POPULAR SCIENCE 433 



expectation. Although, as we pointed out in our last article, 

 the method of freezing tissue in cold brine was a British inven- 

 tion, it is from Germany that published results, in which this 

 more rapid freezing of food has been undertaken, are so far 

 available. It is found, for example, that most fish are suit- 

 able for preservation by freezing, but that the usual method 

 of freezing slowly in air is much less satisfactory than freezing 

 in a brine solution because by the former method large ice- 

 crystals are produced in the fish outside the muscle fibres, 

 which damage the fibres, whereas by rapid freezing in brine 

 the muscle liquid solidifies inside the fibres themselves and 

 hence does not exert any external pressure on the fibres. As 

 a consequence fish frozen in brine is of a considerably higher 

 quality as regards nutritive value, appearance, and taste than 

 fish frozen in air. 1 Similar results are obtained with meat, 8 

 but at present no details have apparently been published in 

 regard to scientific experiments carried out with meat. An 

 attempt has however been made to calculate the relation 

 between the rate of freezing and the condition of the frozen 

 material. 3 These calculations, however, include certain as- 

 sumptions which render the data obtained only approximate. 

 In the results given, a quantity called the " freezing velocity " 

 is utilised. When a block of tissue is frozen the outer partis 

 first frozen, and the limit of frozen tissue continually marches 

 inwards. The rate at which this march proceeds is called the 

 " freezing velocity." It is calculated that when the freezing 

 velocity proceeds at a rate of from i to 2 cm. per hour or 

 quicker, the release of water from the muscle fibres is pre- 

 vented, and consequently the " drip " from the meat on 

 thawing does not take place. 



Contrary to expectation it is stated by the German in- 

 vestigators that the rate of thawing is without influence on 

 the water relations of the tissue. This is a question to which 

 no doubt further attention will have to be given, and the same 

 applies to the changes taking place in frozen food material 

 during storage, about which very little definite information is 

 available. 



In these articles we have selected for consideration some 

 of the scientific aspects presented by the cold storage of three 



1 R. Plank, E. Ehrenbaum, and K. Reuter, " Die Konservierung von Fischen 

 durch das Gefrierverfahren," Berlin, 1916. 



2 R. Plank and E. Kallert, " Ueber die Behandlung und Verarbeitung von 

 gefrorenem Rindfleisch," Berlin 1916. 



3 R. Plank, " Uber den Einfluss der Gefriergeschwindigkeit auf die histolo- 

 gischen Veranderungen tierischer Gewebe," Zeitsch. f. allg. Physiol. 17, 221-38, 

 1918. 



