Happy new year to all.

At our milk bank, we have also had some trouble with some milk freezing. We keep our freezers at a minimum of -20C, well below freezing temperature of milk (which is pretty close to the freezing temp of water). I asked my physicist husband about the problem. Here's his take:
Freshly pumped milk, and in our case freshly pasteurized milk, is close to body temperature, which is pretty warm. In our case, we have found that milk bottles that are surrounded by other milk, i.e. in the middle of the tray of warm bottles, freeze more slowly. Trays stacked 3 high, the inside bottles of the middle tray do not freeze as well. I imagine that hospital freezers are at about the same temperatures as ours, maybe a little warmer, but still well below the freezing temp of milk. Fresh milk  surrounded by other warm milk being frozen will take longer to freeze. Mostly, it has to do with the fans and air/cold circulation in the freezer.

This is not related to alcohol consumption. One would have to consume a huge, probably lethal, dose of alcohol in order for it to make it into the milk in quantities large enough to affect freezing temperatures significantly, if that is even possible.

Fat content may affect freezing temperature, but again, not enough to be affected by a freezer at -15 or 20c.

After pasteurization, we cool our milk in an ice slurry to 30C. We are experimenting with cooling it more, and making sure the bottles have space around them until they freeze. So far that seems to be helping, but it's a work in progress.

Hope this is helpful.

Naomi


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Naomi Bar-Yam Ph.D.
Executive Director
Mothers' Milk Bank Northeast

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office: 617-527-6263
direct line: 617-340-3600
www.milkbankne.org
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