FRECOOKING 



During precooking and cooling, shrinkage taices placs amounting 

 up to 30 percent of the weight of the tuna. Two-thirds to three- 

 fourths of the loss occurs during cooking and the balance during 

 cooling of the fish. This is caused by loss of oil^ solids^ and 

 moisture during cooking^ and loss of moisture due to evaporation 

 and drip during cooling of the fish. Since the cost of the fish 

 represents about 70 percent of the processors cost, any savings in 

 the shrinkage occurring during precooking and cooling is of the 

 greatest importance. 



The butchered tuna are placed in wire baskets with a capacity 

 of 30 to 35 pounds which will hold from one to five or more fish 

 (very large fish may have to be cut and placed in several baskets) . 

 In most plants a layer of special heavy Kraft paper perforated with 

 holes and treated to withstand moisture is laid on the bottom of 

 the basket and the fish is placed on the paper. Thi:-. runinises 

 marking of the fish by the wire of the baskets and makes it easier 

 to remove the fish by preventing sticking of the fish to the basket. 

 The holes in the paper allow juices and oil to drip away. The bas- 

 kets are placed or: racks (usuaJJLy lU basket.- per rji'.k., tliourji 

 larger racks may hold 21 baskets) „ and tlie racks are mounted en 

 wheeled carts which are rolled into the cooking ovenji. A rack holds 

 about 700 pounds of tuna and a cooker will usually hold 9 to 16 

 racks (about 3 to 5 tons). Double-width cockers hold twice tbsse 

 amounts. The cookers are made of sheet Iron supported by iron 

 frames and usually are of rectangujar cross- sfiction dbout t>^\,'< 

 it, X U ft. and 12 ft. to 30 ft. long. Racks are xntroduc-ed through 

 a door in the front and when cocking is completsd. iu:<:- ivli.hdrawn 

 through the same door. In double-ended cookers racks are pushed in 

 the front, and upon completion of the cook, go out a door at the 

 rear. A few plants use improvised cookers by employing standard 

 retorts. 



The cooked fish must cool thoroughly^ a process usually re- 

 quiring about 24 hours. The racks are placed in a separate room 

 or space and allowed to stand j usually overnight. In a few plants 

 air circulation is provided and in one plant refrigerated air holds 

 a constant temperature regardless of outside weather conditions. 



In the precooking operation as n;uch as 20 percent of the weight 

 of the fish is lost. This consists of tuna oil, moisture, and dis- 

 solved protein and other tissue constituents. It is desirable to keep 

 the moisture loss consistent from fish to fish and avoid excessive 

 over-cooking with resultant large shrinkage losses. Large fish require 



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