16 BULLETIN 378, U. S. DEPARTMENT OF AGRICULTURE. 



GENERAL METHODS FOR THE MANUFACTURE OF FISH MEAL. 



Fish meal may be made by the same general methods that are now 

 employed in the preparation of fish scrap for fertilizer purposes; 

 that rs, by steam cooking of the raw material, pressing, and drying. 

 The chief difference, which should be constantly borne in mind, is 

 that the meal is to be used as a stock food and should therefore be 

 prepared from raw material in a perfectly fresh state and under 

 clean, sanitary surroundings. 



A steam- jacketed retort cooker, or one in which the material is 

 heated directly by steam, may be employed. There is also an auto- 

 matic continuous cooker which serves very well for cooking the raw 

 material. 



Pressing of the material may be accomplished by means of the 

 hydraulic press, the rack and cloth type of press, or by the automatic 

 continuous screw press. The material should be pressed while hot, 

 thus insuring the removal of the maximum quantity of oil. 



There are several types of dryers suitable for drying the material, 

 among which are the rotary dryers using direct heat or steam heat, 

 and the stationary steam- jacketed dryers provided with a rotating 

 shaft and blades for stirring the material. In the latter type prefer- 

 ence should be given to the dryer providing for evaporation under 

 vacuum. In the former type, the final dried product is in a granular 

 form, which is very desirable when it is to be used as a poultry food. 

 For use in other stock- food mixtures it would be preferable to have 

 it finely ground. The revolving blades in the latter type grind the 

 material during the drying process to a fairly fine meal, and for all 

 ordinary purposes it should not require further grinding. In some 

 cases wdiere large fish are used, further grinding may be neces- 

 sary to remove the eye balls and large bones. No attempt is made 

 to recommend any particular type or kind of cooker, press, or 

 dryer. These should be selected according to individual require- 

 ments, depending on the character and the quantity of the waste to 

 be converted into meal. The prospective manufacturer of fish meal 

 should thoroughly study all the different forms of apparatus men- 

 tioned above and select the type best suited to his particular needs. 

 The more modern and later methods of manufacture should also be 

 investigated. 



A prominent feature in connection with the preparation of fish 

 and fishery wastes into material for feeding purposes is the produc- 

 tion of a very superior grade of fish oil. The oil rendered from raw 

 material which of necessity must be in a perfectly fresh state of 

 preservation for making into meal for stock food, cannot be com- 

 pared with fish oil obtained from material in any stage of decompo- 

 sition. The former oil would require but little refining, for in the 



