The La Leche League International Guidelines on Human Milk Storage (2012)
Your milk is a living substance so precious some call it "white blood". It is essential to store your expressed (pumped) milk properly to maximize its nutritional and anti-infective qualities. Human milk actually has anti-bacterial properties that help it to stay fresh. Giving your baby the freshest milk you have pumped ensures its high quality.
This information is based on current research and applies to mothers who:
- Have healthy, full-term babies;
- Are storing their milk for home use (as opposed to hospital use);
- Wash their hands before expressing;
- Use containers that have been washed in hot, soapy water and rinsed.
All milk should be dated before storing. Storing milk in 2-4 ounce amounts may reduce waste. Refrigerated milk has more anti-infective properties than frozen milk. Cool fresh milk in the refrigerator before adding it to previously frozen milk.
Preferably, human milk should be refrigerated or chilled right after it is expressed. Acceptable guidelines for storing human milk are as follows. Store milk:
- At room temperature (66-78°F, 19-26°C) for 4 hours (ideal), up to 6 hours (acceptable) (Some sources use 8 hours)
- In a refrigerator (<39°F, <4°C) for 72 hours (ideal), up to 8 days (acceptable if collected in a very clean, careful way)
- In a freezer (-0.4 to -4°F, -18 to -20°C) for 6 months (ideal) up to 12 months (acceptable)
What Type of Container to Use
The best options for storing human milk:
- Are glass or hard-sided plastic containers with well-fitting tops
- Containers not made with the controversial chemical bisphenol A (BPA)
- Are containers which have been washed in hot, soapy, water, rinsed well, and allowed to air-dry before use
- Containers should not be filled to the top - leave an inch of space to allow the milk to expand as it freezes
- Freezer milk bags that are designed for storing human milk
- Put only 60 to 120 ml (two to four ounces) of milk in the container (the amount your baby is likely to eat in a single feeding) to avoid waste
Disposable bottle liners or plastic bags are not recommended. With these, the risk of contamination is greater. Bags are less durable and tend to leak, and some types of plastic may destroy nutrients in milk. Mark the date on the storage container. Include your baby's name on the label if your baby is in a day care setting.
How to Warm the Milk
Frozen milk: thaw in the refrigerator overnight or under cool running water. Gradually increase the temperature of the water to heat the milk to feeding temperature.
Refrigerated milk: Warm the milk under warm running water for several minutes. Or immerse the container in a pan of water that has been heated on the stove. Do not heat the milk directly on the stove. Some babies accept milk right from the refrigerator.
Do not bring temperature of milk to boiling point.
Human milk may separate into a milk layer and a cream layer when it is stored. This is normal. Swirl it gently to redistribute the cream before giving it to baby.
Do not use a microwave oven to heat human milk. It may cause the loss of some of the beneficial properties of the milk. Microwaves do not heat liquids evenly and may leave hot spots in the container of milk. This could be dangerous for infants.
Sometimes thawed milk may smell or taste soapy. This is due to the breakdown of milk fats. The milk is safe and most babies will still drink it.
Previously frozen milk that has been thawed can be kept in the refrigerator for up to 24 hours. While there is limited evidence to date that milk thawed for a few hours may be refrozen, this results in further breakdown of milk components and loss of antimicrobial activity. At this time, the accepted practice is not to refreeze thawed milk. While some mothers and caregivers reheat expressed milk that was leftover and refrigerated after a previous feeding, there is no research on the safety of this practice. There is also no research about whether freshly expressed milk left unfinished at room temperature should be discarded, or can be saved for a short time (perhaps up to one hour as reported by some mothers and caregivers) to finish the feeding if the baby wakens from having fallen asleep or still appears hungry.
Expressed milk can be kept in a common refrigerator at the workplace or in a day care center. The US Centers for Disease Control and the US Occupational Safety and Health Administration agree that human milk is not among the body fluids that require special handling or storage in a separate container.