66 Report of the Department of Bacteriology of the 



This starter is simply milk containing' rapidly multiplying acid- 

 forming bacteria, and while the small amount of acid already 

 formed is useful in quickening the action of the rennet the princi- 

 pal eflfect of a starter lies in the increased activity of the germs. 



Thus, partly as the result of natural causes and partly because 

 of the action of the maker, the milk from which cheese is made is 

 normally well seeded with these lactic-acid bacteria. As these 

 germs are present in the factory milk in such large numbers it is 

 but natural that they should pass over into the cheese. 



the growth of lactic-acid bacteria checks that of other 



FORMS in the milk. 



Conn & Esten^ recently published the results of a careful study 

 of the bacteria present in fresh milk and the rate at which the 

 various kinds develop as the milk becomes older. Up to the 

 time the milk is sour practically all the species of bacteria present 

 in it continue to multiply, although as the latter stage is ap- 

 proached the germs other than the lactic-acid group increase 

 more and more slowly. Very few lactic-acid bacteria are found 

 in the fresh milk but they increase rapidly and in 12 to 18 hours 

 at 20° C. (68° F.) they usually outnumber all those of the other 

 kinds. At the higher temperature to which the milk is commonly 

 exposed during the warmer portions of the summer the growth 

 of all the bacteria is accelerated, and consequently at such times 

 the lactic-acid bacteria more quickly make their presence felt. 

 At the time of souring the acid bacteria commonly make up more 

 than 95 per ct. of the total number. 



While this problem has never before been so carefully studied 

 from the biological standpoint the fact that an abundant growth 

 of lactic-acid bacteria in milk checks the activity of other forms 

 has long been known and utilized in cheese-making. It is a 

 matter of common experience that the effect upon the cheese of 

 various objectionable fermentations in the milk can be modified 

 and often removed by the addition of liberal amounts of a vigor- 

 ous lactic-acid starter in the cheese vat. 



2 Conn & Esten. Ann. Rept. Storrs Exp. Station, 14:i3. (1901.) 



