434 ENGINEERING ASPECTS OF PASTEURIZATION 



in milk are all killed in laboratory tests by the holding method of pasteurization at 

 a temperature of 140° F. for thirty minutes. However, their destruction by either 

 steam or electric-flash pasteurization is in considerable doubt. Extensive tests to 

 settle this point will probably be necessary before flash pasteurization will receive 

 any general acceptance by health officials. 



STANDARDS POR PASTEURIZATION 



Pasteurization may be defined as the heating of milk to a temperature sufficient- 

 ly high to accomplish the complete destruction of disease-producing bacteria found 

 in milk without appreciably altering the taste and nutritional qualities of the milk, 

 followed by prompt cooling. The legal definitions adopted or suggested for ordinances 

 give: (i) the temperature to which the milk must be heated; (2) the time that the 

 milk must be held at this temperature; and usually (3) the temperature to which the 

 milk must be immediately cooled. 



Typical legal definitions are given below: 



1. Standard MUk Ordinance, United States Public Health Service, as approved 

 by the Conference of State and Territorial Health Officers: "The terms 'Pasteuri- 

 zation,' 'Pasteurized,' 'Pasteurize,' and similar terms shah be taken to refer to the 

 process of heating every particle of milk or milk products to a temperature of not less 

 than 145° F., and holding at such temperature for not less than 30 minutes in pas- 

 teurization apparatus approved by the health officer, the temperature and time being 

 automatically recorded by a temperature and time-recording device approved by the 

 health officer." 



2. International Association of Dairy and Milk Inspectors: "Pasteurization is 

 the process of heating milk to a temperature of approximately 145° F., never lower 

 than 142° F., holding every portion of the milk at that temperature for a period of at 

 least 30 minutes and then promptly cooling below 50° F." 



3. Food Inspection Decision 200, issued by the United States Department of 

 Agriculture, established a definition which was adopted by the Joint Committee 

 on Definitions and Standards, composed of representatives of the United States De- 

 partment of Agriculture, the Association of American Dairy, Food and Drug Officials, 

 and the Association of Offlcial Agricultural Chemists, at its meeting January 18-29, 

 1926. The definition states: "'Pasteurized Milk' is milk that has been subjected to 

 a temperature not lower than 145° F., for not less than 30 minutes, after which it is 

 promptly cooled to 50° F. or lower." 



In the last few years considerable controversy has arisen over the proper tempera- 

 ture for the pasteurization of milk when using the accepted thirty-minute holding 

 period. It is well recognized that heating higher than 145° F. reduces the cream vol- 

 ume on the bottle of milk as delivered to the consumer. This is an important com- 

 mercial factor in the sale of milk in view of the extensive practice of using the cream 

 from the top of a bottle of milk for coffee and cereals in the American home. A re- 

 duction in cream line on pasteurized milk is also of indirect public health significance 

 in localities in which it is sold in competition with raw milk, since it may cause con- 

 sumers to favor the purchase of raw milk having a deeper cream line, although it 

 may have no greater butter-fat content than the pasteurized mUk. 



