Useful Rules 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. 
