PASTEURIZATION 459 



surrounding the jar from 160° to 180° F. for about 30 minutes. This 

 is known as pasteurization. Afterwards treat exactly as you did the 

 first jar of milk. 



What is the odor of milk in each jar after 24 and 48 hours? What 

 is the taste of the milk in each jar after 24 and 48 hours? 



What are found in milk that cause it to sour? How do you know? 

 What is the use of pasteurization ? 



Pasteurization. Milk is one of the most important food sup- 

 plies of mankind. It is also one of the most difficult things to get 

 in good condition. This is due in part to the fact that milk is 

 often produced at long distances from the place where it is used 

 and must be brought first from farms to the railroads, then shipped 

 by train, taken to the milk supply depot, bottled, and again taken 

 by delivery wagons to the consumers. During each successive 

 handling and exposure to the air the milk receives more bacteria. 

 When we remember that much of the milk used in San Francisco, 

 St. Louis, Chicago, New York, and other large cities is from twelve 

 to thirty-six hours old before it reaches the consumer, and when 

 we realize that bacteria grow very rapidly in milk, we see the need of 

 finding some way to protect the supply so as to make it safe, par- 

 ticularly for babies and young children. This is done by pasteuri- 

 zation, a method named after the French bacteriologist, Louis 

 Pasteur. 



Preservatives. A few substances check the development of 

 bacteria and in this way preserve the food. Preservatives are of 

 two kinds, those harmless to man and those that are poisonous. 

 Of the former, salt and sugar are examples ; of the latter, formalde- 

 hyde and possibly benzoic acid. 



Sugar. We have noted the use of sugar in canning. Small 

 amounts of sugar are readily attacked by yeasts, molds, and 

 bacteria, but a 40 or 50 per cent solution will effectually prevent 

 such growths. Preserves are fruits boiled in about their own 

 weight of sugar. Condensed milk is preserved partly by the sugar 

 a,dded to it ; so are candied fruits. 



Salt. Salt has been used for centuries to keep foods. Meats 

 are smoked, dried, and salted ; some are put down in strong salt 

 solutions. Fish, especially cod and herring, are dried and salted. 

 The keeping of butter is due to the salt mixed with it. Vinegar 



