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Breast milk: Handling, storage and defrosting

Handling breast milk requires following certain rules. Nothing complicated, but undoubtedly essential to know if you’re pumping.

There’re many guidelines out there for pumping moms, but the most updated and reliable version is Protocol #8 from The Academy of Breastfeeding Medicine*. This document is a compilation of the current research on breast milk. It comes out with a series of guidelines to ensure the preservation of breast milk, to avoid the growth and transmission of harmful bacteria.

Regarding the storage…

Once you express breast milk, you should store it in a container with a lid, or a breast milk bag. The length of time breast milk lasts is:

4-6 hours at room temperature. Avoid extremely hot temperatures over 85 F or 29 C.

24 hours in a cooler with ice packs, at about 15 C.

4 days in the refrigerator. It might last 6-8 days under very clean conditions.

6 months in the freezer. It may last up to 12 months under very clean conditions and in a deep freezer.

Building a milk bank or pumping occasionally?

Now, I’d like to share a few tips that will help you to build your milk bank. If you’re occasionally pumping, only for “emergencies,” the same applies here.

1. Fill breast milk bags or containers with no more than 3 oz. Remember that liquids expand when frozen, and you rather defrost a few bags than waste the remaining milk that your baby didn’t drink.

2. Always mark your bags or containers with date and amount of oz. or ml.

3. Keep your milk bags or containers in a separate compartment of the freezer or inside a separate container to avoid contamination with other foods.

4. If you’re freezing your milk in bags, place them horizontally. That way, you’ll save some space in your freezer, and they will defrost faster.

5. Never mix fresh milk with frozen milk.

6. Do not refreeze milk!

7. If you want to mix fresh milk with milk that has been sitting in the refrigerator, let the fresh milk cool down in the fridge first.

How to defrost breast milk?

You probably have been pumping for a while and have a bunch of breast milk bags or containers waiting to be used. But before you jump to defrost it and pour it into bottles, you may want to consider the following guidelines by the ABM:

1. Thawing of frozen milk should be done either by placing the container in the refrigerator for several hours, or under running warm water. The recommendation is to place the container in lukewarm water for about 20 minutes if you want warm-thawed milk. Microwave is NOT recommended.

2. Thawed milk should not be left out to room temperature for more than 2 hours, and should be used within 24 hours.

3. Once your baby starts drinking from a bottle of breast milk, any remains should be discarded after up to 2 hours. So, you may instead pour small amounts of milk in a bottle and add some more if it’s needed.

4. It is not recommended to refreeze breast milk since there are not enough studies regarding bacterial growth and the loss of nutritional properties in such conditions.

*The Academy of Breastfeeding Medicine. (2017). ABM Clinical Protocol #8: Human Milk Storage Information for Home Use for Full-Term Infants, Revised 2017.

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