PROCESSING FISH MEAL AND OIL 229 



All these methods work by getting enough oxygen to the hot, reactive 

 scrap to bring the oil it contains through its more reactive state, then 

 carry away moisture and heat before these two enemies of meal quality 

 are trapped in a rapidly building scrap pile. 



It is still necessary to ''turn" the scrap during storage, that is, push it 

 to a floor conveyor, lift and drop it in another area, several times before 

 curing is complete enough that the menhaden scrap can be ground and 

 bagged. The number of turnings and the intervals between turnings vary 

 with initial temperature, oil content, oil type, moisture content, and other 

 factors so that it is impractical to set up a curing schedule that will work 

 under all conditions. 



Oil Separation. The hot press liquors are normally run from presses to 

 shaker screens to remove coarse solids, then to some type of centrifugal 

 separator to remove the fine solids. (DeLaval Super de-Cantors and Bird 

 centrifuges are both widely used.) Solids go back to the presses or may 

 be run directly to the dryers, and the liquid, reheated if necessary in a 

 holding tank, is run to the oil centrifuges. The oil phase is usually quite 

 clean and may be pumped to storage and shipped without further treat- 

 ment. However, many plants use a second centrifuge, of slightly different 

 design, to ''polish" the oil, that is, remove residual stickwater and solids. 

 This is accomplished by running the hot oil through the centrifuge with 

 about 10 per cent of its volume of clear, very hot water which washes out 

 the undesirable impurities. 



Oil Refining 



Menhaden oil, which makes up about 80 to 85 per cent of fish oil pro- 

 duced in the United States, varies widely in degree of unsaturation. Iodine 

 values range from 135 to 190, with south Atlantic and Gulf of Mexico oils 

 usually in the lower range ^°. 



Crude fish oil also has undesirable substances present in varying 

 amounts. These are removed by refining or processing to increase its use- 

 fulness as a starting material for the manufacture of industrial products. 

 These undesirable substances may be classed as follows: (a) suspended 

 matter, mucilaginous, colloidal, and resinous or polymeric; (b) free fatty 

 acids present or produced from the natural oil prior to or during the proc- 

 essing of fish; (c) natural occurring oil-soluble coloring matter; (d) volatile 

 odoriferous and flavor compounds dissolved in the oil; and (e) saturated 

 glycerides. 



One of the oldest processes of refining oils is known as "winterization." 

 Here, the oil is chilled until the higher melting and less soluble saturated 

 glycerides precipitate. After filtration to remove the precipitated solids, 

 an oil is produced that has much improved drying properties. 



