Here’s everything you need to know about safely storing, warming, and serving your breast milk to baby. 

Whether you’ve got a baby that will only drink their milk warm (if you know, you know…) or just need to thaw that milk that’s been on ice, there are a few things to keep in mind when it comes to reheating your liquid gold. We’re sharing all of that below, as well as recapping our guidelines for safe milk storage and thawing. 

Keep reading for tips on:

• Safely storing your freshly expressed milk
• Storing and using thawed breast milk
• Reheating breast milk and potential risks
• Safely handling warmed milk 
• And more! 

Storing Breast Milk: Freshly Expressed Milk vs. Thawed Breast Milk

When storing your breast milk, there’s a lot to consider. Do you have access to a fridge? What’s the temperature? How long until you plan on feeding it to your baby? This is why it’s so important to have a plan and follow the guidelines set by the Centers for Disease Control (CDC) and the Academy of Breastfeeding Medicine (ABM).

Remember that these guidelines are recommended for freshly expressed breast milk for healthy, full-term babies only. Always check with your pediatrician if you’re unsure about what’s best for your baby!  

In addition to paying close attention to the temperature and duration of time, it’s important to make sure that your storage conditions are clean, since this will minimize the risk of bacteria growth. That means clean hands and countertops, and no open food containers getting close to your milk in the fridge or freezer! 

Thawing Breast Milk: You’ve Got Options! 

When it’s time to thaw your frozen milk, you have a few options: 

Fridge: Thawing breast milk in the refrigerator can take between 4 and 12 hours, so it’s important to plan in advance! Place your milk storage bag in the fridge standing upright. Make sure that it’s not squished between any containers that could puncture or damage the bag. 

Warm running water:  You can also thaw your breast milk by covering it with a stream of warm running water. Just make sure that the temperature is no higher than 99 degrees! If it’s boiling, you could end up damaging the milk’s nutritional properties, or create “hot spots” that burn your baby’s mouth once the milk has been transferred to a bottle. 

Water bath: You can also place the bag in a bowl of warm water, swirling gently to speed defrosting and to make sure that the fatty parts of the milk (which may separate when frozen) are incorporated.

No matter what, you never want to thaw breast milk in the microwave or by using boiling water. Learn more about different ways to thaw breast milk here. 

Safety Considerations for Reheated Breast Milk

You’ve stored your milk, you’ve thawed your milk, and now you want to warm it up. You might be wondering: do I need to warm my milk before I feed it to my baby? 

The answer is no! Many babies are happy to drink milk straight from the refrigerator or at room temperature. Plus, sometimes reheating your milk simply isn’t an option — for example, you might be traveling and offering a bottle that’s been in an insulated cooler. 

But if they put up a fight (which may happen if they’ve been nursing often or exclusively), there are a few methods for warming it up that you can try: 

Safe Methods for Reheating Breast Milk

Using a Bottle Warmer

Many of your favorite baby brands offer bottle warmers, which make it quick and easy to reheat your milk before serving it. No matter which warmer you’re using, you’ll likely follow the below steps: 

1. Fill your bottle with breast milk (this can be thawed milk or milk that’s been in the fridge)
2. Pour warm water into the warmer’s reservoir (it should never be boiling!)
3. Place the bottle in the warming chamber. Make sure that the cap is screwed on tightly so that no warm water makes its way from the reservoir into the bottle! 
4. Use the temperature settings to select your desired temperature
5. Before serving, always test a drop of milk on your wrist to make sure it’s not too hot

Always remember to follow your manufacturer’s instructions for cleaning the warmer in between each use, and never leave a bottle in the warmer for longer than is recommended. 

Using a Warm Water Bath

You can also reheat your milk by submerging it in a bowl of warm water, and leaving it there until it arrives at a lukewarm temperature. (This is similar to a method you can use to thaw frozen milk!) Holding it under a stream of warm running water will also do the trick, but it will take longer. 

Make sure that your storage vessel is tightly sealed to prevent any leaking, and never use boiling water. Like when using a bottle warmer, you should always test the temperature of the milk on your wrist before serving it to your baby. 

Avoiding Microwaves

For the same reasons that you’ll want to avoid defrosting your milk under a stream of boiling water, you’ll want to stay away from thawing in the microwave. Temperatures that are too high could lead to nutrient loss and put your baby at risk of burning their mouth due to “hot spots” caused by uneven heating! 

How Long is Reheated Breast Milk Good For?

Adding heat to the equation shifts the storage guidelines established for freshly pumped milk. Keep the below in mind! 

Timing Guidelines & Signs of Spoiled Milk

Once milk has been reheated, you should feed it to your baby within two hours, and anything left over should be discarded. Do not put it back in the fridge or freezer, do not leave it at room temperature, and do not reheat it again! Why? Reheating milk more than once can increase the risk of bacteria growth and impact its nutritional value. 

It is possible for breast milk to go bad, especially if you are reheating milk that has been thawed from frozen. 

• The consistency should not be clumpy, stringy, or covered in scum, and it should not smell fishy or rancid — if you do notice this smell, some chemical oxidation has likely taken place. 
• When swirled or shaken, the fat content should re-incorporate easily. If it doesn’t, it’s unfortunately time to toss it out. 
• It is normal for the milk to separate a bit, and to be tinted slightly yellow, blue, or green.

A small percentage of moms may notice a somewhat sour, soapy scent if they are reheating breast milk that has been thawed. This is not harmful to your baby! The smell is due to the presence of lipase, which is an enzyme that helps break down fats. For these moms, when breast milk is kept at room temperature or in the refrigerator, their active lipase enzyme will create a stronger scent. The longer this breast milk is stored, the more lipase activity will occur.

Quick Tips for Handling Reheated Breast Milk

Don’t forget to label!

Whether you’re reheating your breast milk or simply taking it out of the fridge and feeding it to your baby, you should always use your oldest milk first. That’s why labeling your storage bags or bottles is so important! 

Always label with the date, time, and the number of ounces pumped.  

Keep portions small

Since you should only reheat your breast milk once, it’s a good idea to keep your portions small at first, and warm up more if your baby is still hungry. This will help reduce the risk of needing to toss any milk that they don’t finish — this is precious stuff! 

Now you’re ready to feed! 

In this article, we covered everything you need to know about safely storing, thawing, reheating, and handling your breast milk. Here’s a recap: 

• You don’t need to warm your milk before feeding it to your baby. If they’ll drink it cold or at room temperature, that’s totally fine. 
• You can reheat your milk in a bottle warmer, under a stream of warm running water, or in a warm water bath. Never place it in boiling water or put it in the microwave. 
• If you’re reheating milk that has been in the freezer, make sure to follow safe thawing guidelines — before you warm it, your milk should be defrosted in the fridge or in warm water. 
• When handling your breast milk, always make sure that your hands and surfaces are clean. Remember that the more you touch your milk or have it out at room temperature, the bigger risk you run of bacteria spreading. 

For more tips about safe milk storage, check out the Pumping and Breastfeeding section on our blog, and explore milk storage options such as our Portable Breast Milk Cooler. 

Reheating Breast Milk FAQs  

Can you reheat breast milk more than once?

• It is not recommended to reheat breast milk more than once. Reheating breast milk multiple times can lead to a loss of important nutrients and increase the risk of bacterial growth, which can make the milk unsafe for your baby. To avoid waste, it’s best to heat only the amount of milk your baby is likely to consume in one feeding.

How long can reheated breast milk sit out at room temperature?

• Reheated breast milk should be used within 1-2 hours if left at room temperature. After this period, the risk of bacterial contamination increases, which can be harmful to your baby. If your baby does not finish the bottle within this timeframe, it is safer to discard any remaining milk.

What is the best way to reheat breast milk?

• The best methods for reheating breast milk are using a bottle warmer, holding it under a stream of warm water, or placing it in a warm water bath. These methods ensure even heating and help preserve the nutritional quality of the milk. To use a warm water bath, place the bottle or bag of breast milk in a bowl of warm water for a few minutes until it reaches the desired temperature. Avoid using boiling water as it can overheat the milk and destroy valuable nutrients.