120 U. S. BUREAU OF FISHEEIES 



canning of shrimp extends itself well into the afternoon, while the 

 peelers are generally relieved early. The canning operation usually 

 extends -4 hours beyond the time when the last shrimp are peeled or 

 headed. This interval could be used for the steaming of the waste 

 and the acidulation, without requiring that steam be kept up for 

 an extended period. Less care in handling is required wnth this 

 material, and the product is in storage a much shorter time before 

 it becomes softened enough for disintegrating and mixing with 

 other fertilizer material. The yield varies slightly with the stock, 

 but 1 ton of the raw shrimp heads produces approximately 760 

 ])ounds of fertilizer material. 



GENERAL CONSIDERATIONS OF THE VARIOUS METHODS 



Steaming versus cooking in liquids. — Experiments indicated the 

 impracticability of using straight atmospheric steaming process. 

 The resultant stock, after steaming under such conditions for periods 

 as long as 2 hours, is not thoroughly processed, only that portion in 

 thin layers or the waste on the surface appearing to be cooked. 

 This waste easily putrefies and is susceptible to fly infestation. 

 High pressure steaming requires sealed containers to effect the 

 penetration of the steam into the stock. The use of liquid as a 

 cooking medium is to be preferred, owing to the short time necessary 

 for the penetration of the heat and the conversion of the albuminous 

 matter into the coagulated mass in the stock. A 10-minute cooking 

 in water is more effective than a 2-hour period of steaming. 



Necessity of cooking. — Whether cooking is necessary or not de- 

 pends upon the product that is sought. Cooking is necessary for all 

 material intended for feedstuff. For material prepared for fertilizer 

 use, shortening the time of cooking requires more acid to be added 

 to the waste in order to prevent fly and maggot infestation. The 

 amount of acid used varies with the rate of subsequent drying, less 

 acid being required with rapid drying. A safe amount of acid with 

 the cooked stock is G per cent and with the noncooked stock the 

 lower limit is 10 per cent. However, this may be dropped to 8 per 

 cent if the waste is ground to a pulpy mass before the acid treatment. 

 In general it appears to be more economical to cook the shrimp waste 

 before treatment. 



Brine-cook versus water-cook methods. — The concentration of brine 

 greatly influences the keeping qualities of the desiccated stock, since 

 the salt content of the finished product is roughly proportionate to 

 the brine concentration. Therefore, the brine has a distinct advan- 

 tage over the water as a cooking medium. However, if it is desired 

 that the product have a low salt content, then it will be necessary to 

 reduce the brine concentration or eliminate the salt entirely. This 

 last practice requires greater attention and care in handling of the 

 shrimj) after cooking than in the case of the brine cook. The use of 

 brine does not materially affect the iodine, oil, or nitrogen content 

 of the dried w%aste when the results are calculated to the salt-free 

 basis. 



Acid versus nonacld cook methods. — Sulphuric acid has the ad- 

 vantage of reducing the time of cooking necessary for preservation, 

 but less acid is needed the longer the material is cooked. The concen- 



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