If you are freezing fresh breastmilk and feeding your baby previously frozen milk everyday, you may want to reconsider why you’re doing this. Because this is what everyone else is doing? There are too many articles out there teaching you how to generate a freezer stash of breastmilk, and too few articles explaining why frozen breastmilk is inferior to fresh and fridged breastmilk. Frozen breastmilk is still better than formula though.

Do you need a giant freezer stash?

A few weeks ago, I was preparing to transition to working part-time, and one of the issues that came up was creating a freezer stash. I read up about how to create a substantial freezer stash painlessly, and got started a couple of weeks early (thinking I was late to the game actually). In the meantime, I was also starting to go out some times in the afternoons to leave my baby with grandma for practice. Those days, I just leave the pumped milk in the fridge instead of freezing because my baby wants her milk ASAP, and my mom doesn’t always have time to thaw frozen milk if she runs out. It seemed a superior system to me – I don’t have to buy a ton of milk freezing bags, and take up a ton of space in the freezer. I know there are people who leave fresh milk for their babies, but everyone on the internet forums seemed obsessed with pumping up a stash to use. You can tell pumping large quantities is an obsession when “How I pumped and froze 1000oz of breastmilk” is next to the “How I earned $100,000 working from home” ad spam on the sidebar.

How do you use your freezer stash? I am under the impression that people take out the oldest milk, and freeze the day’s pumping, keeping the supply constant. Of course, there are those who freeze 6 month’s worth of milk so that they can stop pumping but continue feeding their LO breastmilk. In the latter case, you will need to freeze your breastmilk. But for most people, the freezer stash is more of a just in case they run low on milk that one day or that one afternoon. If this is your situation, you don’t need more than a day’s worth of milk in the freezer.

Freezing kills the white blood cells in breastmilk

I’m a biology researcher, and in my work we have to carefully consider how to store biological samples depending on their purpose. The freezer is usually an inferior form of storage. Freeze-thawing kills many types of samples, and we usually have to include additives to keep things in good shape. But you can’t add stuff to breastmilk to freeze it.

So what exactly is in breastmilk that will die in the freezer? White blood cells for one. If you remember from high school biology, an animal cell is just a fragile bag of water and stuff. Water expands when frozen, disrupting the membrane and bursting/killing the cell. Those white blood cells in breastmilk are all killed by freezing.

Slightly more complicated are the proteins. We don’t know all of the proteins in breastmilk, but there are probably hundreds of them. Some of them, like amylase and lipase, survive freezing. Those are rare examples. Most proteins will be damaged by the freezing process and inactivated. This is why you can store your freshly expressed milk in the fridge for 5 days, but your thawed milk won’t last 24 hours in the fridge. The antibacterial properties are much diminished by freezing.

Age appropriate breastmilk

There is the other consideration of age of milk. One of the best things about breastmilk is that your body tailors the composition to your baby. There is more fat in breastmilk for older babies, more water in breastmilk in the summer. By rotating your frozen milk out and your fresh milk in, your optimized breastmilk is no longer optimized. An occasional feed of frozen milk won’t make a difference, but if you are feeding your baby frozen milk everyday for 8 hours unnecessarily, you should think again.

My intended milk cycling system

My current freezer stash is ~10 bags of 3oz, saved over random pumping sessions when I was engorged and had to remove the milk (ate oatmeal cookies without realizing how potent they were for instance). I think this is more than sufficient for emergencies.

My plan for when I start work again next week is to pump exactly what my baby needs each day. I’ll be gone for about 5 hours, so it’s 5 x 1.5 oz = 7.5 oz. It seems a little ambitious for one pumping session, so I’ll be pumping in the middle of the night, once at work, and possibly when I get home/before I go to work, depending on when my baby feeds. I’ll store the milk in the fridge for the next day. Friday’s milk will be used sometime over the weekend when we go out – I haven’t figured out how to breastfeed in public, so we bottlefeed when we go out. Any extras will be frozen, and if we need more than 7.5oz, we will take it from the freezer – this also means I will have to start pumping more than 7.5 oz.

As for the freezer stash, if we don’t end up using it along the way, I plan to cycle the bags after a month. I care about the changes in nutritional content as my baby ages, so it would be better to cycle it regularly. If I end up using an emergency bag, I will be replacing it that same day as much as possible.

It will become a lot more challenging when I have to work full-time, but the plan for now is to increase the number of pumping sessions at work. One should be pumping every 3 hours to keep the milk supply, so I would probably have to increase it to at least twice at work, and immediately after reaching home/before I leave for work to last 9 hours (13.5 oz!). I’ll work it out properly when that time comes.