FISH-LIVER OILS 511 



AlkaJi Digestion Method 



"Equipment for the alkali digestion method of processing is somewhat different and 

 more elaborate. The grinder, liver pump, and cooker tanks are similar, except that since 

 the livers are usually diluted with an approximately equal quantity of water twice as 

 many cooker tanks are required for the same capacity as with the steaming method. 

 Agitator requirements are practically the same for the cooker tanks, except that if portable 

 stirrers are used more units should be available so that processing is not delayed in case 

 digestions require longer to complete than had been planned. If the wash-oil technique 

 is to be employed, several additional tanks and stirrers will be needed to accommodate 

 the water from the digestions. Usually a pump is used to transfer the water discharge 

 from the centrifuge to the wash-oil tanks. By means of a second pump the contents of 

 the washing tanks are returned to the centrifuge. If it is so desired, suitable piping ar- 

 rangements may be made to use one pump for a series of tanks for either cooking or 

 washing. The wash-oil tanks should have some provision for maintaining the temperature 

 of the liquor at about 180° F. This may be done by either direct or indirect heating with 

 steam. 



"The alkali process requires a close control over the pH of the liver mass during the 

 digestion period. Several companies make equipment which measure pH. A small, port- 

 able, industrial model costing approximately $150 may be used; or the more elaborate, 

 automatic recording model is available for approximately $750. 



"With the alkali process both the sludger and the oil-purifier centrifuges are necessary 

 unless only small amounts of materials are to be handled. A surge tank equipped with 

 stirring and steam heating facilities should be available to receive the skim from the 

 sludger. Any treatment to facilitate tlie breaking of the emulsion in the skim liquor 

 may be accomplished in this tank before the liquor is passed to the oil purifier. 



"When livers that are expected to yield higher potency oils are processed, the oils 

 are usually collected in separate drums or tanks in accordance with the anticipated 

 potency and the species from which the livers are derived. The wash oils are kept simi- 

 larly segregated. SuflBcient storage facilities must be provided for these lots of oils until 

 they are ready for shipment." 



Sampling of Livers 



Nearly all livers are purchased by the processors on the basis of the vitamin A 

 content. When the livers are landed at port, the cans are opened and the contents 

 examined to determine the species of liver, its color, and condition as to freshness. 

 An experienced buyer can make an approximate estimate of the vitamin content 

 by this preliminary examination. In many cases the livers are sorted according to 

 species, color, and condition of freshness at this point. Since fishermen are usually 

 anxious to receive payment as soon as possible, the livers may be purchased on the 

 basis of this estimate. 



More often this procedure is not satisfactory for either party concerned, and a 

 chemical analysis is made to determine more accurately the amount to be paid 

 for the livers. An ingenious liver-sampling device is in use in most points where 

 livers are landed. The sample is composed of several (usually five) vertical 

 plunges of the sampler through the contents of the can. These borings are located 

 one in each corner of the can and one in the center. The larger 52-gallon drums 

 of livers may be sampled with the same apparatus, and usually more borings are 

 made. 



