When should you store milk in the freezer?  What should milk be stored in?  How long can it be stored for?  Knowing these answers will help properly preserve your milk through good milk storage habits.

A Deeper Look:

Although, freezing reduces some of the beneficial properties of breast milk (for example, the longer milk is in the freezer, the more the levels of vitamins diminish and the more some of the fat in the milk breaks down) if your baby is not going to consume the milk from the fridge within the recommended time, freezing your milk is a wonderful alternative to discarding milk.

Any suggested milk storage times are based on the use of very clean pumping equipment and milk containers.  Further, the following guidelines are for healthy, full-term babies.  If your baby is hospitalized or has a weaker immune system, click here.

For more information on cleaning your pump equipment, click here.  
For more information on when to replace pump parts, click here.  

For healthy, full-term babies, the CDC recommends the following:

(Table detailing breast milk storage guidelines)

What to Store Your Milk In
Once you have determined that your milk should be stored in the freezer, you need to decide how to store it.  If it’s freshly expressed milk in your pumping container, you will want to transfer the milk into a milk storage bag to save room and protect the milk from excess air.  The bags you use should be BPA-free and specifically designed for human milk. Alternatively, if you have the room in your freezer and prefer glass, you can store the milk in small mason jars (there are small 4 and 8 ounce glasses available for this purpose; however, glass jars can break when exposed to extreme temperatures, so take care to thaw the jar first before heating it for consumption).  You can also use BPA-free plastic bottles or jars.  

Labeling and the Amount of Milk
Before you pour, you should label the bag or jar with the date the milk was expressed (if you are combining milk, use the date the oldest milk was expressed) and the amount of ounces.  You may choose to store your milk in increments of 3-5 ounces (or the amount your baby consumes in a feeding) to minimize the potential waste of milk upon thawing; however, if you have limited freezer space, you made decide that maximizing the amount of milk in the storage bag is better for you.  Perhaps, a mix of full bags and half bags is what is best for you.  A kitchen scale can help you accurately measure the amount of ounces in a bag or jar but don’t forget to subtract the weight of the container!  Also, liquids expand as they freeze, so do not fill containers to the tippy top or you might find that the milk breaks you container as it solidifies.

How to Store the Milk in Your Freezer
If you are storing milk in bags that do not stand up on their own, lay the bags flat to freeze first.  According to the CDC, the freezer temperature should be 0˚F, and you should store the milk at the back of the freezer where the temperature is most consistent.  Once the bags are frozen, stack them in a gallon-size Ziploc bag like bricks or storing them in an old soda box or shoebox, placing the newest milk in the back of the box so the oldest milk is easiest to grab.  Use the “first in, first out rule” and feed the oldest milk to your baby first.  

Thawing the Milk
To thaw milk for consumption, move the bag to your fridge and allow it to thaw for a full day.  Alternatively, you can warm the bag in a bowl of hot water or hold it under arm running water.  However, you should never microwave or boil breast milk in any container and you should never refreeze milk after it has thawed.  To catch any leaks and limit the amount wasted, thaw frozen milk inside another bag or clean container.

Once thawed, consume within 24 hours if stored in the fridge.  Thawed milk may smell or look different than fresh milk.  Breast milk naturally separates into a milk layer and a cream top when stored.  If you notice this separation once the milk has thawed, gently swirl the milk in the container or massage the bag gently to reincorporate the fatty hindmilk into the more watery foremilk.  If the milk does not swirl evenly, or if you see chunks, do not use the milk; unspoiled milk will swirl evenly.  If your milk smells rotten or tastes sour—do not use it.  However, if you notice the milk smells or tastes soapy or metallic, it may be an indication you have high levels of lipase enzymes.  Milk that is high in lipase is safe for consumption, but you can prevent the change in smell and taste, which may be necessary if your baby rejects a bottle because of the taste!  For more information on excess lipase activity, click here. 

Power Outages/Freezer Failure
The La Leche League suggests that if you experience a power outage or freezer failure, your milk is “probably okay for up to two days if the freezer is full of food or one day if it is half full.”  The League notes that a freezer compartment in a fridge will thaw faster.  They suggest that you can temporarily store your frozen milk in the snow or deep shade if the temperature outside is below freezing, but take care to protect it from the sun, which could thaw the milk even though the air is cold.  The League’s advice is that milk can be refrozen IF it still has a frozen core.

The EP&Me Take:

The key to being successful with freezing milk is planning and organization.  Even if you are not freezing large quantities of milk at a time, over time your supply can really take over your freezer.  Even though we were using freezer milk one day a week to ensure that none of the freezer milk got too old, by the time I had been pumping for a year, I had stored milk that would last my Little an additional two to three months!

I talked a bit about my storing process in my blog post on storing milk in the fridge, so some of this information may sound familiar if you’ve read that post.

The Kiinde Twist Pouch
I am a big fan of the Kiinde Twist Pouch, which allows you to pump, store, warm, and feed using the same bag.  Kiinde has created a variety of adaptors that are compatible with many battery/rechargeable/electric non-wearable pump systems to allow many different users to use the Kiinde system regardless of their pump preference.  Once you are done pumping, you can screw the cap on, add the date on the side, and store in either the fridge or freezer.  Once you are ready to warm the milk, you can place the bag directly into a bottle warmer and then pop it into the bag holder, squeeze the milk to the top of the bag (to remove excess air), push the nipple on, and start feeding.  My favorite part of using the twist pouch is that I only had to clean the nipple and give the bottle holder a light wash here and there.  And did I mention the bags are recyclable?  It was so freeing to not have to clean so many bottle parts, especially once we started daycare and multiple bottles would come home at the end of the day.

How I Used the Kiinde Twist Pouches
When I first started pumping and while I was still pumping frequently, I did not always pump into the Kiinde bags because I was not filling them enough.  For me, I would pump into a Kiinde bag on each breast if I knew I would pump about 3 ounces from one breast in one session.  Otherwise, I would pump into one Kiinde bag and one bottle and then transfer the milk from the bottle to the bag once I was done pumping.  The bags can stand upright on their own and are incredibly easy to pour into and pour from.  I found comfort and peace in keeping track of the exact amount of milk I pumped each day, so at the end of each pump session, before combining the milk, I would separately weigh each bag or the bottle and bag using a kitchen scale and record the amount pumped for each side in a phone app.  Then I would combine the milk into the bag, date it (there is a specific spot on the side that I found easy to write on even when the bag was full) and pop it into the fridge.  At the end of each day, I would redistribute the milk—I referred to myself during this time as a “Mad Scientist” because I was pouring between many bags of milk and measuring, measuring, measuring!—into 4.5 ounce bags, which was the amount my Little wanted to consume in one feeding.  I often reviewed the milk counting what my little was likely to consume in the next few days and would freeze milk that I didn’t think she would consume before it spoiled.  Sometimes the milk I froze was fresh milk, other times it milk that had been in the fridge for three days.  As long as it still smelled and tasted fine, it was fine to freeze for later.

Pro Tip 1: if you are pouring into a container and are worried about spilling, use your breast flange as a funnel (the two-piece flanges work best for this)

Pro Tip 2: if you are going to be sending milk bags into daycare, I suggest writing your child’s name on them while the bag is empty if you are using bags just meant for storage, or filled with fresh milk if you use the Kiinde bags.  Once the milk becomes chilly, the condensation makes it extremely hard to write on with a Sharpie without causing the sharpie ink to stop.  You do not have to use a Sharpie, but be sure that whatever you use that the ink is waterproof.

Keeping It All Organized
Whatever milk I decided to freeze was taken from our indoor fridge and placed into our indoor freezer.  Once I had a few bags completely frozen in the indoor freezer (or ran out of room in the freezer!), I would log the dates of the bags (and ounces if they differed from my standard amount of 4.5 ounces) onto a legal pad I kept near the fridge and then place the bags in our garage freezer. I organized the frozen milk into cardboard boxes and when possible, tried to keep milk pumped in the same month together; however, based on the space available, this was not always an option.  On the milk log, I would start a new column for each month.  This log allowed me to know how many ounces I had frozen and how many bags I had frozen from each month and each day. When it was time to pull milk from the freezer, I knew what the oldest milk in storage was and which dates I needed to pull out.  When I had found the oldest bags and brought them in to thaw, I would cross the dates off my milk log.  This process really helped make sure no bags went missing, and thus not wasted, in our freezer.

Rotating Your Milk Stash
In order to rotate my freezer stash and ensure that no freezer milk sat for too long in the freezer, we would do one freezer day a week.  24 hours before we planned to use freezer milk, I would pull out the seven bags of frozen milk my Little would need for the next day and thaw them in the fridge.  Any milk I pumped on a “freezer milk day” would get immediately frozen to help make sure I didn’t have more fresh milk than could be consumed within 4 days in my fridge.

Other Ideas
While you may store most of your milk in bags to save space, you may consider freezing a little bit of milk in a small popsicle mold for an older baby to teethe on or in a Milkies tray, which freezes milk in one ounce increments so that its easy to pull out one additional ounce if needed rather than unfreeze another full bag.  Think about what fits your family and baby best—you can get a little creative!

Other Milk Storage Bags
Many milk storage bags leak, and some brands seem to have more leaks than others. We never had an issue with the Kiinde bags but they are not as easy to stack for long-term storage.  Many of my mom friends seemed to like the Lansinoh bags best.  One used to freeze milk flat in the Lansinoh bags and then store them upright in old soda can boxes and her freezer stayed nice and neat!

Leftover Milk
Inevitably, you will have milk that you think has sat out a little too long and you don’t want to feed it to your baby.  We used milk no longer fit for consumption to treat diaper rash in the bath, and I think it helped! We never used milk we believed was truly spoiled, but if fresh milk had been out on the counter for 5 hours or the last half ounce of a bottle sat out for 2 ½ hours, we would pour that milk into a freezer bag and just add to it until the bag was full.  I have not seen research on this, so I cannot tell you that it’s recommended or even safe to do.  This idea was just passed onto us as a tip from one mom to another.

Storage Times
We adhered pretty closely to the CDC guideline that milk stored in the freezer should be consumed within six months.  However, other sources suggest use within 12 months is acceptable.  Additionally, although the CDC does not provide guidelines for consumption of milk stored in a freezer compartment in the fridge, other sources suggest milk stored this way (at a temperature of 5˚F or -15˚C) may be safely used within two weeks of freezing if the milk is stored away from the sides of the freezer compartment and in the back where the temperature is more consistent.

The last thing I want to mention is that many breast milk supplies—such as milk storage bags and replacement breast pump parts—are covered by insurance or considered an eligible item for FSA/HSA accounts, so make sure you check what your insurance covers and whether it’s an eligible item. Storing milk for your baby for the future is an awesome gift. Good luck filling your freezer mama!