Breastmilk storage simplified-How to store breastmilk safely

Breastmilk Storage How to Store Breastmilk

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How confident are you in your ability to safely store breastmilk? Figuring out how to store breastmilk can be tricky. Of course, you know enough not to be outright dangerous – but it’s easy to get confused with so many variables! For example, you pump milk then get distracted and leave it sitting out for 3 hours. Or was it 4? Your husband looks at it suspiciously. You can’t really tell if it smells like it should. And since you probably don’t drink breastmilk very often, you have no idea if it tastes weird. Is it still safe?

Breastmilk Storage How to Store breastmilk

There are several ways to store milk – the refrigerator, the freezer, an insulated cooler, room temperature… and any combination of those methods. With all those possibilities, you could also end up in a scenario like this: a bag of freshly expressed milk is left out for an hour, kept in the refrigerator for 3 days, the freezer for 5 months, then thawed in the fridge overnight, reheated and your baby only eats half of it. Do you keep the rest? Refreeze it? Throw it away? By the end of this article, you’ll know the answer without worrying that you’ve made the wrong choice!

This advice is for feeding healthy, full-term babies. If your baby is hospitalized, premature, or seriously ill, please consult your doctor about safe milk storage.

Before you even express a drop…

There are a few things you need to understand before you express your milk. Let’s call it housekeeping 🙂 When you express milk, every part of the process should be as clean as possible. Now I’m sure you’re probably not dirty per se – but let’s face it, sometimes moms cut corners. I readily admit that I’m the queen of “eh, clean enough.” And while “eh, clean enough” is okay when you’re fixing a sandwich, it’s not okay when you’re pumping milk.

The biology of breastmilk (and why it matters)

Breastmilk is full of white blood cells. I mean absolutely chock full of ’em! These white blood cells play a couple of different roles. First, they keep breastmilk pure by fighting off any harmful bacteria that the milk comes into contact with. And second, they keep your baby healthy by fighting off infection and bacteria in his little body.

Here’s the kicker: white blood cells aren’t invincible. They can only fight for so long before they die.

Whenever you express milk with unwashed hands, pump parts that haven’t been recently sanitized, or in a dirty environment (like in a bathroom) then you’re exposing your milk to any number of contaminants.

Keep in mind that germs can float in the air, so you don’t necessarily have to put a dirty finger in the milk in order to contaminate it from unwashed hands. 

What germs actually do to breastmilk

Once germs are introduced to breastmilk, those amazing white blood cells begin killing the germs off. Remember how I said that white blood cells aren’t invincible? Well if they die off before your baby has a chance to drink the milk, there’ll be none of your white blood cells left to boost his new immune system.

So wash your hands well. Make sure you’re expressing in an area that’s reasonably clean. And always used clean pump parts! I know they’re a pain to wash, so if pumping is your main method then you may want to invest in a couple of extra pump kits. That way you always have a freshly washed set on hand.


The best containers for breastmilk are glass or plastic that’s free of BPA. I highly recommend Lansinoh breastmilk storage bags. When choosing breastmilk storage bags, look for ounce markers, a place to write the date, and bags that are pre-sealed (where you tear off the top edge before using it) for sterility purposes. I think it’s probably standard practice for breastmilk storage bags to have all those components now, but it’s not a bad idea to double check. Just in case.

You don’t want to keep your milk in disposable bottle liners or sandwich bags. They’re made of plastic that’s much more flimsy and prone to bursting. Plus, sandwich bags aren’t usually BPA free. Also, they’re more likely to spill because of weak closures.

how to store breastmilk at room temperature

How to store breastmilk at room temperature

Freshly expressed breastmilk can be kept at room temperature for 4-6 hours, longer if the room is quite chilly and shorter if the room is quite warm. Use your own judgment here. The fresher the milk and the cleaner the environment when it was expressed, the better it holds up to room temperature. I’ve read that breastmilk can stay out in a cool room for as long as 10 hours but that makes me uncomfortable. If you’re approaching that six-hour mark and not about to use it, go ahead and get it chilled.

For frozen breastmilk, it’s not truly “at” room temperature until after it’s fully thawed, so start counting then. It can safely sit at room temperature for about 2 hours after thawing.

How to store breastmilk in the refrigerator

Breastmilk can stay in the refrigerator for up to 6 days. At 6 days, you can still transfer it to the freezer if you need to.

While it may be really really tempting to put expressed milk in the refrigerator door (in what looks like ready-made storage trays, right?), that’s a terrible idea! It’s the warmest area in your refrigerator and also the area with the least stable temperature. You want to store your milk in the back of the refrigerator where the temperature stays consistently cold.

Once out of the refrigerator, breastmilk can survive at room temperature for 2 hours before you need to throw it away.

If you keep breastmilk in a shared refrigerator, label it so there’s no confusion. Also, wash the outside of the container with hot soapy water before you open it. You just never know who has been pawing around the fridge with unwashed hands.

how to store breastmilk in the refrigerator

How to freeze breastmilk

Containers and labeling

For freezing milk, I personally think plastic is the best container choice. You can freeze your breastmilk in a glass container. But glass containers sometimes break when their contents expand. Please be very careful if you’re using glass! Regardless of what container you’re using, be sure to leave a little room for expansion in your container. Don’t fill it all the way to the top! Leaving about an inch of headspace should be just right.

Write the ounces, the date it was expressed, your name, and any other info you need on the container BEFORE you freeze it. It’ll be nearly impossible to get any marker or stickers to stay on there after it’s frozen. Ask me how I know.

How long to keep breastmilk frozen

Frozen milk can stay in the regular freezer part of your refrigerator for 3 months or in a deep freezer for 6 months. After that, a couple of things happen. First, you run the risk of freezer burn and the milk not tasting good. A picky baby is gonna spit that stuff out and refuse to drink it. Second, it begins to break down and the vitamin content diminishes. If you need to use milk that old and your baby is willing to drink it, it’s a good idea to supplement your baby’s diet with multivitamin drops.

Accidentally thawed breastmilk

Since we live in an imperfect world, let’s talk about what to do with accidentally-thawed milk. Like during transport or a power outage. If it still had chunks of ice in there, you can refreeze it and keep going as if nothing happened. But if it thawed completely and stayed very cold, it can last 2 days. And if it came to room temperature, it’s good for two hours. After that, throw it away.

How to thaw & reheat frozen breastmilk

When it comes to thawing breastmilk, the slower it thaws the better. The reason for this is because heat will melt the milk fat, which will then stick to the storage container instead of staying in the milk. What you end up with is a lower calorie, less nutritious breastmilk. Your baby desperately needs that fat!

The best way to thaw breastmilk

So you want to bring frozen milk to room temperature, transfer it to the bottle your baby will use, and then warm it using a bottle warmer, or by putting it in a bowl of very warm water.

Ideally, you’ll thaw milk by putting it in the refrigerator to thaw ever so slowly.

And if you’re like me, then you won’t think a thing about thawing it until you need that chunk of frozen milk to be warm in a bottle right now.

The next best way to thaw breastmilk

So the second best option is laying it out on a towel and letting it come to room temperature. You can also hold it under running warm water or set it in a bowl of warm water. Just make sure the water stays warm.

You can keep thawed milk in the refrigerator for 24 hours. Don’t ever refreeze it!! The only exception is if it never fully thawed and still had chunks of ice in it.

Why thawing in the microwave is bad

I admit I’ve thawed breastmilk in the microwave before. And I’d like to go back in time and lecture myself on why that was wrong. See, I thought the only thing I had to worry about was hot spots. I was wrong. Microwaves change the composition of the milk and damage the vitamins and white blood cells. Not to mention, they melt that milk fat and cause it to stick to the sides of the container. Don’t microwave the milk, mmkay?

Using stored breastmilk

Obviously, the fresher breastmilk is, the healthier it is. That’s not to say stored breastmilk (even frozen for six months) isn’t good. It’s still an incredible source of nutrition for your baby! Breastmilk storage does tend to change the texture of breastmilk though.

If it looks weird…

If it looks strange, like it separated and has watery parts, that’s okay. Just swirl or stir it to blend it back together. Shaking could further damage white blood cells. And shaking it will also fill your milk with air, possibly leading to a fussy baby with an achy tummy.

If it smells weird…

If your milk has a strange smell, maybe soapy or just weird, that’s from lipase in the milk and won’t hurt your baby at all. Some moms just have more lipase than others. No worries!

If your milk is spoiled, you’ll know it. It smells like…well, like spoiled milk. Not a smell you’re likely to miss!

If your baby won’t drink it…

Your baby may refuse to drink stored milk. If that happens, you can blend it with fresh milk to make it taste better for him. A couple of precautions about mixing old and new milk: first, make sure they’re both cool when you mix them and second, use the expiration time of the oldest milk as a guideline for safety (i.e. thawed milk that can stay at room temp for 2 hours mixed with fresh milk can still stay at room temp for only 2 hours).

Easy Peasy

Well, there you have it! That’s about as easy as I’ve ever seen milk storage explained. Fresh milk can stay out for 4-6 hours, refrigerated for up to 6 days, in your freezer for 3 months, or deep freeze for 6 months. Refrigerated breastmilk can sit out for up to 2 hours. Thawed breastmilk is safe for 24 hours, can stay at room temperature for 2 hours, and must never be refrozen. Because storage changes the composition of your breastmilk, there’s no need to worry about a strange texture or odor unless the texture is chunky or it smells like spoiled milk. Throw away any milk that survives longer than suggested by these guidelines.

Is there any aspect of breastmilk storage that confuses you? Please ask your “how to store breastmilk” question in the comments below and I’ll be happy to answer!


Association of Breastfeeding Medicine ABM Clinical Protocol #8:Human Milk Storage Information for Home Use for Full-Term Infants, Revised 2017

La Leche League International

Centers for Disease Control and Prevention

Breastmilk Storage How to Store Milk

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