How much CO2 is produced during fermentation?

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk:

Wables

Well-Known Member
Joined
Oct 22, 2006
Messages
313
Reaction score
143
Location
Duluth, MN
After 20 years of brewing I’m finally moving from buckets and carboys to pressure fermenters. I’ve never tried to figure out how much CO2 is given off during fermentation. Lets say I have 5.5 gallons of 1.060 beer in a 7.9g fermzilla, will I have enough CO2 to:

1) Keep an airlock on it for the first 12 hours of active fermentation to blow any O2 out the top, then
2) Push a 5 gallon keg clear of a full load of star san, then.
3 Add a spunding valve to the keg and force carbonate the fermenter at 15 psi?

Thanks!
 

micraftbeer

Supporting Member
HBT Supporter
Joined
Dec 30, 2015
Messages
622
Reaction score
303
Location
Farmington Hills, MI
Yes. It's complicated to answer "how many gallons" because the volume depends on the pressure. But I did the ol' use fermentation CO2 exhaust to purge my keg, and it went a couple days after the keg was fully purged.
 

hottpeper13

Well-Known Member
Joined
Jan 14, 2013
Messages
1,234
Reaction score
433
Location
Mequon
I have A Handbook of Basic Brewing Calculations that has the info and formula on page 66 and 67.
 

McMullan

wort maker
Joined
Dec 22, 2015
Messages
355
Reaction score
327
It's very difficult to say with any certainty, generally. It's driven by so many factors. Any claim it's predictable or even follows an idealised textbook chemistry equation is hilarious, in biochemical reality. Yeast metabolism during fermentation of wort is infinitely more complicated than theoretical tosh pretends. There is going to more than enough for your strategy. Shed loads!
 
Last edited:

mashpaddled

Well-Known Member
Joined
Sep 25, 2018
Messages
616
Reaction score
361
Location
Denver, CO
I agree you aren't going to get specific calculations of CO2 production from a formula because fermentation is not mechanical and you also need to account for other factors with the brewing environment and your process.

What it sounds like you're asking is whether you can avoid needing a CO2 tank during any part of the brewing process. I would not count on always being able to produce enough CO2 to do all of the steps you want perfectly.
 

hottpeper13

Well-Known Member
Joined
Jan 14, 2013
Messages
1,234
Reaction score
433
Location
Mequon
In Germany they can't use extraneous CO2 ,so what do they do?
For every 1* plato of wort fermented there is a fixed amount of CO2 produced that's how the formula starts I don't know where you 2 get your info from but mine comes from MBAA books and brewing texts, Read the [email protected]#$%^ books.
 

McMullan

wort maker
Joined
Dec 22, 2015
Messages
355
Reaction score
327
In Germany they can't use extraneous CO2 ,so what do they do?
For every 1* plato of wort fermented there is a fixed amount of CO2 produced that's how the formula starts I don't know where you 2 get your info from but mine comes from MBAA books and brewing texts, Read the [email protected]#$%^ books.
By all means read books, but do try to understand the science, especially for C flux in yeast cells fermenting wort, and its limitations in the real world. You know, the one full of diversity and variation that doesn’t conform to idealised textbook equations conveniently 'balanced' by gross assumptions and the crude guesstimates derived from them. What’s far more important (than thumping textbooks) is to just accept more than enough CO2 is going to be produced during fermentation for the OP to achieve his strategy. Attempting to cough up a crude figure expresses little more than a kind of mental masturbation.

At best, under strictly controlled laboratory conditions, CO2 evolved from a specific fermentation is measurable. A professional brewer following stringent SOPs in his brewery could make reasonable predictions based on the lab’s findings, assuming the bench scientists in the lab used his yeast and his brewery wort. That’s about as good as it gets and it’s generally only of true value to that specific professional brewer. It’s unlikely to be of much value to other professional brewers, fermenting different worts with different yeast strains in different breweries. And certainly not of any value to home brewers, whose processes are a lot less standardised, even when they believe they’re not. The belief there’s an applicable relationship between degrees plato and CO2 produced, one that can be applied across all fermentations, is tosh. Inevitably, at some point in the process, assuming all goes well, the primary products of fermentation become ethanol and CO2 for a period depending on wort conditions (fermentability) and yeast strain, condition, pitching rate, growth potential, potential biomass, attenuation/FG, etc., etc. Mash temperature alone is enough to expose the crudeness of any figure you might dare to put forward.

What you’re doing is erroneously accepting idealised textbook models then projecting them on the real world. That’s not how biological systems work. They’re generally a lot more complicated than the limitations of the textbook thumper’s mind.
 

marc1

Supporting Member
HBT Supporter
Joined
Jun 19, 2010
Messages
1,084
Reaction score
708
Location
OH
Here's a calculation for you to peruse:

 

marc1

Supporting Member
HBT Supporter
Joined
Jun 19, 2010
Messages
1,084
Reaction score
708
Location
OH
The calculations above, even if they do not match real life exactly, show that anywhere in the same ballpark is going to be fine for purging O2.

It's not really necessary to use an airlock or push starsan. Jump your fermenter gas post to the serving keg liquid post, then put your spunding valve on the serving keg gas post. For most of fermentation, I keep it set to low PSI, enough to help keep the keg lid set.

If you want to carbonate, you can increase PSI for that, either throughout the fermentation if you want pressure fermentation effects, or near the end.
 
OP
W

Wables

Well-Known Member
Joined
Oct 22, 2006
Messages
313
Reaction score
143
Location
Duluth, MN
The calculations above, even if they do not match real life exactly, show that anywhere in the same ballpark is going to be fine for purging O2.

It's not really necessary to use an airlock or push starsan. Jump your fermenter gas post to the serving keg liquid post, then put your spunding valve on the serving keg gas post. For most of fermentation, I keep it set to low PSI, enough to help keep the keg lid set.

If you want to carbonate, you can increase PSI for that, either throughout the fermentation if you want pressure fermentation effects, or near the end.
I used an air lock for the first 12 hours of active fermentation to purge the fermenter headspace of O2, then switched to a hose to purge my keg of star san. After I was bubbling in my star san collection bucket I added a spunding valve to the gas post on the keg. My only issue has been leaks. I am basically fermenting in all new equipment (2 new fermenter setups). I had a leaking keg lid gasket and a leak between a spunding valve and ball lock fitting. I have one more leak to find that is limiting pressure to 10 psi. The other fermenter is holding at 14 psi. Thanks for the links and replies!
 

marc1

Supporting Member
HBT Supporter
Joined
Jun 19, 2010
Messages
1,084
Reaction score
708
Location
OH
I used an air lock for the first 12 hours of active fermentation to purge the fermenter headspace of O2, then switched to a hose to purge my keg of star san. After I was bubbling in my star san collection bucket I added a spunding valve to the gas post on the keg. My only issue has been leaks. I am basically fermenting in all new equipment (2 new fermenter setups). I had a leaking keg lid gasket and a leak between a spunding valve and ball lock fitting. I have one more leak to find that is limiting pressure to 10 psi. The other fermenter is holding at 14 psi. Thanks for the links and replies!
I'm not sure that purging the headspace first does anything useful - you're in essence wasting CO2 that could be purging the keg as well.
 
OP
W

Wables

Well-Known Member
Joined
Oct 22, 2006
Messages
313
Reaction score
143
Location
Duluth, MN
I'm not sure that purging the headspace first does anything useful - you're in essence wasting CO2 that could be purging the keg as well.
My thoughts were that the headspace contains 21% O2 that I don't want in the keg. I'm only 36 hours into fermentation and everything is purged and up to pressure. There is way more CO2 than I imagined.
 

marc1

Supporting Member
HBT Supporter
Joined
Jun 19, 2010
Messages
1,084
Reaction score
708
Location
OH
My thoughts were that the headspace contains 21% O2 that I don't want in the keg. I'm only 36 hours into fermentation and everything is purged and up to pressure. There is way more CO2 than I imagined.
My point was that the StarSan purge isn't even necessary - as you see, there's enough CO2 to purge the headspace and an empty keg.

I don't think it hurts, it's just more work :)

Maybe if you had a low OG beer, then it would be worth it.
 
OP
W

Wables

Well-Known Member
Joined
Oct 22, 2006
Messages
313
Reaction score
143
Location
Duluth, MN
My point was that the StarSan purge isn't even necessary - as you see, there's enough CO2 to purge the headspace and an empty keg.

I don't think it hurts, it's just more work :)

Maybe if you had a low OG beer, then it would be worth it.
You are probably correct. I just wanted to swing for the fence on this batch to justify the money I spent in going to low O2 brewing. Hopefully I can taste a difference...which is unlikely since I have Covid and can't even taste my coffee.
 

yorkeken

Well-Known Member
Joined
Feb 22, 2016
Messages
129
Reaction score
66
Location
Connecticut
My point was that the StarSan purge isn't even necessary - as you see, there's enough CO2 to purge the headspace and an empty keg.

I don't think it hurts, it's just more work :)

Maybe if you had a low OG beer, then it would be worth it.
I agree. I’ve stopped filling and purging kegs with Starsan. I now just clean and sanitize the keg and purge with the fermentation co2. After racking the beer to to the keg, I give it a couple of blasts of co2 and begin carbonation. I haven’t noticed any issues with oxidation at all and I brew mainly light colored IPA’s (1.062+/-) with a goodly amount of whirlpool and dry hops. I see no sign of darkening in color and the flavor and aroma seem to last until the keg is kicked… usually around a month or so.
 

hottpeper13

Well-Known Member
Joined
Jan 14, 2013
Messages
1,234
Reaction score
433
Location
Mequon
When you purge the kegs without starsan do you hook up to the line in or the line out? Does it matter?
 

yorkeken

Well-Known Member
Joined
Feb 22, 2016
Messages
129
Reaction score
66
Location
Connecticut
When you purge the kegs without starsan do you hook up to the line in or the line out? Does it matter?
I fill 2, 2.5 gallon kegs. The fermentation co2 goes to the first kegs "beer out" post, then out the gas post and from there, into the second kegs out post, then out the gas post into a jar of Starsan.
 

CascadesBrewer

Supporting Member
HBT Supporter
Joined
Mar 24, 2013
Messages
1,719
Reaction score
1,425
Location
VA, USA
I agree. I’ve stopped filling and purging kegs with Starsan. I now just clean and sanitize the keg and purge with the fermentation co2. After racking the beer to to the keg, I give it a couple of blasts of co2 and begin carbonation. I haven’t noticed any issues with oxidation at all and I brew mainly light colored IPA’s (1.062+/-) with a goodly amount of whirlpool and dry hops. I see no sign of darkening in color and the flavor and aroma seem to last until the keg is kicked… usually around a month or so.
I did this once myself recently and it worked great. Transferring directly into a sanitized and purged keg makes the kegging day fast. It was for a Hazy Pale Ale recipe. I took the keg to a weekend campout where it sat out at warm temps (served through a jockey box). The half that came back home with me lasted about a month in my keg. After those conditions the beer was perfectly fine with no signs of oxidation.

The biggest drawback for me is that I cannot fit both my 7-gallon fermenter and a keg into my fermentation chamber. It worked for the mentioned batch since that was fermented warm with Voss.
 

Terpene

Supporting Member
HBT Supporter
Joined
Feb 1, 2019
Messages
97
Reaction score
70
If a brewer thinks they can know the ABV of their beer, then they better also think they can know the amount of CO2 produced in their fermentation, because otherwise they would be arguing against conservation of mass, and nobody should do that.

Conservation of mass is observed in biochemical systems also, including yeast and yeast metabolism.

Therefore it is absolutely possible to estimate the amount CO2 created and evolved in a fermentation.

One way is to start with the stoichiometry and use ABV as your starting point.

1 glucose --> 2 ethanol + 2 CO2
(Six carbons are conserved.)

Basically you produce the *exact same amount* of CO2 as alcohol, on a molar basis. For every mole of alcohol, you get a mole of CO2.

It's straightforward to go from ABV to moles ethanol and then from moles ethanol to moles CO2 and then from moles CO2 to volume CO2.

You'll have to consider how much CO2 remains in your fermenter headspace + dissolved in your beer vs what get evolved, but this should be relatively straightforward to calculate also.

I'll post later to put some meat on these bones, as I don't have time right now. But yes it's absolutely possible to calculate this, and anyone who says different then must admit they also can't calculate ABV. But every brewer on here thinks they know their ABV.
 

McMullan

wort maker
Joined
Dec 22, 2015
Messages
355
Reaction score
327
Mmm! Because measuring ethanol a very straight forward thing to do, even for professionals, isn't it? Another textbook thumper.
 

StayThirsty

Member
Joined
Jun 29, 2021
Messages
14
Reaction score
14
I purged 5 gallons of StarSan from a keg in 25 minutes with the blowoff from a 10 gallon Voss Kveik batch. That thing was cranking!

There is a ton of extra Co2. The oft-cited rule of thumb is you get about 1 volume of Co2 from every 2 gravity points drop. So if a 5 gallon batch ferments from 1.070 to 1.016, you'll have enough Co2 to purge about 27 5 gallon kegs (i.e. (70-16)/2).

The hard part is storing that much Co2 at or near atmospheric pressure (i.e. 0-30 psi).
 
Last edited:

Terpene

Supporting Member
HBT Supporter
Joined
Feb 1, 2019
Messages
97
Reaction score
70
Assuming a 20 L batch size for simplicity. Assuming 1.060 OG gives ~6.5% ABV beer.

That gives 1.3 L of ethanol, which is about 1026 grams of ethanol, which is about 22.3 moles of ethanol, which gives us 22.3 moles of CO2.

At 68 F (20 C), an ideal gas occupies about 24 L per mole.

22.3 mol x 24 L/mol = ~535 L of CO2 or 141 gallons of CO2.

No need to bother with further calculations of headspace and dissolved CO2, as 141 gallons is over 28 kegs worth of CO2.

Fairly close to StayThirsty's rule of thumb.
 
OP
W

Wables

Well-Known Member
Joined
Oct 22, 2006
Messages
313
Reaction score
143
Location
Duluth, MN
So in theory, if you brewed a batch every 4 or 5 days, you could run your fermenter at 12ish psi and run your kegerator with lots of CO2 left over.

Perhaps you could run your fermenter at 30 psi and tie in a well water tank into the CO2 system. You wouldn’t need to force carb and would probably have enough serving CO2 to only need to brew once every couple weeks.
 
Last edited:

jseyfert3

Well-Known Member
Joined
Apr 6, 2020
Messages
304
Reaction score
133
Location
South-Central Wisconsin
If a brewer thinks they can know the ABV of their beer, then they better also think they can know the amount of CO2 produced in their fermentation, because otherwise they would be arguing against conservation of mass, and nobody should do that.
Exactly this. This came up in another thread and after one person went into detailed math, I did a ballpark calculation based on change in specific gravity assuming volume stayed constant and the mass change almost exactly equaled the mass of CO2 he calculated in a way similar to what you did. This makes sense because of the conservation of mass. If you know the SG and volume before and after fermentation, and assuming only CO2 is produced as a gas, then the change in mass of the liquid measured by change in SG is going to be the mass of CO2 produced during fermentation. If you had a sensitive enough scale you could just weigh the fermenter before and after and directly measure this, but measuring SG is probably going to be easier.

There will be some loss of water vapor as well some other negligible vapors, but these are going to be very small as a percentage of CO2 produced.
 

McMullan

wort maker
Joined
Dec 22, 2015
Messages
355
Reaction score
327
Yes, mass loss is a better measure than ‘ABV’, as it doesn’t assume (like idealised textbook models) all glucose metabolised is associated with ethanol or CO2 production. But it requires high end equipment to measure accurately. Either way, we’re left with reasonable guesstimates, like a 'shed load'.

To summarise:

PE = SL

Where PE is Plain English, the most effective form of communication, even among home brewers; and SL is Shed Loads, confirmed as being more than enough for the OP’s strategy.

It’s important to embrace neurodiversity, of course. In all its dazzling glory.
 

McMullan

wort maker
Joined
Dec 22, 2015
Messages
355
Reaction score
327
Yeah, and skipped the very important introductory section on 'limitations'. Assuming the authors understood the limitations themselves. A potential measure of something there, I guess. Reminds me of those ridiculous digital burp-counting airlocks that at least two firms pitched to the home brew market a few years ago. I think they read the same textbook and figured, quite naively, evolved CO2 was a good surrogate for predicting fermentation therefore ABV. Guess who correctly predicted how shite they were going to be, before they were rolled out? ;)
 

jseyfert3

Well-Known Member
Joined
Apr 6, 2020
Messages
304
Reaction score
133
Location
South-Central Wisconsin
I mean not everything in life needs to be measured on a mass spectrometer to get numbers well within the ballpark or even highly accurate ones.
 
OP
W

Wables

Well-Known Member
Joined
Oct 22, 2006
Messages
313
Reaction score
143
Location
Duluth, MN
OP here. The new all-rounders have been great. My 10 year old checks them every couple hours and reports on the yeast progress. I’m going to have to buy him a couple of Tilts for Christmas and pair them to his iPad. To settle this ABV measurement discussion, I suggest we agree on a new measurement, such as PTS (pints to shitfaced).
 

micraftbeer

Supporting Member
HBT Supporter
Joined
Dec 30, 2015
Messages
622
Reaction score
303
Location
Farmington Hills, MI
But what I'm really hoping for more than anything, is someone to come in and post something that contradicts both the "equation science camp" and the "esoteric science camp" and definitely claims the OP won't make enough CO2!
 
OP
W

Wables

Well-Known Member
Joined
Oct 22, 2006
Messages
313
Reaction score
143
Location
Duluth, MN
I can definitely say that I made so much CO2 I’m thinking of ways to harvest it.
 

McMullan

wort maker
Joined
Dec 22, 2015
Messages
355
Reaction score
327
I suggest we agree on a new measurement, such as PTS (pints to shitfaced).
Sounds like a perfectly acceptable measure to me. Probably more accurate than my p*ssed hydrometer.
 

McMullan

wort maker
Joined
Dec 22, 2015
Messages
355
Reaction score
327
I can definitely say that I made so much CO2 I’m thinking of ways to harvest it.
Daisy chain as many empty kegs as you can. I cranked up the spunding pressure to about 30psi to get a good carbonation level towards the end of fermentation.
 

Gnomebrewer

Well-Known Member
Joined
Jul 9, 2014
Messages
2,811
Reaction score
1,595
Location
Hobart
Well I do like a maths question! Yes, I'm aware that the question is already answered (there is enough CO2), but to put a rough figure on the amount (there are some simplifications and I've made some assumptions, but should be in the ballpark).......

A 1.060 beer, fermented to 1.010 uses 50 points of gravity. That equates to about 1.25Kg of fermented sugar per 10L.
5.5 gallons is about 22L or 2.2cl.
2.2cl x 1.25Kg/cl = 2.75Kg of fermented sugar (glucose).
Glucose has a mass of about 180g/mol.
2.75Kg/0.18Kg = about 15 moles of fermented glucose.
Each mole of glucose gives 2 moles of CO2, so that's about 30 moles of CO2.
CO2 has a mass of about 44g/mol, so 30 moles has a mass of about 30mol x 44g/mol = about 1300g, or 1.3Kg (2.86lbs). So a bit over half a 5lb CO2 cylinder!
In volume terms, 1 mole of gas at stp has a volume of 22.4L, so 30 moles of CO2 is between 600 and 700L!!!
Assuming my maths is correct. Which it probably isn't. Let me know if I've made a mistake and I'll be suitably embarrassed!

TLDR: 5.5 gallons of1.060 beer fermented to 1.010 produces about 1.3Kg/2.86lbs or 600-700L (150 to 170 gallons) of CO2.
 

Terpene

Supporting Member
HBT Supporter
Joined
Feb 1, 2019
Messages
97
Reaction score
70
TLDR: 5.5 gallons of1.060 beer fermented to 1.010 produces about 1.3Kg/2.86lbs or 600-700L (150 to 170 gallons) of CO2.
Yup, sounds about right. :yes:

My numbers were a bit different, but it's in the ballpark. Remember, for gases, STP is 0 Celsius -- at room temp, volume will be greater than 22.4 L.

I came up with 22.3 moles of CO2 for a 20 L batch, with slightly different assumptions than yours. Both ways get a decent ballpark number.
 
Last edited:
Top