Breast milk storage best guidelines

Some women choose to pump and feed their babies with stored breast milk. You may decide to do this when you return to work after your maternity leave. This allows you to continue feeding your baby breast milk through a bottle. You can buy or rent an electric or manual breast pump. Some hospitals and insurance plans offer one for free.

This article provides answers to common questions about pumping and storing breast milk.

General recommendations

  • Wash your hands before expressing and handling milk.
  • The containers to store milk must be well washed (with hot water and soap). You can use the dishwasher if you prefer.
  • Use fresh (not frozen) milk whenever possible.
  • The milk that will not be used for several days, must be freezed as soon as possible.
  • If you can’t freeze your milk immediately after pumping it, store it in a refrigerator until you use it or freeze it.
  • Store breast milk in small amounts (1.7 – 3.0 Oz) so that only the milk that the child will drink immediately can be thawed.
  • Label containers of frozen milk with the date.
  • Always thaw the oldest milk.
  • Once the milk is thawed, stir it well. It can be mixed for the same intake, milk that have been pumped on different dates.

Recommendations on thawing

  • Whenever possible, heat the milk immediately after taking it out of the freezer.
  • Otherwise, maintain the milk cold until it can be heated.

What should NOT be done

  • Heat in a bain-marie (put the cold or frozen milk in a container with cold water and heat it all up in the fire).
  • Heat the milk directly in the fire.
  • Defrost the milk in the microwave.

What you can certainly do

  • Heat water in a saucepan and, once out of the fire, put the container of pumped milk inside until it reaches the desired temperature.
  • Heat in the microwave (*) and then stir the milk well so that its temperature is uniform.
Breast milk storage guidelines

Preserving breast milk for use at home

Type of breast milkTemperatureRefrigeratorFreezer
Freshly squeezed in a closed container 6-8 hours (77°F or less) 3-5 days (39°F or less) 2 weeks in the freezer compartment inside the refrigerator
Previously frozen, defrosted in the refrigerator but not heated or used 4 hours or less (until next intake) 24 hours Do not refreeze
Thawed out of the refrigerator, in hot water Only until the end of the intake 4 hour intake or until the next intake Do not refreeze
Leftover from the intake Only until the intake is finished, then discard Discard Discard

Types of containers

The containers can be either plastic or glass (with a lid that closes effectively) and preferably food-grade which are marked with the corresponding symbol. If they also have a wide opening, cleaning is made easier.

There are also plastic bags for freezing (single bag or ice bucket type) which are practical and inexpensive, although they also spill easily as they are more unstable and can be punctured and dripped.

It is preferable to store the milk in a double bag. There are also special bags that attach to the extractor but are expensive and single-use.

filled and empty bags of expressed breast milk

Flavor changes in stored milk

Some women have commented that their frozen milk smells sour and even rancid. That smell is attributed to a change in lipid structure as a result of freeze-thaw cycles in the freezer-refrigerator with automatic defrosting.

Although it may happen that occasionally a child rejects it, this is usually not the case and it is not harmful to the baby either.

Freezing milk quickly after pumping and warming it immediately after removing it from the freezer seems to contribute to this problem to a lesser degree.

Breast milk pump and several bags to store milk

Some mothers find that lipase acts very quickly and within a few hours their milk smells sour. In these cases what the mother can do is: put her milk in a saucepan and put it on the fire. If she has a thermometer (especially for cooking), she will wait for the milk to reach 140 ºF, take it out of the fire, store it in the container where it will be frozen, cool it quickly (a little cold water with ice will do), and freeze it.

If you do not have a thermometer, you must control the heating process, when the milk makes very small bubbles on the sides of the pan, take it out of the fire and continue with the previous procedure.

How to feed the baby

Milk from your breast milk storage can be given to the baby in a cup or bottle. It is a process that requires learning and patience. Delay using the bottle until the baby is well fed and breastfeeding is well established. It is not necessary to feed the baby in a bottle as long as you can breastfeed and you both are together.

(*) Breast milk can be heated in the microwave. Although improper use can destroy most of the living cells in breast milk, the nutritional value of the milk remains the same.


Lawrence, R.A. Breastfeeding Mosby/Doyma Libros, S.A. Madrid 1996 Royal
College of Midwives. Breastfeeding. Handbook for professionals.
ACPAM, Barcelona 1994 Aguayo, J. Breastfeeding. University of Seville, 2001 ACPAM. Practical manual on breastfeeding.

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