Storing breast milk after expressing:
Do you have other questions, such as where to store breast milk at work, and what to do when the power goes out?
Visit Frequently Asked Questions.
Use breast milk storage bags or clean, food-grade containers to store expressed breast milk. Make sure the containers are made of glass or plastic and have tight fitting lids.
Avoid bottles with the recycle symbol number 7, which indicates that the container may be made of a BPA-containing plastic.
Never store breast milk in disposable bottle liners or plastic bags that are not intended for storing breast milk.
Freshly expressed or pumped milk can be stored:
At room temperature (77°F or colder) for up to 4 hours.
In the refrigerator for up to 4 days.
In the freezer for about 6 months is best; up to 12 months is acceptable. Although freezing keeps food safe almost indefinitely, recommended storage times are important to follow for best quality.
Source: CDC
Link: https://www.cdc.gov/breastfeeding/recommendations/handling_breastmilk.htm