546 STATE BOARD OF AGRICULTURE. 



KEEPING QUALITIES OF BUTTER. 



V. PASTEURIZATION AND ITS INFLUENCE (CONTRIBUTION). 



A STUDY OF THE FACTORS WHICH INFLUENCE THE RESISTANCE OF LACTIC 



ACID BACTERIA TO HEAT.* 



CHAS. W. BROWN AND KURT PEISER. 



INTRODUCTION. 



The facts that commercial pasteurized milk develops an acidity 

 and loppers in a manner characteristic of milk which has not been pas- 

 teurized, that plates made from pasteurized market milk and cream 

 usually show a high percentage of acid-producing microorganisms, and 

 that butter made from pasteurized cream without the addition of starter 

 has lactic acid bacteria as the predominating flora, have directed our at- 

 tention to the lactic acid group of bacteria. Inefficient pasteurization 

 and subsequent contamination through utensils and containers of milk 

 and cream which have been efliciently jjasteurized were thought to be re- 

 sponsible for the presence in pasteurized milk and cream of large num- 

 bers of this group of bacteria. 



PURPOSE. 



The purpose of this work is to ascertain whether lactic acid bacteria 

 in milk and cream survive pasteurization at a temperature commonly 

 considered as eflScient and whether such survival is due to an inherent 

 property of the organism or due to some external protection exerted by 

 the constituents of milk. 



*A report on this work, presentedTbefore the Society of American Bacteriologists 1914-15, is 

 abstracted in Science n. ser. Vol. 42, p. 320. 



