For years, I’ve fielded tons of questions about freezing milk for newborns or older infants. In the last decade or so, the number of questions I’ve had from parents and providers about freezing milk in home freezers has intensified.
I’ve been following the research on milk storage since the late 1970s. Most of the studies are small, low in the hierarchy of evidence, and they sometimes contradict one another.
Many of the “right” answers start with the phrase, “It depends …”
All that being said, I’ll address the facts about frozen milk and safety.
1. What’s the ideal temperature for freezing milk?
Many or most studies state that the temperature for freezing human milk is less than -4° C (24.8° F).
2. How long can you freeze milk?
The biggest factor to consider is the type of freezer being used. To my knowledge, there are three main types of freezers.
- Type 1: Freezer inside of your refrigerator. The freezer in your office mini fridge or at your kid’s dorm is probably one where the freezer is inside of the refrigerator.
- Type 2: Freezer as a separate compartment in your refrigerator. Here, the freezing compartment is behind a separate door. Top-and-bottom or side-to-side refrigerators have this feature. This is generally what you’d find in a standard household kitchen.
- Type 3: A deep freezer. This is a stand-alone unit that has only a freezer function. These can be vertical or horizontal. Chest freezers are commonly referred to as deep freezers.
Type 1: I can’t recall seeing any research that addresses how long you can keep human milk in this type of freezer. But let me ask you this: Have you ever forgotten about a packaged frozen dinner stored in this type of freezer? And found it several months later? It looks completely unappetizing, right?
Type 2: All authorities agree that human milk keeps well for about 3 months without losing worrisome amounts of any critical components. Others say up to 6 months. Some make no differentiation of storage times, whether it’s in a standard refrigerator’s frozen compartment or a deep (chest) freezer.
Hold on until I talk about loss of nutrients and immunoprotective (or bioactive) factors when freezing milk. But don’t give this “loss of components” issue a second thought if the baby is routinely consuming some of the frozen milk and plenty of fresh milk.
Type 3. The deep freezer.
Some authorities say that it’s “optimal” to keep milk in the deep freezer for up to 6 months. Others, including the Centers for Disease Control say it’s okay for 12 months.
Honestly, I doubt we’ll ever get the “real” answer here.
Further, I’m guessing that the family opens the Type 2 freezer several times during the day, whereas they open the Type 3 freezer far fewer times in a day.
Does it matter? We might never know.
But keep in mind the one hard, cold fact that we do know. It’s a principle that I harp on in my 95-hour course: Human milk (and probably most food) loses nutrients and bioactive factors with
- extreme temperatures (either hot or cold)
- extended exposure to those temperatures
So, try to avoid or minimize “extreme” and “extended” conditions.
3. After being stored, what, exactly, goes “bad”?
Okay, time out. Herein lies the reason why it’s so hard to discuss this whole topic about freezing milk. Because “bad” is a subjective term.
When I was a young nurse, we only looked at bacteria. Too many bacteria are bad. Hence, it was about safety.
Now, we have more refined ways of looking at what is in the milk that shouldn’t be (e.g., harmful bacteria) and what isn’t in the milk that should be (i.e., nutrients and bioactive factors.)
If this milk is the infant’s sole source of nutrition, loss of some nutrients and bioactive factors can be concerning.
4. When should you throw it out?
Simple answer: Never.
We have no data to show that the milk “goes bad” at some arbitrary point. The quality can diminish, the taste may change, but that doesn’t mean it’s “bad.”
Some parents have used older milk in pudding for adults or children. Some have used it on or with an older infant’s cereal.
Even if it seems unappetizing, you still shouldn’t throw it out. Why so?
Kim Updegrove at Mother’s Milk Bank in Austin asks that you call her and arrange to ship it to her so she can use it for research purposes. We need to know more about human milk. Get details from Kim by contacting her through Mother’s Milk Bank here.
5. Does freezing destroy the nutrients?
As previously mentioned, some nutrients are diminished with extreme temperatures and extended storage times.
Consider your circumstances, as I previously mentioned. If this is a baby who can get some milk that is short of Vitamin C, or otherwise get formula that may cause side effects, I’d go with the frozen milk.
6. Does freezing destroy the immunoprotective factors?
We could probably argue that some loss of some components occurs. The question is, what — and how much — is diminished or destroyed? And will it matter?
Yet, I stand by what I said earlier: Length of time and extreme temperatures can and do affect the immunoprotective factors.
Cells, immunoglobulins, cytokines, oligosaccharides, mucins, hormones, antioxidants (the list goes on and on) are sensitive to extreme temperatures. This is fairly well documented.
However, keep in mind one very important principle: Formula does not contain any live cells. Ever.
If you want to do the deep dive, I can suggest some resources. The best sources I know of are by my own mentor, Dr. Ruth Lawrence (author of Breastfeeding: A Guide for the Medical Profession).
The following two seminal articles belong in every professional’s library.
Here, Dr. Lawrence clearly says that “freezing destroys cellular activity”. Here, she talks about the processes and says that “the number of cells in human milk is reduce by storage.”
Don’t you dare tell me that these articles are more than 20 years old. These sources are likely to be the very best compilation of evidence that we’ll ever have. It’s unlikely that we’re going to get new funding to prove what we already know about the process and effects of freezing milk.
These aren’t the only questions about freezing milk. They’re just the questions I hear most frequently from both parents and professionals. My go-to reference for all questions about storage is the Academy of Breastfeeding Medicine’s protocol.
Let me remind you of what I said when I started this post. Often, the answers start with “it depends.”
What’s your biggest question about freezing milk?