226 FISHERY INDUSTRIAL PRODUCTS 



Pressing. The cookers are usually placed high enough so that the hot, 

 cooked fish feeds directly into the presses by gravity. The presses, being 

 of very heavy construction, usually are on the ground level on a heavy 

 concrete base. The simple, straight screw press is still in almost universal 

 use. Renneburg and Enterprise presses have almost a monopoly of the 

 field. Both are effective and often are found side by side in the same plant. 



The pressing operation has the objective of reducing the oil content 

 from as high as 20 per cent in the raw fish to, ideally, about 3 per cent 

 in the press cake. This would yield a meal with 6 per cent fat, but, in fact, 

 meals from oily fish rarely contain less than 8 per cent, average about 

 10 per cent, and may run as high as 12 to 17 per cent fat. This indicates, 

 and most plant operators readily agree, that pressing is a step that is 

 difficult to control and normally is less than ideally efficient. 



Condition of the fish is the main trouble spot, but as this varies from 

 hour to hour, from boat to boat, and with the time the fish has been held 

 in the raw box, efficient pressing requires almost constant supervision of 

 both cookers and presses. Without indicators or automatic controls, this is 

 entirely dependent on the skill and experience of the pressman. Temper- 

 ature indicators on the fish from the cookers and power-input meters for 

 the motors driving the presses help to make this more science than art, 

 but this equipment is not yet in general use. 



Drying. It is said with some accuracy that dryers never wear out, and 

 this has delayed major reform in this step of the process. In many instal- 

 lations the same long cylindrical dryer used in 1910 can still be found. 

 Yet progress has been made! The change from coal to fuel oil, and in 

 many Gulf Coast installations to natural gas, has permitted much greater 

 control over dryer temperatures. Improved fire box design, baffling, and 

 other techniques have taken the flame out of the dryer and merit for 

 many installations the designation of ''hot-air" rather than flame dryers, 

 as they have been known. Powerful turbine blowers greatly increase the 

 air flow and drying rate. They also pull the rapidly drying fine particles 

 through to be trapped in the ''cyclone" before they can be overheated 

 or charred as they often were in old installations that relied entirely on 

 natural draft. 



Recently progress has been made through altering the design of the 

 drying cylinder itself — an example being the Renneburg "Dehydromat." 

 Here change in rate of air flow and a temperature drop is attained through 

 step increases in the tube diameter. Somewhat the same effect is obtained 

 in the triple-pass dryers, short and squat compared to the straight tube 

 installations, in which the air travels first down the center tube and then 

 expands into concentric outer jackets. 



Rotary steam dryers, at one time advocated as the sure answer to 



