Re: What is the freezing point of beer?

Howdy.  Great question.  I've wondered the same thing every time a beer
gets forgotten in the freezer!  Off the cuff, I'd say the best way to find 
out the answer to this question is to experiment!  A beer is a complicated 
mixture of stuff including water, ethyl alcohol, and lots of different 
flavor compounds (amongst other things).  In Utah, beer sold in the 
supermarket must be 3.2% by volume (I think it is by volume) or less.  If 
we assume that a "Bud" is 3.2% by volume, then 3.2% of 355mL is the 
ethanol (ethyl alcohol) content of the beer.  You probably know that 
alcohol has a lower freezing point than water (liquor, for example, 
doesn't freeze in the freezer, and is usually 80 proof (40% alcohol).  
Since ethanol freezes lower, you'd expect anything containing alcohol to 
freeze lower.

Now, let's step aside for a moment.  I'd guesss that the amount of other 
stuff in the beer is small, relative to the alcohol and water.  I'd also 
guess that dissolved CO2 (carbonation) wouldn't have much effect on the 
freezing point of the beer (it's a stable gas and has little interactions 
with the stuff in the beer).  As such, we might expect that the alcohol is 
the dominant thing that affects the freezing point.  You can do a 
calculation using a formula for "freezing point depression" which can be 
found in any introductory chemistry text, and get an idea of what the 
freezing point of the water alcohol mixture is (I have all my books packed 
up as I'm starting a new job).  I'd guess that it would be about -5C.

You can test that calculation out by opening up a beer, pouring it into a 
clean glass, and putting it in the freezer.  Try adjusting your freezer 
until you just get the right temp to freeze the beer.  It might be 
interesting to try this experiment out with a "non-alcoholic" (like 0.5% 
alcohol) beer too.  See if it freezes near zero, which is what we'd expect 
(since it also has most of the same stuff in it, without the alcohol).  
This will be a test of our hypothesis, and will tell us whether or not 
assuming the other "stuff" doesn't affect the freezing point is right or 
not.

Hope this helps!!

If you have more questions, or have a hard time with the calculation of 
freezing point depression, drop me a line:  weibel@chemistry.chem.utah.edu

Beers,
Mike