I am one of those people who has been a college student numerous times. Once
upon a time, I was a graduate student in Food Science. I had courses such as
Food Microbiology and Food Engineering.

Among the trivial information I remember is that the main reason not to
refreeze food is due to texture changes. Ice crystals have a pretty definite
mechanical effect; mountains are broken down by frozen water! I found the
information about soponification of fats in frozen milk to be interesting.
The storage container could also make a difference. Soapy-tasting,
plasticy-tasting milk would not be very tasty.

Microbes would not be expected to grow if the food remained too cold for the
critters. Recommendations for thawing frozen turkeys are that the
refrigerator is best (but longest) but another alternative is in cold water.
Hot water would warm parts of the food to a temperature promoting microbial
growth.

My opinion, based upon my coursework, is that the partially thawed milk would
not be in great condition, even though I would not expect it to be teeming
with bacteria. It would most likely be "safe", but not very tasty. An adult
with a good sense of smell and taste could render a verdict, but I suspect
that the best idea is for the mom to start a new milk collection.

Becky Engel, RN, IBCLC
Athens, GA