No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 15/ 



This skimmed oil is usually, with fresh fish, of a pale yellow colour 

 and is altogether of the first class ; when it first ascends to the 

 surface it is limpid and almost water-white but soon becomes yellow, 



19. The boiled mass is then transferred to draining tanks, and 

 the oil from these tanks is also of better quality than pressed oil. 

 From the draining vats the mass is transferred to the presses. The 

 actual cooking time is from 20 to 30 minutes, and it is obvious that 

 there must be a large quantity of effluent water from boiling and 

 draining vats, charged with organic matter and therefore highly 

 putrescible and liable to be the cause of nuisance ; moreover the 

 organic matter is apt to be a loss of fertilizer unless it can be 

 utilized direct to crops, trees, etc. 



20. The most modern method, now general, is to substitute a 

 steam continuous cooker for the open boiling and draining vats, 

 which, in 1912, were found, it is said, only in one State, viz., North 

 Carolina. This is a long cylinder some 40' x 2', provided with a 

 longitudinal revolving shaft to which are affixed plates, blades, 

 or wings (" flights ") set at a slight angle ; in this way the fish are 

 constantly stirred and broken up, and moved, by the action of the 

 bladed shaft, towards the discharge end. Steam is admitted, 

 preferably by a numerous series of narrow pipes at the bottom of 

 the cylinder set along the greater part of its length ; it may also 

 be admitted by the shaft which is then made hollow. The raw 

 fish are fed into the cylinder by a hopper ; no water is added since 

 the fish and steam supply sufficient and since no skimming is 

 possible. Arrived at the discharge end the fish with the mixed oil 

 and water fall into a conveyor which takes them either to drainage 

 vats or direct to the presses, the latter being now usual as saving 

 time and space. The object of the draining vats when used is 

 probably to secure drained oil which is superior to pressed oil, and 

 also to minimize bulk and unnecessary fluid in the presses. 



The fish remain at most 15 minutes in the cooker, and the capa- 

 city of a single cooker of the above size is said to be 120,000 lb, 

 (60 U,S,A, tons) per hour. The capacity under the vat system 

 depends of course on the number and size of vats employed. The 

 amount of steam used per cooker is not stated, 



21. Pressing. — The old manual screw press, usually set in a 

 wooden frame, speedily gave way to powerful presses, generally 

 hydraulic, and these again in recent times have been largely 

 supplanted by continuous presses. 



