176 CONTROL OF THE MILK-SUPPLY. 



protect the public, but to keep the milk from souring. Milk 

 distributers have found it difficult to furnish milk that will keep 

 without preservatives, but have learned that the application of heat 

 enables them to do so. For this reason pasteurization has become 

 adopted by some large milk companies. 



Pasteurization is sometimes applied to cream, to enhance its 

 keeping and enable it to find a market. The cream keeps well, 

 but loses some of its consistency. It appears thinner than before 

 treatment, and will not whip so well as ordinary cream. Its consist- 

 ency may be restored by adding a little of a material called viscogen. 

 This is made by adding a strong solution of cane-sugar to freshly 

 slacked lime, and allowing the mixture to stand until the upper part 

 of the mixture is clear. This clear liquid is poured off and added 

 to the cream in the proportion of one part to one hundred or one 

 hundred and fifty parts of cream. This restores the consistency to 

 the cream, but, since it is an addition of a foreign substance, its 

 use is illegal. 



In our larger cities a considerable part of the milk on the market 

 is pasteurized; sometimes it is sold as pasteurized milk and some- 

 times it is not so labeled. 



Preparations of Milk. The microorganisms that spoil milk 

 will not grow in it if the water is removed, and several methods have 

 been devised for producing a form of milk that will keep, all of which 

 are based upon the removal of the water. Condensed milk is the 

 oldest and has a wide use. It consists of ordinary milk evapo- 

 rated to about one-third of its original bulk, to which is com- 

 monly added a large amount of sugar. The sugar prevents the 

 growth of bacteria, and this condensed milk, put up in cans, keeps 

 well. In some forms of condensed milk the sugar is not added, but 

 the product is preserved by sterilizing by heat. When subsequently 

 diluted with water, condensed milk does not exactly replace the 

 fresh article, because of the added sugar in the one type and the 

 effect of sterilization in the other. A product known as concen- 

 trated milk has recently been placed on the market. In this case 

 the milk is first skimmed and then subjected -to a heat of 140 F. 

 till enough water is evaporated to bring the milk to about one-fifth 



