How to Store Breast Milk Safely

There are many reasons you might want to collect and store your breast milk. Read on to learn how to collect and safely store breast milk, and how to defrost and warm it up when it’s time to give it to your little one.

The Benefits of Storing Some Breast Milk

There are lots of reasons to express and store breast milk. For example:

  • So your partner or a babysitter can take over some of the feeding duties if you need to go back to work or can’t be there to breastfeed for any other reason – for example, you’re taking the afternoon off for some ‘me time’ or you want to hand over a night-time feed so you can get some much-needed sleep

  • To relieve the pressure on overfull or engorged breasts or give sore nipples a chance to heal.

  • To prevent or help ease mastitis, a painful breast inflammation that may be caused by blocked milk ducts

  • To help boost your milk supply

  • If your baby finds it hard to latch on efficiently when breastfeeding , but you still want to feed your little one with breast milk

  • If you are advised or choose to start expressing your first milk, known as colostrum in the last few days or weeks of your pregnancy. This is strongly recommended if there’s a risk of complications (for example, if you have diabetes). But even if there aren’t any known risk factors, it’s a great way to max out the health benefits of colostrum for your little one – such as protection from infections and dehydration, and better digestion to name a few.

How to Collect Breast Milk

There are three main ways to express your milk:

  • By hand. Your midwife or health visitor can help you with this.

  • With a mechanical breast pump. This could be an affordable and easy-to-maintain option for expressing your milk.

  • With an electric breast pump. This might be the best option for efficiently expressing large volumes of milk. Electric pumps cost more to buy but may also be available to hire. Ask your midwife or health visitor what’s available in your area.

What Containers to Use

You can store your freshly expressed breast milk in any sterile airtight container, but breast milk storage cups, bottles or bags designed specifically for this purpose might have useful extra features, such as:

  • Calibrated markings so you can see at a glance how much they contain

  • A writable strip to make it easier to mark the date and time of expressing

  • Single-use milk storage bags may be pre-sterilised (check the manufacturer’s instructions to make sure)

  • If you use a breast pump, you might be able to buy compatible milk storage bottles or bags that you can express your milk into directly, to help reduce the possibility of contamination.

How to Store Breast Milk

When storing your breast milk, follow these easy steps:

  1. Clean and sterilise the breast milk containers before collecting and storing breast milk

  2. Mark each storage container with the date and time that you expressed the milk. Always use the oldest stored breast milk first, as long as it’s still within its use-by limit.

  3. If you’re going to place the container in the freezer for storage, make sure to leave a couple of centimetres air space at the top because the liquid will expand when frozen.

Portioning the Breast Milk for Storage

It’s best to store milk in small portions, especially if you’re planning on freezing the breast milk. That way it’ll be easy to defrost just what you need.

The definition of a ‘small portion’ can change with time, as the amount your baby drinks at each feed increases as he or she gets older. For example, at three days old your little one only needs around 22 to 27 millilitres at every feed, but by the age of 1 month this may already have risen to around 80 to 150 millilitres per feed.

Hygiene Guidelines

It’s important that the items you use to pump and store your breast milk are very clean to help prevent transmitting bacteria to the breast milk and to your baby.

Before using your breast pump make sure to sterilise all its parts, including the storage bottles and any other parts that come into contact with your breasts or the milk.

Sterilise by boiling the parts for at least 10 minutes or use an electric steriliser or a sterilisation container that can be placed in a microwave oven. Alternatively, soak the parts in a cold-water sterilising solution for at least 30 minutes.

Always follow the manufacturer’s instructions for sterilising and follow the recommended boiling or sterilising time in case it’s a little different for the product you have. Let sterilised items cool down after boiling or steaming and handle them with caution.

After you use the pump, every time, make sure to wash the parts in hot, soapy water, or in the dishwasher if the parts are dishwasher safe.

The same hygiene guidelines apply to the bottles or storage containers you use to store the breast milk. Check the instructions that come with the product for guidelines specific to it, just in case it’s a little different to the general guidelines we’ve described here.

Each time you use the pump or handle breast milk, wash your hands thoroughly first.

How Long Does Breast Milk Last in Storage?

How long you can store breast milk depends on the temperature you keep it at. As a general rule, the colder it is, the longer it lasts, but there are a few extra things to keep in mind:

  • If you’re storing your breast milk in a fridge, put it in the back of the main compartment rather than in or near the door. That way, it’s less likely to be affected by temperature changes when you open and close the fridge door

  • If your fridge or freezer doesn’t display its temperature, consider buying a fridge thermometer to check how cold it is

  • If you’re travelling, breast milk that’s already been chilled in a fridge can last up to 24 hours in a cool box with deep frozen ice packs

  • If your baby was born prematurely or has any health issues or vulnerabilities, you may need to follow different breast milk storage guidelines. Ask your midwife or neonatal unit about these.

Depending on where it’s kept, freshly expressed or pumped breast milk can be stored for the following lengths of time:

Defrosting Breast Milk

Follow these tips for thawing breast milk that’s been stored in the freezer:

  • Ideally, allow the frozen breast milk to thaw out gradually in the fridge. This can take up to 12 hours, so plan your defrosting a little in advance, for example, thaw the milk overnight. If the milk is still frozen after 12 hours in the fridge, thaw it out by sitting the container in warm water, and use it straight away.

  • If you need to defrost some milk for immediate use, a quicker method is to sit the container in a jug of warm water or hold it under a warm running tap

  • Sometimes the defrosted breast milk may separate into a watery and a creamy part. If this happens, gently shake the storage bottle to mix it up again

  • Once the milk has thawed, give it to your baby within 24 hours

  • Don’t defrost breast milk at room temperature or in a microwave oven

  • Never refreeze thawed breast milk.

How to Warm Chilled Breast Milk

Breast milk stored in the fridge, whether it’s been previously frozen or not, can be warmed up if you would like to give your baby warm milk.

Keep in mind, though, that breast milk doesn’t need to be given to your baby warm – it’s also OK to feed your baby breast milk that’s chilled or at room temperature if he or she prefers it like that.

Follow these steps to warm breast milk after storage in the fridge:

  • Place the bottle of breast milk in warm water. Use a pan or bowl of warm water to warm up your baby’s bottle or use a bottle warmer.

  • Don’t heat bottles on a cooker or in the microwave. This can create ‘hot spots’ that could burn your baby’s mouth.

  • Check that the milk’s not too hot. Before feeding your baby, test the temperature of the breast milk by squirting it on the underside of your wrist – where the skin is more sensitive – to ensure it’s not too hot for your baby. It should feel warm or neutral on your wrist.

  • Don’t wait too long to give the breast milk. Once you’ve warmed the breast milk, it should be used within two hours.

Is Stored Breast Milk Any Different From Fresh Breast Milk?

Breast milk that’s been in storage, either in the refrigerator or thawed from the freezer, can look different from freshly expressed or pumped breast milk. It may even separate into a creamy layer and a more watery layer. This is completely normal. Gently shake the milk storage bottle or container to mix it back together.

If your freezer has an automatic defrost cycle, the frozen milk may seem frothy after you thaw it out. In this case, as long as the defrosted breast milk doesn’t smell sour, it’s usually OK. If you do notice a sour or rancid smell, throw the milk away.


Breast milk can usually be stored outside the fridge at room temperature for up to six hours. To be safe, always try and leave as little time as you can between taking the breast milk out of the fridge and giving it to your baby.

The Bottom Line

For busy mums like you, expressing or pumping breast milk and then storing it can be a lifesaver.

Having breast milk in storage can make it easier to keep up with your baby’s feeds – even during periods of cluster feeding – and allows you to share feeding duties with others.

Using the info in this article and by giving it a try, you’ll soon get the hang of storing, defrosting, and reheating breast milk and it will become a natural part of your life with your little one.

How we wrote this article The information in this article is based on the expert advice found in trusted medical and government sources, such as the National Health Service (NHS). You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.

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