How long can pumped breast milk stay at room temperature

Sometimes a breastfeeding mother might need to express and store her breast milk for her baby.

A common question from mothers is: How long can breast milk be at room temperature?

There are many reasons for expressing breast milk.

You might need to express milk for your baby who was born prematurely, or because you’re experiencing milk engorgement.

Some mothers express breast milk if they need to leave their baby for longer periods, or to build up a freezer supply if they’re returning to work. 

Whatever the reason, safe storage of your expressed milk is important.

How long can breast milk be left out of the fridge?

There’s nothing more disappointing than putting in the effort to express breast milk then wasting it because of incorrect storage.

How long can breast milk be at room temperature, and left out of the fridge, before it’s not safe to use?

How long can breast milk be at room temperature – freshly expressed?

Freshly expressed milk can be stored safely at room temperature for 6-8 hours. This is provided the temperature of the room is no higher than 26C. 

It’s logical to assume the warmer the room, the more potential there is for bacteria to grow.

Regardless of the room temperature, it’s better to refrigerate the milk straight away if there’s a fridge available.

Whenever possible, it’s best to use the breast milk, or store it in the refrigerator or freezer, within 4 hours.

How long can breast milk be at room temperature – previously frozen?

For thawed breast milk that’s been previously frozen, it’s safe to store at room temperature for 4 hours. This also applies to previously frozen milk that has been thawed in a refrigerator.

Once the previously frozen milk has been thawed at room temperature, it shouldn’t be put back in the refrigerator or freezer.

Any previously frozen milk that’s been thawed at room temperature should be used within 4 hours or discarded.

Safe storage guidelines for expressed breast milk

At a glance, here are the best practices for safe storage methods of expressed breast milk, as advised by the Academy of Breastfeeding Medicine:

• Room temperature (up to 29C): 4 hours (optimal) or 6-8 hours (acceptable in very clean conditions)
• Refrigerator (4C): 4 days (optimal) or 5-8 days (acceptable in very clean conditions)
• Freezer (-18C): 6 months (optimal) or 12 months (acceptable in very clean conditions).  

When storing expressed milk in the fridge or freezer, place it as close to the back as possible (not on the door). This ensures the milk stays as cold as possible.

Is breast milk good if left out overnight?

It’s always best to use, refrigerate or freeze expressed breast milk as soon as possible.

But it often happens that expressed milk is accidentally left out overnight. You might wake up the next morning and wonder: how long can breast milk be left at room temperature and safely used?

If expressed milk has mistakenly been left out overnight, the previously mentioned recommendations still apply.

If it’s freshly expressed breast milk, it can be left for 6-8 hours. If it’s previously thawed breast milk, then it can be left out for 4 hours.

After this period the milk needs to be discarded.

Can I put breast milk back in the fridge after baby drinks from it?

Once your baby has started to drink your expressed milk, any left-over milk should be discarded. This is because potentially harmful bacteria could have entered the milk.

You shouldn’t feed the remaining milk to your baby later, and you shouldn’t re-refrigerate it, freeze it, or add it to another supply of stored milk. 

Can I pump into the same bottle all day?

It’s perfectly ok to mix freshly expressed breast milk with previously stored breast milk. 

Freshly expressed milk that has just come from your body is still warm. The warm milk needs to be cooled down before adding it to other refrigerated or frozen milk.

You can cool your freshly expressed milk in the refrigerator, then add it to previously refrigerated or frozen milk.

What is the best way to store breast milk?

The best way to store pumped milk is in clean, tightly sealed breast milk bottles, or breast milk bags. When you use breast milk bottles, you can place sterile, disposable bottle liners inside them, to guarantee cleanliness.

It’s also ok to use containers that haven’t been specifically designed for breast milk storage.

A clean, food grade, glass container that can be properly sealed is suitable. The same goes for a clean, BPA-free plastic container.

Plastic bags that haven’t been designed to store breast milk are not recommended. Research suggests that soft plastic bags and zip lock bags can potentially leach harmful chemicals.

Top 7 do’s and don’ts for storing breast milk

#1. Don’t cry over spilt milk!

No matter which method of storage you use for your expressed milk, make sure it’s properly sealed.

The old saying, ‘Don’t cry over spilt milk’ wasn’t invented by a breastfeeding mother!

Whatever the reason for expressing, it takes time and effort. Nothing can be more disappointing than seeing that liquid gold accidentally spilled all over the kitchen countertop.

Using correct storage containers that can be properly sealed can save a lot of potential heartache.

#2. Don’t overfill milk storage containers

If you are freezing your pumped milk, allow some extra room in the storage container.

Like water, breast milk expands when frozen. If you fill your storage container to the top it could crack or burst. Instead, leave it around three quarters full.

#3. Don’t use a microwave to warm expressed milk

Using a microwave to warm expressed breast milk can damage important nutrients and antibodies.

Microwaves can also heat unevenly, which can cause hot spots in the milk and scald your baby’s mouth.

The best way to warm expressed milk is to let it thaw in the fridge (if previously frozen), then heat it under warm running water or in a bowl of warm water.

#4. Don’t shake breast milk

It’s normal for refrigerated or frozen breast milk to settle in layers, with the fat rising to the top.

Shaking your expressed milk to mix it back together can cause damage to the proteins within the milk. A gentle swirl is all that’s needed before feeding it to your baby.

#5. Do label your storage containers

Pop the date on your expressed milk so you can keep track of how long it’s been stored.

It’s better to use the milk in date order, so none is wasted. It’s also important because your breast milk changes over time.

The milk you express when your baby is 3 weeks old will be different from the milk you express at 3 months.

Your milk is specially tailored to meet your baby’s changing needs at different ages.

It’s best to use the milk most closely related to your baby’s need at that time.

#6. Do keep track of day and night milk

Not only is it handy to label your storage containers with the date the milk was expressed, but also with the time of day.

Did you know nighttime milk is different from daytime milk?

The milk your body produces at night contains special hormones to help your baby get to sleep. Add an ‘AM’ or ‘PM’ to your label, depending on what time of day your milk was expressed.

#7. Do smell (or taste) thawed milk

Some mothers find their previously frozen breast milk smells or tastes funny. Sometimes their babies will even refuse to drink this milk.

This has nothing to do with their breast milk being ‘bad’, or ‘off’. Usually, it’s because of an enzyme called lipase.

Some mothers have a higher lipase content in their milk than other mothers, which causes the fats in their breast milk to break down more quickly.

This isn’t noticeable in fresh breast milk. Over time, though, when your milk has been refrigerated or frozen, it can cause a change in the smell and the flavour of the milk.

If you’ve noticed a soapy or metallic smell or taste to your stored milk, it could be due to lipase.

If your baby rejects this milk, you can save it to mix with solids (once the baby is 6 months old).

You can also prevent the change in flavour by taking the following steps, before refrigerating or freezing your expressed milk:

•       Put your expressed milk in a saucepan over medium heat
•       Heat until little bubbles appear around the edge of the pan (not a rolling boil)
•       Remove milk from the pan and allow it to cool; then store, as normal.

More information on storing breast milk

For further information on safely expressing and storing breast milk, you can refer to the Australian Breastfeeding Association’s guidelines here.