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How Long After Re-Heating Can Breast Milk Be Left Out

How Long After Re-Heating Can Breast Milk Be Left Out?

Medically reviewed by

Dr. Nicole Nabatkhorian
Dr. Nicole Nabatkhorian

MD / PGY-2 Pediatrics

Disclosure: Some of our articles contain links to recommended products or services in which we may receive a commission if you make a purchase.

Feeding your baby is one of the most important parts of motherhood, and it is something that causes a lot of worry to new parents.

Ensuring that your baby eats enough is something that you will likely stress about for the first few months of being a parent, and depending on your choice of feeding method, this could cause you more stress.

If you choose to breastfeed, like many parents do, then you might choose to express milk.

Expressing milk allows you to feed your baby breast milk, without the mother having to do every single feed.

Instead, the milk can be expressed, stored, then reheated and served in a bottle to the little one.

But if you express breast milk, you might find yourself left with a lot of questions.

This may include how to store the expressed breast milk, how to reheat the breast milk, and how long after reheating the breast milk can be left out.

Typically, once expressed, breast milk can be stored safely in the refrigerator for up to 4 days.

Once reheated, the breast milk should be used within 2 hours and cannot be stored again after this.

After the breast milk has been reheated, it should be used to feed your child or it should be thrown away.

Once reheated, it is not safe to store breast milk to reheat again in the future.

Things To Do Before Handling Breast Milk

When it comes to expressing breast milk, and handling it once it has been expressed, it is very important that you take caution.

This milk will be used to feed your child, so it is very important that you are very hygienic and clean when handling breast milk.

Before you express breast milk, you should clean out the pump kit. This is incredibly important if you share a pump kit, or if you have purchased one second-hand.

To do this, make sure that you clean down the power switch, the dials of the pump, and the countertop where you will be placing the pump.

Ensure that it is completely clean and disinfected.

Clean your hands with soap and water, and double-check that the entire pump kit is completely clean before you get started.

Once you have done this, you are ready to start pumping. You can either pump manually or use an electric pump.

Once pumped, you can then store the breast milk. We will take a look at some of the different methods that you can use for storing breast milk now.

What Is The Best Way To Store Breast Milk?

How you choose to feed your baby is something that is heavily debated in the parenting community.

There are some people who will constantly push that “breast is best”. However, as long as your child is being fed, it doesn’t really matter whether that milk comes from your breast or a box of formula.

Likewise, it doesn’t matter whether the milk comes directly from the breast or from a bottle. As long as the baby is being fed, that is the main thing.

If you are feeding your baby formula, then storing milk is often a lot easier.

You can simply prepare a bottle as and when you need it, and don’t really need to worry about storing the milk once it has been prepared.

As it will only be prepared when it is going to be fed to your child. In contrast, once breast milk has been expressed it will need to be stored somewhere.

You will need to be careful with where you store it to ensure that the milk remains safe for your baby to consume.

The best way to store breast milk is in the refrigerator. You can also freeze your breast milk, but we would only recommend doing this if you plan on storing it long-term.

In the short term, it is best to store the milk in the refrigerator as it is the safest way to protect the milk from bacteria while ensuring it remains high in antioxidants, fat and vitamins.

Essentially, refrigerating breast milk ensures that it retains all the goodness that makes breast milk healthy for your baby.

How Long Should You Store Breast Milk?

How long after expressing you should store your breast milk will differ depending on how you plan on storing the milk.

You can store your breast milk at room temperature, in the refrigerator, and in the freezer too. The option that you choose will impact how long the breast milk will be safe to consume.

If you are a new mom, and you find yourself expressing breast milk, you will usually do this a handful of times a day.

If you express while your baby is having a nap, but know that they are due a feed soon, then you may choose to store the breast milk at room temperature.

Breast milk stored at room temperature is safe to consume, but it will need to be consumed within 4 hours of expression to ensure that no bad bacteria has contaminated the milk.

This amount of time is calculated based on the assumption that “room temperature” is between 25 and 60 degrees Fahrenheit.

However, if the room temperature is towards the cooler end of the scale, it is probably safe to consume for up to 6 hours.

As you would expect, breast milk that is stored in the refrigerator can last for much longer than breast milk stored at room temperature.

Once expressed, breast milk can be stored in the refrigerator for 4 days.

Finally, breast milk that is stored in the freezer will last for the longest. Expressed breast milk can be stored in the freezer for an incredibly long time, so it is always a good idea to store milk in the freezer if you have a good supply of breast milk.

Assuming your freezer is kept below 0 degrees, like most freezers will be, your breast milk will be safe to consume for up to 12 months, but it is best if consumed within 6 months.

So if you have expressed more milk than you need, it is always a good idea to store the excess milk in the freezer. You never know when it might come in handy in the future!

It is important to note that breast milk that has been frozen, then thawed to be used will not last as long as freshly expressed milk that has been placed in the fridge.

Once thawed, breast milk that has been frozen should be used within 2 hours if kept at room temperature, and 24 hours if kept in the refrigerator.

How Long After Re-Heating Can Breast Milk Be Left Out

Top Tips For Storing Breast Milk

If you are somebody whose body produces quite a lot of breast milk, more breast milk than you need on a day-to-day basis anyway, then storing it for future use is a great idea.

But if you haven’t stored breast milk before, then it can be fairly daunting. So here are some great tips for storing your breast milk.

Keep Your Milk Cool On The Go

Storing your breast milk among ice packs in a cooler bag is a great way to keep your milk cool for long car journeys. It also ensures that your milk stays cool enough that any unused milk on the journey can be frozen again once you reach home.

Clearly Label Your Milk

Even if you are the main person who feeds your child, a situation may occur where somebody else has to access your frozen milk or breast milk stored in the refrigerator.

To avoid any confusion, ensure that you clearly label the sachets of breast milk before you store them.

This also comes in handy for days when you may feel particularly tired after the night feeds.

Clearly labelling each sachet or tub of milk with the date of storage, the date by which it needs to be used, and the amount of milk stored in the receptacle.

That way you will clearly know how much milk is stored in each sachet, and when it needs to be used by.

Be Strategic With Where You Store Your Milk

While your fridge is designed to keep things cool, there are some areas of the refrigerator that are cooler than others.

The main shelves of your refrigerator, right at the back, have the most consistent temperature, so you should store your milk here. Rather than on the refrigerator door where the temperature fluctuates more frequently.

The same goes for your freezer. The front of your freezer is much more susceptible to temperature changes than the back, and this can ruin the quality of your milk.

So store it near the back to ensure that your milk remains completely frozen while it is in the freezer.

Portion Before Storage

Before you store your breast milk (no matter whether that be in the fridge or freezer), you should portion it into drinkable amounts.

You know how much milk your baby is drinking at any one time, so we would recommend that you portion into the amounts that your child will drink before freezing it.

This will reduce waste and also make it easier to store the breast milk in your freezer. When you need a portion of milk, simply take one out of the freezer and leave it to thaw before using it to feed your baby.

Use Tight Caps On Bottles

If you are storing breast milk in bottles in the fridge, you should always use a tight cap on the bottle.

Do not store the bottles with the nipples attached, instead remove the nipple attachment, pop the lid on and seal it tightly. This will preserve the breast milk and extend its shelf life.

Store Upright

All breast milk should be stored upright, no matter where you are storing it. This will ensure that no breast milk leaks out of the container, and reduces the amount of waste that you generate.

When freezing breast milk in freezer-bags, you should store the breast milk upright in a container in the freezer until it has frozen.

Only once the milk has frozen should you store it horizontally. If you are storing at room temperature or in the refrigerator, you should always store the breast milk upright.

Move Quickly

Finally, if you are storing your breast milk in the freezer, and you know that you will be freezing it, you should do this as soon as possible.

If you plan on freezing the breast milk, there is no need to place it in the refrigerator. Instead, you should simply pop it in the freezer as soon as possible to preserve the quality.

It is also worth noting that breast milk expands when frozen, so make sure you leave room in the receptacle for the milk to expand before you place it in the freezer.

How To Store Your Breast Milk: 3 Methods

Now that we have taken a look at some tips for storing your breast milk, let’s take a look at how to do this safely for each method.

Storing Breast Milk In The Fridge

First, let’s take a look at how to store breast milk in the fridge. This is really easy to do and one of the most popular methods implemented by parents.

The first thing that you need to do is express the milk and store it in a container. Some people choose to store breast milk in bottles in the refrigerator, ready to use it to feed their child.

With your breast milk ready to place in the fridge, you should search for the coldest area of the refrigerator.

This will typically be at the back of the fridge, on the lowest shelf above the vegetable drawer. This is the best area to store the milk as it will keep it safe to drink for longer.

Place the milk in the fridge asap after expressing it, and never store it in the same container as chilled milk if the milk is at room temperature.

Then simply leave your milk in the refrigerator until you are ready to use it.

Storing Breast Milk In The Freezer

Storing Breast Milk In The Freezer

Storing breast milk in the freezer is a great choice.

This is the method that will extend the shelf life of the breast milk by the longest amount of time, so it is great if you have a lot of breast milk that you know you are not going to use immediately.

Once the breast milk is expressed, you should transfer it into containers. A good choice for storing breast milk in the freezer is BPA-free freezer-safe bags.

Transfer the milk into these freezer bags in amounts that you would normally feed your child, then seal the bags.

Use a pen to label the bags, stating the date of freezing, the amount of milk in the bag, and the date by which it should be consumed.

Then pop your breast milk in the freezer, For the most consistent temperatures, you should store your milk close to the back of the fridge.

Then simply take a bag out when you need to use it.

Storing Breast Milk At Room Temperature

To store your breast milk at room temperature, you should keep it away from anything hot.

This will include the microwave, oven and any other kitchen appliances that generate heat too.

Seal the container or bag, then cover the container with a cloth. Push to the back of the worktop until you want to use it. Remember, you must use the breastmilk within 4 hours!

Thawing Frozen Breast Milk

When it comes to thawing breast milk, it is always good practice to use the oldest breast milk first.

Simply grab the container of milk from your freezer and place it on the side in your kitchen to thaw. Once the milk has thawed, it should be used within 2 hours.

If you want to extend the amount of time that you have to use the milk, you can thaw it in the fridge instead.

However, it will take more time to thaw in this case. Once thawed, the breast milk will be safe to consume for up to 24 hours.

If your baby doesn’t finish all the bottles of milk that you have thawed in one sitting, then it is safe to leave the leftovers on the side for up to 2 hours.

But after this it should be discarded. Milk thawed at room temperature can be served at room temperature, it doesn’t have to be re-heated.


In conclusion, after breast milk has been reheated, it can only be left out on the side for around 2 hours before it will need to be thrown away.

But, if you are thawing breast milk, you do not need to reheat it if you thaw at room temperature. Instead, it can simply be served at room temperature.

We have looked at this in more detail in this guide.

Thanks for reading!

Joshua Bartlett
Joshua Bartlett

My name is Joshua Bartlett I run this blog with my wife Jarah. We have more than 11 years of parenting experience including three girls and one boy. I started this blog in late 2018 when I realized that I was dealing with baby-related issues on a constant basis…please read more about me here!