Pasteurizing breast milk requires heating it to 62.5°C (144.5°F) and holding that temperature for exactly 30 minutes, followed by rapid cooling in an ice bath. This is the standard used by milk banks worldwide, known as Holder pasteurization. You can replicate this process at home with basic kitchen equipment, though the details matter: heating too long destroys protective proteins, while heating too little leaves pathogens alive.
What Pasteurization Actually Does
The goal is to kill bacteria and viruses without destroying everything beneficial in the milk. At 62.5°C for 30 minutes, pasteurization completely eliminates HIV, cytomegalovirus (CMV), human papillomavirus, Ebola, and Marburg virus. It also wipes out the vast majority of common bacteria. In one large study of over 800 milk samples, 87% of unpasteurized samples grew Staphylococcus colonies, while only 7% of pasteurized samples grew any bacteria at all.
The method isn’t perfect against every pathogen. Hepatitis B surface antigens and DNA can persist after Holder pasteurization, and spore-forming bacteria like Bacillus cereus occasionally survive. However, testing of those surviving B. cereus cultures found they did not carry the genes needed to produce dangerous toxins.
The Holder Method Step by Step
This is the method used by every milk bank accredited by the Human Milk Banking Association of North America (HMBANA). You need a pot or water bath large enough to surround your milk container, a reliable thermometer (digital is best), glass jars or food-grade polypropylene bottles, and a bowl of ice water for cooling.
- Prepare the water bath. Fill a pot with enough water to reach at least the level of the milk inside your container. Heat the water to about 65°C (149°F) to account for the slight temperature drop when you place the milk container in.
- Fill and place the milk container. Pour expressed breast milk into a clean glass jar or polypropylene bottle, leaving some headspace. Place the container into the water bath. Use a thermometer clipped inside the milk (not the surrounding water) to monitor core temperature.
- Hold at 62.5°C for 30 minutes. Once the milk itself reaches 62.5°C, start your timer. Adjust the heat source as needed to keep the temperature steady. You want to stay as close to 62.5°C as possible. Going significantly higher or holding longer than necessary degrades the milk’s beneficial components.
- Cool rapidly in an ice bath. As soon as 30 minutes are up, transfer the container into a bowl of ice water. The goal is to bring the milk below 10°C as quickly as possible, ideally down to 4°C. In a proper ice bath, this takes roughly 15 to 20 minutes for a small bottle. Swirl the container gently to speed cooling.
A sous vide immersion circulator works well for maintaining a precise, steady temperature during the 30-minute hold. Set it to 62.5°C, submerge the sealed container, and let the circulator do the work of temperature control. You still need to cool the milk rapidly in ice water afterward.
The Flash-Heat Method for Low-Resource Settings
If you don’t have a thermometer or precise temperature control, flash heating is an alternative developed for use in resource-limited settings. Place expressed milk in a glass jar, then set that jar into a pot of water. Heat both on a stove until the water (not the milk) reaches a rolling boil. As soon as the water boils, remove the jar immediately. Then place it in cool water or an ice bath to bring the temperature down.
Flash heating is simpler but comes with trade-offs. It preserves less of the milk’s immune components compared to the Holder method. One study found flash heating retained only 25% of total IgA antibodies, compared to about 79% with Holder pasteurization. Lactoferrin activity dropped to 39% with flash heating versus 71% with the Holder method. If you have the equipment to do Holder pasteurization properly, it’s the better choice for preserving the milk’s protective qualities.
What Pasteurization Costs the Milk
No heat treatment leaves breast milk completely unchanged. At 62.5°C for 30 minutes, about 72% of secretory IgA (the main antibody in breast milk) survives. Lactoferrin, an antimicrobial protein, takes a harder hit, with only about 22% retained. Lysozyme, which breaks down bacterial cell walls, retains roughly 39% of its original level. Signaling molecules like interleukins IL-8 and IL-10 survive both methods without destruction.
Interestingly, research has shown that lowering the temperature to 57°C for 30 minutes retains at least 90% of all three key immune proteins while still eliminating 99.9% of tested bacterial species. This lower temperature isn’t yet standard practice in milk banks, but it highlights why precision matters. Even a few degrees of unnecessary heat, or a few extra minutes of processing, meaningfully reduces the nutritional and immune value of the milk.
Avoiding Common Mistakes
The most frequent errors all fall into the same category: imprecise temperature control. Overheating the milk, even by a few degrees, accelerates the breakdown of proteins, fats, and vitamins including C and B12. Holding the milk at temperature for longer than 30 minutes has the same effect. On the other side, not reaching 62.5°C or cutting the time short leaves the milk insufficiently treated.
Contamination after pasteurization is the other major risk. Anything that touches the milk post-treatment, including lids, spoons, or feeding equipment, needs to be sterilized. Slow cooling is also a problem. Letting the milk cool gradually at room temperature instead of using an ice bath creates a window where surviving bacteria can multiply. Always use an ice water bath, not just cold tap water, to bring the temperature down within minutes rather than hours.
Storing Pasteurized Milk
Once cooled, pasteurized breast milk should go straight into the refrigerator or freezer. The standard recommendation from milk banks is a three-month shelf life when frozen at -20°C, but research has found that macronutrient and energy content remain stable for up to eight months at that temperature. In the refrigerator, pasteurized milk should be used within 24 to 48 hours, since the pasteurization process also eliminates the milk’s own natural bacteria that help suppress pathogen growth in raw milk.
Label each container with the date of pasteurization. If the milk smells off or has visible changes in color or texture after thawing, discard it. Pasteurized milk that has been thawed should not be refrozen.