140 Dairy Bacteriology. 



est possible care in selecting the milk that is to be used 

 as a basis for the starter. 



3. For the propagation and perpetuation of the starter 

 from day to day, it is necessary that the same should be 

 grown in milk that is as germ-free as it is possible to 

 secure it. For this purpose sterilize some fresh skim- 

 milk in a covered can that has previously been well 

 steamed. This can be done easily by setting cans contain- 

 ing skim-milk in a vat filled with water (fig. 32 A) and 

 heating the same to approximately the boiling point. 

 The temperature should be maintained for an hour or 

 more. This destroys all but the most resistant spore- 

 bearing organisms 1 . 



4. After the heated milk is cooled down to about 70 

 F., it can be inoculated with desired culture. Some- 

 times it is desirable to ' ' build up ' ' the starter by prop- 

 agating it first in a smaller volume of milk, and then 

 after this has developed, adding it to a larger amount. 



This method is of particular value where a large amount 

 of starter is needed for the cream -ripening. 



5. After the milk has been inoculated, it should be kept 

 at a temperature that is suitable for the rapid devel- 

 opment of the contained bacteria, 60-70 F., which tem- 

 perature should be kept as constant as possible. 



6. This can best be done by filling water- vat (A) with 

 water and heating the same to desired temperature, cov- 

 ering the vat with a wooden cover or heavy cloth during 

 the night to maintain proper temperature. 



7. The starter should not be thoroughly curdled and 

 solid when it is needed for use, but should be well soured 



1 A number of tests made by the writer at the Wis. Dairy School 

 Creamery, showed that the bacteria in skim-milk were practically 

 destroyed, only 7-30 bacteria per cc. remaining after this sterilizing 

 process. 



