FISH MEAL AND OIL 481 



an asphalt binder between the walls, reduced the oxidation and deterioration. This 

 method of handling makes it possible to sack the meal as it leaves the drier, saves 

 the labor required to handle it on the floor, and improves its quality. 



Calculation of Yields 



There are several factors which influence the yield of dry fish meal and oil in 

 the operation of a plant. In general 1 ton of fish will furnish 400 pounds of dry 

 meal and 1,600 pounds of press liquor. The press liquor will contain approximately 

 280 pounds of oil, and 65 pounds of solid protein particles are carried through the 

 press with the liquor. 



If the fish are of poor quality, there will be a deviation from this generalization. 

 Early in the season the fish are often fatter and the yield of oil will be greater. 

 Poor quality fish are often the cause of more suspended particles of protein in 

 stickwater, and if not recovered may cause higher production losses. Even the type 

 of equipment and its manipulation influence the final profits of the plant. The per- 

 centage of protein in fish is quite constant regardless of the species, but the water 

 and fat vary considerably. Since a fat fish contains less moisture than a lean one, 

 the average proportion of meal recovered is constant, while the oil yield varies 

 with different species. 



Daniel and McCollum (1931) have reported the analysis of several samples of 

 fish meals from different species of fish, dried by different methods (Table 104). 

 In the same report they indicate that vacuum-dried fish meals have a higher 

 nutritive value than flame-dried. They also report that vacuum-dried cod and 

 menhaden meals have a similar feeding value. Most animal nutritionists agree 

 that flame drying generally reduces the feeding value of fish meal. This defect 

 can be overcome by lowering the temperature of the flame drier. 



Table 104. Composition of Fish Meals Manufactured in Various Ways. 

 Method of Drying and Species 



Steam-dried menhaden 

 Flame-dried menhaden 

 Flame-dried whitefish 

 Vacuum-dried whitefish 

 California pilchard 



Source: Daniel, E. P., and McCollum, E. V., "Studies of the Nutritive Value of Fish 

 Meals," U. S. Fish and Wildlife Service, Investigational Rept., 2 (1931). 



Press Liquor and Oil 



The liquid fraction which passes through the screen of the press and is caught 

 in a drip pan or some other device contains water with some soluble portions 

 of fish, oil, and suspended protein. These materials are separated by first being 

 passed through a vibrating screen or some other type filter. This removes all of 

 the suspended material, which is then put through a small "foots-press." The solids 

 recovered in this device are added to the meal. The liquor is either placed in 

 settling tanks for gravity separation of the oil or put through a centrifuge system 

 for the separation of the oil and water fractions. In the most efficient plants centrif- 

 ugal separators have largely replaced the settling tanks for the recovery of the oil. 



