Today my son and I each came home with a gallon of milk. Normally we have to race to drink one gallon before it expires. Can I just freeze the spare? I recall from my youth in Michigan that milk expands 10% when it freezes, so I will allow for that.
But will it separate or spoil anyway somehow?
It will separate, but be otherwise perfectly drinkable. Personally, I think milk that has been frozen is nasty but it’s a texture thing; the taste is fine and it’s perfectly safe.
You might want to open the jug and pour a bit out then recap it, to allow for expansion when the milk freezes. I was listening to a NPR “Talk of the Nation” podcast in which someone was talking about cost-saving measures and how he’d burst a number of plastic jugs of milk by not doing this on his first freezing attempt.
I freeze milk all the time (whole and skim), to cut down on how often I need to go to the supermarket. I have no problem with it. It may separate slightly (oddly, this seems to be more of a problem with skim milk than whole), but giving it a good shake before drinking mixes it again. Thawing it out slowly seems to cause less separation problems.
I have no problem freezing it as it comes in the half-gallon plastic jugs I buy. The expansion due to freezing is not enough to pop the cap off. This perhaps could be a problem with a different style of cap. I don’t know how well freezing a cardboard carton would work.
My grandmother used to freeze them. I don’t recall any problems; the cartons would bulge, naturally, but never burst.
If I were stuck with an extra gallon of milk, I’d make a big ass batch of instant pudding and freeze some of that.
Milk freezes just fine. I have worked on ships and seen hundreds of gallons frozen and never a burst or break. That does not mean it wont happen I have just never seen it. As for separation I have only done it with whole milk and a but of a shake is all is anything is even needed. I never drank a glass but there was never a complaint.
Milk is cheap. I’d use this happy accident as an excuse to make a dish that calls for a lot of milk in order to use it up. Perhaps a cream based soup or a pudding as mentioned above. Maybe make a giant batch of sawmill/sausage gravy and have biscuits and gravy for breakfast twice this week.
As other posters said, I found once the milk freezes, the water part seperates and it’s hard to get it all back together again. Whole, 2% or skim, it all is hard to put back together 
My grandmother always used to freeze it. I think it has something gross about it ever after, but that’s just me.
The first time I froze milk, the yellow color it turned made me wonder about things, but the white comes back when you thaw it out.
Never had a problem with taste, texture, or separation, but I’m a fiddler. I shake milk up before freezing and I’m always checking up on thawing milk–shaking it up and down and side to side, swirling it around, etc.