616 SCIENCE PROGRESS 



The main distinction between food substances at presenl 

 in regard to cold storage appears to lie in their methods ol 

 preservation. These are two in number and are as follows : 



i. The temperature is kept above a certain value (o° C. 01 

 a little lower) whereby no change in the physical state of the 

 produce is caused, such as in the case of chilled beef, fruits 

 eggs, etc. On the other hand, at these storage temperatures 

 certain chemical processes take place which bring about the 

 maturing of the substances or their deterioration. 



2. Low temperatures are employed which cause an im- 

 mediate alteration of the physical structure of the substance 

 as a result of freezing. On the other hand any chemical actions, 

 including enzymatic processes, will proceed at an extremely 

 slow rate, and so the keeping properties of the produce will 

 be enhanced. We are here mainly concerned with the ques- 

 tion whether the processes involved in the freezing of the 

 substance can be made reversible on thawing, so that the 

 substance presents its normal appearance and retains its 

 qualities, in regard to nutrition and taste. A much wider 

 scope for variation in method is provided in this class of pro- 

 cess, and one of the chief objects of investigation at present 

 must be to transfer as many food substances as possible from 

 the first group to the second. 



Any classification is of course artificial, and the two classes 

 are connected by a series of transitional substances. The 

 further research progresses the more the sharpness of the 

 distinction between the two groups will be effaced. 



We shall in the following deal in succession with examples 

 from these two classes. As an example of the first class we 

 shall consider the cold storage of fruit, a produce which dis- 

 tinctly belongs to the first group, as up to the present its 

 preservation by freezing has only been employed in excep- 

 tional cases. On the one hand not much variation in method 

 is possible, but on the other hand a close study of metabolic 

 processes is necessary in order to determine at what stage of 

 development it is best to store the fruit and to discover for 

 how long the fruit can be kept in store. It must also be borne 

 in mind that with fruit it may be a case of preserving normal 

 appearance, as when the fruit is sold as such to the consumer, 

 or on the other hand storage may be a measure for dealing with 

 gluts of fruit which is subsequently used in the manufacture 



