182 PASTEURIZATION 



ing objectionable flavors and odors and partly, because the pas- 

 teurizing heat removes from the cream gases and volatile and 

 soluble substances which possess undesirable odors. 



Experimental results conducted at various experiment sta- 

 tions in this country and abroad have conclusively demonstrated 

 that efficient pasteurization destroys over 99 per cent of the 

 micro-organisms present in the cream. The type of micro-organ- 

 ism most damaging to the quality of butter is the liquefying 

 bacteria those which attack the proteins and fat, and certain 

 species of yeast and molds. Bacteriological analyses of cream 

 before and after pasteurization show that the per cent decrease 

 of these undesirable germs is practically the same as that of the 

 lactic acid bacteria. 



Pasteurization expels from the cream, vapors and gases, espe- 

 cially carbondioxide gas, which carry with them objectionable 

 volatile substances which may have been absorbed mechanically 

 or which have developed in the cream due to bacterial action. 

 This expulsion is further facilitated by the reduced viscosity of 

 the hot pasteurized cream. Gases are less soluble and more 

 volatile at high temperatures, therefore they escape more read- 

 ily from pasteurized cream. In raw cream they tend to go in 

 solution, they remain in the cream and may be carried into the 

 butter. 



Soluble decomposition products, such as may be present in 

 cream that has yielded to fermentation, are more easily expel- 

 led from the cream and butter made from pasteurized cream 

 than from raw cream. The clusters of fat globules break up, 

 and offer a greater surface for the liberation of these biprod- 

 ucts. Some of these products as well as the curd, that harbor 

 faulty odors, are precipitated more completely by pasteurization 

 and in this condition pass off in the buttermilk. The curd con- 

 tracts and squeezes out soluble substances, so that part of 

 the curd which subsequently does become a part of the butter 

 is freer from these undesirable, soluble bi-products. 



Improves Keeping Quality. Since certain species of bac- 

 teria, yeast and molds that may be present in the cream, cause 

 deterioration of the butter in storage, the elimination of these 



