Breast Milk Storage


Many mothers find it convenient or even necessary to collect their breast milk and store it to be used at a later time.  Such is the case for mothers who are returning to work or school or for mothers who may need to be separated from their infants.  The guidelines offered below may answer the many questions mothers have about safely storing their breast milk.

Collecting Breast Milk

  • Wash hands well with soap and water.
  • Wash all the collecting bottles and breast pump parts that touch your breasts or the milk.  Use hot, soapy water or a dishwasher.  Rinse carefully.  Air dry on a clean towel.  When soap and water are not available use Medela Quick Clean products.  If your baby is premature or ill, the hospital may ask you to sterilize your pump parts.
  • Read the instruction book that comes with your pump and follow the suggestions.  Sterilize your pump parts once a day as described.
  • Practice pumping when you are rested, relaxed and your breasts feel full.  Once a day try to breastfeed your baby only on one side and pump the other breast.  Or pump for a few minutes if your baby skips a feeding or breastfeeds for only a short while.  Read the Breast Milk Storage chart to learn how to store breast milk.  Be sure to use the right size breast shield so that your nipple fits comfortably.  Medela makes different sizes of PersonalFit breast shields to fit all nipple sizes, from small to extra large.
  • Employed moms can help their baby learn to take a bottle once breastfeeding is going well.  It is best to wait for three (3) to four (4) weeks to introduce bottles.  If you are having problems breastfeeding, ask for help from a lactation consultant or health care provider.
  • Begin to pump to store milk one (1) to two (2) weeks before returning to work.  Many employed moms use the fresh milk they pump at work for feedings the next day.  They refrigerate Friday's milk for use on Monday.  Save your frozen milk for emergencies.
  • Pump three (3) times during an eight (8) hour work shift, or every three (3) hours you are away from your baby.  Ten minutes of pumping during breaks and 15 minutes of pumping during lunch with a good pump will help protect your milk supply.  If you can't pump three (3) times, pump as much as you can during each day. 
  • Breastfeeding in the evening and on days off helps maintain your milk supply and protects your special bond with your baby.

Storing Breast Milk

Breast Milk Storage Guidelines

  • It is normal for pumped milk to vary in color, consistency and scent depending on your diet.  Stored milk separates into layers.  Cream will rise to the top.  Gently swirl the warmed bottle to mix the milk layers.
  • You can continue to add small amounts of cooled breast milk to the same refrigerated container throughout the day.  Avoid adding warm milk to already cooled milk.
  • Pumped milk may be added to frozen milk provided it is first chilled and the quantity is less than what is frozen.
  • Store your milk in Medela's breast milk collection bottles or in disposable bags specifically designed for breast milk, such as  Pump & Save Bags, by Medela.
  • Freeze milk in two (2) to five (5) oz portions.  Small amounts will thaw more quickly.  You will waste less milk this way and will avoid over-feeding.  Aqueous liquids expand when frozen.  Be sure to leave some extra room at the top of the container so the bottle or bag won't burst.
  • Seal containers tightly.  Write the date on a piece of tape on the bag or bottle.  Use the oldest milk first.

Breast Milk Odor and Taste Changes

  • Causes of breast milk odor and taste changes
    Changes in breast milk odor and taste can be caused by medications, mother's diet, smoking and exposure of milk to light or cold temperatures during storage. In most cases, infants do not seem to mind odor/taste changes in breast milk.
  • Odor due to lipase
    Some mothers produce milk that, when frozen, develops an off-odor and taste due to a normal breast milk enzyme called lipase. When thawed, this milk is often described as smelling unpleasant, rancid or soapy. It is safe to use and many infants will accept it. However, some infants may refuse to drink it, either with their first taste or later as they develop taste preferences and volitional (non-reflexive feeding) feeding behaviors.
  • Test prior to freezing
    Before freezing large amounts of breast milk, mothers can test their milk for odor and taste changes due to lipase. Collect and freeze 1-2 bags or small containers of breast milk for at least 5 days. Then evaluate the odor and see if your infant will drink it.
  • To eliminate lipase-induced milk changes during freezing
    If milk changes smell and taste during test freezing, mothers can scald their fresh milk before they freeze it. Scalding milk after it has been frozen will not correct the odor/taste problem.
  • To scald fresh milk:
    - Heat it in a pot until tiny bubbles form around the edges of the pan (approximately 180° F).
    - Remove the milk from the stove and quickly chill it before freezing.

    Scalding milk reduces some of the beneficial components in breast milk, so whenever possible, give your infant fresh breast milk.

Special Situations
Mothers of neonatal intensive care (NICU) infants may need to pump and store milk for a long time. We know that in normal home freezers, liploysis increases with longer storage times. However, many NICU freezers store breast milk at super-cold temperatures of -70° to -80° C. At these temperatures, milk odor and taste changes due to lipolysis do not occur.

Mothers of NICU infants who have lipolysis-induced milk changes during freezing should consult with the NICU lactation consultant about milk storage temperatures in the hospital. Together they can develop a plan for her breast milk storage while the baby is hospitalized.

If your baby was born premature, these guidelines may differ slightly.  You should check with your health care provider for the recommended storage guidelines for your specific situation.

Never microwave breast milk.  Microwaving can cause severe burns to baby's mouth from hot spots that develop in the milk during microwaving.  Microwaving can also change the composition of breast milk.


  • Thaw milk overnight in the refrigerator, or hold the bottle under warm running water to quickly thaw.  You can also place the sealed container in a bowl of warm water for 20 minutes to bring it to body temperature.
  • Thawed milk is safe in the refrigerator for 24 hours.  DO NOT REFREEZE.

Your Milk Supply and Your Baby's Needs

  • We used to think that mothers needed to make more and more milk as their babies grew.  Scientists now know that a healthy milk supply remains fairly constant over the six (6) months of exclusive breastfeeding.
  • During the early weeks, babies eat very frequently and grow very quickly.  By Day 10, babies should recover any lost birth weight.  For the next few months, little girls should gain about an ounce a day, and little boys slightly more than an ounce a day. 
  • Around three (3) to four (4) months, a breastfed baby's rate of growth begins to slow down.  Continuing to gain weight rapidly after this time may contribute to obesity later on.  This means that the milk supply established in the early days will continue to satisfy the baby until it is time to introduce solids at 6 months.
  • By the end of the first week of life, women who are breastfeeding one baby normally make between 19 to 30 oz of milk each day.  Infants between one (1) and six (6) months of age normally drink an average of 19 to 30 oz a day.*  An average size "meal" for a baby is between three (3) to five (5) oz of breastmilk.  Formula is harder to digest and less well absorbed.  Formula fed babies may need larger feeds.  Consult your doctor for advice.

*Daly S, Owens R, Hartmann P:  The Short-Term Synthesis and Infant-Regulated Removal of Milk in Lactating Women, Experimental Physiol 1993; 78:209-220.

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