694 MARINE PRODUCTS OF COMMERCE 



but must be put through a knife cutter or crushed between corrugated rollers 

 under great pressure. 



Hogged or minced material can be conveyed by bucket and bar conveyors, 

 never by the chain because the fibrous material is tough and slimy and immedi- 

 ately gums any chain conveyor. A great deal of oil exudes during the process. 



Cold-rolling and pressing, without the application of heat, has been tried, 

 especially in Japan, in the reduction of oil from blubber, but is not yet a per- 

 fected method. 



Meat is not mixed with blubber though the great layers of pure fat from the 

 viscera may be thrown in. Not even the grooved blubber from the throat and 

 chest of rorqual and humpback whales should be placed with blubber lest the 

 slight amount of meat in the thin muscle of this area color the oil and raise the free 

 fatty acid content. The grooved blubber can be digested with bone. 



Oil is separated from the water and fiber by gravity-water separators and 

 centrifuges. The simple gravity-water separator can hardly be utilized on ship- 

 board though a modification of it exists on the rotary digesters to separate the 

 crude brei into oil and residue. At a shore station there may be a series of 2 to 4 

 gravity separators in tandem. The oil, after settling for a time in the first, is 

 spilled into the second by pumping water at the bottom. The process is repeated 

 several times until the oil is practically pure. However, a whirl in a centrifuge 

 helps to remove practically all of the moisture and sediment which may later 

 give trouble in storage. Some shore stations centrifuge only the sludge from the 

 first gravity separation and the stickwater from the digester. 



Factory ships use a whole battery of special whale-oil centrifuges— enough to 

 take all the maximum oil production from the continuous rotary digesters without 

 storing uncentrifuged oil. Sometimes the oil is filtered before centrifugation. After 

 centrifuging, all the oil is stored. 



Emulsified oil and water from improper digestion or from the presence of 

 watery fat has to be discarded or handled in special emulsion-breaking centrifuges. 

 Breaking of emulsions depends more on the size of the oil droplets than on the 

 force of the centrifuge; the finer the droplets the harder to break is the emulsion. 



Oil should never be stored for any period without being refined to remove 

 all the moisture and free fatty acid. Then it should be kept in the dark, at low 

 temperatures if possible, and away from moisture or moving air. Storage under- 

 ground or in high altitudes gives desirable low temperatures, and replacement of 

 air by nitrogen over the oil helps prevent oxidation. All protein fibers are auto- 

 matically removed with the moisture during filtration and centrifugation. 



Cooking meat for meat meal and oil is also done by several methods. The 

 simplest is to mince or hog the meat in a prebreaker, cook it for a short time in 

 an open pot over water with live steam, then tap off what oil is present, and press, 

 dehydrate, grind, and sack the residue. The oil from the pot and press goes to the 

 oil separators, and the stickwater to its own treatment. Another way is to deposit 

 large chunks of the meat in a batch grid digester and cook them for 18 hours or 

 so under 55-pounds steam pressure. This is the slowest and most ineflBcient way; 

 the stickwater is blown off at the bottom and the oil comes oflF in small quantities 

 during the digestion. The graks are shoveled out by hand after the digester has 

 been cooled and opened. Grids in the digester are absolutely necessary as they 



