How can breastmilk be stored?

Reading Time: 3 minutes
Always make sure that supplies are clean and wash your hands before handling breastmilk.

Breastmilk 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.1

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

  • Pump into a clean bottle connected to the pump.
  • When finished expressing or the bottle is full, store directly in the bottle or transfer into an clean and approved breastmilk storage container.
  • The MayoClinic states: “You can add freshly expressed breast milk to refrigerated or frozen milk you expressed earlier in the same day. However, be sure to cool the freshly expressed breast 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 breast milk to frozen breast milk because it will cause the frozen milk to partially thaw. Keep milk expressed on different days in separate containers.”2
  • Store expressed milk in small amounts, and increase amount as a baby eats more per feeding. Freezing milk in small amounts (2-4 oz) is most convenient to avoid waste.
  • If milk is to be frozen for storage, this is best done immediately after expressing.
  • Previously frozen milk can be stored in the refrigerator for 24 hours.
  • Remember that breastmilk will expand when frozen, so do not overfill the container, especially if using a glass container.
  • Mark name, date, amount of milk, and age of 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.
  • Please do not freeze milk in the door of the freezer as the temperature fluctuates too much.

Thawed, non heat-treated milk can be kept in the refrigerator for 24 hours. According to the USDA, “Once food is thawed in the refrigerator, it is safe to refreeze it without cooking.” In this protocol, Dr. Anne Eglash, M.D. writes: “At this time, there is little information on refreezing of thawed [fresh –ed.] 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 amount of bacteria in the milk at the time of expression. At this time no recommendations can be made on the refreezing of thawed human milk.”

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 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.

For more information about storing breastmilk and which containers to use, please visit this page from the MayoClinic and this Protocol of the Academy of Breastfeeding Medicine.

Please see the section ‘How long can breastmilk be stored?’ for information on length of storage. If storing breastmilk in order to ship it, please see ‘How can breastmilk be shipped or transported.’

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

Next: How long can breastmilk be stored?


  1. In ‘Nursing: The 3 M’s of Breast-feeding the Preterm Infant’: “Studies measuring these factors [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 a poor choice for milk storage […] owing to their non-sterile condition, greater loss of fat (adherence to sides of bag), and difficulty in handling.” 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 breastfeeding. []
  2. However, the CDC states: “Do not add fresh milk to already frozen milk within a storage container. It is best not to mix the two.” []

3 Responses to How can breastmilk be stored?

  1. Pingback: Contaminated Breast Milk Study: Biased and Misrepresented | Natural Family Today

  2. Anne Eglash says:

    2 things:
    1. you may want to reference the human milk storage protocol from the Academy of Breastfeeding Medicine, updated in 2010.

    2.I am writing up my research survey on health professional attitudes on wet nursing and milk sharing. I am referencing Eats and Feets, but should I be changing that to HM4HB? I am a little confused on this. BTW- you will like the results of my survey!
    Anne Eglash MD

    • Eats On Feets says:

      Hello, Anne!
      Thanks for that link. I will look into it.
      And no, Eats On Feets is its own network, with its own information and research.
      Please also check out our website
      Looking forward to your survey! Please send me information about this when ready! Thanks!

Leave a Reply