rejects of tuna because of spoilage became 

 alarmingly large, the boat owners faced a 

 critical situation. The progressively 

 longer distances that the ice boats trav- 

 elled created this situation and forced 

 boat owners to adopt a new refrigeration 

 system. Land and Farber recommended the 

 adoption of the brine freezing system, and 

 since then the rejects, from all causes, 

 have declined drastically. On the whole 

 this system of preservation has worked well 

 and the type of quality deterioration which 

 we find today is different from what it 

 used to be in ice boats. 



Many of the tuna clippers now bring 

 in tuna with little evidence of spoilage or 

 even of incipient spoilage in the fish as 

 measured by the organoleptic test or by the 

 use of conventional chemical spoilage tests. 

 In spite of this, it is evident that the 

 tuna has undergone certain physical and 

 other changes which are undesirable. These 

 changes are, in our view, due to changes 

 which occur when the freshly caught tuna 

 either is not frozen soon enough after cap- 

 ture, or not fast enough, or not kept at a 

 low enough temperature while in transit. 

 If these assumptions are valid, any study 

 of means for the improvement in quality of 

 tuna while in transit should be focused on 

 the chemical engineering aspects of the 

 problem rather than primarily on the chem- 

 ical aspects. In view of this, we have in 

 our recent work laid more emphasis on the 

 chemical engineering aspects of the problem. 



The rate at which freshly caught tuna 

 in a well may be cooled and frozen depends 

 upon several factors. One is adequacy of 

 refrigeration capacity on board ship; 

 another is the rate at which the refriger- 

 ant removes the natural heat from the tuna. 

 In a sense the well of a vessel may be con- 

 sidered a heat exchanger where exchange of 

 heat takes place between a fluid and a solid. 

 In such an exchange the interstitial volume 

 and surface of the packed tuna play pre- 

 dominant roles. The interstitial volume is 

 also of interest to the practical question 

 of how many pounds of tuna can be stored in 

 a well per cubic foot of well space. Should 

 it be 60 pounds or 50 pounds or liO pounds 

 per cubic foot? If considerations of quality 

 were unimportant, it should be about 60 

 pounds. Under such conditions, however, 

 there would be little interstitial volume 

 and interstitial area and, therefore, no 

 internal heat exchange between the solid 



block of tuna and the circulating brine. 

 The result would be slow cooling and 

 freezing and the development of "hot spots" 

 in the tuna and consequent damage to qual- 

 ity. Furthermore, when the tuna finally 

 has been slowly frozen and thawing starts 

 in port, it will proceed at a very slow 

 rate leaving possible "cold spots" in the 

 tuna and causing excessive salt penetra- 

 tion, and warped and mutilated fish will 

 also result. Some tests carried out in 

 our laboratory on the interstitial volume 

 of tuna and other fish in a state of ag- 

 gregation similar to that which obtains 

 in a well, varied from h0 percent to lU 

 percent. The interstitial area will, of 

 course, vary with the interstitial volume, 

 but this relationship has not been meas- 

 ured yet. It should be done. 



The importance of finding a value for 

 interstitial volume which will permit a 

 fast rate of cooling and freezing of tuna, 

 so long as that is being done exclusively 

 in the wells, will also apply to the sub- 

 sequent thawing process. Inasmuch as heat 

 exchange in thawing is the opposite of 

 freezing, the physical laws governing 

 freezing will apply but the flow of heat 

 if reversed. The present method of thawing 

 is not, it seems to me, taking full advan- 

 tage of that principle and could, therefore, 

 likely be much improved, thereby avoiding 

 unpleasant salt penetration and other ef- 

 fects which contribute to quality deteriora- 

 tion. A cut in thawing time resulting from 

 such improvements should also cut the time 

 the vessel stays in port and improve the 

 general economy of the clipper boat. It 

 is hoped that an opportunity will soon 

 present itself so that a guided and speeded 

 up thawing procedure, which we have in mind, 

 may be tested. 



A study of the chemical engineering 

 features involved m the preservation of 

 tuna while in transit on the clipper, has 

 revealed the desirability of collecting 

 more data on the physical properties of 

 tuna in the frozen as well as the unfrozen 

 state. Such data are being collected now, 

 data such as specific heat of tuna, specific 

 gravity and the change of volume of tuna 

 with temperature change, etc. A paper on 

 the importance of interstitial volume and 

 area in heat exchange problems is under 

 preparation. 



It is my hope that there will be 



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