DAIRY FARMING — DAIRYING. 673 



The pasteurization of dairy by-products, W. D. Dotterkeb and R. S. Breed 

 {New York State Sta. Bui. Jfl2 {1915), pp. 581-610).— The work reported in 

 this bulletin, which was conducted in cooperation with the New York State Com- 

 mission for the Investigation of Bovine Tuberculosis, was planned in order to 

 study the effect of pasteurization on the whey and skim milk, the efficiency of 

 the present methods of pasteurization, and the best methods of pasteuriza- 

 tion. 



Visits were made in the course of this inquiry to seven Cheddar cheese fac- 

 tories and to two skimming stations at which pasteurization of whey or skim 

 milk was being carried out. According to the 1915 list there are about 950 

 cheese factories in the State, of which 55 are known to be pasteurizing whey. 

 Thirty-one of these factories- make Cheddar, 13 make Swiss, 9 make Limburger, 

 and 2 make brick cheese. At but one of the cheese factories visited were the 

 temperatures used in pasteurization high enough to meet the lowest require- 

 ment (178° F.) usually specified by law. At this factory the temperature used 

 only occasionally reached this figure. All but two factories, however, were 

 using temperatures which would meet the requirements of the Michigan law 

 (145° for 30 minutes). The two factories which used lower temperatures 

 than this were also losing part of the value of the pasteurization by adding 

 separator slop or water after the temperature was so low as to be ineffective 

 in killing bacteria. One other factory followed this same practice so that the 

 pasteurization which would have otherwise been effective was rendered un- 

 satisfactory. The four factories which were securing satisfactory results 

 were all pasteurizing by means of a steam line running into the whey tank. 



It was found that the process of heating the whey aided in preserving 

 the whey in good condition for feeding until it was convenient to use it. This 

 was due to the fact that the fat did not rise so quickly nor so completely on the 

 heated as on the unheated whey, thus preventing the formation of an unde- 

 sirable scum of fat on the whey tank. The heating also killed all of the 

 organisms which ordinarily cause fermentations in the whey with the exception 

 of Bacilltis hulgaricus, an organism which causes a lactic acid fermentation. 

 The growth of this organism was retarded by the heating, so that the heated 

 whey, as delivered to the farmers, had an acidity of about 0.4 per cent while 

 the unheated whey had an acidity of about 1.1 per cent. 



The pasteurized whey was found to be free from yeasts and to undergo a 

 practically pure lactic acid fermentation due to B. hulgaricus. On two suc- 

 cessive days at one cheese factory the same organism was also found to be the 

 predominant organism in the making vat instead of the more common Bac- 

 terium lactis acidi. 



"The use of direct steam and the combination of direct steam and jetting 

 were found to be the best methods of pasteurizing whey. They can be operated 

 at a sufficiently low cost to make the process of pasteurization a highly de- 

 sirable one for all parties concerned. Double jetting Mathout supplementary 

 heating is not satisfactory because the temperatures reached are not so high 

 as they should be. This method has one advantage, however, in that a 

 careless or unreliable cheese maker can not escape using the jet pumps while 

 such a man may be tempted to shut off steam more quickly than he should 

 where direct steam is used. 



" In the course of this investigation 40 butter factories and skimming stations 

 were found which pasteurize skim milk. This number does not include all 

 that follow the practice. The best procedure is to return the skim milk to the 

 patrons' cans at a temperature high enough to remain above 145° for 30 minutes. 

 This pasteurizes the milk in the final container and increases the keeping 

 qualities of the skim milk." 



