How Long to Store Breastmilk (and where)
Here is what La Leche League says about how long to store breastmilk. For me, I tended to keep it in the refrigerator if I knew I'd use it in a day or so, but if I got too far ahead then I'd just freeze it.
The fresher the better-- when I was pumping full time, I'd try to give my daughter freshly pumped milk, and if the timing didn't work, I'd go to the refrigerator. If I'd misjudged how much to keep out, I'd have gone to the freezer supply. However, once I went to the refrigerator, I took the oldest milk there, same with the freezer.
Keep the milk in the coldest part of the refrigerator/freezer, which means as far from the door as possible.
How much to freeze?
You don't want to freeze too much milk per container, since once it is thawed, you need to use it in 24 hours, and it can't be refrozen. On the other hand, storing too little wastes space and containers. The recommendation I hear most is 2-4 ounces. I'd stick closer to 2 ounces when the baby is small, 4 when it is bigger. If you know the baby will be eating a lot at a time (like a full day at daycare rather than an occasional relief bottle) you could store some in larger quantities. Storing differing amounts makes sense-- if your baby normally eats 4 ounces at a time, storing some 4 ounce packages makes sense, but also some 2 ounce ones, in case your baby is hungrier than usual, or you don't use them until your baby is older and eating more.
You may want to mix milk from multiple pumpings together, so you can refrigerate or freeze in more sane quantities.
Never add warm milk to frozen milk-- cool the new milk first, since warm milk could thaw the frozen milk, and you don't want that to happen.
I've heard both ways on adding warm milk to cold milk-- some say it is fine, others say don't do it. I haven't seen any studies or definitive statements. I know many people add warm milk to cold, and I've never heard of any problems. My take is to cool the new milk before combining it if you can, but if this is difficult, I wouldn't worry too much about it, because of the magic anti-germ properties of breastmilk.
Bottles and Bags
What should you store your pumped breastmilk in? I find bottles are much more convenient than bags to pump into. Bags take up much less freezer space, and don't need to be cleaned.
I've heard various things about plastics reacting with the breastmilk, and leaching "good stuff" from it. I don't know anything definitive. My inclination is to stick with bottles/bags designed for breastmilk until I find out more about the issue. If you know something, please write me.
In my collection, I have Medela, Ameda-Egnell, and Gerber bottles.
I've used the Medela CSF bags, and the Mother's Milk bags.
I am currently using the Mother's Milk bags for the breastmilk I'm freezing. I put ~30 ounces of milk in one large ziploc freezer bag for additional protection.
Marking for storage
Be sure to mark the date on the bag/bottle. I use a wet erase marker on the lid of the bottle for the breastmilk I have in the refrigerator. You may also want to mark the time if your find your milk varies over the course of a day.
I find it very useful to mark the quantity on the bags of milk. You can use a small kitchen scale to weigh the milk to measure it. 1 ounce = 1 ounce, 1 gram= 1 ml (or close enough).
Mark any medication you've taken. I'm told some organized moms write anything unusual they ate. Great idea :-).
Some people have milk that goes bad very quickly upon refrigeration/freezing. Scalding the milk immediately after pumping is supposed to help. I'll have more info on this soon, hopefully
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