatory studies in 

 this time so that present conclusions must be 

 regarded as tentative until repeated. 



Fish at tropical and subtropical ocean tem- 

 peratures deteriorate rapidly and have to be 

 chilled to retard bacterial, enzymatic, and ox- 

 idative spoilage. As the temperature falls, so 

 does the rate of deterioration and the nearer 

 the temperature to the freezing point, the more 

 stable is the tuna. (However, much lower 

 freezing temperatures are needed to stop enzy- 

 matic and oxidative changes.) Advantage is 

 taken of this fact in the chilling stage for raw 

 tuna when the fish are put into 30° F seawater 

 to cool before freezing, and in many cases to 

 hold them until more fish are caught to fill the 

 well. In order to maintain good quality fish, 

 it is essential to chill it rapidly. Temperatures 

 of less than 40° F are an absolute necessity. 

 We have chilled whole tuna in 30° F seawater 

 and held them at this temperature. Samples 

 of albacore lasted 35 days before being spoiled 

 to the point of rejection (Crawford and Finch, 

 1968), and samples of bluefin lasted 22 days 

 with no apparent spoilage as shown by the or- 

 ganoleptic evaluation of canned samples ( Craw- 

 ford, unpublished) . This contrasts remarkably 

 with the normal time for which wet tuna may 

 be held aboard a tuna vessel which is usually 

 only 7 to 10 days before serious deterioration 

 sets in. It was reasoned that the diflference is 

 probably due to various factors such as the 



relatively poorer cooling in commercial wells, 

 especially when they are overpacked, resulting 

 in a lower ratio of brine to fish, which may be 

 as little as 1 to 5.5, and the consequent poor 

 circulation. This not only limits effective cool- 

 ing, but the accumulation of dirt, blood, and 

 slime forms a perfect medium for the growth 

 of the spoilage organisms contributing to the 

 deterioration of the fish when temperatures are 

 relatively high. It appears that poor brine cir- 

 culation (and not the characteristics of the fish 

 themselves) is the most important factor which 

 limits the time for which tuna may be held 

 in chilled storage and leads to quality de- 

 terioration when the tuna is held for longer 

 periods. This is important because if correct, 

 it means that improved chilling on vessels 

 would enable tuna to remain in better condition 

 after the same length of chill storage. Alter- 

 natively, under conditions of slow fishing, tuna 

 might be held longer at the same temperature 

 without spoilage — thus increasing the flexibil- 

 ity of the freezing system. 



A further important point revealed by the 

 chilling experiments was that fresh tuna, at 

 least as harvested by present commercial meth- 

 ods, showed numerous blood flecks, spots, and 

 prominent dark blood vessels on canning. After 

 continued chill storage, blood appeared to dif- 

 fuse into the suri'ounding tissues so that the 

 blood vessels became progressively less evident 

 (Crawford and Finch, 1968). This explains 

 why prominent blood vessels are usually asso- 

 ciated with albacore and bluefin which being 

 caught relatively near to canneries are usually 

 landed in a much shorter time after catching 

 and before the blood has had time to diffuse. 

 Another factor reported by Crawford and 

 Finch was that fresh fish had a greater tend- 

 ency to scorch, which diminished on chilled 

 storage. This factor could be especially sig- 

 nificant with institutional packs which are re- 

 torted for long times. 



In U.S. commercial practice, the chilled tuna 

 are frozen in brine to temperatures near 20° F 

 to pi-eserve them during transport. Then the 

 brine is removed to avoid excessive salt pene- 

 tration. This freezing operation takes place 

 at a much slower rate than is usually regarded 

 as satisfactory for freezing fish. For example, 

 Crawford et al. (1969) found that a 50-lb. blue- 

 fin tuna took 170 hr to freeze to 20° F, in a 



