A Complete Guide To Storing Breast Milk

Whether you plan to freeze it or use it in a few days, here’s everything you need to know to prepare it safely for your baby.

The 2023 New Parents Issue

Let’s face it, when you are breastfeeding, every drop of milk you produce is a precious commodity — and that’s not just the postpartum hormones talking. Of course, in order for it to remain viable food for your baby, once pumped or hand-expressed, breast milk needs to be properly stored and handled so that it can be used whenever you choose.

Some people will have a full stock of milk frozen by the time they head back to work and others will have just a few emergency bottles or bags at the ready for short separations (think dinner or a date night). Regardless of how much you store — and why you store it — the way to handle breastmilk for the future follows rather uniform guidelines.

This guide will cover the following and more:

  • How to decide whether to store breast milk in a fridge or freezer.
  • Steps to safely store breast milk in a fridge or freezer.
  • When to start pumping or hand expressing to store breast milk, and how much.
  • How to choose the best breast pump and storage bags for you.
  • How to safely prepare breast milk from the fridge or freezer.
  • How to store colostrum if it is advised.

Reasons to store breast milk

Parents who choose to feed babies any amount of breast milk from the bottle will have to pump and store it safely. But even exclusively breastfeeding mothers may want to store breast milk to prepare for an unexpected (or planned) period of separation. Reasons to pump and store breast milk might include, but are not limited to:

  • An immediate separation in which a baby is in the NICU after delivery.
  • The lactating parent returning to work and needing a family member or caregiver to feed a baby bottles.
  • Making it possible for other family members to feed and bond with the baby.
  • Having a medical procedure or taking medication that is incompatible with breastfeeding.
  • A planned vacation that takes the lactating parent away from home.
  • A family situation in which the parents are separated and the non-lactating parent is caring for baby.
  • An oversupply that leads to the production of more milk than needed to feed at any given time.
  • Wanting a rainy day supply of milk that allows the lactating parent room for flexibility and emergencies.
Alina Rudya/Bell Collective/DigitalVision/Getty Images

When to start pumping and storing breast milk

There is no one-size-fits-all answer to when to start pumping and storing breast milk or why. “This is different for every family and depends on how breastfeeding is going, the baby’s ability to latch and transfer milk, milk supply status, and the family’s personal goals around breastfeeding and bottle-feeding,” lactation consultant Lisa Binderow tells Romper.

For planned separations, say a return to work or a vacation, NYC-based lactation consultant Leigh Anne O’Connor suggests beginning to pump once a day two to four weeks before needing the supply. She says this should be done “ideally in the morning when the milk supply tends to be higher and after you have fed the baby.”

How much milk should you pump and store before going to work, on vacation, etc.?

To help you calculate how much you should pump and store, consider these numbers: Babies consume 24 to 32 ounces daily, plus you’ll want a small “emergency” stock of 8 to 16 ounces, says O’Connor.

Emilija Manevska/Moment/Getty Images

How to choose a breast pump

Having a good pump definitely facilitates the process, although what is a necessary feature for one might not be needed for another.

What to consider when selecting a breast pump

  • Ease of use and comfort.
  • Insurance coverage.
  • Cost of accessories.
  • How often you plan on pumping.
  • Portability.
  • Your lifestyle (do you travel a lot, have long days at the office, work from home).
  • If you want it to pump directly into breast milk storage bags.
  • If it is a closed-system pump (more common; there is a protective barrier between the pumping motor and the milk receptacle to prevent contamination) or open-system pump (typically easier to clean, but there is no barrier between the motor and bottles/tubing).
  • If it is hospital-grade (has a stronger motor).

Binderow mentions efficacy and efficiency as top breast pump priorities. “I recommend sticking with the hospital grade closed system pumps or a double electric personal use pump,” she explains. “These pumps have the strongest motors and are the most comfortable. I do not recommend the wearable pumps when trying to establish a milk supply.”

What to consider when shopping for breast milk storage bags

Again, this might be dependent upon the particular breast pump you choose if you are hoping to pump directly into storage bags. But no matter what type or brand, Binderow advises, “be sure to use bags or containers specifically designed for breast milk storage,” adding that any plastic should be food-grade and BPA-free to ensure safety. She notes that breast milk storage bags often have a double zipper seal to prevent leaking, which helps as they are ideally stored “flat and stacked” in the freezer.

You can read our complete guide to the best breast milk storage bags here.

How to store breast milk in the fridge or freezer

If pumping becomes an integral part of the feeding routine, then eventually these steps will feel like second nature. According to the experts (and the CDC guidelines for storing and preparing breast milk), pumping and storing sessions should look like this:

  1. Wash hands.
  2. Set up the pump, making sure the pump parts and tubing are clean.
  3. Pump into food-grade, BPA-free glass or plastic bottles or milk storage bags. (If bottles are to be stored in the fridge, they must be done so with a tight-fitting lid.)
  4. If transferring milk into a storage bag for the fridge or freezer, Binderow says to “remove the excess air by laying the bag flat on the counter and folding at the seam to seal.” She also says to freeze in small amounts (2- to 4-ounce increments, or enough for a full feed if you can guarantee the exact volume) so that milk never goes to waste if not finished.
  5. Label the bags (or the bottles) with the date of the pumping session.
  6. When freezing, lay breast milk storage bags flat for easier storage and to help them thaw faster. “Keep it away from the door to avoid constant temperature changes,” O’Connor advises. This also goes for fresh milk stored in the refrigerator.
  7. When ready to use, thaw the oldest milk first.
Sutthiwat Srikhrueadam/Moment/Getty Images

How to prepare stored breast milk for baby

If you’re not giving your baby freshly expressed milk within four hours, then it will need to be chilled or frozen. Here’s how to safely prepare pumped or expressed milk before giving it to your baby.

  1. Always follow the “first in, first out” rule for breast milk storage and preparation — this is, defrost the oldest milk first.
  2. Thaw or warm just what you need.
  3. Test a few drops of prepared milk on your wrist to ensure it’s a good temperature for baby. Some babies do not mind cold milk straight from the fridge. If you are warming the milk, “there is no ideal temperature, though it should be noted that heating it too hot could be dangerous for the baby and potentially degrade the quality of the milk,” Binderow says. “Think something like lukewarm water.”
  4. Swirl the milk in the bottle before feeding if you notice the fat has separated.

Preparing stored milk from the freezer

Frozen breast milk can be placed in the fridge to defrost the day before use, says Binderow. This milk should be used within 24 hours from complete thaw.

The frozen storage bag or bottle can also be placed in a bowl or cup of warm water, under warm running water, or in a bottle warmer to bring it to the desired temperature. Breast milk should never be microwaved or heated using boiling water for fear of destroying nutrients and creating hot spots in the milk that can burn a baby’s mouth.

Preparing stored milk from the fridge

Breast milk from the fridge can actually be served cold or warmed up in a bowl or cup of warm water, under warm running water, or in a bottle warmer.

Can you refreeze or chill thawed milk?

No. Once it is warmed, stored milk should not be placed back in the fridge. It can, though, be reused for up to two hours after a baby’s initial feeding. “I advise the families I work with to try and use it at the next feeding,” says Binderow. “You can avoid throwing out unused milk by warming smaller amounts and adding as needed.” (This is also the reason experts recommend freezing milk in small quantities.)

Combining stored milk with fresh milk

This is actually OK — as long as you combine the milk at the same temperature. “This means that freshly expressed milk should not be combined with cold milk from the refrigerator,” Binderow explains. “You should either warm both and then combine” for a feeding, “or chill both and combine for storage.” And remember, if combining for storage, it should be labeled for use according to the oldest day.

JGI/Jamie Grill/Tetra images/Getty Images

How long is breast milk good for?

The time frame for how long expressed breast milk lasts can vary slightly with how the milk is handled, the way it is stored, and the temperature of the room, the fridge, or the freezer. Here are some guidelines from the CDC (and experts) for freshly pumped or expressed milk:

  • At room temperature: Good for up to four hours on the countertop.
  • In the fridge: Good for up to four days at 40 degrees Fahrenheit.
  • In the freezer: Best within six months at 0 degrees Fahrenheit or lower, although it can be used up to 12 months. (O’Connor suggests using within three to four months if in a regular freezer, while a dedicated deep freezer — meaning a standalone unit — can keep milk for six months or longer.)
  • After thawing: Previously frozen milk defrosted in the refrigerator should be used within 24 hours of complete thaw.
  • Left over from a feed: Can be reused for up to two hours from the feed start time.

How to clean and sterilize bottles and pumping equipment

Before their first use, “it is important to initially sterilize the pump parts and bottles,” says O’Connor, but not the tubes. Thereafter, she says that if “a baby is term and healthy, there is no need to sterilize after the initial sterilization.” Simply wash pump parts that come in contact with the breast and breast milk with hot soapy water (or on the top rack of the dishwasher if the specified parts are dishwasher-safe) after each use to prevent germs — and be on the lookout for any mold that might be lurking in parts like tubing.

For bottles and parts washed by hand, the CDC recommends using a dedicated wash basin or large bowl (and washing that after) for bottles and pump parts, as well as making sure that all items are thoroughly air-dried (not towel-dried) on a clean towel or paper towel to prevent the transfer of germs. And, as always, remember to wash your own hands before pumping or handling bottles or pump parts and to make sure the actual pump and area the pump rests on are clean.

Should pumped breast milk be frozen immediately?

“Not necessarily,” O’Connor says. “If you know you will not be using it in the next couple of days, it is good to freeze it. But fresh milk has more stability than frozen milk.” That means fresh breast milk that is used within its safe window might better retain all its properties, such as antibodies that fight infection, than breast milk frozen for the long haul.

Binderow agrees, adding that “while expressed milk does hold nutritional value when it’s frozen, there are studies that show that after 90 days the concentration of its nutrients do begin to decrease.” That’s why the first in, first out rule is an important one to follow. She also notes that “the components of milk change throughout the day and throughout the first year of your baby’s life.” In other words, she explains, breast milk is both tailored to specific times of the day and a baby’s developmental needs, as breast milk at one week postpartum is different from the milk produced at six months.

Image Source/Image Source/Getty Images

How to store colostrum

Colostrum — the first milk produced by the mammary glands — is high in antibody and protein content and is specifically meant to immediately nourish your newborn. While Binderow says it’s best to give your baby all this good stuff right away, it is possible to store it in feeding syringes that can be refrigerated (for roughly two to three days) or frozen in colostrum collectors that you can sterilize and bring with you to the hospital, if you are advised to do so. A lactation consultant can advise on the best method to extract colostrum.

While it is not necessary or advised for most, some people harvest their colostrum through hand expression in the imminent weeks before a baby’s birth if they anticipate a separation immediately after childbirth or have a history of low milk supply, says O’Connor. This should not be done without first consulting your physician.

How to maximize pumping while minimizing stress

For some, feeding a baby, let alone a newborn around the clock, is a stressful experience — especially if the process of either breastfeeding or pumping (or both) aren’t seamless. Binderow acknowledges that the postpartum period can be both exciting and overwhelming, and recommends doing some prep work during pregnancy by taking a course or workshop or joining a local support group. “It will help you prepare for feeding, determine your personal feeding goals, and help you to set expectations around feeding in the early days,” she explains.

And, once your baby arrives, she recommends reaching out to your pediatrician or lactation consultant as soon as feeding becomes a struggle: “There are people out there who can help you to optimize feeding based on your personal goals.” And, while it really is all so personal, having a pumping plan and specific dos and don’ts in mind for the process can help.


Lisa Binderow, IBCLC, lactation consultant

Leigh Anne O’Connor, IBCLC, an NYC-based lactation consultant