Storage Timing

Why we pump...

We pump in the middle of the night, we pump when we first get to work, we pump at lunch and it feels like every moment in between. We try desperately to fill our freezers with food for our babies and we have to stop and wonder, "am I doing this right?”

There are many reasons why we pump. We're told that the immunological properties of breastmilk can't be matched by formula, we're told that our milk adapts to our baby's needs and changes as they change, and for many of us, the breastfeeding relationship is precious and unlike anything we've experienced.

Why do we store breast-milk? Maybe we go back to work, maybe our baby has trouble latching, maybe we want to donate our milk to a local hospital for premies in need.  There are many reasons why we store our milk, and regardless of the reason, we want to make sure that it's safe once it gets to the baby.

How to Store...

When we're storing milk, we want to make sure of two major issues, 1. that pumping and storing and thawing doesn't introduce bacteria into the milk we've expressed, and 2. that the immune factors in the milk are still there- we know breastmilk is good for a baby's immune system, so I hope they stay good when I store it!

Why our defaults are set the way they are...

Here's the take-home from evidence based research on expressed breastmilk: “under temperate climatic conditions,” breastmilk stored for up to 72 hours in the refrigerator is bacteriologically acceptable. (Ogundele). From a meta-analysis published in 2016 we know that when we store expressed milk in refrigerators for 96 hours, fat content did not seem to be negatively affected.

When we store in the freezer, the "bacterial numbers plummeted considerably." (Peters) but the components of expressed breastmilk do degrade in the freezer. When milk is stored at -80C, fewer detrimental impacts upon antioxidant activity of the milk were noted, especially when less than 30 days.  

TL;DR: The basic rule is this: the longer you freeze milk for, the more components of the milk break down, so cycling your milk is a great idea. When you freeze it, keep your milk as cold as possible. Storage of expressed breast milk is safe and contains a good amount of nutrients for up to 6 weeks in the freezer, but no more than 96 hours in the fridge. Cycling through your milk, using the oldest as soon as you can, is your best bet at getting your baby the nutrition he or she needs, safely.  Remember, there are varying recommendations, but I'm giving you data from a meta-study done in 2016 which is the most recent one I was able to find.


Ogundele, M. (2000). Techniques for the storage of human breast milk: Implications for anti-microbial functions and safety of stored milk. European Journal of Pediatrics, 159(11), 793-797.

Peters, Mcarthur, & Munn. (2016). Safe management of expressed breast milk: A systematic review. Women and Birth, 29(6), 473-481.

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