How to Defrost Breast Milk Safely

Article By
Sonni-Ann
Published On
23 May, 2023
Read Time
3 minutes

So, you've expressed breast milk and popped it in the freezer for storage. But now you're wondering how best to defrost it, ready to feed your little one.

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 fridge 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.

Defrosting breast milk in the fridge

You can gradually defrost frozen breast milk in the fridge.

Using warm water

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

Running frozen breast milk under warm water

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

Breast milk can be given to a baby cold if they'll take it this way, but if they prefer their feed warmed slightly, you can warm it up 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 reheated if your baby doesn't finish their feed. So, it's a good idea to warm only a small amount at a time.

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

How long does breast milk take to defrost?

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.

What to avoid when defrosting 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 defrost at room temperature.
  • Don't re-freeze breast milk that's been thawed.

Tips for freezing breast milk to reduce 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.

Give baby the oldest milk first

When getting milk out of storage to feed 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, so you know you're using the oldest milk first.  

Use milk storage bags to speed up thaw time

Our pre-sterilised breast milk storage bags are made for breast milk, and help it thaw faster.

Freeze breast milk in a sterilised ice cube tray

Most ice cube trays have individual sections that hold around 1oz each. These can be handy for measuring out the right amount of breast milk needed for each feed.

Place bags of breast milk in a sandwich bag when thawing in warm water

This 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. Always leave some room for expansion.

Check that your container is freezer-friendly

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

How long can breast milk be frozen?

It's recommended that breast milk is thawed and used within 90 days of being frozen. This is because the fat, calories and protein in breast milk decrease over time once it's frozen.

However, breast milk can be safely stored in the freezer at -18°C or below for up to six months. If it's not used within this time, it can be used in milk baths or to treat rashes.

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.

If it's been defrosted in the fridge, 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.

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.