How much CO2 is "5 lbs", and similar/related

[olie]

Hey all -- I'm looking at CO2 systems, and not quite understanding the units.

How many (5gal) kegs' worth of force-carbonation is 5lb of CO2? Assume 2.5 volumes per.
How many kegs (or pints or however you care to measure -- just tell me the units! ) of pressurized pour is 5lb of CO2?

Everyone sells CO2 tanks by the lb, but I have no sense at all about how much a pound of CO2 is.

And before you answer "more than you'll need for your home-brewing needs", don't assume that I brew at the same rate as everyone else. <G> I'm interested in moving toward a nano-brewery but, for now, let's just imagine that I brew, force carbonate and tap a 5lb keg every week.

(I don't, yet, but I'm looking to size my system to handle that. Once I'm there, I'll be looking to upgrade everything but, for now, I'm just trying to get a sense of "how much is that?!" at the 1/6-keg-a-week scale, to help me think about future directions.)

It seems to me that a 20# tank doesn't cost significantly more than a 5# one (certainly not 4x!), so the long-term cheapskate in me says go that route. But I don't know how much CO2 is 20# either, other than that it's 4x as much as 5#, which I don't know how much that is!

Tangent: when one speaks of "2.5 volumes of CO2", do they mean that 5gal x 2.5 = 12.5 gallons of CO2 (at STP, I assume) gets desolved into 5 gallons of liquid beer? Or does it mean something else? 1 gallon is 0.133681 cubic feet, so 12.5 gallons of air (CO2) would be just over 1.67 cu.ft. If I knew that 5# was, say, 50 cu.ft., I could do the math, but I don't know that, either.

Semi-self-answer: aha! Over on some grow site, I found this: "a pound of liquid CO2 in a tank contains 8.741 cubic feet of gas" (5# = 43.7 -- my guess was close!), so now I'm just looking for verification of the meaning of "X-volumes of CO2".

 

[Smellyglove]

Enter metric units

If I want a beer carbed to 7g co2 pr liter its 7*amount of liters. Very simple. I have a 6kg co2 keg so the math is easy. 1kg is 1000g.

that whole lbs and volumes is to me confusing, when I can go direct.

 

[Mark Buster]

Here is a good link that tells us we can expect to serve (but not force carbonate) roughly 15-22 5 gallon kegs of beer from a 5 pound tank. That seems a little high based on my experience.
If you add force carbing into the equation, that number will dip significantly.
The amount of CO2 used to carbonate the beer will depend on the desired volumes of carbonation, and the temperature the been is served/stored at.
I personally keep a 20 pound tank on hand for my general purposes. I swap this tank out at a local Airgas location for significantly less cost than a 5 gallon swap at the closest local homebrew shop to me.
That said, I do keep a 5 gallon tank on hand as a backup in case of emergency (once your regulator starts to show low tank pressure, it goes down FAST).
As for how many kegs you can both carbonate and serve from a single 5 lb tank, my own personal experience wants me to say 5-8, depending on the beer, temp, whether I was able to keg a full 5 gallons, etc.
Of course, one little leak in the system and the answer becomes 0. That's another reason I keep two tanks....

 

[Mark Buster]

Sorry, was unable to post the link or edit the post, the forum software thought it was 'spam-like'

 

[olie]

Smelly: I've never seen "carbonate to Ng per liter" -- everything I've seen so far is to volumes.

But even *I* can convert lbs to Kg, if I knew the other!

Mark: So I'm hearing carbonate and serve 1 5gal keg per lb of CO2-ish, and that may be a bit conservative, so some left over. (Assuming no leaks. Otherwise, yeah.)

 

[PADave]

Keep in mind that filling a 20lb tank is only about 2x as much as filling a 5lb tank, but you get 4x more. You can get at least 4-5 kegs out of a 5lb tank, probably more. I have both, started with the 5 lb on my single tap system, then went to a 20 lb for my 4 tap keezer. Now I use the 5 lb when filling kegs and as a backup. Still on the original fills for both tanks. They last quite a while, as long as you don't have any leaks.

 

[olie]

Yeah, for what I want to do, it sounds like 20# + a 5# for backup is the way to go.

Thanks all!

(The math on the whole thing is still screwy, if you ask me, but those industry guys hardly ever ask me! )

 

[beernutz]

I have both a 5# and a 20# CO2 tank which I get refilled/swapped at a regional gas company for $9 and $17 respectively IIRC. AirGas OTOH wanted $22 and $60 to swap them out and they would not refill.

Anyway if you have room it is a no-brainer to get a bigger tank. I have 4 taps, force carbonate everything and use CO2 to push starsan out of kegs before filling them and the last time I filled the 20# tank was about 2 years ago. I use the 5# as a backup or portable tank when I take a keg on the road. Harbor Freight sells a decent regulator that works with argon/nitrogen and C02 for a little over $30 and I used a 20% off coupon for mine.

I bought my 5# new in the 90s for $50 empty and got my 20# tank full on craigslist three years ago for only $55 so you don't have to spend a lot. I'd recommend making sure a used tank is still certified if you aren't sure the place you want to fill/swap it will take them otherwise. Both Wesco, the regional gas company, and Airgas will swap no-longer-certified tanks.

 

[ClaudiusB]

Enter metric units

If I want a beer carbed to 7g co2 pr liter its 7*amount of liters. Very simple. I have a 6kg co2 keg so the math is easy. 1kg is 1000g.

that whole lbs and volumes is to me confusing, when I can go direct.

I am a metrics guy and think in grams of CO2 dissolved too.

 

[Smellyglove]

Smelly: I've never seen "carbonate to Ng per liter" -- everything I've seen so far is to volumes.

But even *I* can convert lbs to Kg, if I knew the other!

Mark: So I'm hearing carbonate and serve 1 5gal keg per lb of CO2-ish, and that may be a bit conservative, so some left over. (Assuming no leaks. Otherwise, yeah.)

I didn't realize that's a thing too until maybe a year ago. I'm in metric-europe so for me it was natural to change from volumes. Still have to do some calculation in my head (1vol *1,96 = g/l) because I started like most of us with volumes. It's liters and grams, my beer is measured in liters and my co2 is measured in grams (or kilos, where 1kg is 1000g).

 

[SleepyCreekBrews]

I generally get about 10 -12 5gallon kegs (carbing and serving) out of my 5 pound tanks

 

[doug293cz]

1 volume of CO2 is equal to 1.9768 g/L. So, to get lb/gal we adjust units as follows:

1 volume = 1.9768 [g/L] * 3.7854 [L/gal] / 453.5924 [g/lb] = 0.0165 lb/gal​

Now freshly fermented beer contains about 0.8 volumes of beer, so to carbonate to 2.5 volumes, you need to add an additional 2.5 - 0.8 = 1.7 volumes of CO2. Thus to carbonate 5 gal to 2.5 volumes we need:

5 [gal] * 1.7 * 0.0165 [lb/gal] = 0.14 lb​

To calculate how much CO2 to serve 5 gal, let's assume we are serving at 10 psi(g) or 24.7 psi(a). CO2 has a density at STP of 0.0165 lb/gal, so density at 24.7 psi(a) is:

0.0165 [lb/gal] * 24.7 psi / 14.7 psi = 0.02772 lb/gal​

So serving 5 gal @ 10 psi requires:

5 [gal] * 0.02772 [lb/gal] = 0.1386 lb​

Note that I didn't bother with the temperature correction from 32°F to serving temperature. Using the lower temp gives a more conservative estimate (i.e. slightly higher CO2 requirement.)

Lest you think we are done, you still have to account for the CO2 needed to purge the headspace of (almost) all air (especially O2) after filling. We'll do this for the case of filling a keg that has not been purged prior to filling (i.e. open keg racking.) The headspace volume for a 5 gal corny containing 5 gal of beer is about 0.35 gal (based on measurements I made personally.) Getting the residual O2 in the headspace down to 0.11 ppm (110 ppb) requires 13 purge cycles at 30 psi (assuming 0 O2 in the CO2 source.)


So 13 purge cycles will require (again ignoring the temp correction factor):

13 * 0.35 [gal] * 0.0165 [lb/gal] * 30 [psi] / 14.7 [psi] = 0.1532 lb​

Thus each 5 gal of beer will require:

0.14 [lb] + 0.1386 [lb] + 0.1532 [lb] = 0.432 lb​

If you get the full 5 lb of CO2 in your cylinder, then you can carb and serve:

5 [lb] / 0.432 [lb] = 11.57 or about 11 5 gal cornies​

Unfortunately, most cylinder fills are light, so you don't get the full 5 lb, and your number of kegs processed will be correspondingly lower.

If you have leaks, sloppy procedures that waste CO2, or use CO2 for purposes other than what's accounted for above, then you will get fewer kegs per 5 lb of CO2.

Brew on

 

[Setsumi]

2kg of co2 is about 1100 lt co2. At 2.5 volumes you can do about 440lt of beer. At 20lt a keg you can carb 22 kegs from 2kg co2. But allow for higher use as psi increase AND leaks.

 

[mikeschmidt69]

My 2kg bottle is just about empty. I have carbed 11 19L (5gal) kegs, served 9 of them, performed 3 closed transfers from connical to keg including prepurging kegs, purged about 20 bottles with beergun before bottling from keg.