[case thrower]

I broke down and got a 2.5 gallon keg with a charger kit since I don't have room (or permission) for a kegerator.  My first batch in it I primed like I would with bottles, but the instructions say you can carbonate using multiple cartridges, also.  Using 16 gram cartridges, how can I figure out how many cartridges would get me to a certain volume of CO2?

[dmtaylor]

Good question.  Without a gauge it would be hard to guess -- need some trial and error until you get it right.

When I've kegged in the past in the small 5-liter kegs, what I did was prime with like 1 tablespoon cane sugar, then let that sit for a couple of weeks.  This would usually be enough pressure to push out 2 or 3 pints.  Then after that, I would add "a squirt" or two of CO2 to maintain the carbonation until next pour.  This worked well, but again, required some trial and error.  If you tried this with 2.5 gallons, I would guess you'll need twice as much, maybe 3 "squirts" of CO2 to maintain.  By "a squirt", I mean you're pushing the CO2 trigger for perhaps 1/3 to 1/2 second per squirt.  Play around and see what works.

Somebody out there must have way more experience and can give you a better idea to start out.

[case thrower]

Sorry, Dave, didn't make myself clear.  When I go to push this batch out, I know I'll just use small 'squirts.'  What I'm looking at here, though, are future batches.  Instead of priming with some kind of sugar, I want to just use CO2 cartridges.  The directions with the charger say you can inject 2 or 3 cartridges depending on you carbonation preference.  I'd just like to know how many volumes each cartridge would put into my beer.

[dmtaylor]

I know what you meant.  I guess I'm just not much help as I never went with straight cartridges!  If that's what the instructions say, you could give it a try.  But find out if the instructions are meant for 2.5 gallons, or for 5 gallons, or what.  If for 5 gallons, then start with no more than half as much, and maybe even less, maybe 1/3 as much.  At least, that's what I would try.

[case thrower]

Yeah, the instructions specify a 2.5 gallon keg.  I'm sure there must be a formula or a way to figure a formula, but I'm sufficiently math challenged that my old brain would freeze up and have me babbling in no time at all.  High school math was a LONG time ago.  If push comes to shove, I can just put a couple in and see what happens after each one.  Thanks.

[Stevie]

I paintball tank may be more affordable in the long run and doesn't take too much space.

[a10t2]

Assuming 2.5 vol CO2 at serving and 0.9 vol after fermentation (i.e. ale temps):

9.5 L * (2.5 - 0.9) * 2.0 g/L = 30 g CO2

[case thrower]

Assuming 2.5 vol CO2 at serving and 0.9 vol after fermentation (i.e. ale temps):

9.5 L * (2.5 - 0.9) * 2.0 g/L = 30 g CO2

I'm not trying to be obtuse.  Where does the 2.0g/L come from?  I get the rest.  So 2-16gr cartridges would result in a little over 2.5 volumes CO2.  Thanks.

[a10t2]

That's the density of CO2 at STP. 1.97 g/L to be more precise.

[case thrower]

That's the density of CO2 at STP. 1.97 g/L to be more precise.

Aha!  Standard Temperature & Pressure.  Thanks.