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https://www.breastfeeding.asn.au/bf-info/breastfeeding-and-work/expressing-and-storing-breastmilk

Previously frozen— thawed in refrigerator but not warmed

4 hours or less (ie the next feeding)

Store in refrigerator

24 hours

Do not refreeze

But in freezer the temperature is still below normal, still is there a probability of bacteria growth?

I wish to understand the reasons behind the warning. Answers with references will be appreciated.

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2 Answers

This is just a guess, but I don't think this is a food safety issues, its more a case of 'this food is gross now' issue.

When I was a teenager I worked in a frozen food processing plant. The freezers were giant boxes where freon was condensed on gigantic coils into a liquid and then the liquid freon would rain down on to the food passing under on a conveyer belt. The vegetables were frozen instantly and it was quite tasty - frozen just a few minutes after being cleaned.

As industrial freezing is very quick and such flash freezing, the quality of the food is preserved in a pretty fresh state. [its horrible for the ozone in the atmosphere but this was in the 80s and I hope they changed the process].

Milk is a mixture of water based nutrients and globs of fat, which give the milk is homogeneous white color and its smooth texture. Freezing milk in a typical refrigerator would take hours and ice crystals would form and separate out the two phases - the fatty portions would separate. Try it with a glass of milk and see. This is the same reason that you don't re-freeze ice cream, which has even heavier creme proportions (even fattier). The texture is completely gone.

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so how would fat separation effect health? Is harmful? –  TheIndependentAquarius Nov 23 '13 at 15:52
    
I don't think it would- it might be a bit more like skim milk. The nutrients are still there and if its been frozen after only a short period there shouldn't be too much bacterial growth, but if you think food should be appetizing to be healthy you might not completely feel its as good as if it hadn't been refrozen. On a molecular scale there could be some differences; if I was having lactovegans over for dinner I'd throw it out. If I was starving and waiting for a check to come in I wouldn't think twice about drinking it. –  shigeta Nov 23 '13 at 23:28
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I think this recommendation is simply to be on the save side in terms of degradation. You don't want to feed babies with milk which is not ok anymore - so you take measures that exclude this for sure. Breast milk is a raw product, so if its not handled with care, it can be contaminated. –  Chris Jan 23 at 8:45
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i agree @Chris . if you refreeze how long can you keep the milk between freezings? what temperature is the bottle? how clean is it? too complicated for a public guideline. –  shigeta Jan 23 at 11:55
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When I lived in the UK, most supermarket frozen foods came with a "Do not refreeze after opening pack" warning. This is only anecdotal, but I've never heard of anyone getting sick after ignoring this advice. I myself used to ignore that advice quite regularly. –  Chinmay Kanchi Jan 23 at 12:34
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I don't know why I can't comment, but this seems simple enough that you could do an experiment and freeze it and see what happens. One possibility that comes to mind is that fat globules formed during freezing will clog the nipple on the bottle and make it harder for the baby to drink. Breast milk isn't homogenized, so the fats are more likely to separate than normal cow milk from the store. It also isn't pasteurized, so it will spoil faster than store bought milk too, but if you keep it cold and don't let the experiment run for more than a couple days it should be ok. To be safe, don't feed the experimental sample to the baby.

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