Guide to Storing Breastmilk in Mason Jars

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I am passionate about sustainable living. I was raised in a home where we were conscientious about avoiding waste, and the 3 R’s, (reduce, reuse, recycle). Sustainability involves three parts: economic, social, and environmental continual well-being. 

For example, shopping for clothes at Goodwill is a sustainable choice because it keeps clothes out of landfills (environmental), provides jobs to people with disabilities (social), and saves up to 50% off, if not more than the item's original price (economical).

I am going into month 5 of breastfeeding our twin babies, and I pump for three reasons: one to help maintain my supply, two to help express milk when I am engorged, and three to have milk on hand for when a babysitter is watching our babies. I store my breastmilk in 4oz Mason jars in the fridge and freezer. I love the 4oz size because they easily stack on each other, and they do not take up a lot of space in the fridge.

I remember in my babysitting days, I worked at an in-home daycare for a mom who was breastfeeding. She used plastic breastmilk storage bags to store breastmilk in the freezer. I did not like the bags because they weren’t the easiest to transfer into bottles and they leaked.

Upon finding out I was pregnant, I began researching all the things of course, and one of them being if breastmilk can be stored in glass jars. I did not want to have to keep buying pricey storage bags that I could only use one time. I already had 4oz Mason jars, so I would like to use them for breastmilk. Ball mason jars are my favorite brand, but other glass jars can work too! Mason Bottle offers milk + food storage for babies too. 

Any content provided by my blog, Merry Madden is in my opinion and is not intended to replace medical advice from a healthcare provider.


-Have to make sure they are completely flat when freezing

-Hard to add more milk into

-Can leak 

-Only use once 

-Can only be used for breastmilk 


-Can be used for other purposes (I am going to use these for baby food once the twins are 6 months old!)

-Multiple uses


-Easily stackable

-Easily add more milk


  1. Amazon sells smooth-sided 4oz mason jars, but the “quilted” kind will also work, however, I prefer smooth-sided jars to easily see how much milk I have in each jar.
  2. Ball also has leak-proof lids which are dishwasher safe, and they will not rust.
  3. Use Haaka or breast pump to express breastmilk.
  4. Sterilize both the lids and jars either in the dishwasher or in a baby bottle sterilizer (I used Phillip’s sterilizer during our babies’ first three months).
  5. Label the top of the lids with the date and the time. Keep breastmilk in the fridge for up to 4 days, and then if not used, transfer to the freezer for up to 6 months. 


Labeling breastmilk: To make life simpler, instead of writing the exact time it is, I round down to the nearest hour. This way I am giving myself an extra buffer when it comes to the freshness of my milk. For example, if I finished pumping at 12:37 pm, I write 12pm on the label. 

I use reusable labels that can be erased with either a magic eraser or any eraser. These reusable labels are dishwasher and freezer-safe safe. However I have noticed our dishwasher will cause the labels to come off, so I just wash the lids by hand. 

If you want to know exactly how much milk is in each jar, you can use a food scale to find out the amount of ounces in each jar. First place a clean, empty jar on the food scale, and make sure to set it to tare. Then add in breastmilk to the jar, and the scale will only show how much milk is in the jar. I bought my Taylor scale in 2021, and it is a kitchen staple for me!

Best of luck mama! Breastfeeding and pumping is no easy task. I hope this article is helpful to you and your little one. 


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