CHAPTER IV.* 

 THE PRESERVATION OF FOOD BY CHEMICALS. 



The addition of preservative substances to foods is a very ancient 

 practice, and as no extensive equipment is required it is one of the cheap- 

 est ways of preserving food, especially on a small scale. The resulting 

 alteration of the food in appearance and composition is greater than when 

 it is preserved by cold storage, for the preservative substance added be- 

 comes a more or less permanent constituent of the food, but the changes 

 are not necessarily undesirable. The addition of chemical preservatives 

 is often practised in conjunction with desiccation or cold, or sometimes 

 even in canned or bottled foods sterilized by heat. All the substances 

 employed as preservatives owe whatever efficiency they may possess to 

 their ability to restrict the activity of microorganisms, that is, their anti- 

 septic properties. 



THE EFFECTS OF PRESERVATIVES UPON FOODS IN GENERAL. 



In only a few instances are chemical preservatives added to foods to 

 be sold as fresh foods, and these practices are generally regarded with 

 disfavor. Their most important use is in the prepared foods, the preserv- 

 ative being incorporated with the food during the process of preparation 

 for storage. 



THE PROCESS OF CURING. The procedures employed necessarily 

 vary with different foods. Physical alterations in the food, such as changes 

 in form, texture and water content are usually involved, as well as the 

 solution of the preservative in the juices of the food. Chemical changes 

 due to the intrinsic enzymes of the food, to the various accessory pro- 

 cedures such as drying, cooking or soaking in pickling solution may 

 produce marked alteration. In some cases the preservative reacts 

 chemically with some constituent of the food. During the curing 

 process microbic activity may be more or less prominent at various 

 times, playing its part in the chemical changes. Bacteria, yeasts and 



* Prepared by W. J. Mac Neal. 



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