UTILIZATION OF THE FISH WASTE OF THE PACIFIC OCEAN. 29 



COOKING. 



The upright, cylindrical retort is in general use. It is provided 

 with openings in top and bottom for charging and discharging, re- 

 spectively. If the fish is to be cooked under pressure the opening in 

 the top is generally smaller than otherwise, so that it more readily 

 may be closed and rendered tight enough to retain the steam at the 

 pressure at which it is admitted to the retort. 



The manner in which the steam is admitted and the length of time 

 during which the charge in the retort is subjected to the cooking 

 action of the steam vary from plant to plant. In certain instances 

 the steam is injected at the bottom and allowed to permeate the mass 

 of waste undergoing cooking. When it appears at and issues freely 

 from the top the charge is deemed sufficiently cooked. In other cases 

 the cooking is continued for 12 hours under a pressure of 20 pounds 

 of steam. As each operator regards his methods as the best, it may 

 be said that all of the methods give equal satisfaction. 



After cooking, the charge may be allowed to stand to settle, or it 

 may be drawn off at once into the presses. If the former procedure is 

 observed, much of the oil released in the cooking rises to the surface 

 and is drawn off in any suitable manner. In any case the charge is 

 admitted to the presses hot. As a result of the cooking the material 

 may be thoroughly disintegrated to form a thin soup, or it may be 

 broken, up into coarse particles. The only essential seems to be the 

 disintegration of the heads. 



What is considered a good practice is to run the charge as soon as 

 sufficiently cooked from the retorts into a storage vat or " slush box." 

 This is provided with steam coils so that the material may be kept 

 hot. From this vat the cooked fish is admitted to the presses. This 

 system admits of greater elasticity, making the rate of cooking inde- 

 pendent of that of pressing. 



PRESSING. 



Presses of the hydraulic or the " knuckle " type are in general use. 

 Owing to the fine state of subdivision of the material to be filtered, 

 the part of the press functioning as a filter must have very fine aper- 

 tures in order that the separation between liquids and solids may be 

 effected. The readiness with which such fine material closes the 

 apertures of a filter and retards separation necessitates a very large 

 filtering surface for a comparatively small amount of material. 

 These conditions are fulfilled in the salmon-waste filter presses by 

 the use of a heavy and compactly woven sort of burlap bagging 

 ("hop cloth ") , in which only small portions of the waste are put to 

 be pressed. 



The charge for the presses is made up in the following manner : A 

 framework of 1-inch strips of wood inclosing a square of about 3 

 or 4 feet is placed on a truck and over it is thrown a square of the 



