Breast milk storage: all you need to know

woman breastfeeding

You’ve mastered the art of expressing, now to turn your hand to storing your breast milk. Breast milk storage can sound complicated but really the guidelines are fairly simple – soon enough, it'll all be second nature to you.

On this page

Breast milk storage advice
Defrosting and reheating breast milk
Storing breast milk at work
Storing breast milk for a premature baby

What breast milk storage bags and equipment do I need?

First things first: you need to get your kit sorted. If you’re not keen on hand expressing, you’ll need a breast pump to do that bit. But for the actual business of storage you’re looking at either breast milk storage bags, which are like sturdier, smaller zip-lock plastic bags, or plastic bottles or lidded cups. For very small amounts, you could freeze breast milk in ice cube trays, but it would need to either be a tray with a lid, or you’d need to keep it inside a sealable plastic bag.

How do you use breast milk storage bags?

Bags are great as they take up so little space in the freezer. Write the time and date on your bag before you start. Once you’ve expressed your milk, pour it (carefully – there’s a knack to this) into the bag, leaving a little space at the top otherwise it might burst when it expands on freezing. Try and squeeze the air in the top out as you seal the bag closed.

Some pro tips for you: when you have space, freeze the bags lying down flat, so they’re easier to store standing up once frozen solid as they won’t be bigger at the bottom end than the top. If you then stand them in a small Tupperware box, Marie Kondo style, and always put your latest bag of breast milk at the back and take from the front, you’ll always know you’re taking the oldest one out to use first. But we’re getting into the realms of really nerdy breast milk storage admin now. Let's move on…

breast milk storage bags

Some companies, such as Tommee Tippee and Medela do special bags that fit onto their breast pumps so you can express directly into the bag before popping it into the fridge or freezer, avoiding the tricky issue of getting it from pump into bag, which is often like pouring a cuppa from a 40-year-old Brown Betty with a wonky spout.

Which bottles and cups can I use for breast milk storage?

Most of the big bottle manufacturers, such as Avent, Tommee Tippee, Philips, Medela and Mam, have a range of containers to suit your needs. If you have enough space in your freezer, or are planning to use your expressed milk quickly, you could simply use the bottles that come with your breast pump, express straight into the bottle, pop the teat and lid on and store it like that. Then it’s ready to feed your baby as soon as it’s up to room temperature.

If you’re planning to store quite a few feeds and freeze them, you’ll find the bottles take up a lot of space and bags may be easier.

You can also buy breast milk cups, which are just like little Tupperware food containers. These are a bit smaller than bottles but still stand up on their own in the fridge or freezer, unlike bags.

Bottles and cups also have the advantage that you can add to them (see below) if you’re expressing in small amounts during the same day and leaving your milk in the fridge.

breast milk bottles

Can I use glass bottles to store breast milk?

No. Glass bottles can easily have small cracks and chips that you can’t see and which can harbour germs. Also, drop a plastic bottle on the floor and it just bounces. Drop a glass one and you’ll be crying over spilt milk. And have a hideous clean-up job on your hands.

Breast milk storage general advice

Here are a few general principles to remember when storing milk.

  • Keep it clean, so if you’re usually a rancid-lettuce-at-the-back-of-the-fridge culprit, it’s time to clean up your act. Keep expressed milk far away from milk, eggs and meat.
  • Also, as cold as possible. Expressed milk shouldn’t be kept in the fridge door as it’s not as cold as the rest of the fridge. It should be kept as close to the back of the fridge as you can.
  • Stay organised. If you’re putting bags of expressed milk in the freezer, pop them in a clean container that you change and wash regularly, rather than just letting them kick around at the bottom with errant chicken nuggets. Keep an eye on dates and use your oldest milk first.
  • Keep equipment clean, too. Bottles and containers should be sterilised or cleaned in hot soapy water and allowed to air dry completely before you store milk in them. Bags usually come sterile. You should also ensure any cool bags and ice packs you use in transportation are kept thoroughly clean, too.
  • Get a good fit. Check that any container you are storing milk in has a secure, tight-fitting lid and isn’t damaged in any way to avoid spills or contamination.
  • Remember less is more. If you’re worried about whether your baby will manage a whole 6oz bottle in one go, freeze it in two 3oz portions then none will be wasted if they only want a light lunch on the day.
  • And finally, don’t forget to date all your ‘produce’. There’s nothing worse than staring at an unlabelled batch of milk wondering if it’s OK to give to your baby or not.

How long can I store breast milk for?

Storage times depend on how cold the environment is. Here's a quick guide:

  • At room temperature (ie not in the fridge, at no more than 25C) – up to six hours.
  • In a cool box with ice packs – up to 24 hours. This applies to both freshly expressed milk and milk cooled in the fridge first. Take care to wrap the ice packs in a tea towel or similar so they don’t freeze parts of the milk.
  • In the fridge (never in the door, always the main part of the fridge, preferably at the back where it’s coldest) – Up to five days. Your fridge should be four degrees or colder.
  • In the freezer compartment of a fridge – up to two weeks.
  • In a proper freezer – up to six months. The freezer should be -18C or colder.

How long can you leave expressed milk out of the fridge for?

Up to six hours when first expressed, but best to pop it in a fridge or cool box if you have access to one. If taking milk out of the fridge, use it as soon as possible. Same goes for milk that has been defrosted.

Defrosting and reheating expressed breast milk

The best way to defrost breast milk is slowly, in the fridge. If you freeze your milk in breast milk storage bags, remember they will go floppy and fall over once defrosted so stand them in a mug. You can also defrost frozen milk at room temperature.

If you’re in a real hurry you can run the milk (inside its bag or container, obviously) under a cold, then a warm tap.

Can you reheat stored breast milk?

Yes. Once defrosted stand it in a bowl of hot water to warm through. Don’t use a microwave to heat it up as microwaves heat unevenly, which can leave hot spots in the milk that could burn your baby’s mouth.

Can you refreeze stored breast milk?

No. Once it has been frozen and then defrosted, anything unused needs to be thrown away. In fact, even if a feed hasn’t been frozen, once it’s been in your baby’s bottle everything they don't drink needs to go down the sink, sadly.

breast milk storage bags

Is it safe to mix milk from two different expressed feeds?

You can mix milk that was pumped at different times as long as you:

  • Ensure the fresh milk is cooled for half an hour in the fridge first.
  • Use both feeds together within the time limit of use for the oldest milk.
  • Only mix two feeds if there is more frozen milk than fresh milk.

Is it OK to use stored milk when it has separated?

Yes, it might look a bit funny but as long as it’s within its use-by limit and smells OK it should be fine. Milk often separates when it has been frozen. Just give the bottle a good shake if you don’t like the way it looks.

Where should I store expressed breast milk at work?

If you’re expressing having returned to work, you can store your milk in a pre-sterilised bottle or container in the fridge. (Do label it, if you don’t want an awkward conversation after the next tea run).

If you don’t have access to a fridge, you can put the milk in a cool bag with freezer packs to keep it cool. A cool bag is also helpful for transporting milk from work to home at the end of the day.

Breast milk storage for a premature baby

If you’re expressing because your baby was premature and is in a neonatal unit, speak to the staff there about the best way to express, store and give your baby your milk. Fresh milk has more antibodies than frozen so they may want to help you work out a way to get your baby their milk as soon as possible after expressing.

Is fresh breast milk better than frozen?

Marginally, yes. Some of the antibodies in breast milk are lost upon freezing. However, frozen breast milk is still considered to be superior to formula milk, so it’s definitely worth persevering with if expressing is working out for you.

There are times when you are better off using fresh rather than frozen. If, for example, your baby has diarrhoea and vomiting or the rest of the family has the bug and you’re trying to avoid your baby getting it, fresh milk will give your baby more antibodies, which might help prevent them picking up the lurgy or help them recover quicker.

Despite the rumours, there’s no basis in the theory that milk expressed when you and your baby had thrush can reinfect you later. Although freezing is not enough to kill off the yeast infection, La Leche League’s recommendations are that milk expressed during a bout of thrush is fine to give your baby.

woman using breast milk pump

Breast milk storage containers and pumps

If you're feeling at sea when it comes to breast milk pumps, bags and bottles, don't worry. We've got a few suggestions – recommended by Mumsnet users and, in a couple of instances, tried and tested by us.

Medela Breastmilk Storage Bags, £7.99

With freezer-proof, double-zipper protection, these bags are about as leak-proof as it gets. And if you haven't got a huge fridge/freezer, their flat shape ensures that they don't take up too much space. The shape also allows the milk to thaw quickly – perfect if you're short on time.

“Medela bags are the best. Hands down.”

Buy now from Amazon

MAM Manual Breast Pump, £101.43

One of the best breast pumps we reviewed, the MAM 2-in-1 functions both as an electric and manual pump – which gives you a fair bit of bang for your buck. It's also ideal if you need to express on the go.

“I've got a MAM 2-in-1 which is brilliant. I like the fact that it has a battery so I can take it around with me if I need to.”

Buy now from Amazon

Avent Reusable Breast Milk Storage Cups, £14.99

Easy to stack, these handy storage cups are sealed with a leak-proof, twist-on lid. Holding 6oz of milk, you can also mark the lids should you want to organise them.

“I didn't get on with the bags so I got some reusable Avent breast milk storage cups, and they've worked really well for me. You can firmly reseal them which is helpful.”

Buy now from Amazon

Spectra Breast Milk Storage Bags, £5.95

Pre-sterilised and BPA-free, these bags can store up to 200ml of breast milk. They're self-standing, too – so can easily stand upright in the freezer and save space. Double-lined and tightly-sealed, you don't need to worry about any overnight leaking.

“I used these and they were great. Zip-seal them shut and pop into the freezer.”

Buy now from Amazon

Ardo Calypso Double Plus Breastpump, £119.99 (with code MUMSNET10)

It may be a tad pricier than most, but the Ardo Calypso was our Best breast pump of the year for good reason. Efficient, sturdy and quiet, it can be used either as a single or double pump, and comes with a variety of breast shields. If that wasn't enough, the Ardo is also WHO code-compliant and ethically-produced.

Use the exclusive code MUMSNET10 for a discount.

“This pump has turned out to be a lifesaver.”

Buy now from Ardo

All prices correct at the time of publication.

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