July 22, 1922] 



NA TURE 



still in the experimental stage, although a description 

 of it is to be found in the British patent specification 

 of Hesketh and Marcet of 1899. The advantage of the 

 method over that of air freezing lies in the much more 

 rapid cooling that results, and rapid cooling, as men- 

 tioned above, is a characteristic of the most successful 

 refrigeration. Brine is the only salt solution employed 

 in present practice, but other salts, such as magnesium 

 or calcium chloride, might conceivably be used. The 

 process of brine freezing has its inherent difficulties ; 

 not only may the food cell contents pass outwards into 

 the cooling medium, but salt may also pass from the 

 latter into the tissues of the food. Penetration of salt 

 into the food material is in some cases {i.e. fish) not 

 objectionable, but in certain instances chemical action 

 may occur between the foodstuff and the salt with 

 undesirable consequences. Thus, while large pieces of 

 beef frozen in brine were found to be in some respects 

 superior to air-frozen beef, a reaction takes place 

 between the salt and the pigment of the beef which so 

 changes the appearance of the latter that its market 

 value may be considerably reduced. The penetration 

 of salt into the food substance cannot be prevented, 

 but it can be minimised by a judicious selection of 

 physical conditions. 



The methods adopted for the storage of frozen food 

 require the same careful consideration as those employed 

 for freezing ; the inherent difficulties are just as great. 

 Physical changes, such as evaporation of water and 

 aromatic flavouring substances, chemical changes in- 

 cluding autolytic reactions, hydrolysis of fats and 

 oxidation of the hydrolytic products, and finally the 

 growth of moulds and bacteria, must be guarded against. 

 All these changes can be retarded by lowering the 

 temperature of the storage chambers, but economic 

 conditions impose a limit at which reduction of tempera- 

 ture must stop, ft becomes, once more, a question of 

 selecting the least injurious conditions for each particu- 

 lar food ; the conditions in storage chambers should, 

 it may be emphasised, be different for different foods. 



The use of liquid air on a large scale in the freezing 

 and storage of food appears a remote possibility at the 

 present time ; but it is perhaps not entirely fanciful to 

 picture a liquid air plant supplying nitrogen for use in 

 the refrigeration industry and oxygen for other in- 

 dustrial purposes. 



Prof. Stiles gives a brief summary of the available 

 information concerning thawing of food. This side of 

 the subject is not without importance, since the rate of 

 thawing of frozen food has a significant effect upon its 

 character. 



A considerable proportion of the report is devoted 

 to an examination of the relative merits of air freezing 

 and freezing in salt solution in the case of both fish and 

 NO. 2751, VOL. I 10] 



of meat. The comparison, so far as the ultimate value 

 of the food is concerned, is much in favour of the latter 

 process. Parenthetically it may be added that Prof. 

 Stiles does not deal with the economic side of the 

 refrigeration industry. Despitg its advantages and 

 the fact that it has been known for a considerable time, 

 the freezing of fish in a solution is a process which has 

 only been employed during recent years, and on a 

 small scale. Its chief advantages are the maintenance 

 of weight, appearance, and general food value of the 

 fish due to the reduced time of freezing and consequent 

 minimised histological change. A quantity of experi- 

 mental evidence obtained by the author and his co- 

 workers under the Food Investigation Board, as well 

 as by other workers in the subject, is collected in the 

 report, and merits careful study by those who are 

 concerned with the design and installation of food- 

 preservation plant. 



For the refrigeration of meat, freezing by immersion 

 in brine has not yet been technically employed ; the 

 only process utilised is that of freezing in cold air. 

 Beef which has been preserved in the frozen state is 

 frequently inferior to fresh beef on account of the drip 

 of meat juice which occurs on thawing. This loss may 

 amount to as much as 15 per cent, of the weight of 

 the meat. Consequently beef is, wherever possible, 

 transported in the chilled condition ; but since it 

 cannot be kept in this state for more than three or four 

 weeks, it is not possible to import chilled beef into the 

 United Kingdom from Australia or New Zealand. 

 From far distant countries beef must come " on the 

 hoof " or in the frozen condition. Mutton, on the 

 other hand, can be imported in the frozen state from 

 the countries named in perfectly satisfactory condition. 

 The discovery of a method of freezing beef which will 

 obviate the difficulties mentioned is evidently a matter 

 of importance, and the attempts made by the Food 

 Investigation Board in this direction are of considerable 

 interest. Small preliminary experiments indicated 

 that rapid freezing by immersion in cold brine was an 

 effective way of preservation so far as absence of drip, 

 and appearance and flavour of the product after thaw- 

 ing were concerned. Larger -scale experiments have 

 not yet gone sufficiently far to yield conclusive results. 

 One rather serious objection has already been 

 mentioned. This is the discoloration of the surface 

 layers of the lean of the meat owing to the conversion 

 of haemoglobin into methsmoglobin. The discolora- 

 tion detracts seriously from the appearance and market 

 value of the meat, but it is hoped that the cause, and a 

 method of prevention, will be discovered in the course 

 of further work. The successful application to beef of 

 the method of brine freezing would lead to a very 

 desirable expansion of our source of supply. 



