154 DESCRIPTION OF IMPORTANT FISHERIES AND THEIR PRODUCTS 



Regardless of the type of weighing equipment employed, this unit of 

 measure is used throughout the industry to express the quantity of catch. 



The size of the raw box varies according to the processing capacity of 

 the plant and the number of vessels employed. Most raw boxes hold 

 between 300 and 600 tons of fish, but some of the larger ones have a 

 capacity of several thousand tons. They may be constructed of wood, 

 concrete, or steel, but are of the same design. They are rectangular in 

 shape, varying from 12 to 25 feet in depth and up to almost 200 feet in 

 length, with a floor that slopes toward the middle. An enclosed drag or 

 screw-type conveyor is located at the bottom and runs the full length 

 of the box. Fish are fed into the conveyor through removable grates or 

 wooden sections and carried to hoppers which feed the continuous cookers. 



Cooking. The cooking process usually is begun simultaneously with 

 the unloading of the carrier vessels. During cooking, the raw fish are 

 exposed to jets of live steam for approximately five minutes. The extent 

 of cooking is controlled by regulating the speed at which the fish are 

 passed through the cooker as well as the amount of steam. The tempera- 

 ture of the fish during cooking averages about 180°F. Moderate control 

 of the cooking process is essential, since it is desirable only to coagulate 

 the protein and rupture the fat cells without overcooking. Most plants 

 are equipped w4th more than one cooker, each having a capacity of from 

 15 to 35 tons of raw fish per hour. The cooking process usually is completed 

 within 12 to 15 hours after the catch has been unloaded. 



Pressing. The thoroughly cooked mass of fish and oil, along with the 

 condensed steam used for cooking, is conveyed to hoppers which feed 

 the continuous screw presses. During the passage through the presses, 

 the water, oil, and soluble components, called press liquor, are squeezed 

 out of the cooked material. The discharged press cake contains about 

 50 per cent water and some residual oil. 



Separation of the Press Liquor. The press liquor is pumped to vibrat- 

 ing or rotary screens which remove much of the suspended solids. Finer 

 solids may be removed by basket centrifuges. The oil and aqueous frac- 

 tion from the screening process is fed into a battery of centrifuges for 

 separation of the oil. In some plants, the oil is then passed through 

 centrifuges, known as purifiers, where the residual water and solids are 

 removed. The resulting ''polished oil" is pumped into large capacity 

 storage tanks to await shipment to market. A number of plants employ 

 settling tanks for removal of residual water and solids prior to storage 

 of the oil. 



The liquid fraction removed during oil separation, called stickwater, 

 is sent through evaporators which concentrate the material approximately 

 ten times. The resulting syrup, known as condensed fish solubles, is 

 pumped into storage tanks to await shipment. A recirculating system 



