A good compromise for home pasteurization is to heat the milk to 165Â°F (74Â°C) in a double boiler and to hold it at this temperature for 15 seconds while stirring constan…tly. Then, cool it immediately while stirring to 145Â°F (63Â°C) by setting the top of the double boiler in cold water. Add ice to the cooling water to cool the milk further, stirring occasionally until the temperature of the milk falls below 40Â°F (4Â°C). Store the cooled milk in clean, covered containers and keep it at a temperature below 40Â°F (4Â°C) until used. This is the preferred method over the 30-minute/150Â°F (63Â°C) method because if at any time during the 30-minute period the temperature drops below 150Â°F (63Â°C), the milk must be reheated for 30 consecutive minutes. Another method is using jars for 30 minutes in a waterbath canner, again, provided care is taken to maintain the temperature at 150Â°F (63Â°C), and the milk is promptly cooled to 40Â°F (4Â°C) or less. All stirring devices, thermometers, or any other utensil that comes in contact with the milk must remain in the milk for the entire process-do not remove them at any time during the process-to prevent contamination..
source: Michigan State University ( Full Answer )