Here’s a question that I have answered several times from new moms.
Can I mix breast milk that I pump at two different times?
By experience, here’s what I do:
1. First express – put in fridge (not in freezer)
2. Second express – put in fridge (not in freezer)
3. After few hours assuming 1 and 2 are now in same temperature, combine 1 and 2 in a milk storage bag.
4. Freeze the storage bag from #3.
5. Repeat 1-4 for the succeeding expression.
I do not recommend to store milk in the freezer in milk bottles to avoid damaged parts. There are few good reasons why I suggest storing milk in appropriate milk bags. Read this.
For mommies in the Philippines, I recommend Milking Momma for affordable and quality milk storage bags. IG account: https://instagram.com/milkingmomma/