Food Preservation: Pasteurization of Raw Milk for Home Consumption

Pasteurization is the process of heating milk to a specific temperature for a defined amount of time to kill (inactivate) organisms in milk that may cause spoilage or disease if consumed. This process has been used for over 100 years to keep consumers of commercial milk safe by following the standards of the Grade "A" Pasteurized Milk Ordinance. Unlike sterilization, pasteurization does not eliminate every microbe in the product, but it does ensure that 99.999% of pathogens are destroyed.

Most of the bacteria found in milk from healthy cows, goats, and sheep are harmless if the milk is kept in clean surroundings. However, even with careful production, contamination of milk with disease-producing microorganisms is possible if it comes into contact with tainted water, soil, animals, or other contaminated sources. Outbreaks of food poisoning, gastroenteritis, typhoid fever, diphtheria, septic sore throat, dysentery, and Q-fever have been traced to raw milk. Diseases such as tuberculosis and undulant fever have also been transmitted from infected cows to humans through raw milk. The transmission of these diseases is especially problematic among people consuming raw milk who are susceptible to foodborne illness, such as pregnant women, young children, older adults, and those with cancer, HIV/AIDS, or another immune system disease.

Many states, including Ohio, have laws requiring the pasteurization of milk sold directly to the consumer. The purpose of such laws is to protect the health of the consumer. Dairy farm families and others who milk cows, sheep, or goats should pasteurize all dairy products and milk used as an ingredient in foods that do not require cooking or baking.

Benefits of Pasteurization

Pasteurization destroys all disease-producing organisms that may be present, making milk safe to drink. These organisms can include salmonella, listeria, E. coli O157:H7, campylobacter, and influenza. Pasteurization reduces the number of harmless bacteria in milk that can produce off-flavors. The process also eliminates bacteria that can produce off-flavors and gas during the manufacture and storage of cheese and other cultured dairy products.

Raw Milk Quality

Pasteurization helps preserve but does not improve the quality of milk. All raw milk contains microorganisms. In order to be pasteurized, raw milk must have a low microbial count, which results in the best flavor while also retaining the quality and other desirable characteristics of milk and milk products. A low microbial count in raw milk is possible if the cows, sheep, and goats providing the milk are clean and healthy with teats that are cleaned before milking. All utensils and equipment that are used to milk must also be clean and properly sanitized.

Pasteurization Methods

Methods for pasteurizing milk are based on time-temperature relationships that ensure the complete destruction of any disease-producing organisms. The higher the temperature, the less time it takes to destroy the disease-producing organism.

Several time-temperature combinations are used for the commercial pasteurization of milk. Practical methods for pasteurizing milk in the home are also available. One is the batch method, which requires that every particle of milk, including the foam, be heated to a minimum of 145 degrees Fahrenheit and held at that temperature for at least 30 minutes. Milk may also be pasteurized by heating it to 161 F for at least 15 seconds.

Home Pasteurization

Milk can be home pasteurized in a double boiler, in canning jars, in glass milk bottles, or in a batch-type home pasteurizer. To pasteurize milk, follow general home-pasteurization procedures:

Double Boiler (Most Common Method)

1. Place milk in the top and water in the bottom of the double boiler.
2. Place an accurate, metal-stem thermometer, and a spoon in the milk during the entire pasteurization process. A metal-stem thermometer is preferred over glass because it will not break.
3. Heat the milk to 161 F while stirring constantly and hold at that temperature for at least 15 seconds. Constant stirring is important to evenly distribute the heat and ensure that all the milk is heated to 161 F.
4. At the end of the 15-second holding time, place the top portion of the double boiler containing the milk in a pan of cold water. Continue stirring the milk to achieve rapid cooling.
5. When the milk temperature is below 130 F, replace the cooling water with ice water and continue to cool the milk, with occasional stirring, until the temperature is 40 F or below.
6. Pour the cooled milk into clean containers, cover the containers, and store them in the refrigerator at 40 F or colder until used.

Bottles and Canning Jars

1. Place milk in glass milk bottles or canning jars. Fill only four-fifths full to allow for the expansion of milk when heated.
2. Place the bottles or jars on a rack inside a large canner. Fill the canner with warm water until the water level is slightly above the milk level in the jars.
3. Start heating. Stir the milk in each container with a long-handled spoon to achieve uniform distribution of the heat. Monitor the temperature with a metal-stem thermometer. As the temperature approaches 145 F, stop stirring, and then loosely cover all the jars but one with lids (milk bottles can be covered with aluminum foil). Cover the remaining jar with aluminum foil. Punch a hole in the center of the foil and insert the thermometer.
4. Continue heating until the temperature is 145 F or slightly above. Adjust the heat to maintain 145 F for 30 minutes. If at any time the temperature drops below 145 F, reheat and hold at 145 F or above for 30 minutes.
5. After 30 minutes, gradually replace the hot water with cold water to cool the milk. If this is not done gradually, the bottles or jars may break.
6. Continue cooling until the milk temperature is 80 F or less. After reaching 80 F or less, use ice water to cool the milk to 40 F or colder. Tighten the covers and store the milk in the refrigerator at 40 F or colder until used.

Batch-Type Electric Home Pasteurizer

Electrically operated, batch-type home pasteurizers are available that automatically control the pasteurization time and temperature and pasteurize from two quarts to two gallons of milk. Such units make it possible to easily pasteurize milk with minimum attention. Some of these units can even be attached to your sink and will automatically cool the milk using water.

Microwave Oven

It is possible to pasteurize with a microwave oven, but this is not recommended for home pasteurization because it is difficult to achieve the uniform heat distribution that ensures all the milk has been heated to 161 F for at least 15 seconds. Microwave heating also adversely affects the flavor and other properties of milk.

Storage

Milk should be stored in your refrigerator in a section that is at 37 F. This is often on a lower shelf and close to the back. Milk should not be stored in the refrigerator’s door as this is the warmest spot in your fridge. Storage of milk at temperatures above 40 F can shorten its shelf life.

Additional Resources

Check out the following resources for more information on home milk pasteurization:

• U.S. Department of Health and Human Services, Public Health Service, Food and Drug Administration. (2019). Grade “A” Pasteurized Milk Ordinance.
  fda.gov/media/140394/download?attachment
• Oregon State University Extension Service. (2025). Food safety & preservation: Home pasteurization of raw milk (SP 50-932).
  extension.oregonstate.edu/food/preservation/home-pasteurization-raw-milk

Originally written in 2009 by Valente Alvarez, Specialist, Food Science and Technology, Ohio State University Extension; Mary E. W. Kershaw, Associate, Food and Nutrition, Ohio State University Extension; and Lydia C. Medeiros, Specialist, Nutrition, Ohio State University Extension.