Precautions must particularly be taken against Salmonella contamination. This organism is destroyed in the cooking plus pressing process provided the temperature is raised above 80°C, but poor hygiene beyond this point could result in re-infection of the meal. It must be stressed that although high air temperatures are reached in the dryers, the fish material in the dryer may not reach a sufficiently high temperature for sufficient time to destroy Salmonella. To minimize the risk, the manufacturers should observe the following precautions:
a.The land around the factory should be well kept and regularly maintained to keep down rodents. birds. flies and all insects. Very strict control in this respect is necessary in areas where fish material is processed and fish meal stored.
b.Ventilators and other openings in factory and storage buildings should be protected by insect screens and rat wire.
c.In order to keep the product dry, storage buildings should have concrete floors and leak-proof walls and roofs and, if necessary, roof insulation to avoid condensation and drip; conveyors should have covers.
d.Walkways to storage areas should be kept clean and foot bath mats charged with a disinfectant. Such as phenolic or quaternary ammonium compounds, should be available for personnel at storage entries.
e.It is desirable to keep the wet and dry areas of the plant separate and to reduce to a minimum the passage of personnel and equipment from one section to the other.
f.A proper factory cleaning scheme is necessary. Empty storage bins and unloading areas should be cleaned as soon as possible after use. Process machinery should be cleaned regularly by high pressure jets of hot water and detergent solutions.
g.Stick water concentrate and decanter sludge must be heated to 93°C or more before adding to the press cake. For about three quarters of an hour after the start of operations, while the machinery is warming up to normal operating temperature, all press cake produced must be returned to the cooker intake for recooking and repressing in case contamination might have occurred.
Should Salmonella, nevertheless, be detected in fish meal, the contaminated lots must be disinfected, for example in special apparatus in which the meal is heated at about 90°C with live steam for 10 to 15 min and then redried. Alternatively, biocides such as formic and propionic acids can be used to treat infected fish meal. These are expensive processes, however, and it is far more economical to comply with the outlined precautions.