Can you mix defrosted breast milk from different days

Most mothers protect their breast milk like it is liquid gold — for good reason. Because of this, many new moms have questions about milk storage, specifically combining milk from different pumping sessions or even different days. While the internet often provides conflicting information on topics like these, most experts tend to agree on what is and isn't allowed when it comes to mixing breast milk from different days.

Table of Contents Show

What Is Wrong With Combining Breast Milk From Different Days?
How To Safely Mix Breast Milk From Different Pumping Sessions
Your Guide to Safely Storing Breast Milk
Rules for Combining Breast Milk From Different Pumping Sessions
Length of Storage for Combined Containers of Breast Milk
Other Breast Milk Storage Tips
Can you combine multiple days of breastmilk?
Can you mix thawed out breast milk?

What Is Wrong With Combining Breast Milk From Different Days?

Formula_and_breastmilk via Wikimedia Commons/Jengod

Whether you're a working mom, a stay-at-home mom who is exclusively pumping, or a mom who alternates between breastfeeding and pumping, there may be times when the milk you pump from one session isn't quite enough for what your baby is currently consuming when bottle-fed. When this happens, you may want to combine breast milk from different days to fill it out.

However, the team at Verywell Family says you should be careful whenever you combine breast milk from different days because this can cause bacteria growth or other complications if not done properly.

For example, you should not combine freshly pumped breast milk with a previous day's supply that is already refrigerated. Doing this will warm back up the already chilled breast milk, which can cause the milk to expire faster or become contaminated with bacteria. Even if you think it will not matter, the repercussions of this will not be pleasant.

Similarly, adding freshly pumped breast milk into a batch of already-frozen milk will cause it to thaw. This will cause the milk to also expire, meaning it won't remain viable for long after you combine the two versions of milk. Once thawed, frozen breast milk is only viable for 24 hours. So instead of saving more milk, you're actually losing some of your supply through this practice.

How To Safely Mix Breast Milk From Different Pumping Sessions

fl51330400188-image-kycinzss via Rawpixel

Although combining freshly expressed breast milk with already cooled milk in the fridge or freezer isn't recommended, there are ways to combine milk from different pumping sessions if needed. In fact, the Centers for Disease Control and Prevention (CDC) says there's an easy way to safely mix breast milk from different pumping sessions or even different days.

To begin, you must take the freshly expressed breast milk and cool it in the fridge or with ice packs for at least 30 minutes before combining it with other breast milk already in the fridge.
Once cooled, you can combine with other milk in the fridge, assuming it is not yet past its shelf life of 4 days — just make sure you do so in a safe, sanitary way that doesn't risk contamination.
Also, make sure you label the milk with the correct date for the oldest batch in the combination, as that milk won't magically gain extra shelf life just because you mixed newer breast milk in with it.

Similarly, you can also combine freshly expressed breast milk with milk that is already at room temperature, assuming you will use it all within 4 hours of when the older milk first adjusted to room temperature. However, you should not do this if you're wanting to refrigerate the milk you just pumped, as milk that has been warmed up cannot safely go back into the fridge a second time.

Finally, the Mayo Clinic never recommends combining breast milk into amounts that exceed what your child consumes in a single feeding. If you have more than that after you pump, consider splitting up the milk into smaller batches so none of it goes to waste.

Breast milk storage is anything but easy. However, getting these rules down will help keep your child happy and well-nourished without any tummy troubles down the line.

Sources: Verywell Family, Centers for Disease Control and Prevention, Mayo Clinic

Your Guide to Safely Storing Breast Milk

Stockpiling your breast milk means your baby can always have your milk even when you're away. But safe storage is essential.

You're working to build your breast milk stockpile, but you only have so much space available in your fridge and freezer. Maximizing storage by combining milk from different pumping sessions makes sense, but it is safe? The answer is yes. You can combine milk as long as you follow certain guidelines to cut down the risk of bacterial growth.

Rules for Combining Breast Milk From Different Pumping Sessions

It's generally safe to combine fresh milk with previously expressed and stored milk. But it's important to first chill the fresh milk, so it's the same temperature as the older milk. Keeping milk cold helps prevent bacterial growth. If you add warm breast milk to the cold refrigerated milk, it increases the temperature and can make it susceptible to bacteria. If you add warm milk to frozen milk, it can partially thaw the milk.

The following combination situations are acceptable as long as the new milk is chilled first:

Fresh milk combined with milk from a previous session that day
Fresh milk combined with refrigerated milk from a previous day for continued storage in the fridge
Fresh milk combined with refrigerated milk to move to the freezer for longer storage
Fresh milk combined with previously frozen milk for continued storage in the freezer
Two containers of refrigerated milk from different pumping sessions combined into one container for continued storage in the fridge or freezer

Length of Storage for Combined Containers of Breast Milk

How long you store the milk affects the nutritional value and safety of the milk. When you store milk, it gradually loses its ability to fight off bacterial growth. If you store milk for longer than the recommended times, you could risk food poisoning caused by bacterial growth. Your baby may also miss out on key nutrients that can diminish over time, so it's important to use the milk as soon as possible.

When combining milk from two different pumping sessions, always use the date from the oldest milk as your guide for determining the storage length. Put the date on the container for the original pumping session, and don't change it if you add fresh milk later.

Storage times for breast milk vary by storage type:

Fresh milk at room temperature in a warm room: Three to four hours
Fresh milk at room temperature: Four to eight hours
Fresh milk in the refrigerator: Three to eight days; 72 hours is optimal
Thawed milk in the refrigerator: 24 hours
Self-contained freezer compartment: Six months
Deep freeze unit: 12 months; six months is optimal

If you combine fresh milk with refrigerated milk from two days ago, you can keep it in the refrigerator for another one to five days instead of the full three to eight days based on the oldest milk date. If you add fresh chilled breast milk to a container of frozen milk from one month ago, you can still store it in the freezer for up to five more months.

Other Breast Milk Storage Tips

Keep these tips in mind when storing breast milk, whether you combine milk or not:

Always write the date on the container to avoid keeping the milk for too long.
Store milk near the back of the refrigerator or freezer so the milk doesn't warm up every time you open the door.
Store milk in small portions to avoid waste. Once your baby starts eating a serving of breast milk, it's best to use it all or discard the leftover to prevent bacterial growth.
To avoid contamination, wash your hands before pumping or handling breast milk.
To keep contaminants out of the milk, store milk in containers that seal well.
Leave space in the container if you plan to freeze the milk. The liquid expands as it freezes, so it needs room in the container.
Use the oldest breast milk from the freezer first.
Thaw frozen breast milk by putting it in the fridge for about 12 hours. If you need to thaw milk quickly, pop it in a bowl of warm water.

Can you combine multiple days of breastmilk?

You should NOT combine your breast milk if: Different-day collection: You are collecting breast milk on a different day. It is not safe to add breast milk that you pumped today to a container of breast milk that you pumped yesterday or last week.

Can you mix thawed out breast milk?

You will have to throw away any leftover breast milk that has been thawed and warmed. It's safe to layer (or add more pumped milk) your frozen breast milk as long as the fresh milk is cooled and refrigerated first, AND all of the milk is collected on the same day.