Breastmilk Storage Guide: What Is the Best Way to Store Milk?


There are a myriad of questions new mothers to breastfed babies ask themselves. Sometimes, those pertaining to breastmilk storing and preparation get lost in the mix. However, these are important topics that both moms and dads need to know the basics of, and with CBS News reporting over three-quarters of moms initiate breastfeeding at birth, this information is in demand.

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Expression Method Matters

A bottle of breastmilk on the white table.

Whether you’re hand expressing or using a pump, clean tools are vital. This means clean hands for manual expression and clean pump parts if pumping. What you’re planning to store your milk in also matters. Plastic storage bags are the most efficient method for freezer storage. They take up the least amount of cubic space since you can lay them flat and stack them, and they are made with BPA-free materials now to satisfy parents of all kinds. BPA, otherwise known as Bisphenol A, can act like estrogen in the body, which can lead to hormonal imbalance and even cancer, per Medical News Today.

Bags come clean and ready to use, but if you’re using bottles, sterilization is necessary even when they’re brand new. Fancy bottle sterilization equipment is fine if you want to spend the money or add it to you shower registry, but a dip in boiling water still works great. After the first use, washing and a thorough drying should suffice. When combining milk from separate pumping sessions, don’t add the second batch to the cooled first batch until the second one is cool as well.

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Fridge or Freezer

Bottles of breastmilk in fridge.

Breastmilk, being the amazing substance that it is, can also be stored at room temperature — no higher than 77 degrees Fahrenheit — for six to eight hours. So don’t stress about making it to the fridge after that middle-of-the-night pumping session; it really can wait until morning.

If you plan to store bottles in the fridge, make sure your fridge settings are steady between 32 and 39 degrees, and ensure that the seal on your fridge is smooth and adhering well to the door upon shutting. Typically, the easiest way to store breastmilk in the refrigerator is to pump straight into the bottles you plan to store it in. You’ll want to rotate your supply so that the oldest milk is always at the front and ready for grabbing. One of the most common questions new parents have pertaining to breastmilk storage is how long it keeps. This answer varies depending on the storage method you use. Milk that is promptly refrigerated after pumping will keep for up to eight days, per the La Leche League. If you won’t be pumping and storing often enough to go through a regular supply of stored bottles, it might be a good idea to label them with the date and time of expression, or consider freezing instead.

Freezing your milk allows it to keep longer — much longer. While bottles are an option, plastic can warp and glass takes up a lot of space. Likewise, heating up frozen bottles is very risky. Plastic bags are the leading method of storage for the freezer method. The preprinted measurements listed on these storage bags are often incorrect. Also, it’s almost impossible to determine the correct measurement from simply holding the bag up in the air or placing its bottom on a flat surface. So the best way to note output when using bags is to measure the milk in bottles prior to pouring it into the bags.

[Relevant: Storing breast milk]

When you’re freezing breastmilk, you have to be careful to leave a little space in whatever container you use for the milk to expand as it freezes. An inch of headspace is plenty. Freezing the milk in a side-by-side upright or top-half freezer kept at zero degrees gives it a shelf life of three to six months, while deep freezing it extends its life to as long as a full year. Deep freezers need to be kept at -4 degrees Fahrenheit. Take note, if you have a freezer compartment that is internal to the fridge, milk will only keep for roughly two weeks in these, per Kids Health.

Since you’re going to be building a supply over time, it’s wise to label each bag you place into the freezer with the date and time that it was expressed or pumped. In addition, you’ll want to rotate your stockpile over coming months so that when you do go looking for milk to use, you use the oldest first.

Composition Confusion

Milk composition on the table.

If you’re planning to breastfeed, you may have heard already that breastmilk changes its composition over time to reflect the needs of the baby. This is true — and awesome! The journal Pediatric Clinics of North America notes, “Unlike infant formula, which is standardized within a very narrow range of composition, human milk composition is dynamic, and varies within a feeding, diurnally, over lactation, and between mothers and populations.” However, this leads many moms to worry that stored milk from when their baby was younger won’t satisfy their needs when they’re older and thus shouldn’t be used. This isn’t actually the case.

Even though the composition changes, it becomes denser in vitamins than calories. The properties that are more concentrated when babies are younger are there to build strong antibodies and strengthen the immune system. There is certainly nothing wrong with reintroducing these antibodies when your baby is older. Nonetheless, some parents prefer to cycle the stored breastmilk in and out throughout the week between feedings with fresh milk. You can do whatever makes you comfortable, but know that there is nothing inadequate about milk expressed weeks or months prior as long as it’s not spoiled.

Overall, storing breastmilk will become second nature to you once you’ve done it a few times. Keeping a chart secured on the fridge in the early weeks might help everyone to adjust and get into the routine. Frozen milk can be thawed in the fridge for a day, or by running it under warm water. When it’s time to use the stored milk, remember that it must be used within an hour from when the baby starts drinking from the bottle. Following these guidelines will offer your baby the protection he or she needs throughout your breastfeeding relationship.


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