Place a dairy thermometer, or one in an unpainted tin case, in the milk; heat, preferably in double boiler, as quickly as possible, to a temperature of not less than 140 degrees F. and keep it there for 40 m., or raise to 158 degrees F. for 10-20 m. Cool rapidly. The rapid heating and cooling are necessary because a warm temperature is most favorable for the development of germs and the spores of germs which (spores) are not destroyed by this treatment of milk.
When milk is to be kept for several hours it should be heated in air-tight bottles or in bottles which have stoppers of sterilized cotton, by starting them in cold water and keeping them at a temperature of 149 degrees F. for a half hour after bringing the water to that point.
Pasteurizing milk does not give it the cooked taste that a higher temperature does.
When it is not possible to carry out these directions, just bring milk to the boiling point, or set bottles of milk or cream in cold water, bring the water to boiling and boil for 10-20 m. Of course the bottles should have something underneath them, to keep them from touching the bottom of the vessel in which they are standing.