title_body: How long does it take to cool a keg of beer?
upvoted_answer: I know I'm a few days late but the worry I'd have leaving a keg outside in cold weather is the pressure changes.  CO2 absorbs more in colder conditions, but if anything freezes, even partially, CO2 gets driven out of solution.  Normally when you refrigerate kegs indoors they're hooked up to gas, so as pressure in the headspace drops it's less likely the keg will unseal itself.  Also, if the keg did freeze a bit the CO2 being forced into the headspace could conceivably go over the pressure limits of the keg, depending on how carbonated it was to begin with among other things.
  
  Think of leaving a bottle or can in the freezer to chill it quickly then forgetting about it.  Odds are instead of a beersicle you got beer and glass sprayed all over the inside of your icebox.  It's anecdotal, I'll admit, but I've seen it happen so I wouldn't risk a keg and either leave it outside uncarbonated or chill it in a temperature controlled fridge.
  
  Anyway, this is long since past so my fear mongering is moot.  Let us know how it went for you.  You should be able to leave and accept an answer to your own question and it would be good for the site.