How can human milk be stored?

Ensure that supplies are clean and wash your hands before handling human milk

Human milk can be stored at room temperature, in the refrigerator, in the freezer, or in coolers depending on how long it needs to be stored. It can be stored in capped glass or plastic containers, specialized ‘breastmilk storage trays’, or in specialized milk bags.

Studies measuring the factors of size, need to recycle, ease of cleaning/sterilizing, protection of nutrients, considerations regarding bacteria, and ability to connect directly to the pump flange conclude that glass and hard clear plastic (polypropylene) are the recommended choices for milk collection/storage. Plastic bags are not sterile, not recyclable, and result in a greater loss of fat due to the adherence of fat to the sides of the bag. They also can result in easy leaking and thus milk waste.1 Plastic bags can however be more convenient. Plastic bags specially designed for freezing expressed human milk are available from many companies that specialize in products for human feeding.

Always handle breastmilk with clean hands2 and follow the manufacturer’s instructions for properly cleaning your pump.

  • Pump into a clean bottle connected to the pump.3
  • When finished expressing or the bottle is full, store directly in the bottle or transfer into a clean and approved breastmilk storage container.
  • You can add freshly expressed human milk to refrigerated or frozen milk you expressed earlier on the same day. However, be sure to cool the freshly expressed milk in the refrigerator or a cooler with ice packs for at least one hour before adding it to previously chilled milk. Don’t add warm human milk to frozen human milk because it will cause the frozen milk to partially thaw. Keep milk expressed on different days in separate containers.4
  • Store expressed milk in small amounts, and increase the amount as a baby eats more per feeding. Freezing milk in small amounts (2-4 oz) is most convenient to avoid waste.5
  • If milk is to be frozen for storage, this is best done immediately after expressing it.
  • Previously frozen milk can be stored in the refrigerator for 24 hours.6
  • Remember that breastmilk will expand when frozen, so do not overfill the container, especially if using a glass container.
  • Mark the name, date, amount of milk, and age of the baby on the container.
  • Storage bags should be stored carefully, away from other items in the freezer to avoid any damage. Laying storage bags flat for freezing is most space-saving: simply stack them when frozen. Some parents have made clever dispensers as well.7
  • Please do not freeze milk in the door of the freezer as the temperature fluctuates too much.

For foods that have thawed in the refrigerator, it is generally safe to refreeze them without cooking within 3 or 4 days.8 However, there is so far little information on refreezing thawed human milk. Bacterial growth and loss of antibacterial activity in thawed milk will vary depending on the technique of milk thawing, duration of the thaw, and the number of bacteria in the milk at the time of expression.9

It is said that once breastmilk has been expressed, it is important not to shake it, especially if the milk is also to be frozen because shaking allegedly denatures the shaped molecules of the protective proteins. We have however not found any evidence-based research to support this claim. The research that does address shaking breastmilk evaluates mechanical shaking or so-called vortex shaking.10

If expressed milk will be shipped, please see How can human milk be shipped or transported.

For recipients:
Upon receiving the breastmilk, store it in the freezer or in the refrigerator as given, or use it within 6-8 hours depending on the need.

Next: How long can human milk be stored?

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  1. Nancy Hurst. 2007. The 3 M’s of Breast-feeding the Preterm Infant ↩︎
  2. CDC –When and How to Wash Your Hands ↩︎
  3. OASH – Pumping and storing breastmilk ↩︎
  4. Mayo Clinic – Breast milk storage: Do’s and don’ts ↩︎
  5. AskDrSears – Transporting and Storing Breast Milk ↩︎
  6. OASH – Pumping and storing breastmilk ↩︎
  7. GreenLightBites – Breast Milk Storage ↩︎
  8. USDA – Freezing and Food Safety ↩︎
  9. Anne Eglash, et al. BREASTFEEDING MEDICINE Volume 12, Number 7, 2017. ABM Clinical Protocol #8: Human Milk Storage Information for Home Use for Full-Term Infants ↩︎
  10. BT&C, Inc. – Maintenance of Protein Stability ↩︎