KILLING BACTERIA BY HEAT 



served fruits keep indefinitely because of the sugar in them ; 

 bonbons and confections become stale, but they do not decay, 

 because they contain too much sugar for the growth of bacteria. 



Salt is a universal preservative of foods. Herring, cod, and 

 mackerel caught in the spring are salted and then shipped all 

 over the United States for use as food during the winter. Salt 

 pork and corned beef are safe against decay. Cheese closely 

 wrapped with salty wet cloths, or soaked in saltwater, does not 

 spoil, and well salted butter keeps longer than unsalted butter. 



Vinegar and most acids stop the growth of bacteria. Pickled 

 beets keep for days in warm weather, while fresh buttered beets 

 spoil rapidly; pickled cucumbers or pickles keep for months 

 and years, but fresh cucumbers become stale in a few days. 

 The Germans pickle a great many vegetables, some of their 

 most common winter dishes being pickled beans and cabbage. 



Killing bacteria by heat. Low temperature does not kill 

 bacteria, it merely keeps them inactive, but high temperature 

 destroys them. Low 

 temperatures hinder 

 growth, moderate tem- 

 peratures permit slow 

 growth, temperatures of 

 70 F. to 95 F. cause 

 rapid growth, tempera- 

 tures above 95 F. check 

 growth, and a high tem- 

 perature such as that of 

 boiling water not only 

 checks growth but de- 

 stroys all bacteria. Raw 



FIG. 48. Pasteurizing apparatus, an arrange- 

 ment by which milk is conveniently heated to 

 destroy disease germs. 



or uncooked milk is dangerous for young children because of the 

 bacteria it contains; well heated milk is safely fed to young 

 children because the dangerous bacteria in it have been de- 



