View Full Version : Determining CO2 output during Fermentation

12-03-2009, 02:40 PM
I am trying to find an equation to get a rough estimate of CO2 produced during fermentation. I figure that it should be able to be calculated by Degree Plato per Bbl. So to figure CO2 produced over fermentation one could go CO2(by the ton)=(Bbls)*(x)*(O.G.-F.G). So for one Bbl changing one degree it would be CO2=(1)(x)(1). I just need to know if this is reasonable and what one Bbl produces, which would be my "x". I believe this should be somewhat constant as it just reflects CO2 output by amount of sugar metabolized by yeast. I also realize that the actual amount would vary depending on specific yeast strain, amount of CO2 dissolved into beer (although I don't really see this being applicable unless it is secondary cask fermentation), amount of various esters and phenols produced, etc. Anyone?

12-04-2009, 06:23 AM
MBAA Handbook says around 1.4 standard cubic feet of CO2 is created during 24 hours of one barrel of ale fermentation at high krausen with a drop of 4 degrees Plato.

Good place to start anyway for rough estimation.

12-04-2009, 11:15 AM
Thanks! So with that I figured that if one cubic foot of CO2 weighs .1234 pounds then 1.4 cubic feet should weigh .17276 Lbs therefore I said .17276(pounds of CO2)=(1Bbl)(4[drop in degrees Plato])(x) solving for x I got .04319. So I kind of suck at this kind of thing but I think that this might be how much CO2 is produced in pounds per Bbl per degree Plato?

01-24-2010, 06:10 AM
Your numbers make sense, but they don't agree with this fairly simple approach:

-Fermentation produces about 0.49lb of CO2 for each lb of extract (fermentation byproducts by weight are around half CO2 and half ethanol).
-One degree of Plato in one barrel of 12P beer equals 2.7lb of extract. This number will increase with gravity, e.g. a 30P beer will have 2.9lb/P of extract.
-The amount of CO2 produced would be 0.49lb*2.7lb = 1.323lb.

If you go to http://sites.google.com/site/republicbrewpub/, you can download a spreadsheet that predicts the gravity at which you should cap a fermenting beer to capture a desired amount of CO2. It uses the above calculations and predicts a required capping gravity of about 0.4P above terminal gravity for typical ale fermentations (68 degf, 20% of the fermenter volume is headspace, pressure can't exceed 15 psig). A brewery I used to work at capped its ale fermentations at 1P above their expected terminal gravities, which worked pretty well (although I'd periodically need to vent overpressurized tanks), so my method probably needs some tweaking. Plugging your CO2 production into my spreadsheet, however, results in a predicted capping gravity of 12.3P above terminal. We all know that would result in fermenter explosion, so I'm thinking 1.3-1.4 lbs of CO2 per degree Plato per barrel of beer is closer to the truth.