[chris (OP)]

Because I am a lazy so and so and cannot be bothered to keep going to the shop to buy milk, I often send my wife to the supermarket to buy several 4 pint bottles at a time.

I then freeze all but one of them, and when it's close to running out I thaw out a frozen bottle.

Interestingly, the frozen ones are urine-yellow, but they go white when they defrost. What do you think is going on? Is the yellow the fat separating from the water as it freezes?

Chris

[iko]

Because I am a lazy so and so and cannot be bothered to keep going to the shop to buy milk, I often send my wife to the supermarket to buy several 4 pint bottles at a time.

I then freeze all but one of them, and when it's close to running out I thaw out a frozen bottle.

Interestingly, the frozen ones are urine-yellow, but they go white when they defrost. What do you think is going on? Is the yellow the fat separating from the water as it freezes?

Chris

It might happen the very same thing as with human plasma.
We prepare cryoprecipitates from plasma by freezing the bags and centrifuging to concentrate some particularly useful plasma proteins like fibrinogen, Factor VIII and vWF.  They are not soluble at low temperature so can be separated from the rest of citrated plasma and concentrated in a small volume.
If you mix them up afterwards, cryo plus supernatant, you get fresh unfrozen plasma again.

ikoD

http://www.ams.cmu.ac.th/depts/bloodbank/bbwebpage/Copy_of_cry2.jpg

BTW breast milk freezing has been recently discussed right here:

http://www.thenakedscientists.com/forum/index.php?topic=7154.0

[Karen W.]

I do believe that is the occurence. I used to buy several gallons and freeze and the cream seemed to become more yellow as it separated from the rest. when thawed and shook up again it went back to its normal color!

[chris (OP)]

Mmm, but it could be the proteins rather than just the fat separating from the water as it forms ice?

Chris

[iko]

Mmm, but it could be the proteins rather than just the fat separating from the water as it forms ice?

Chris

Right, the proteins,
as I suggested above!

ikod

[Karen W.]

That is interesting!

[neilep]

You can freeze milk ?

[iko]

You can freeze milk ?

This "library on your desk" is just unbelievable.
Call it Google or PubMed or www...

In the last few years freezing of breast milk has actually been investigated for a possible positive effect like viral (CMV) inactivation, but these tiny bugs seem to freeze quite nicely and peacefully wait for thawing to go around and snag cells...using all their well preserved bits and pieces!
So bottles/bags/disposabledevices producers can only claim a more 'practical' way to feed your baby.

"...the freezing breast milk at -20°C preserved biochemical and immunologic quality of milk; however, late viral RNA and viral infectivity was also preserved..."

page 302; click here:   http://www.abpblh.org.br/Citomegalovirus%20e%20Leite%20Humano-Miron%20e%20cl%20-2005.pdf

http://babycare.iloveindia.com/gifs/rht-feed.jpg

By freezing and thawing, certain proteins,
especially lipoproteins may 'denaturate'
a bit loosing their enzyme capabilities
but certainly not nutritional value.
Flavour is another story.
I know you wanna go to the market once
every 3 months, lazy folks!
...And stay online 24hrs a day.

ikod   []

[Karen W.]

I always froze my milk when the kids were small as It was cheaper to go to Costco buy it bulk and freeze it just like Chris did. I never noticed a difference in flavor unless I forgot to shake it up after it defrosted!

[neilep]

Can I freeze semi skimmed or only full fat ?

[Karen W.]

I froze everything, but you must let it fully defrost whilst in the refrigerator so as it stays safe and then shake the crud out of it before you open it!

[paul.fr]

similar question, but no answer here:
http://www.thenakedscientists.com/forum/index.php?topic=8056.0