For Jul...
RE: CHOICE OF A STORAGE CONTAINER
When a baby is only receiving expressed milk occasionally, the type of storage container is not a major consideration; however, if a baby is receiving most of his nourishment from expressed breastmilk, the type of storage container used should be considered carefully. Plastic containers are the best choice for storing breastmilk in the refrigerator as more of human milk's leukocytes or white cells adhere to glass. If the milk is to be frozen, glass is the preferred choice as it is less porous and offers the best protection. Most of the leukocytes in human milk are killed with freezing anyway. For this reason, milk that can be used within 8 days of expression should be refrigerated rather than frozen, because the antimicrobial properties of human milk are better preserved with refrigeration.
Another good choice for refrigeration or freezing is the milk storage bags that are designed specifically for human milk (see CSF milkbags). They are pre-sterilized and are thicker (2-ply), coated with polyethylene, and lined with nylon which prevents the fat from adhering to the sides. Hard plastic containers of any kind are also good choices for both refrigeration and freezing. Other milkbags, sold specifically as bottle liners, are not as durable, making them an unacceptable alternative when freezing the milk as the seams may burst during the freezing process perhaps causing a leak during thawing. Also, one study found that there was a 60% decrease in the milk's antibodies and a loss of fat that adhered to the sides of these bags. If this type of bag is still chosen, the milk can be better protected by placing the liner bags in a larger gallon size freezer bag or in a hard plastic container.
When milk freezes it expands, so it is necessary to leave about an inch at the top of the container to allow for expansion. For this reason, bottle caps or container lids should not be tightened until the milk is completely frozen.