Now that you have figured out what the refrigerator shelf life of your breastmilk is, another important test is freezing and defrosting your milk.

A small percentage of woman have overactive lipase in their milk, which can turn breastmilk rancid faster than average. Lipase is an enzyme found in all breastmilk. It breaks down fats to help baby digest them.

This is sometimes apparent after the milk has been in the refrigerator for too long and is almost always apparent once milk has been defrosted from the freezer.

So, before you go building your freezer stash for your return to work, check to make sure you can freeze and defrost your milk without any difficulty.

The freezer experiment requires only two ounces of milk: one ounce of freshly expressed milk and one ounce that has been in the refrigerator for the maximum number of days your milk stays fresh in the fridge.

Whenever you freeze milk, you want to put it in the back of your freezer, not the door. If you are storing in a bag, lay the bag flat so it freezes like a playing card. Be sure to date whatever you are freezing and be sure to note the volume you are putting in the bag because the measurement marks on the bags are not reliable once the milk is frozen.

Let your milk freeze for about 24 hours, then defrost. You can do this by either putting it out on the counter for a few hours or by setting the bag in a cup of hot water or in a bottle warmer. Don’t microwave your breastmilk.

Oh, and if you are going to use the hot water method and you are using a  storage bag, consider throwing it in another regular ziplock just in case there is a little tear in your breastmilk bag.

Here is another trick for getting breastmilk slushies out of the bag and into the bottle: cut or fold the top!

Now that you have a bottle of defrosted milk, smell it and taste it. Ideally, have a second person smell it and taste it as well.

Yes, smell it and taste it. If this skeeves you out, please refer back to the shelf life blog with my opinion on this.

You will be doing this with your freshly expressed milk and your milk that sat in the fridge. The results of this test will tell you if you can safely freeze milk that has sat in the fridge or if you must freeze it shortly after expressing it.

This defrosted milk will fall into one of the following categories:

  1. Just the same as your freshly expressed or refrigerated milk. Obviously, this is fine to give to your baby.
  2. Soapy. Some moms notice a slightly soapy smell and/or taste to their milk. This is perfectly fine. Your milk isn’t spoiled; the lipase has just broken down some fats. Some babies (those with a discriminating palate, I suppose) will not drink this milk. If you have a hoity-toity baby who will only accept the freshest and finest breastmilk, you may need to follow the directions for the third scenario below.

Note: Sometimes babies who refuse bottles are actually refusing the taste of the milk in the bottle, especially in the case of soapy milk. Try to give this baby freshly expressed milk and see what happens.

  1. Stinky. Some women, and my heart goes out to them, have stinky milk. The lipase in their milk works fast and a little too well. This milk defrosts and smells obviously spoiled. You may not even need to taste it to know for sure, but if you do, it will taste like sour milk.

I am so sorry. If your milk spoils when you freeze it, the milk you have already frozen is unsalvageable. If this is you, I am so, so sorry.

Moving forward, in order to freeze your milk and avoid spoilage, you will need to scald your milk. It is a pain in the ass, but not too overly complicated. Scald some milk, freeze it, and defrost it. It should be milky fresh and ready for your baby.

Final note on freezing: don’t refreeze your milk. Breastmilk is typically good for about 24 hours after it is fully defrosted, but can’t be refrozen and defrosted again.

Scalding Your Breastmilk

Supplies Needed:

  • Small sauce pan for stove
  • Breastmilk (freshly expressed)
  • Clean bottle to transfer milk into
  • Funnel
  • Container with ice bath (to cool milk immediately)
  • Freezer storage containers (bags, trays, etc.)


Collect all supplies and set up first. This scalding process does not take long. Have your clean bottle, funnel, and ice bath ready for transfer.

Place your freshly expressed breast milk into a small sauce pan on the stove. Turn to medium or high heat.

Watch carefully for bubbles to start forming around the edge of your milk. Depending on how much you put into this saucepan, this could take maybe three minutes. You do not want this to boil, so watch carefully. Small bubbles means STOP.

Once you see the small bubbles forming, remove immediately from heat and transfer via funnel into your clean bottle (resting in ice bath).

Let rest approximately five to ten minutes. Then transfer into your freezer storage container (bag, tray, etc.) Be careful not to place this bag directly next to any of your already frozen bags of milk as this milk will be a higher temperature than the already frozen milk. Label and date bags accordingly before placing in freezer.


Literature: “My expressed breastmilk doesn’t smell fresh. What can I do?” on KellyMom

VideoScalding breastmilk on Youtube