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How Do I Thaw Frozen Milk?

Milk storage bag thawing in a bowl of water.

It seems simple. You can thaw your milk just like you’d thaw ground beef or a chunk of chocolate cake, right? Not so fast there. Before you thaw frozen milk, ask yourself a few questions.

What really matters?

If your baby is very premature or compromised, you should diligently use the “best practices.” If your baby is consuming only previously-frozen milk, also use “best practices.” In these situations, every drop of fat, every tiny amount of nutrient or immunoprotective component critically counts.

If you are not in the above-mentioned situations, you can be a little less cautious. 

What are the four basic methods for thawing milk?

Consider one or more of these four methods to thaw the container of milk:

  1. place it in the refrigerator, overnight
  2. hold it under running, lukewarm water
  3. set it inside of another container of water
  4. use a commercial-grade warmer

Which method you choose will depend on where you are, and what you’re trying to achieve.

Refrigerator

The ideal way to thaw frozen milk is by placing it in the refrigerator overnight. This method results in less fat loss than by thawing in warm water.

If your baby is already failing to thrive, or has been slow to gain weight, or is compromised in some way, use this method.

However, the truth is, most people aren’t thinking far enough ahead to make this happen. Hence, in one breath I’ll say it’s a best practice, and in the next breath I’ll say, it might be unrealistic.  

Under running lukewarm water

For decades, I’ve struggled to understand why using the running water method is preferable to immersing the container into a bowl of water. But honestly, I don’t understand.

In a bowl of water

Placing the container of milk in a larger container of water might be just fine. But read on.

Few people thaw frozen milk in a bowl of cold water. But in theory, this should be advantageous. The milk would still be considered “cold” and could therefore be refrigerated after thawing.

As far as I can tell, there’s no research for or against this practice. It’s probably fine, although a little slow.

Some people thaw the milk in a container of warm water. That’s probably fine.

Many people frequently put the milk in HOT water. That’s far from optimal.

Placing the milk in a container filled with hot water (80° C) creates little spots of high temperature in the milk because it hasn’t been stirred. So, if you want to do that, try to “stir” the milk (or swirl it, or whatever) to try to overcome that problem.

I’d be more concerned about how the hot water affects the milk. Multiple studies have shown that heat results in a denaturing and inactivation of the milk’s bioactive proteins, and a reduction in fat content.

So again, as you ponder how to thaw frozen milk, I’d say, what’s your situation?

Using a commercial warmer

I’m not an expert in this area. There are many conflicting opinions, and relatively little research to support or refute this method.

Here’s what I do know. Most professionals consider that a bottle-warmer is not the same as a commercial-grade milk warmer. So let me be clear that I’m addressing only the milk warmers.

Milk warmers are used in some hospitals. There are two basic designs for these units: water or waterless. It appears that there is no difference between the water and the waterless warming units in terms of changes in fat, protein, lactoferrin, and secretory IgA.

The two big players in this market are the Medela Milk Warmer™ and the Penguin™ Deluxe Nutritional Bottle Warmer.

Some worst practices

We often talk about “best practices.” We seldom mention “worst practices.” So, I will.

You should never thaw frozen milk at room temperature. There’s no evidence to support that practice. Yet, I doubt that’s the “worst” practice I’ve ever heard of. Read on!

Heather Townsend, a guest on my podcast, told me some disturbing stories. In a very large, well-known children’s hospital, a registered nurse heated up the mother’s milk in the microwave before giving it to the baby.

That nurse was just a wee bit behind the times.

Hibbard’s 1988 case report described a palatal burn that occurred after the milk had been warmed in a microwave.

Also, Quan’s 1992 study showed a dramatic decrease in activity for all of the anti-infective factors after warming the milk in a microwave.

Heather also described what I’d classify as other “worst practices.” She has seen people — including NICU nurses — warm up the mother’s milk in a crock pot, and even in an automatic coffee pot! (A Keurig. I’m still having trouble figuring out how that could happen!)

But I am far from perfect on this stuff. I remind myself that when I was a very young nurse, we frequently put milk into the very premature, very low-birthweight babies’ isolettes to thaw frozen milk. There’s no evidence to support that.

Does it do any harm? We may never know.

Be sure to read previous posts on the facts of freezing milk and tips for freezing milk.  Stay tuned for upcoming post where I will share tips for re-heating, storing, thawing, and more!

And yes, so many of the answers come down to, “It depends!”

If you want additional information, listen to my podcast with Dr. Anne Eglash, who is the lead author of the Academy of Breastfeeding Medicine’s protocol on storage.

How do you thaw frozen milk? Share your preferences and tips in the comments below!

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