PROCESSING FISH MEAL AND OIL 225 



through. Steam is introduced through a series of pipes leading from one 

 or, more often, two manifolds that run the length of the cooker. Cooking 

 is at essentially atmospheric pressure since only the mass of fish in the 

 screw and in the feed hopper retains the steam, which may blow back if 

 the feed-in is stopped for a short time for any reason. 



Ideally this type of plant is designed so that the presses can handle 

 most of the fish from the cookers and the dryers can take care of all the 

 press cake coming from the presses. When equipment is matched in this 

 way, there is neither an accumulation of cooked fish nor press cake when 

 all the equipment is operating at its normal capacity. Irregular input or 

 underloading results in inefficient pressing and overheating in the dryer 

 as well as blowback in the cookers. It is for this reason that all the large 



MATERIAL FEED 



Figure 16.2. Diagram of fish meal direct steam cooker. 



plants have a ''raw box" or equivalent storage capacity for raw fish. This 

 permits the accumulation of enough material to carry the process line 

 through the intervals between arrival of the fish boats and the time 

 needed to shift vessels and hook up the discharge pumps. Normally the 

 plant, once started, runs continuously until the last of the fish are 

 cleaned up. 



A relatively recent modification, in limited use by the industry, is the 

 indirect cooker in which the steam is retained in the jacket of the vessel 

 and usually also in the special hollow conveyor screw. The indirect cooker 

 has the advantage of reducing the amount of press liquors that need to 

 be centrifuged and later evaporated. It also reduces the loss of solids and 

 increases the yield of scrap and meal. Cost of this type of cooker is higher, 

 and some operators believe that the excess water from condensed cooking 

 steam is necessary to ''wash out" the oil during pressing. 



