476 EXPERIMENT STATION RECORD. [Vol.37 



114.77 per cent in the case of old milk. " Bacteria increase more rapidly in 

 unclarified milk than in clarified milk. The fat content before and after 

 clarification is practically the same. The percentage of total solids is slightly 

 reduced by clarification. This is probably due to the slime removed. The 

 development of acidity is slightly more rapid in clarified milk than in unclarified 

 milk. The keeping quality of milk remains about the same after clarification 

 as it was before. About 99 per cent of the insoluble dirt in milk is removed 

 by clarification. The volume of cream that is separated by gravity is reduced 

 from 2 to 3 per cent by clarification. This is probably due to the agitation of 

 the milk in passing through the clarifier." 



Average analyses of eight samples of clarifier slime show the following per- 

 centage composition: Water 71.33, total solids 28.67, nitrogen 0.33, casein 2.13, 

 fat 4, and ash 3.15. 



A bibliography of 18 titles is given. 



Pasteurization of cream, C. Larsen, J. M. Fuller, V. R. Jones, H. Gregory, 

 and M. Tolstbup (South Dakota Sta. Bui. Ill (1916), pp. 529-548, figs. 6).— 

 The objects of the experiments reported in this bulletin were to determine the 

 eflSciency and practicability of the coil cream vat as a cream pasteurizer in 

 the manufacture of butter, the effectiveness of different temperatures of cream 

 pasteurization, and also the keeping properties of the butter made from the 

 cream pasteurized at the different temperatures. The cream used in the ex- 

 periments was obtained from the regular college creamery patrons and con- 

 tained about 30 per cent of fat. 



In one series of experiments 19 vats of cream averaging 761 lbs. each were 

 pasteurized at 140° F. With a steam pressure of 73.9 lbs. it required an 

 average of 1G.8 minutes to raise the temperature from 56.5 to 140°. In pas- 

 teurizing cream at 160° 20 vats were used, averaging 765 lbs. each. With a 

 steam pressure of 72.3 lbs. it required an average of 22.2 minutes to raise the 

 temperature from 56.8 to 160°. In a third series 19 vats of cream averaging 

 758 lbs. each were pasteurizeil at 180°. With a steam pressure of 74 lbs. It 

 required an average of 34.4 minutes to raise the temperature from 57.6 to 180°. 



The cream pasteurized at 140° was cooled to the churning temperature at 

 an average rate of 2.9° per minute, that pasteurized at 160° was cooled 3.4° 

 per minute, and that pasteurized at 180° was cooled 3.9° per minute. In the 

 cooling experiments the water at the intake averaged about 50° in temperature. 



The authors conclude that " in pasteurization of cream at different tem- 

 peratures, namely, 140° for 25 minutes. 160° for 10 minutes, and 180°, with 

 immediate cooling, the temi^erature of 160° for 10 minutes was the most effec- 

 tive in destroying total microorganisms. Pasteurization of cream at 160 or 

 180° proved more efficient in killing molds and nonacid-formlng organisms than 

 pasteurization at 140°. 



" The only noticeable change In composition of cream due to pasteurization 

 was a slight decrease in percentage of water, and a consequent Increase in 

 percentage of total solids. There was a slight decrea.se In acidity of the cream 

 after pasteurization at temperatures of 140 and 160°. Cream pasteurized at 

 180° showed on the average less decrease in percentage of acid. . . . The nu- 

 merous microscopical examinations of fat globules in raw and pasteurized 

 cream show that at the higher temperatures (160 and 180°) the fat globules 

 tend to coalesce or unite. . . . 



" In no in.stance was it noticed that the high pasteurization temperatures 

 unfavorably affected the body of the butter. Butter made from cream pas- 

 teurized at 180° retained its keeping qualities the be.^t. The different tem- 

 peratures of pa.steurization did not liavc :iny important effect on the chemical 

 composition of the butter." 



