THE TUNA INDUSTRY 93 



lightens the vessel load. The refrigeration is usually left on in the coils, 

 and the fish temperature falls very slowly. Brine is not usually used 

 more than twice owing to the accumulation of blood and slime from the 

 fish. Sometimes when boats intend to unload tuna without thawing, e.g., 

 when transhipping at sea or to a freezer plant, the wells are not ''dried 

 up," but the cold brine is left on the tuna and subsequently pumped off 

 prior to unloading the wells. However, most of the tuna is brought direct 

 to the cannery and thawed by a reverse process of adding brine and 

 circulating without refrigeration until the temperature has risen suffi- 

 ciently when the well is pumped dry for unloading. The aim is to remove 

 the tuna at about 28°F, when it is soft enough to eviscerate, but firm 

 enough to handle. 



This freezing system is a practical compromise arranged to be applied 

 in a wide variety of operating circumstances. As such it is far from ideal. 

 The operating margin is often critical so that many boats lose some fish 

 at times through spoilage, especially where big sets are made. Freezing 

 is fairly slow and holding temperatures high so that tuna received at the 

 plant deteriorates a good deal in quality as compared with the fresh fish. 

 Salt penetration is influenced considerably by a number of factors, mak- 

 ing it impossible to produce a truly consistent flavor in the end product. 

 Some objections might be overcome by the use of alternative freezing 

 methods or media^^, but, so far, apart from local ice boats, brine freezing 

 remains the practice in American vessels. 



Imported tuna i§ received in several forms, but most commonly as 

 frozen ''round" and "gilled and gutted." Before processing, this is 

 thawed in the plant using water sprays or tanks holding several tons 

 each. The temperature of the tuna is gradually raised by vigorous cir- 

 culation of sea or fresh water, until it is ready for unloading. 



The Canning Operation 



Preparation. The following account is only general in nature and prac- 

 tices and equipment vary somewhat from one operation to another. 



On arrival at the plant, the thawed fish is transferred by buggy, con- 

 veyors, or flumes to be weighed (Figure 7.2) and then to the butchering 

 table, which is a conveyor belt surfaced with 1 by 4-inch pine slats. 

 There the tuna are aligned on either side at a 45° angle to present them 

 conveniently to the butchers who, with two deft strokes, open the belly 

 wall and remove the viscera. The fish pass on under a rinse spray to an 

 inspector who removes any spoiled fish (Figure 7.3) and then to rackers 

 who place them according to size on galvanized wire mesh baskets which 

 are stacked in wheeled frame racks. The tray or basket size is typically 

 15 X 30 inches with 3-inch high sides. To prevent sticking and to reduce 



