(4) Heating was continued for from 15 to 30 minutes at full steam 

 pressure until contents of the barrel had reached 200° F, 



(5) Heating at 200° F., with agitation, was continued until a sample 

 of the liquor showed little if any solids remaining other than 

 bone particles. The digestion time was 70 to 90 minutes depend- 

 ing on the size of the heads and the initial temperature of the 

 offal. 



(6) When the test sample of the liquor indicated complete digestion, 

 the heating and agitation was discontinued and the liquor was 

 allowed to stand for 10 minutes to facilitate settling out of 

 solids (bony materials for the most part). 



(7) Meanwhile the centrifuge had been started and thoroughly heated 

 by the passage of 10 gallons of hot water (210° F.) through the 

 machine. 



(8) The contents of the barrel (other than the solids) were passed 

 through the centrifuge. 



(9) The oil recovered was weighed, the color was noted, and the 

 samples for vitamin A analyses were hermetically sealed in tin 

 cans. 



Suitability of Alkali Digestion Method for Processing Salmon Offal 



The alkali digestion technique advocated by Anderson (1) as being 

 suitable for the recovery of oil from salmon heads and collars was used 

 as the starting point for the project. These former experiments had shown 

 that salmon heads and collars could be satisfactorily processed, using 

 sodium hydroxide to the amount of 1.5 percent of the weight of the fish. 



When this project was begun, it was assiomed that the oil from the 

 salmon heads would be needed to collect, by oil-solvent extraction, 

 the vitamin A known to be present in the relatively less oily visceral 

 material. After the first few digestions it became apparent that no 

 particular difficulties existed with respect to the processing of total 

 cannery waste by the technique outlined above. The protein portion of the 

 waste was readily liquified, the bony portion settled out of the liquor, 

 and upon centrifuging, an oil of excellent color and odor was obtained. 

 Next a digestion was completed using only the soft portions of the waste — 

 the gonads, liver, and digestive tract — and again there was no great 

 difficulty encountered. The quantity of oil recovered was small — about 

 1.5 percent of the weight of the waste used — but the color and odor were 

 as good as for the oil obtained from the heads. The vitamin A content tests 

 of the oil so produced brought out the diluting effect of the oil contri- 

 buted by the salmon heads whoi they were digested with the visceral por- 

 tion of the waste. 



38 



