Breast milk storage basics

If you’re breastfeeding, this might means that you’ll also pump and express breast milk — either when returning to work or just so that loved ones can occasionally feed your baby from a bottle. Let’s go over how to store milk safely so you can be confident Baby is having milk that’s not just tasty and nutritious, but also safe.

How can you store your breast milk?

There are a number of storage options — from glass bottles, to BPA-free plastic bottles, to specially designed plastic or silicone milk storage bags. Whichever option you choose, the containers should be clean and properly sealed before they are stored (keep in mind that milk will expand when frozen). 

Ideally, milk is stored in a variety of sizes ranging from 2-5 ounces (the size range of an average breastfeed). A variety of serving sizes can be helpful in case your little one needs a full meal, snack, or even just needs to eat quickly. 

You’ll always want to clearly label the bottles or bags with the date that the milk was expressed and the amount inside. If you’ll be sending the milk off to childcare with Baby, you’ll also want to make sure their name is on the label.

How long does expressed milk stay good for? 

How long milk can be stored depends on just where it gets stored.

  • Out at room temperature: If you’ve just pumped and are fairly confident that your baby will drink the fresh milk soon, it can sit out unrefrigerated or unfrozen for six to eight hours (at up to 77°F or 25°C), but using or storing the milk in a colder space within four hours is ideal. The milk should be covered and kept as cool as possible, so if it’s a particularly hot day, you may want to move the milk to a fridge or freezer right away. 
  • In a cooler or insulated cold storage bag: If you pump and are then traveling with expressed milk, you may very well decide to store it in a cooler or insulated bag as you travel. It’s best to keep ice packs against the milk containers and to not to open the cooler or bag unless necessary. All recommendations suggest avoiding storing milk like this for longer than 24 hours.
  • In a refrigerator: It’s optimal to store milk in the refrigerator for three to five days, although it’s acceptable to store there for up to eight. It’s also recommended that you store the milk in the back of the fridge (as opposed to close to the front or on a door) where it’s a bit chillier. 
  • In a standard freezer (meaning a freezer that is part of a refrigerator but has a separate door): Milk can be stored for between three and six months.
  • In a deep freezer: Milk can be stored here for up to 12 months (though 6 months is ideal).
  • Partially used bottle: A feeding that was not finished can be used again within 2 hours

Milk that gets stored longer than these recommended times in a fridge runs the risk of spoiling. Milk that gets stored longer than these recommended times in a freezer is usually still safe, but some of the fats may break down and some of the nutrients may be lost. 

Thawing frozen milk

You can thaw frozen breast milk by placing it in the fridge several hours before you plan to use it, or thaw it more quickly under warm running water or in a bowl of warm water. Some research shows that milk warmed quickly via a warm water bath retains better fat and nutrient profiles. And some babies might even prefer that refrigerated milk be warmed up (what refined taste!). Heating it on the stove or in the microwave is not recommended, because the milk might heat unevenly or get a bit too toasty for Baby. Once frozen milk has been thawed, if it goes unused, it can be refrigerated for later use for up to 24 hours, but it should not be refrozen. However, if frozen milk has been partially thawed (as sometimes happens in the event of a power outage), as long as it still contains ice crystals, it’s considered safe to refreeze.

As you begin to pump and store your milk, you might notice that it’s a particular color or that the color changes over time or even depending on what time of day you pump. When chilled, you might also notice that it will separate into milk and cream layers. And once thawed, you may notice the milk looks like it’s of a somewhat different consistency or smells slightly different than when it was freshly pumped. As long as the milk has been stored properly, this is normal. But use your judgment; a little sniff should tell you if things have gone bad. (Milk that smells soapy is still safe and nutritious for your baby, it just happens to have excess lipase activity. Lipase is a normal enzyme found in all milk, but your little one might not love the taste. Scalding the milk quickly, for just a few seconds before freezing, can fix this issue. You can read more about milk with excess lipase activity and how to scald it here.) If you ever have questions or are really concerned that the quality of the milk is questionable, it’s better to err on the side of caution and toss it.

When it comes to storing milk for long periods of time, keep in mind that the quality and makeup of your breast milk changes over time as Baby gets older and has different needs. This means if you expressed a lot of milk when Baby was first born, it’s best to use that when they are still fairly young, and not save it until they’re nine months old.

Reviewed by the Ovia Health Clinical Team

Read more


  • Mayo Clinic Staff. “Breast milk storage: Do’s and don’ts.” April 7 2015. Retrieved August 11 2017. Mayo Clinic. Mayo Foundation for Medical Education and Research.
  • “Proper handling and storage of human milk.” Centers for Disease Control and Prevention. U.S. Department of Health & Human Services, July 24 2017. Retrieved August 11 2017.
  • “Storing breast milk.” Cleveland Clinic. Cleveland Clinic, March 25 2015. Retrieved August 11 2017.
  • “What are the LLLI guidelines for storing my pumped milk?” La Leche League International. La Leche League International, July 8 2014. Retrieved August 11 2017.

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