482 MICROBIOLOGY OF SPECIAL INDUSTRIES 



common salt, 5 per cent sugar, and i per cent saltpeter. The brine is renewed once 

 or twice at intervals of a week or ten days. After about a month the hams are 

 washed in warm water, dried and hung in wood smoke for several days. They are 

 then stored in a cool place. The proportions of the various constituents of the 

 pickling solutions are subject to rather wide variation, and in general it may be 

 said that the higher the temperature of the storage room, the more concentrated 

 must be the pickling solutions to insure satisfactory preservation. 



Dairy Products. — Butter is usually salted ^th sodium chloride 

 to impart the desired taste, and this salt also acts to some extent as a 

 preservative by increasing the osmotic tension of the moisture remain- 

 ing in the butter. Antiseptics such as boric acid, saltpeter, salicylic 

 acid and formaldehyde have been employed in the preservation of 

 butter, the first-mentioned appearing to be the most satisfactory. 

 One half of i per cent of boric acid incorporated with high-grade butter 

 previous to storage greatly delays rancid change. 



Fresh milk and cream are also sometimes treated with antiseptics 

 such as formaldehyde, but the use of any chemical preservative what- 

 ever in these dairy products is unnecessary and generally disapproved. 



Prepared Vegetable and Fruit Foods. — ^These foods are some- 

 times preserved by vinegar, sugar or alcohol, the presence of which is of 

 course very evident to the consumer. Other substahces less readily 

 detected, such as sulphurous acid and sulphites, boric acid, salicylic acid, 

 benzoic acid and sodium benzoate, and formaldehyde, are also em- 

 ployed in foods which must be kept some time after exposure to the air. 

 These substances are incorporated with the food before it is packed,, 

 and serve to prevent the activity of microorganisms which gain access 

 to it. 



The Nutritive Value or Preserved Foods 



The nutritive value of a food depends upon the amount of utUizable 

 food principles it contains. The food-principle content can be readily 

 measured by chemical analysis, and in general there is no important 

 difference between a preserved food and the corresponding fresh food 

 in this respect. The utilization of the food principles, however, 

 depends upon a number of factors and may be greatly influenced by 

 individual peculiarities of the consumer. One important factor in the 

 utilization of a food, and probably the most important factor in deter- 

 mining its market value, is palatability. Iri general, preserved foods 



