152 Dairy Bacteriology. 



2. If a home-made starter is employed, use the greatest 

 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 containing skim-milk in 

 a vat filled with water and heating th* same to 180 F. or 

 above. The temperature should be maintained for a half 

 hour or more. This destroys all but a few of the most re- 

 sistant spore-bearing organisms. This will give a cooked 

 flavor to the milk, but will not affect the cream to which 

 the starter is added. Dairy supply houses are now intro- 

 ducing the use of starter cans that are specially made for 

 this purpose. 



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

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

 times it is desirable to " build up " the starter by propagat- 

 ing 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 development 

 of the contained bacteria, 65-75 F., which temperature 

 should be kept as uniform as possible. 



6. This can best be done by setting can in vat filled with 

 warm water and covering the same with a wooden cover 

 or heavy cloth during the night to maintain proper tem- 

 perature. 



