COLD STORAGE PROBLEMS 155 



temperatures; the other methods will therefore he mentioned but 

 briefly. 



The Use of Harmless Preservatives 

 Sugar and acids are perhaps the most important of these. By add- 

 ing large amounts of sugar to perishable foods, such as berries or their 

 expressed juice, and dissolving the sugar by heat, the berries may be 

 kept in good condition for unlimited periods. The same result is ob- 

 tained by the use of acids in the preparation of pickled vegetables, 

 pickled meat, the curing of hams, etc. Spices also act as preservatives 

 and many delicacies are preserved in oil. 



The Use of Chemical Preservatives 



Of these benzoate of soda, formalin, boric acid and salicylic acid are 

 used to some extent. Whether these are unwholesome in the small 

 quantities used is still disputed. The relative amounts are certainly 

 very small and harmful results can only be incurred by continued use. 

 Alcohol is also a powerful preservative and is produced by allowing 

 fruits, etc., to ferment. The perishable grape is thus transformed into 

 stable wine. 



The Application of Heat 



The enormous canning industry uses heat as a preservative, followed 

 by exclusion of air. First the microorganisms are destroyed by heat 

 and then renewed invasion is prevented by sealing the containers her- 

 metically. Temperatures, lower than those used for canning, are ap- 

 plied in pasteurizing milk and beer. Pasteurization is carried out by 

 heating milk or beer from 140 to 145° F. for 20 to 30 minutes. This 

 process does not kill all microorganisms, but the great majority, in- 

 cluding disease germs. If pasteurized milk is cooled rapidly and kept 

 cold it will remain sweet for days. Pasteurized beer^vill keep much 

 longer, since the amount of alcohol contained in it aids in protecting 

 against decomposition. 



Conservation by Desiccation 

 Desiccation — the abstraction of water — has been applied to the 

 preservation of fruits, meat, eggs and milk. Fruits are dried in the 

 open air exposed to the sun or by artificial heat. Desiccated products, 

 of course, can be of no better quality than the original substance. Poor 

 fruit, dirty milk, decomposed meat and aged eggs can not be expected 

 to improve by desiccation. Milk should be clean before desiccation, but 

 unfortunately this is not often the case, and the production of eggs is 

 not as sanitary and well regulated as might be desired. Eggs are 

 rarely, if ever, sterile when freshly laid, the term sterile applying to the 

 total absence of microorganisms. It is certain that, after laying, bacteria 



