Safe Storage of Pumped Breastmilk

AngelaRD, LDN, CBS

Read time: 6 minutes

What to know about storing your pumped breastmilk

  • Know which breastmilk storage containers are available

  • Understand how long breastmilk can be stored at room temperature, refrigerated, or frozen

  • Learn how to safely thaw breastmilk

  • Tips on storing breastmilk and using stored breastmilk

For many breastfeeding mamas, being away from their little one is unavoidable. Missing one or even several feedings will be much less disruptive if you have a supply of pumped breastmilk on hand, ready for use.

But knowing how to properly handle and store breastmilk is critical. Doing so the correct way will help prevent contamination and maintain breastmilk’s nutritional quality.

Read on to learn how to safely store, freeze, thaw, and feed stored breastmilk.

Containers to store breastmilk

Before use, make sure all bottles and materials that will be touching breastmilk are washed in hot, soapy water and thoroughly dried.1

For short-term storage, breastmilk can be stored in glass or BPA-free plastic bottles, or other food-grade containers with tight-fitting lids.2 Breastmilk storage bags can also be used.

For long-term storage, such as freezing, breastmilk storage bags work best as you can freeze the milk compactly.1,2

Glass can also be used for freezing, but know there is a higher risk of breakage so more caution may be needed.

It is common to store milk in 2-to-4-ounce portions.5 If you know about how much milk your baby typically takes at each feeding, storing the milk in those portions can help reduce waste.

If you are concerned about pumping due to the cost of equipment, know that breastmilk storage containers, as well as pumps and pumping supplies, qualify as tax-deductible breastfeeding equipment.3

Learn about: Choosing the Best Bottles and Nipples for your Baby

Guidelines for storing breastmilk

The following breastmilk storage recommendations are for healthy, full-term babies. Babies born prematurely may have much more stringent storage guidelines to help prevent bacterial contamination of breastmilk.4

Room temperature: Freshly pumped breast milk can be stored for 4 hours at room temperature (60 - 85 degrees F). Note that it is best to refrigerate milk as soon as possible if not being used within this time frame.1,2,5

Cooler with ice pack: Freshly pumped breast milk can be saved for 24 hours in a cooler with ice packs (at 59 degrees F or lower).1,2,5

Refrigerator: Freshly pumped breastmilk can be kept in the refrigerator for 4 days at 39 degrees F or lower. Breastmilk can be transferred to the freezer at any point during this time.1,2,5

Freezer: Pumped breast milk can be frozen for 3 to 6 months (at 0 degrees F) in the coldest area of the freezer. In a deep freezer, breastmilk may maintain most of its nutritional and bioactive quality for up to 9 months. If using a refrigerator freezer, do not store milk close to the front or on the door, as milk here will warm each time the door is opened.1,2,5

*Note that breastmilk expands when frozen, so be sure to leave a bit of extra room in the container.

Read about:

Top Tips for Pumping Breastmilk

How to Choose the Right Breast Pump

How to thaw frozen breastmilk

When you’re ready to use breastmilk from the freezer, it can be thawed in several ways:

  • In its container in the refrigerator overnight (which typically takes about 12 hours)

  • By placing the breastmilk container directly into a container of warm water

  • Holding under running warm water1,2,5

When slowly thawed in the refrigerator, there is less fat loss from the breastmilk than when thawed quicker in warm water.1

Tips for thawing breastmilk

  • Do not leave breastmilk out in room temperature to thaw.7

  • Remember to thaw and use the oldest milk first. Think: *First in, first out*7

  • Do not use the microwave to thaw breastmilk.5 This could damage the milk and heat it unevenly, creating hotspots that could burn your baby.1

  • Thawed milk is safe in the refrigerator for 24 hours, after that it must be thrown out. Start the 24-hour-countdown once milk is completely thawed, not from the moment you take it out of the freezer.7

  • Once the milk is warmed (to room temperature or more), use within 1-2 hours.

  • Do not refreeze thawed breastmilk.2

Keep in mind that milk does not HAVE to be warmed. If your baby accepts or prefers cold breastmilk, it is perfectly safe to provide it chilled.

Read about: Dealing with Low Breastmilk Supply

Can I mix breastmilk that was pumped at different times?

After pumping it is safe to mix breastmilk that are the same temperature (warm with warm and chilled with chilled).6 Never add warm breastmilk to milk that is refrigerated or frozen breastmilk – be sure to cool it first.

If the milk you are mixing is from different days, label your final storage container with the oldest date.1

Have questions about pumping or storing breastmilk? Reach out to our team of registered dietitian nutritionists and lactation consultants for free! They’re here to help on our free to live chat from Monday – Friday 8am-6pm (ET). Chat Now!

Tips for storing breastmilk and using stored breastmilk

How long can breastmilk sit out after it has been refrigerated or thawed?

For freshly pumped then refrigerated breastmilk:

  • If you remove milk from the fridge and baby does not drink from the container, it is safe for about 4 hours at room temperature and can be put back into the refrigerator at any point during this time.1

  • After taking refrigerated breastmilk out and feeding some to your baby, the rest should be refrigerated and drank within 1-2 hours.1,2 After this time, the milk should be discarded to reduce risk of bacterial growth and introduction to your baby.1

For previously thawed breastmilk:

Whether baby has drank from it or not, it must be used and/or thrown out after 1 to 2 hours of being out of the refrigerator.1

Wash your hands

Before pumping or handling breastmilk, be sure to wash your hands with soap and water or clean your hands with hand sanitizer if you don’t have a nearby sink.7

Label breast milk storage containers

Write the date, the volume of milk, and (if traveling to a childcare provider) your child’s name on every container. Be sure to use the oldest milk first.1,2 *First in, first out*

Mix the fat back in

Oftentimes, the fatty portion of the milk will separate and settle at the top of the container. To mix everything back together, gently shake or swirl the container.8

*Note: Shaking versus swirling breastmilk is a controversial topic. Proponents of swirling state that shaking may denature the proteins in breastmilk or damage the bioactive properties. However, there is currently no research indicating that either of these things happen when breastmilk is shaken. Those who question the “swirl only” philosophy indicate that the shaking may not be forceful enough to cause damage.

To be safe, if you shake, do so in a gentle matter. Be sure that all the fat has come off the container sides and is mixed into the milk, and there are minimal bubbles created.

Learn about: How do I Relieve Gas in my Formula or Bottle-Fed Baby?

Get in the habit of chilling your milk right after it’s expressed

Unless you are giving the milk to your baby in the next 3-4 hours, immediately place the milk in a cooler pack, fridge, or freezer.6

If you know you will not need the milk you just pumped in the next 3 days, go ahead and freeze it.

Why does my refrigerated and thawed breastmilk smell different?

Sometimes stored breastmilk has a slightly different smell than fresh breastmilk.12 It is often described as a ‘soapy’ smell. This is thought to be from the natural process of lipase enzymes breaking down fats in the milk.1

Interestingly, this process also has an antimicrobial effect, which helps prevent the growth of bacteria in the milk (for a limited amount of time at least).9

This milk is still safe for baby to drink and there is no indication that this change in smell affects the taste.1 Most babies do not mind and will still drink the milk without a problem.

My baby is refusing my frozen breastmilk! What do I do?

Occasionally babies will refuse milk that has been stored for too long, which may be from overactive lipase activity.12 This lipase enzyme changes the taste of milk enough so that the babies no longer find it appealing.

The good news is that some babies will accept milk that is stored for a shorter amount of time – giving the lipase less time to break down fats.12

If you think taste or lipase is an issue, here are some things to try:

  • Refrigerate and/or freeze for less time before using

  • Mix stored breastmilk with some fresh breastmilk10

Some professionals recommend gently scalding breastmilk before refrigerating or freezing to help stop lipase activity.11

If you feel lipase is a problem, chat with a lactation consultant about this option. They can provide guidance to help ensure the quality of your milk mostly stays intact during the process.

Other reasons your little one may be refusing stored breastmilk is if the pump or storage containers are not fully clean or are imparting a taste or smell that your baby does not like.

Try sanitizing containers and pump equipment once per day. Check out the guidelines from the Centers for Disease Control (CDC) on cleaning and sanitizing here.

You could also change the type of container you are storing breastmilk in to see if that alters the taste or smell of your breastmilk.13 For example, if you are storing in plastic or using plastic bottles, try glass for one or both instead.

Learn about: What is Paced Bottle Feeding

How do I know if refrigerated or thawed breastmilk is still good?

While a change in the smell of your breastmilk may be normal, if the milk smells sour or rancid – as cow’s milk may when it turns bad – then the breastmilk may not be good any longer.

A taste test may also be useful, but only if you have also tasted non-rancid breastmilk as a comparison. Taste test freshly pumped milk as well as milk that has been stored for short periods of time to help you know when/if milk has gone bad.

What happens if my power goes out? Do I have to throw away my frozen breastmilk?

The good news is that if there are still ice crystals in the breastmilk, it is still considered frozen and you can refreeze it once the power is back on!6

If the breastmilk is fully defrosted, but still feels cold, it can be kept in the refrigerator and used within 24 hours. 6After that, it must be thrown out.

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Our Happy Experts are a team of lactation consultants and registered dietitian nutritionists certified in infant and maternal nutrition – and they’re all moms, too, which means they’ve been there and seen that. They’re here to help on our free, live chat platform Monday - Friday 8am-6pm (ET).Chat Now!

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For more on this topic, check out the following articles:

Breastfeeding: How to Support a Good Milk Supply

Managing Leaking While Breastfeeding

Understanding your Baby’s Hunger and Fullness Cues

How Much Should I Eat While Breastfeeding?

Should I Breastfeed On Demand or on a Schedule?