PROCESSING FISH MEAL AND OIL 221 



conditions. River herring, the ''alewife" of Chesapeake Bay, is a source 

 of meal and oil as whole fish or more commonly as the waste from canned 

 ''herring" roe or salted and pickled products. 



The blue crab industry of the central and south Atlantic and Gulf 

 states produces large amounts of waste — over 80 per cent of the live 

 weight — and a portion of this, perhaps J-s to }^, is dried to yield a low- 

 protein meal. Shrimp waste from the canneries on the Gulf of Mexico 

 Coast also yields a small amount of meal, limited by the fact that most 

 of the catch have heads removed at sea. Whale and seal carcasses have 

 been rendered and dried for oil and meal. Both are more properly classed 

 as meat products, and neither is available in quantities large enough to 

 support a reduction plant under present conditions. 



General Processes 



Several basically different processes have been evolved for the manu- 

 facture of meal and oil from whole fish or waste products from food fish 

 processing. The wet process is by far the most widely used, being con- 

 tinuous and capable of handling large quantities of oily fish. The solvent 

 extraction processes also can be used with oily fish but have several dis- 

 advantages which have made them little used in the past for production 

 of fish meals. They represent, however, the basic procedures for the pro- 

 duction of the edible fish protein products formerly termed fish flour and 

 now known as fish protein concentrate. Dry reduction processes have been 

 used for non-oily raw material, and various digestion processes employing 

 both chemicals and enzymes have been used to a limited extent on similar 

 material. 



Wet Process. This process is used almost exclusively for processing oily 

 fish, including menhaden, herring, pilchard, and tuna cannery waste. In 

 the wet process the raw material is first cooked with steam in a continuous 

 cooker, then pressed in a screw-type continuous press. The press cake is 

 dried in some type of rotary dryer, while the press liquors are centrifuged 

 to separate the oil from the stickwater, so-called because it contains 

 "gluey," water-soluble nitrogenous matter. Stickwater also has some 

 residual oil, suspended fine solids, and dissolved minerals and vitamins. 



Not many years ago this was discarded but now most of it is concen- 

 trated to 50 per cent solids, and this concentrate is marketed as "con- 

 densed fish solubles." The oil fraction may undergo various refining steps 

 depending upon the end use for which it is intended. 



The wet process, because of its importance, will be described in con- 

 siderably greater detail in a subsequent section. 



Dry Process. The wet process can only be operated efficiently when 

 there is a fairly large and/or steady supply of raw material available, with 

 a suflftcient oil content to justify recovery costs. When only relatively 



