A Complete Guide on How to Defrost Breast Milk

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Published On
23 May, 2023
Read Time
3 minutes

Once you've expressed breast milk, it's best to store it in the refrigerator or freezer as soon as possible.

But if you do freeze it, you may be wondering how best to defrost it so it's ready to feed your baby.

To help you out, we're going to run through how to safely thaw frozen breast milk and cover some top breast milk storage tips to save you both time and effort.

How to thaw frozen breast milk

When it comes to defrosting breast milk that's been frozen, it's important to make sure it stays safe for your baby. So, let's break down the process step by step.

  • Breast milk is best defrosted slowly in the refrigerator or using lukewarm water.
  • You should never leave frozen breast milk to defrost at room temperature and don't thaw frozen breast milk in a microwave or using boiling water.
  • Once defrosted, gently swirl the liquid breast milk. This helps you make sure that no frozen parts remain and mixes any separated fat.
  • Never re-freeze breast milk once thawed.


You can gradually defrost frozen breast milk in the refrigerator.

Bowl of warm water

You can defrost frozen breast milk that's in a sealed container by putting it in a jug of warm water.

Warm, running water

Alternatively, you can run warm water at a maximum temperature of 37°C over a bottle or bag of frozen breast milk.

How long to defrost breast milk

The amount of time that breast milk takes to defrost depends on which method you choose:

  • Fridge: This is the best method, but it can take breast milk up to 12 hours to defrost in the fridge. So, it's recommended you get out what you need for the next day the night before to give it time to thaw overnight.
  • A bowl of warm water: This breast milk thawing method should take around 20 minutes.
  • Running warm water: This method takes around five to 10 minutes, but it's not the most eco- or wallet-friendly option.

How long does defrosted breast milk last?

Once fully thawed, defrosted breast milk that was previously frozen can be kept at room temperature for up to two hours or stored in the fridge for up to 24 hours.

Safety guidance for using frozen breast milk

Let's run through some things to avoid when you're defrosting breast milk for your baby.

  • Never defrost or warm breast milk in the microwave - this can heat it unevenly and can lead to burns.
  • Don't use thawed breast milk after 24 hours.
  • Don't leave breast milk at room temperature to defrost.
  • Don't re-freeze breast milk that's been thawed.

Tips for using frozen breast milk without the waste

We know that pumping, freezing and defrosting breast milk is a lot to think about! The following tips may help simplify the process and reduce the risk of any precious breast milk going to waste.

Feed baby the oldest milk first

When feeding your baby, use a first-in, first-out approach. It can help to label your expressed milk with the date it was pumped before you store it in the freezer. That way, you know you're using the oldest milk first. 

Storage bags can speed up thaw time

Our pre-sterilised breast milk storage pouches are made for breast milk. They help it thaw faster and have space for you to write on the date your breast milk was expressed for organised and safe storage.

Use sandwich bags to minimise spillage

Placing bags of breast milk in a sandwich bag when thawing in warm water means that if the bag your breast milk was frozen in does split, it's caught and not wasted.

Don't overfill

Breast milk expands as it freezes. So, don't fill your storage container more than three-quarters full and always leave some room for expansion.

Check that your container is freezer-friendly

Some materials like glass can crack at very low temperatures. This means that your breast milk could go to waste.

How long can defrosted breast milk stay in the refrigerator?

If it's been defrosted in the refrigerator, breast milk should be used within 24 hours. You should start counting the time when the milk is completely thawed and not from when you first put it in the fridge.

Slowly defrosting breast milk in the fridge is best. But if you need to thaw frozen breast milk fast, you can defrost it in a jug of warm water or run it under running warm water.

Breast milk can be given to a baby cold if they'll take it this way. But if they prefer their breast milk warmed, you can do so once it's defrosted by: 

  • Placing the bottle in a fresh warm jug of water.
  • Running under the warm tap.
  • Using a specially designed bottle warmer.

Test the temperature of the milk before feeding it to your baby. You can do this by placing a drop on your wrist or the back of your hand. The milk should feel warm, not hot.

It's important to note that breast milk shouldn't be reheatedif your baby doesn't finish their feed. So, warm only a small amount at a time.

Don't warm breast milk in a microwave. This can destroy the nutrients in the milk and cause hot spots that can burn your baby's mouth.

Breast milk that's been frozen can sometimes smell different from fresh - some parents say it smells like soap or has a slightly metallic taste. This is because of the release of fatty acids but won't cause any harm.

Don't worry, if you've followed the guidelines we've covered above, your thawed breast milk will be safe to give to your baby.