Dry Ice - carbonating a keg

[fraser_john]

Now, my math, especially where chemistry is concerned is absolute crap, but I now regularly get dry ice at work. I have been using it simply to purge kegs and fermenters of air and then just capping them till I need to use them.

I was thinking of weighing a small chunk and chucking it in a keg before putting the lid on.

Any one know how to do the calculation on how much to weigh out in order to carbonate to a given level?

Safety Note
I was also going to fit one of those pressure relief valves set at say 20psi, just to ensure the keg did not blow up on me!

 

[vykuza]

It would be technically possible, but probably not a good idea.

Here's something on it found on another forum:

Unfortunately, it's probably a very dangerous way to carbonate beer (either in bottles or kegs). As many have pointed out, dry ice sublimates rapidly in liquid, creating large bubbles that do not readily dissolve into solution. This causes a pressure buildup in the head space that could VERY likely lead to bottle (or keg) bombs. The pressure buildup is so rapid that a Corny keg's pressure relief valve would probably be overwhelmed. The only way to decrease the pressure is to violently shake the vessel, causing the gas to be absorbed into solution. I doubt you could successfully achieve that with a 5 gallon keg, and it's impractical to shake every bottle of beer you fill.

 

[vykuza]

Here's the maths:

http://antoine.frostburg.edu/chem/senese/101/gases/faq/co2-volume-from-dry-ice.shtml

 

[fraser_john]

Yeah, someone raised the idea of infection as well, which is one thing I'd prefer to avoid more than anything.

 

[boonchu]

also dry ice is not made to be food grade