Breast Milk Storage


Collection and Storage

Many mothers find it convenient or even necessary to collect their breast milk and store it to be used later. Such is the case for mothers who are returning to work, school or if they are separated from their infant due to health issues. The guidelines offered below may answer many questions mothers have about safely collecting and storing their breast milk.

Collecting Breastmilk

  • It is important to wash your hands thoroughly with soap and water, or use an alcohol-based hand sanitizer that contains at least 60% alcohol.4
  • Breast pump parts, bottles and the area where you'll be pumping must be clean. Refer to your pump instructions for use for complete cleaning instructions.5
  • Breast and nipples do not need to be washed before pumping.4
  • Practice pumping when you are rested, relaxed and your breasts feel somewhat full.
  • Try pumping for a few minutes after your baby finishes breastfeeding. Your breasts are rarely completely empty after nursing and you can begin to pump whatever is left in the breasts to store for later.
  • You may try breastfeeding your baby on one side and pumping the other breast.
  • Some mothers like to try pumping between feedings to get some milk while baby is napping. Don't worry if you get much milk at all when you first start pumping. Remember pumping is a skill that takes practice. The more you try pumping, the easier it gets.
  • Refer to the Breast Milk Storage chart below to learn how to store breast milk.
  • Be sure to use the right size breast shield to ensure proper fit, maximized comfort and efficient pumping. Medela makes different sizes of PersonalFit™ breast shields to fit all nipple sizes, from 21mm to 36mm.
  • Begin to pump to store your breast milk about one (1) to two (2) weeks before returning to work.
  • When you are away from the baby, 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 research-based pump will help protect your milk supply. If you can't pump three (3) times, pump as much as you can during each day.6
  • Breastfeeding in the evening and frequently on days when you are off work, helps maintain your milk supply and protects your special bond with your baby.

Storing Breastmilk

The following storage guidelines are only for healthy babies who were born at term. If your baby is hospitalized or was born preterm, the guidelines may be different. Check with your healthcare provider for specific instructions for storing breast milk for your baby.


Breast milk that is stored will separate into layers, with the cream rising to the top. It is recommended to gently swirl the bottle to mix the layers before feeding.6

You can store your milk in bottles that are made without BPA, such as Medela's breast milk collection bottles or in disposable bags specifically designed for breast milk6, such as Pump & Save™ Bags, or Breast Milk Storage Bags.

Freeze milk in small amounts (1-2 oz.), it will thaw more quickly.2 You will waste less milk this way and will avoid over-feeding. Also, it is important to remember liquids expand when frozen, so be sure to leave some extra room (about an inch) at the top of the container so the bottle or bag won't burst.6

You can add freshly expressed breast milk to already cooled or frozen milk, however, it is best to cool down the newly expressed milk first before adding it to older stored milk.1

Write your baby's name and date on the storage container.

Wait to tighten the bottle caps or lids until the milk is completely frozen.

Refrigerate or chill the milk right after pumping, if possible. "Pumped milk is OK without being refrigerated up to 2 hours is best, up to 4 hours is okay."4

Storage of left-over milk is different than storage of your freshly expressed milk, due to bacteria from your baby’s mouth. The ABM Clinical Protocol #8 Human milk storage information for home use for full-term infants states “Once an infant begins drinking expressed human milk, some bacterial contamination occurs in the milk from the infant’s mouth. The length of time the milk can be kept at room temperature once the infant has partially fed from the cup or bottle would theoretically depend on the initial bacterial load in the milk, how long the milk has been thawed, and the ambient temperature. There has been insufficient research done to provide recommendations in this regard. However, based on related evidence thus far, it seems reasonable to discard the remaining milk within 1-2 hours after the infant is finished feeding. To avoid wasting or discarding unfed milk, mothers may consider storing milk in a variety of increments such as 15, 30, or 60 mL.”1

Changes in the Smell and Taste of Breast Milk

Changes in breast milk smell and taste can be caused by medications, mother's diet, smoking and exposure of milk to light or cold temperatures during storage. Some mothers produce milk that, when frozen, develops an off-smell 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 the milk and many infants will accept it and don't seem to mind odor/taste changes. However, some infants may refuse to drink it, either with their first taste or later as they develop taste preferences.2

You can scald freshly expressed milk before you store it, which will inactivate the lipase. To scald fresh milk:

  • Heat milk to about 180°F (82°C), or until you see tiny bubbles form around the edges of the pan (not to a full, rolling boil).7
  • Quickly cool and store.

Special Situations

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.6 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. 4 You can also place the sealed container in a bowl of warm water for 20 minutes to bring it to body temperature.4 Make sure the water does not come up to the level of the collar of the bottle.2Thawed milk is safe in the refrigerator for 24 hours. Once thawed, 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 constant over the six (6) months of exclusive breastfeeding. During the early weeks, babies eat very frequently and grow very quickly. By Day 10- 14, babies should recover any lost birth weight. Babies will gain 4-7 ounces per week in the first month (about 1 ½ lbs. - 2 lbs./month)3, and will usually double birth weight by 4 months.2

1. Eglash A, Simon L, AMB. ABM clinical protocol #8: human milk storage information for home use for full-term infants, revised 2017. Breastfeeding Medicine 2017; 12(7): 1-6.
2. Lawrence R, Lawrence R. Breastfeeding: a guide for the medical profession, 8 ed. Philadelphia PA: Elsevier; 2016.
3. Paul IM, Schaefer EW, Miller JR, Kuzniewicz MW, Li SX, Walsh EM, et al. Weight change nomograms for the first month after birth. Pediatrics 2016; 138(6): 1-7.
7. What can I do if my storage problem is due to excess lipase?