THE SARDINE, MACKEREL, AND HERRING FISHERIES 141 



Cooking. The offal and trimmings from the cannery operations may 

 be accumulated in a suitable concrete pit. They are conveyed by a screw 

 or drag conveyor, usually located overhead in the meal plant, to a cooker. 

 The cooker consists essentially of a closed steel screw conveyor filled with 

 steam jets. The speed of the screw conveyor is regulated so that the offal 

 stays in the cooker 10 to 15 minutes. During this time the jets of steam 

 cook the fish offal and thereby impart upon the fish pulp physical proper- 

 ties which are favorable for a separation by pressure of this cooked mate- 

 rial into a liquid and a solid portion. 



In other countries, particularly those with high fuel costs, the cookers 

 are of a somewhat different design. The offal is cooked by indirect steam 

 by introducing the steam into a jacket surrounding the cooker. This 

 saves the cost of fuel by avoiding the removal, by evaporation, of the 

 condensate which adds to the volume of the press water (see Condensed 

 Fish Solubles). 



Pressing. The cooked fish pulp upon leaving the cooker is fed into a 

 press usually located directly below the cooker. The press is either a 

 screw press or a disc press. The screw press is an expeller type of con- 

 tinuous press, and as the fish pulp is moved through the screw barrel, 

 it is subjected to increasing pressure which causes the press water to 

 seep through the apertures of the barrel while the pressed solids are 

 discharged at the end of the press as a press cake. The press water, also 

 called stickwater, contains an appreciable amount of fish oil, usually in 

 a high state of dispersion. It is worth noting that the press, in fraction- 

 ating the cooked fish pulp into a liquid press water (stickwater) and a 

 solid press cake, does not accomphsh a very complete separation. Upon 

 emerging from the press, the press cake more often than not contains 

 more than 50 per cent moisture, and the press water usually contains 

 small amounts of solid protein in suspension plus roughly 3.5 per cent 

 of water soluble proteins. The separation of the fish oil originally present 

 in the cooked fish into one or the other of the two fractions is not very 

 complete either. Depending upon circumstances, the press cake may 

 contain as much as 10 to 20 per cent of the total oil, leaving the rest 

 in a highly dispersed state in the stickwater. 



The screw press has, in some instances, been replaced with the con- 

 tinuous conical disc press, also popularly called the P&L disc press. 

 This press consists of two four-feet diameter press shells. The wheels 

 rotate by means of ring and pinion gears. The face of each wheel is 

 made up of six removable perforated cast steel plates covered with metal 

 screen. The angle at which the press wheels are set on the hub provides 

 a uniform, continuous pressing action from the intake side towards the 

 discharge side, and when properly adjusted seems to work very well on 



