The option to pump and store breast milk is a modern one, which unfortunately generations of women before didn’t have. Breast milk is very different than formula and will last longer both at room temperature and refrigerator, but there are some important things to keep in mind when storing breast milk.
How breast milk is stored – whether it be fresh, refrigerated, or frozen – will affect if and when it can be combined with formula or more breast milk. This article will explore when it is safe to combine breast milk, what to combine it with, and how means of storage affects combination options.
Can You Add Warm Breast Milk To Cold? When And How To Combine Breast Milk.
Breast milk is the healthiest first food for your newborn, packed with vital nutrients that not only help your baby grow, but helps ward off illnesses. Breastfeeding also has positive effects for the mother – including but not limited to quicker healing, reducing the risk of postpartum depression and anxiety, and the release of the bonding hormone oxytocin.
There is no doubt that the ability to pump and store breast milk has had a world of positive effects for mothers and children everywhere – especially given that the majority of mothers today work outside the home.
The following chart is from the Centers of Disease Control (CDC) and dictates how long breast milk can be stored in each medium.
| Type of Breast Milk | Countertop: 77 F (25 C) | Refrigerator: 40 F (4 C) | Freezer: 0 F (-18 C) |
| Freshly Pumped | Up to 4 hours | 4 – 5 days | 6 – 12 months |
| Thawed, Previously Frozen | 1 – 2 hours | Up to 24 hours | Never refreeze breast milk after it has thawed |
| Leftover from Feeding (Baby didn’t finish bottle) | Use within 2 hours | Use within 2 hours | Use within 2 hours |
When You Can Combine Breast Milk
You can combine breast milk in the same form, that is, fresh breast milk with fresh breast milk or refrigerated breast milk with refrigerated breast milk. However, keep in mind that the storage duration is based off when the old breast milk was stored rather than the new milk.
For example, if you have a bag of stored breast milk that was placed in the refrigerator 2 days ago and a bag that was placed 1 day ago, you can combine the two amounts into one bag – but the storage duration is now based off the 2-day-old breast milk, regardless of the newer milk being added.
Make sure to clearly label storage bags or other containers with the correct date of collection, or the date of when the older milk was collected when combining old with new.
When You Can’t Combine Breast Milk
Immediately combining breast milk of different temperatures speeds up the growth of bad bacteria by heating up the colder milk too fast. Fresh, uncooled breast milk shouldn’t be added to refrigerated or thawing (previously frozen) breast milk for this reason.
You also don’t want to combine breast milk that has gone bad. This is milk that has been stored past its expiration guidelines, even if it smells fine.
Depending on several variables including temperature of your home, refrigerator, or freezer, stored breast milk can go bad even within its expiration guidelines. For example, if you live in a hot climate, leaving breast milk out at room temperature for any length of time isn’t recommended.
According to the La Leche League International, the following smells can tell you if breast milk has gone bad:
- Soapy smell
- Fishy or rancid
- Spoiled or sour smell or taste
If you find yourself having to throw away leftover milk frequently, consider storing in smaller amounts. This is especially true when freezing, as defrosted breast milk has the shortest shelf life.
Also, don’t combine breast milk from two separate mothers. This can only be done safely in a hospital setting, where donor milk is sometimes used to supplement a mother’s milk.
Adding Fresh Breast Milk To Room Temperature Breast Milk
Fresh breast milk and room temperature breast milk can be combined as long as the room temperature milk hasn’t been out too long. While fresh breast milk can last at room temperature for up to 4 hours, it’s best to only add fresh breast milk to room temperature breast milk if the latter has been out less than 1 or 2 hours.
Adding Fresh Breast Milk To Refrigerated Breast Milk
The CDC advises against adding fresh breast milk to refrigerated breast milk because warm milk can reheat cold milk, causing bad bacteria to form.
However, you can combine the fresh breast milk if you cool it before adding it to refrigerated milk. This way both milk amounts are the same temperature, and you don’t risk bacterial growth.
Adding Freshly Expressed Breast Milk To Defrosted Breast Milk
Freshly pumped breast milk can be added to defrosted breast milk, but be sure to cool the fresh breast milk first to keep it from heating up the thawed breast milk too quickly and fostering rapid bacterial growth. Use within 1 – 2 hours and don’t refrigerate or refreeze.
Adding Fresh Breast Milk To Defrosted Breast Milk To Store
Fresh breast milk should be cooled before adding to defrosted breast milk. Once breast milk is defrosted, it can’t be refrozen.
Defrosted breast milk is only good for 24 hours in the refrigerator – this is true even if it has fresh breast milk added to it. Keep this in mind when combining.
Adding Fresh Breast Milk To Frozen Breast Milk
While there is a safe way to add fresh breast milk to defrosted milk, don’t add fresh breast milk to frozen breast milk for freezing. If you intend to freeze the fresh milk, place the fresh breast milk in its own freezer-safe storage bag, label it with the date it was collected, and place it in the freezer.
Once a bag of breast milk is placed in the freezer, it shouldn’t be unsealed unless you intend to thaw it and use it.
Final Thoughts
Breast milk is a natural source of nutrition for infants, so it’s no surprise that many mothers want to ensure their baby is getting the best possible feedings. But when it comes to adding warm breast milk to cold, mothers may be wondering if this is a safe option.
The good news is that yes, you can add warm breast milk to cold without compromising the nutritional quality or safety of your baby’s meal. It’s important to remember though that you should never reheat breastmilk that has already been warmed up once before – this can have an adverse effect on its nutritive value and could also put your baby at risk for foodborne illness.
When adding warm breastmilk to cold, make sure it has been freshly expressed and cooled safely in order to avoid any potential contamination or spoilage.