How do you freeze breast milk and store it?

Freezing breast milk allows mothers to store excess breast milk for future use. Properly stored frozen breast milk maintains its nutrients and antibodies and is safe for babies to consume up to 6 months later. Freezing breast milk requires following important steps like using the right storage bags or containers, labeling them properly, and using the optimal freezer temperature.

Why should you freeze breast milk?

There are several reasons why freezing breast milk can be beneficial for both mother and baby:

  • Allows you to store excess breast milk when supply is more than baby’s demand
  • Provides emergency feed for your baby in case you are unable to breastfeed
  • Allows you to maintain supply if you need to stop breastfeeding temporarily
  • Enables someone else to feed the baby your breast milk when you are away
  • Saves milk for when baby starts daycare or you return to work
  • Lets you donate excess milk to milk banks for babies in need

What containers can be used to freeze breast milk?

The best containers to freeze breast milk include:

  • Breast milk storage bags – Special bags designed for storing breast milk. They are made from food-grade plastic and come with tight sealing zippers or double zip seals to prevent leakage or contamination.
  • Plastic containers – Hard plastic containers made specifically for freezing breast milk like Lansinoh or Medela bottles. They have tight sealing lids to prevent spills.
  • Glass jars or mason jars – Borosilicate glass or tempered mason jars with new lids and rings can also be used. Avoid using regular kitchen glass which may crack when frozen.

Avoid bags and bottles with BPA. Do not reuse disposable bottle bags. Also avoid regular plastic bottles, formula bottles, food storage bags or used food containers.

How much milk should you put in each storage container?

To allow for expansion during freezing, do not overfill the storage containers. Follow these fill levels:

  • Breastmilk storage bags – Leave 1 inch air space at the top
  • Plastic bottles or jars – Leave 1.5 inches air space at the top

Storing smaller 2-4 ounce portions allows you to thaw only what you need for one feeding session. However larger storages bags can hold 6-8 ounces if your baby drinks more per feeding.

How to freeze breast milk?

Follow these steps to safely freeze breast milk:

  1. Wash your hands before expressing or handling breast milk.
  2. Use a clean pump kit, bottles and parts every time.
  3. Pump milk into a clean container or bottle. Do not fill all the way.
  4. Seal the container properly. Remove any air bubbles.
  5. Label the container with date expressed and baby’s name.
  6. Place in the back of the freezer where temperature is most constant.
  7. Frozen milk can be stored in the freezer compartment inside the refrigerator or a standalone deep freezer.
  8. Leave space around containers for air circulation while freezing.
  9. Once frozen, the containers can be stacked closely or transferred to a milk storage bag.
  10. Avoid keeping the milk in the door of the freezer which may lead to temperature fluctuations.

How long does frozen breast milk last?

Frozen breast milk stays fresh and retains its nutritional value for:

  • Deep freezer at 0°F – Up to 12 months
  • Freezer compartment of a refrigerator – 6-8 months
  • Self-contained freezer unit of a refrigerator – 3-6 months

Do not refreeze thawed milk. Only previously frozen milk that was thawed in the refrigerator can kept for up to 24 hours in the fridge before it needs to be used.

Does freezing affect the composition of breast milk?

Freezing and thawing does lead to some loss of nutrients and antioxidants in breast milk. However, research shows that frozen breast milk still retains most of its essential components:

  • Protein, fat, and carbohydrates remain stable
  • Vitamin D and Vitamin A levels may decrease by up to 10-30%
  • IgA and lysozyme immunologic factors decrease slightly
  • White blood cell count reduces over time but remains sufficient to benefit the baby
  • Freezing kills off some good bacteria but many beneficial probiotics still survive
  • Most nutrients like lactose, vitamins B6, B12, E, potassium and magnesium are unaffected

Frozen breast milk may undergo some separation with the cream rising to the top after thawing. Gently swirl, but do not shake vigorously to remix it well before feeding baby.

Does alcohol in breast milk get reduced on freezing?

Alcohol content in breast milk reduces over time as alcohol leaves the blood and tissues. But freezing breast milk does not speed up the rate of alcohol dissipation. Frozen breast milk expressed after drinking alcohol can still retain alcohol traces based on:

  • Amount of alcohol consumed
  • Mother’s body weight
  • Time elapsed between drinking and pumping

To prevent high alcohol going to the baby, if you plan to drink, pump before drinking. After drinking, wait at least 2-3 hours before next pumping session, longer if you’ve consumed more than 1-2 drinks.

How to thaw and warm frozen breast milk?

Never thaw or heat breast milk in the microwave which can destroy nutrients. Here are safe ways to thaw and warm milk:

  • Thaw overnight – Thaw oldest frozen milk first. Place frozen milk in the refrigerator for thawing over 24 hours.
  • Thaw under warm water – Hold sealed frozen milk under warm running water. Avoid direct hot water contact.
  • Warm bath – Place frozen milk container in a bowl of warm water for 20-30 minutes till thawed.
  • Bottle warmer – Use a bottle warmer prefilled with warm water. Do not microwave bottles with milk.
  • Warming plate – Electric bottle warming plate to gently heat refrigerated milk to body temperature.

Gently swirl the milk after warming to mix any separated fat. Spot check temperature before feeding baby. Milk should feel warm or at room temperature, not hot.

How to handle thawed breast milk?

Once thawed, breast milk needs to be handled properly for baby’s safety.

  • Refrigerate thawed milk if not used within 1-2 hours
  • Use within 24 hours after thawing in refrigerator
  • Do not save any leftover milk after baby has fed
  • Do not refreeze thawed milk
  • Discard any spoiled or older thawed milk

How to store freshly pumped breast milk?

In addition to freezing, freshly pumped milk can also be stored at different temperatures:

Storage temperature Duration
Countertop, room temperature (up to 77°F or 25°C) 3-4 hours
Insulated cooler bag with ice packs 24 hours
Refrigerator (39°F or 4°C) 3-8 days

Use oldest refrigerated milk first before fresher milk. Smell milk before feeding to check for spoilage. Discard if it smells soapy, sour or rancid.

How to transport frozen breast milk?

Transporting frozen breast milk is safe if proper temperature is maintained. Some tips for transporting frozen milk include:

  • Use a cooler bag or box with several ice packs
  • Put frozen milk containers towards the bottom and sides near ice packs
  • Place ice packs below and above milk containers if using a cooler box
  • Keep bag/cooler box in the passenger cabin, not in a hot trunk
  • Limit opening the cooler
  • Store in freezer as soon as reaching destination
  • In hot weather, transport in early morning or night when its cooler

If transporting refrigerated milk, use plenty of ice packs to keep it as close to 39°F (4°C) as possible.

How to maintain freezer milk supply?

To build and maintain a good freezer stash of breast milk, follow these tips:

  • Start early, even before returning to work, to stash away extra milk
  • Pump after the first morning feed when supply is highest
  • Pump between breastfeeding sessions to collect excess milk
  • Look into getting a double electric pump to express from both breasts at once
  • Pump extra on weekends or days off from work
  • Try power pumping for an hour a day to boost production
  • Maintain pumping schedule and pump at least every 3 hours at work
  • Drink plenty of fluids and stay hydrated
  • Use breast massage and hot compresses before pumping

Rotate frozen milk batches using oldest milk first. Consume refrigerated milk within a few days before tapping into the frozen stash.

How to donate excess frozen breast milk?

If you produce more milk than your baby needs, consider donating the excess to a human milk bank. Your donated breast milk can provide critical nourishment to premature or sick babies.

To donate frozen breast milk, take note of:

  • Contact a HMBANA milk bank that is near to you
  • Get screened as a donor by completing a blood test and health questionnaire
  • Pump milk and store it as per the milk bank’s guidelines
  • Label milk bags with required details like date pumped, amount, etc.
  • Freeze milk flat in small 2-4 oz portions
  • Keep frozen for at least 14 days before donation
  • Ship milk to bank in dry ice or freezer packs

By donating to a milk bank, you can help nourish sick and premature infants with your breast milk.


Freezing is an excellent way for breastfeeding mothers to conveniently store and preserve their extra milk. With proper storage guidelines and precautions, frozen breast milk retains its nutritional value and antibodies that continue to nourish babies even months later. Storing breast milk requires the right freezer-safe containers, careful labeling, optimal freezing temperature, and avoidance of temperature fluctuations. Thawing also needs to be done carefully and milk should be consumed soon after. Building a freezer stash takes some effort but gives mothers the flexibility and peace of mind to continue providing breast milk to their babies.

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