THE SARDINE, MACKEREL, AND HERRING FISHERIES 143 



volume of gases is less. In any event, the moisture-laden gases from the 

 drying kiln are vented to the atmosphere through a cyclone arrangement 

 while the dried meal discharging at the exit end of the kiln, together 

 with that trapped in the cyclone system, go to a dry grinder, usually a 

 hammer mill or a Rietz vertical disintegrator, where the dried meal is 

 finally reduced to the particle size usual for fish meal. The meal is then 

 carried in ducts to storage bins from where it is ultimately taken to be 

 blended and sacked in 100-pound net weight paper or burlap bags or 

 stored in hoppers for bulk shipments. The transportation of the fish 

 meal in ducts, sometimes over distances of several hundred feet, cools 

 the fish meal sufficiently so that excessive heating subsequent to storage 

 or sacking is avoided. 



Fish meal plants are often located in areas of relatively low popula- 

 tion density. In California, however, a rapid increase in population and 

 the peculiar atmospheric conditions of some of those areas have caused 

 some fish meal manufacturers to install in their plants equipment to 

 eliminate fishy odor that otherwise would escape into the atmosphere. 

 Such equipment, consisting of scrubbers or after-burners, effectively 

 eliminates odors from the relatively large volume of exhaust gases that 

 usually are involved in fish meal operations. Such equipment is, however, 

 costly and, therefore, adversely affects the production costs of a com- 

 modity which already is hard pressed in a falling market. 



Separation of Oil and Stickwater. As mentioned above, the fish meal 

 presses release from the cooked fish pulp a liquid called press water or 

 stickw^ater. This liquid contains the major part of the oil in the sardine 

 or mackerel which is, therefore, recovered by suitable treatment of the 

 press water. The fish oil in the press water is usually in a highly dispersed 

 state; this renders mechanical separation difficult. The tendency of the 

 highly dispersed oil globules to be coated with a proteinaceous film not 

 only prevents coalescence of the individual oil globules to larger ones, 

 but gives to some of the globules a density equal to the surrounding 

 aqueous medium and thus prevents their separation by gravitational 

 means. 



The usual procedure followed in the treatment of stickwater is to 

 pump the warm stickwater from the fish meal press to an overhead tank 

 from where it is fed by gravity into a centrifugal separator. The separator 

 is usually a large bowl DeLavel or Sharpies separator which divides the 

 stickwater into three parts: (1) a fraction consisting predominantly of 

 oil with a small part stickwater, (2) a stickwater fraction from which 

 most of the oil has been removed, and (3) a sludge fraction consisting 

 of a small part of stickwater containing most of the solid proteinaceous 

 matter suspended in the press water as it comes from the fish meal press. 



