Useful Rtiles and Tests 355 



STEPS IN PROPAGATION 



1. Take three one-quart milk bottles or fruit jars. Glass is prefer- 

 able, as it allows the operator to see when all of the dirt has been 

 removed, and the condition of the curd can easily be inspected through 

 the transparent wall. Three bottles should be employed, for in heating 

 glass is likely to break; and it is always well to have a sufficient num- 

 ber of containers from which to choose. 



2. Use fresh, clean milk, which must have a nice flavor. It may be 

 either whole milk or skimmed milk. Usually it is advisable to use 

 whole milk, for it is easier to choose desirable samples before milk has 

 passed through the separator than afterward. 



3. Fill the containers one-half to two-thirds full of milk. If they are 

 filled full, it is difficult to prevent contamination from the covers, which 

 are hard to sterilize when the pasteurization is done in hot water. Protect 

 the containers with regular covers (caps or tops) or with glass tumblers. 



4. Pasteurize by heating to 180 to 200 F. for 30 minutes or longer. 

 A temperature of 150 F. kills all sporeless bacteria. Higher tempera- 

 tures up to 212 F. do not kill the spores, but they are so weakened by 

 the higher heat that they germinate more slowly and their harmful 

 effect is retarded. This fact and the results of experience indicate a 

 temperature of about 185 F. to 200 F. as best. The heating and cool- 

 ing can be done in cans immersed in water. Stirring hastens the pro- 

 cesses, but is not necessary when the heating surface is not hotter than 

 about 200 F. Where the heating is done by steam, stirring is neces- 

 sary to prevent scorching. 



After heating, cool to a ripening temperature of 60 to 75 F. Pas- 

 teurization may be accomplished by tying a string about the necks of 

 the bottles and suspending them in a pail or vat heated by steam, or 

 in a kettle or dish heated on a stove,. (If pasteurized over a fire, do not 

 let bottles rest on the bottom of receptacle.) Other supports may be 

 used to keep the containers from tipping over. The temperature should 

 be raised and reduced slowly to prevent breaking the glass. 



5. After pasteurization the milk is ready for inoculation. Inoculate 

 in a quiet place where the wind cannot blow dirt and bacteria into this 

 clean seed bed. With dry fingers remove the cover and place it in a 

 bacterially clean spot, as in a recently scalded dipper. Pour in all of 

 the commercial culture, or 2 to 10 per cent from the previous day's 

 culture. Be sure that the curd from the previous day is well broken. 

 After inoculation, shake the freshly inoculated sample to distribute 

 the bacteria. 



