Breast Milk Storage & Transport

By Krista Gray, IBCLC. Last updated February 5, 2013.

Tags: ,


What type of container should I use to store my milk?

If your baby primarily gets his nutrition from your breast then the type of container you use is really not that important.  However, if most of his nutrition comes from expressed milk, then it is important the container you use keeps as many of the nutrients as possible.

While this is important, there is not a lot of research about the best type of container to store your milk.  Both glass and plastic that is free of polycarbonate (BPA free) are suitable.  Whichever you choose, make sure that they have tight-fitting lids (rather than one that has a nipple/teat).  Some experts recommend glass as the ideal container for freezing milk because it is the least porous, giving the best protection for nutrients in expressed milk.  However, many moms like the convenience and practicality of milk storage bags.  It is easier to store more milk because they take up less room, and there is also less to wash since they are disposable.

Studies have shown that both glass and plastic containers retain more nutrients in expressed milk than stainless steel containers.1

 Which type of containers should I avoid using for storing milk?

Bottle liners should not be used to store milk because they are too thin.  Thicker, milk freezer bags are typically not recommended for preterm/hospitalized babies but are fine for healthy, full-term babies.  One study found that antibodies decreased by 60% and milk fat content was reduced in milk frozen in thinner bags however this study did not test thicker milk storage bags.2   Nor have these results been duplicated.

How should I clean milk storage containers?  Is it necessary to sterilize them?

You should clean milk storage containers with warm/hot soapy water and let them dry before expressing milk in them.  This, along with washing hands, is enough to thoroughly clean pump parts and storage containers.  Unless you have a preterm or hospitalized baby it is not necessary to sterilize your pump parts or milk storage containers.

Where should I store my milk – fridge or freezer?

Where you store your milk depends on when you will use it.  Breast milk can be used from the refrigerator for up to 8 days after expression.  However, 5 days or less in the refrigerator is optimum.  If you are unsure, smell the milk.  Milk that is spoiled will smell sour.  Milk in a separate freezer door on your refrigerator will keep 3-4 months and 6-12 months in a deep freezer.  Always use oldest milk first from the freezer.  The fresher the milk the better.

How much should I store in each container?

It is best to store milk in 2-4 ounce batches, which is about how much a baby will drink at each feeding. 3   Alternatively, you could store a small quantity of milk in 1-2 ounce batches until you learn how much your baby will drink at each feeding.  Smaller quantities can be defrosted more quickly and this amount is good if your baby needs a little extra at one feed.

Make sure to write the quantity, date, and time on each batch of milk.  If milk is combined from multiple pumping sessions, write the oldest date/time on the batch.  Freeze milk in tightly-sealed BPA-free plastic, glass, or milk freezer bags.

How long can I store my expressed milk?

The column on the left shows the location of the milk.  The top row shows the state of the milk.

Mature Milk Storage Times for Full-Term Healthy Babies at Home
Temp. RangeDuration
Room Temperature66° - 72° F
19° - 22° C
6-10 hours
(4 hours if 77° F)
Insulated Cooler59° F
15° C
24 hours
Refrigerator32° - 39° F
0° - 4° C
Up to 8 days
Freezer Compartment in RefrigeratorVariable
0° F
-18° C
Up to 2 weeks
Freezer Compartment with Separate DoorVariable
0° F
-18° C
3-4 months
Deep Freezer0° F
-19° C
6-12 months
Taken from LLLI “Expressing and Storing Milk” & Breastfeeding And Human Lactation (2010) by Riordan J. and Wambach K., p. 439.

Taken from LLLI “Expressing and Storing Milk” & Breastfeeding And Human Lactation (2010) by Riordan J. and Wambach K., p. 439.

How do I transport my expressed breast milk?

Breast milk is a living substance and has amazing properties that can actually gain beneficial microflora when left at room temperature.  If you will be home to refrigerate your milk within 4-10 hours (depending on the heat of the day) after pumping, you could leave it at room temperature until you arrive home and can put it in the refrigerator.  However, once breast milk has been refrigerated you cannot leave it out for long periods without spoilage.  Therefore, once you refrigerate your milk, you should only take it out when you are ready to feed your baby.  If it has been refrigerated at work, you should transport it home in a cooler with a reusable freezer ice pack or ice to help maintain the cool temperature of a refrigerator. Refrigerate or freeze the milk as soon as possible.

If the milk you are transporting is frozen, it is important it does not begin to thaw.  Ensure there is plenty of ice, dry ice, or ice packs to keep it frozen in the cooler during transportation.  Place this milk in freezer as soon as possible.

How should I defrost frozen milk?

The best way to defrost frozen milk is in the refrigerator.  Once frozen milk has been defrosted, it should be used within 24 hours.  Never refreeze defrosted milk.  If you are unable to defrost milk in the refrigerator then you can run the frozen milk container under cool water for a few minutes or place the container in a pan of warm water.  Never heat milk on the stove or in the microwave and make sure that water doesn’t seep into the lid while it is defrosting.  Once defrosted, milk should not remain out of the refrigerator unless it is being fed to baby.


Show 3 footnotes

  1. Williamson, M. T., & Murti, P. K. (1996).  Storage, time, temperature, and composition of containers all have an impact on biologic components of human milk.  Journal of Human Lactation, 12(1), 31-35.
  2. Goldblum, et al. (1981)  Human Milk Banking: Effects of Container upon Immunologic Factors in Mature Milk. Nutrition Research, p. 449-459
  3. Kent et al., (2006) Volume and frequency of breastfeedings and fat content of breast milk throughout the day. Pediatrics, 117(3): 387-395.