Preservation of Milk. 105 



Copenhagen Dairy Co. sterilize their gravel filters by high 

 heat. In other cases lime water is used in cleansing. Fil- 

 ters of this type remove practically all dirt and a consider- 

 able proportion of the contained bacteria, but they are in- 

 tended more to clean the milk than enhance its keeping 

 quality. Woodfiber (cellulose) has also been tested as a 

 filtering substance with success. 



Centrifugal cleaning: of milk. The familiar coating of 

 slime and dirt that collects on the inner face of the sepa- 

 rator bowl shows that centrifugal force can be successfully 

 used in cleaning or clarifying milk. While the ordinary 

 types of cream separators are able to remove this material 

 in a satisfactory way, special machines have been devised 

 for this particular purpose. A bacteriological examination 

 of separator slime shows it to be teeming with myriads of 

 organisms, and the rapid decomposition which it undergoes 

 is evidence of its high germ content, but there is practi- 

 cally little or no improvement in the keeping quality of 

 milk that has been treated in this way. This is in part 

 due to the fact that bacteria reproduce so rapidly that a 

 marked variation in numbers is soon obscured by relatively 

 more rapid growth. Eckles and Barnes 1 find that from 

 37 to 56 per cent of the total number of bacteria present in 

 milk are thrown out lay passing milk through separators. 

 Where milk is cleaned in this way, the cream and skim 

 milk is generally mixed again immediately, but the pas- 

 sage of cream through the separator bowl tends to break 

 down- the size of the normal fat-globule clusters and so 

 lessen the consistency of the product. Such a diminution 

 in " body " diminishes materially the ease with which cream 

 can be whipped. 



i Eckles and Barnes, Bull. No. 59 Iowa Expt, Stat., Aug. 1901. 



