DAIRY FARMING DAIRYING. 85 



milk heated for 20 min. at temperatures ranging from -io to 7(» C. 

 Over 91» per cent of the bacteria present in the unpasteurized milk 

 was destro^^ed by pasteurization at 140 F. 



Viscometer tests made according to the method previousl}'^ described 

 (E, S. R., 9, p. 181) showed practically no difference in the consistency 

 of raw cream and cream pasteurized at 140° F. for 30 min. 



The following summary is given: 



"The temperature recommended for the pasteurization of milk and cream in tlie 

 past has been 155° F. for a period of 15 to 20 minuten. This limit was chosen 

 because it had been regarded as the point at which the tubercle bacillus is destroyed 

 in a moist medium. When, however, cream or milk is heated to a temperature of 

 140° F. or above, the physical condition of the fat globules is changed so that cream 

 appears much thinner and milk loses its i)roi3erty of rapid creaming. This objection 

 can be overcome, as is shown by the preceding experiments, if milk or cream is not 

 heated above this temperature. 



' ' Not only is the creaming property of the milk, and the ' body ' or consistency of 

 cream unaffected, but the keeping quality is practically as good as it is where the 

 product is heated to a temperature of 155° F. All that is necessary to secure good 

 keeping quality is to destroy the vegetative bacteria, and as this is accomplished at 

 the temperature of 140° F. if the exposure is made for a sufficient period of time, no 

 advantage in this respect is to be gained by heating to a higher temperature. This 

 being true, it only remains to determine with certainty how long an exposure must 

 be made to destroy the tubercle bacillus. The temperature limit that has heretofore 

 been considered necessary where the exposure was made at 140° F. was 1 hour, but 

 recent extensive experiments by Theobald Smith, in which all conditions have been 

 most carefully controlled, show that this time can be materially shortened where 

 milk is agitated during pasteurizing. A thorough retest of this point is now being 

 made under factory conditions and the exact time period will be determined on the 

 Imsis of these trials." 



Pasteurization of skim milk, E. H. Farrington ( Wisconsin Sta. 

 Rpt. ISdd^'jjp. l'£l-l'28^Jigs. 2). — The methods and advantages of pas- 

 teurizing skim milk at creameries are discussed, and a device for 

 heating skim milk by means of exhaust steam, constructed by J. C. 

 Fortiner of the University creamery, is described. 



This skim-milk heater consists of an ordinary tin pail which is sus- 

 pended over the storage vat, and into which the pipe conveying the 

 skim milk from the separator and the one conducting the exhaust steam 

 from the creamery engine empty. The skim-milk pipe extends about 

 18 in. up into the steam pipe, which arrangement is thought to aid in 

 utilizing all the heat of the exhaust steam and to prevent the skim 

 milk from being blown from the pail by the steam. The skim milk is 

 thus heated as it comes from the separator and flows over the top of 

 the pail into the large vat from which the patrons of the creamer}^ are 

 supplied. In practice about 2,500 lbs. of skim milk per hour was 

 heated to 160° F. and 4,000 lbs. to 140°. It was found that skim 

 milk heated in this way remained sweet about 1 day longer than 

 skim milk not heated. Only perfectly sweet milk can be used where 

 this method of pasteurizing the skim milk is employed. 



