Hi Jeanette:

I found out the hard way a few years ago that even though the mother believed
her milk had not thawed, the opening & closing of the freezer door had, over
time caused a bit of thawing and refreezing.  I refused to believe her
complaint that the milk had "gone bad" until I tasted it myself and it was
quite sour.  I'm now very careful to instruct moms to pack it in ice &/or
place the milk in the back of the freezer (unless they are using a deep
freeze to begin with, in which case this isn't a problem.

Nancy