Just reporting in; after some research, we guessed that the higher than average fat content might be keeping it soft (20 percent, when high-end ice creams are 16) so we dropped that down, lowered the alcohol content slightly (sigh) and used the turbo-boost button on our chest freezer. Voila! It was delicious. Thanks everyone!

Definitely the alcohol keeping it soft. It may firm up a bit in a day or two, but I wouldn't worry about it - just call it Rum Raisin Semifreddo and pretend it was intentional. (Sounds delicious with the buttermilk, btw.)

Hi likestocook, I keep posting because coincidentally I just made delicious homemade ice cream. Your ratio sounds so low that I really [really really] think it will firm up if left in there a couple more days, of course assuming your freezer is functioning normally. It does sound divine! Nearly all ice cream has sugar as a main ingredient so even that is probably OK! Happy Thanksgiving!

The ratio is about 1 part alcohol to 27 parts other liquids (cream, milk, etc.) - so, pretty small! Reducing the sugar and giving it a hard freeze sound like good options. Thanks!

This is sorta like the moral of Toy Story: You can't play with your Woody when you've got a Buzz. It's okay. It happens to everyone sometimes. (TWSS)

Sugar also prevents ice cream from becoming rock hard, so you might tweak that down a little.

I made a still-freeze (ie no churn) delmonico-style ice cream a week or so ago with a ratio of 2 cups cream (+ 2 whipped egg whites) to 1/8 cup Grand Marnier; a day later it was not as hard as I wanted [T.W.S.S.] but a week later it was SUBLIME. I also made a pear sorbet that was probably a volume of 2 cups liquid (pureed cooked pears with maple syrup) with 1/8 cup cognac, which also took more than a day to get to the right degree of hardness. Too much alcohol can make it too soft but the right amount will make it perfect and not too ice-hard. I say keep it in the freezer, it might be on the softer side but probably still delicious, or it might be perfect . . .

yum yum yum
Serve it soft.

Adding to the consensus that it's the booze keeping it from hardening fully (that's what she said - sorry, couldn't help it). Seriously though, two thoughts: take half the rum called for and boil it down by half. Use the reduced rum & more straight rum in the recipe. You'll still get the rum flavor, but less alcohol. Second, don't worry about it and serve a soft, boozy ice cream. A super-fancy ice cream place in San Francisco (Humphrey Slocombe) serves a bourbon-rich ice cream called Secret Breakfast. It's never hard and they make no apologies for it - it's just deliciously boozy.

The alcohol will keep it soft. You could try cooking the alcohol off, but I think you'd loose a lot of the tang that it adds to the ice cream. You might try using a bit less? I remember an ice cream shop in Northampton (Bart's) that experimented with a tequila sunrise ice cream. tasty, but they never could get it totally hard.

I think a few more nights in the freezer will get it harder than it is. I just served homemade sorbet and ice cream for dessert and it was definitely harder than it was after one night. How much alcohol is in there -the ratio of alcohol to other liquid ingredients?