58 FERMIiNTS IN MILK 



kept at this temperature will, in most cases, providing it has pre- 

 viously been properl}- treated, develop a pleasant acid taste, will 

 curdle into a smooth uniform coagulum, and will contain a pre- 

 ponderance of the species of germ mentioned above. 



At as low a temperature as 50° F. acid-producing types of 

 bacteria do not develop very well. But Conn maintains that 

 miscellaneous species of bacteria that produce unfavorable 

 results develop at this temperature. While milk does not easily 

 sour at this temperature, it should be remembered that undesir- 

 able germs are constantly developing. 



As it is practically impossible to exclude all of the bacteria 

 from milk during milking and the handhng of the milk, it is 

 very essential that the multiplication of the germs present be 

 checked, or at least retarded; and this can be done by controlling 

 the temperature of the milk. As low temperature is effective in 

 checking the niultiplication of the bacteria, the sooner the milk 

 can be cooled after it is drawn, the better it will be likely to keep. 



Moisture. — Moisture is one of the essentials for bacterial 

 growth. As milk is composed largely of water, bacteria find in 

 milk a good medium for growth. All the other required food 

 elements are also found in abundance in milk. Damp utensils 

 and rooms are always more conducive to the growth of germs 

 than are utensils and rooms which are thoroughly dried and 

 ventilated. This is well illustrated by a refrigerator. A very 

 damp dark refrigerator is always more conducive to the growth 

 of molds in butter than is a dry refrigerator. 



Unfavorable Conditions for Bacterial Growth. — The reverse 

 of the favorable conditions mentioned above would be unfavorable 

 to the growth of bacteria. As it is practically impossible to make 

 conditions unfavorable for the growth of bacteria by taking 

 away food, other means must be used. Extremeh' high tem- 

 peratures destroy bacteria. Low temperatures check their 

 growth, but so far as known do not destroy them. Absence of 

 moisture and j)resence of direct sunlight are conditions which are 

 not conducive to bacterial growth. Certain chemical substances 

 when added to milk, or to the medium in which the bacteria are 

 present, are very unfavorable to their growth. Some of these 



