REFRIGERATION OF FISH 521 



is a temperature zone below 21° in which coagulation occurs, but that 

 if the albumen is passed quickly through this zone in freezing and 

 defrosting coagulation does not occur. Coagulation that is progres- 

 sive through the storage period has been observed in frozen haddock. 

 Brine-frozen fish, not being damaged by internal crystallization, 

 are, because of coagulation, firmer than fresh fish. They are of a 

 firmness strongly suggesting rigor mortis, even after months of 

 storage, and this firmness does not pass away after a brief period as 

 rigor mortis does. Kept in a cool place, brine-frozen fish will remain 

 in this artificial rigor for days, until they are spoiled. The effect 

 probably is due to a small amount of salt that penetrates during the 

 freezing. 



HEMOLYSIS 



The red substance of blood — hemoglobin — is contained in micro- 

 scopic corpuscles. On freezing, many of these corpuscles are ruptured, 

 and the contained red hemoglobin diffuses into the blood plasma and 

 surrounding tissues, discoloring them. This is noticeable in fish 

 mainly in the neighborhood of the large arteries, especially those near 

 the backbone, where the red matter diffuses into and discolors the 

 muscle tissue. 



INTERNAL CRYSTALLIZATION 



The freezing of fish is essentially the freezing of a watery gel. A 

 large part of the water is transformed into the crystalline solid state. 

 It is well known to chemists that when substances crystallize the size 

 of the crystals formed is determined by the time required for them to 

 form. Diamonds are large crystals of carbon, requiring prolonged 

 periods to form. Man, in the short time available for his processes, 

 has been unable to duplicate nature's effort. Rock candy is sugar 

 crystallized slowly over a period of days or weeks. Fudge is also 

 sugar, but is crystallized quickly by cooling a hot solution in a 

 few seconds. One is composed of large crystals, the other small. 

 Water frozen slowly to ice in ice factories splits easily because its 

 internal structure is characterized by large crystal faces or planes of 

 cleavage, while rapidly frozen ice is hard and shatters like stone 

 because its internal crystals are small and numerous. Crystals grow. 

 A nucleus or seed is formed and more substance is laid on in layers, 

 if time permits, until the liquid substance is exhausted in building 

 large crystals. If heat is extracted too fast, this growth does not 

 have time to take place, and the crystals are small and numerous. 



This principle applies to the freezing of fish. When a piece of 

 fish is frozen with extreme rapidity by dipping in liquid air and 

 examined under the miscroscope while still frozen, no perceptible 

 change except solidification will be found to have taken place; but 

 if it is frozen somewhat less rapidly (as in the outer portion of fish 

 frozen in very cold brine) and examined while still frozen, there will 

 be observed several parallel columns of clear ice running length- 

 wise of the muscle fibers. Part of the water originally contained 

 in the protein gel has separated and frozen as long crystals of clear 

 ice. If this piece of fish is defrosted, the water is slowly reabsorbed 



