Brainstorming about ways of recapturing CO2 from fermentation

[Justin Dean]

I daisy chain my kegs and purge from the co2 from fermenter. All works fine . Sounds like I making mistake by doing that and beer would be better purging kegs from food grade co2 canister? How would co2 from fermenter reach that grade? Some sort of charcoal scrub?

 

[Agentgonzo]

I daisy chain my kegs and purge from the co2 from fermenter. All works fine . Sounds like I making mistake by doing that and beer would be better purging kegs from food grade co2 canister? How would co2 from fermenter reach that grade? Some sort of charcoal scrub?

I don't see a problem in purging using the CO2 from the fermenter. Plenty of other people do it. When the beer goes into the keg it'll displace all the CO2 anyway. What's wrong with the CO2 produced by fermentation that you're concerned about???

 

[Clint]

Doesn't Co2 absorb in the beer at very low temps?
Many times I've seemingly had a pressure barrel go "flat" but it was due to the outside temp dropping to freezing.

 

[Jim Brewster]

Doesn't Co2 absorb in the beer at very low temps?
Many times I've seemingly had a pressure barrel go "flat" but it was due to the outside temp dropping to freezing.

Yes. It's a function of temperature and pressure, so chill the beer or increase the pressure and more CO2 can absorb /dissolve. Conversely when you release the pressure or warm it, the CO2 is less soluble and comes out of solution as gas bubbles.

...however it gets a bit less clear cut when you chill a beer post fermentation as it was already in equilibrium at the higher temperature. It all gets a bit confusing when you calculate priming sugar and which temperature to use I usually just say it'll be fine

 

[RoomWithABrew]

Don't forget the rapid diffusion that will occur across your " bag ", won't be long before you have a bag with CO2, Oxygen and Nitrogen in it.

Given time it will contain something called air!
Diffusion gradient remains the same I think regardless of the pressure in the bag which is barely above atmospheric.

 

[Hacksawbob]

If I was to do it, and I have thought about it. For example to purge a keg prior to filling. I would fill the keg with water and a sodium met tab. Displace the water via gas in. Probably best to daisy chain a second keg to product port with a spunding valve to back pressure say 5psi. So at the end you will have a CO2 purged keg ready to fill. There are other byproducts of fermentation (esters/alcohols) that would be captured, but these would be released from the keg on fill, possibly reabsorbed though. Might save yourself a some CO2 over time

If you want to know how a commercial brewery does it on a 'small scale' Eddie Gadd's blog goes into detail.
http://gaddsbeershop.blogspot.com/2022/09/co-2-capture-in-small-brewery-acase.html?m=0

 

[Doddybrewer]

Take a look at Henry's Law

Henry's Law​

Pressure has very little effect on the solubility of solids or liquids, but has a significant effect on the solubility of gases. Gas solubility increases as the partial pressure of a gas above the liquid increases. Suppose a certain volume of water is in a closed container with the space above it occupied by carbon dioxide gas at standard pressure. Some of the CO2CO2 molecules come into contact with the surface of the water and dissolve into the liquid. Now suppose that more CO2CO2 is added to the space above the container, causing a pressure increase. In this case, more CO2CO2 molecules are in contact with the water and so more of them dissolve. Thus, the solubility increases as the pressure increases. As with a solid, the CO2CO2 that is undissolved reaches an equilibrium with the dissolved CO2CO2, represented by the equation:



CO2(g)⇌CO2(aq)


At equilibrium, the rate of gaseous CO2CO2 dissolution is equal to the rate of dissolved CO2CO2 coming out of the solution.

When carbonated beverages are packaged, they are done so under high CO2CO2 pressure so that a large amount of carbon dioxide dissolves in the liquid. When the bottle is open, the equilibrium is disrupted because the CO2CO2 pressure above the liquid decreases. Immediately, bubbles of CO2CO2 rapidly exit the solution and escape out of the top of the open bottle. The amount of dissolved CO2CO2 decreases. If the bottle is left open for an extended period of time, the beverage becomes "flat" as more and more CO2CO2 comes out of the liquid.

The relationship of gas solubility to pressure is described by Henry's law, named after English chemist William Henry (1774-1836). Henry's Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. Henry's law can be written as follows:



S1/P1=S2/P2


S1 and P1 are the solubility and the pressure at an initial set of conditions; S2 and P2 are the solubility and pressure at another changed set of conditions. The solubility of a gas is typically reported in g/L.

​

 

[MashBag]

I have recycled bottled gas from corny to corny with a gas to gas fitting.

You could collect and then compress (perhaps a car compressor) with 2 cornies upto about 4 or 5 bar. But that won't help the purity.

 

[Agentgonzo]

You could collect and then compress (perhaps a car compressor) with 2 cornies upto about 4 or 5 bar. But that won't help the purity

I looked at these options. Car compressors take in from the surrounding air, so it would be hard to compress the CO2 and not air.

You would also need to probably add HEPA filters etc as car compressors can add all sorts of impurities, oils etc as they are not design to be food safe.

 

[Justin Dean]

I don't see a problem in purging using the CO2 from the fermenter. Plenty of other people do it. When the beer goes into the keg it'll displace all the CO2 anyway. What's wrong with the CO2 produced by fermentation that you're concerned about???

I am not but on this thread some suggest it is bad co2

 

[Agentgonzo]

I am not but on this thread some suggest it is bad co2

There are different kinds of CO2?

 

[Justin Dean]

Read up the thread about nasty co2 from the fermenter

 

[Sadfield]

BBC Bitesize: Pure Substances

 

[Hacksawbob]

It's not ideal as it contains esters and alcohols you would have vented from the fv normally. It would need to be scrubbed, dried, compressed, frozen and packaged to get 'pure' CO2.

 

[Justin Dean]

Not enough to make any difference. Ultamately it up to the brewer. Do not need to be a chemist to brew beer

 

[Sadfield]

You don't need tastebuds to drink beer.

Again, why would you want to force carbonate with contaminated CO2?

 

[evil.soup]

Take a look at Henry's Law

Henry's Law​

Pressure has very little effect on the solubility of solids or liquids, but has a significant effect on the solubility of gases. Gas solubility increases as the partial pressure of a gas above the liquid increases. Suppose a certain volume of water is in a closed container with the space above it occupied by carbon dioxide gas at standard pressure. Some of the CO2CO2 molecules come into contact with the surface of the water and dissolve into the liquid. Now suppose that more CO2CO2 is added to the space above the container, causing a pressure increase. In this case, more CO2CO2 molecules are in contact with the water and so more of them dissolve. Thus, the solubility increases as the pressure increases. As with a solid, the CO2CO2 that is undissolved reaches an equilibrium with the dissolved CO2CO2, represented by the equation:



CO2(g)⇌CO2(aq)


At equilibrium, the rate of gaseous CO2CO2 dissolution is equal to the rate of dissolved CO2CO2 coming out of the solution.

When carbonated beverages are packaged, they are done so under high CO2CO2 pressure so that a large amount of carbon dioxide dissolves in the liquid. When the bottle is open, the equilibrium is disrupted because the CO2CO2 pressure above the liquid decreases. Immediately, bubbles of CO2CO2 rapidly exit the solution and escape out of the top of the open bottle. The amount of dissolved CO2CO2 decreases. If the bottle is left open for an extended period of time, the beverage becomes "flat" as more and more CO2CO2 comes out of the liquid.

The relationship of gas solubility to pressure is described by Henry's law, named after English chemist William Henry (1774-1836). Henry's Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. Henry's law can be written as follows:



S1/P1=S2/P2


S1 and P1 are the solubility and the pressure at an initial set of conditions; S2 and P2 are the solubility and pressure at another changed set of conditions. The solubility of a gas is typically reported in g/L.

​

I have little to add to the argument, other than, what a brilliant post! It kind of sums up why I'm enjoying brewing so much, who knew there was so much science involved!

Yes, I'm a bit of a geek!

 

[MashBag]

I looked at these options. Car compressors take in from the surrounding air, so it would be hard to compress the CO2 and not air.

Put it in the collecting vessel and reverse the safety valve.

 

[hoppyscotty]

Not true. It will be absorbed under standard pressure... Just not a lot

But the beer will have absorbed as much co2 as it can in the fermenter so transferring to a keg and attaching a bag full of co2 won’t absorb any more co2. You can cool the beer and it will absorb more co2 of course assuming you didn’t cold crash in the fermenter, but it won’t be carbonated.

Best thing to do is to use the co2 to push starsan out of a keg to purge it and maybe vent it into a greenhouse if you have one close as plants love co2.

 

[RoomWithABrew]

Best thing to do is to use the co2 to push starsan out of a keg to purge it and maybe vent it into a greenhouse if you have one close as plants love co2.

If you can spund the fermenter and carbonate, purge your receiving keg of starsan and pressure it to the same level as you are spunding.
Disconnect the keg and then cold crash, pressure will be lower post cold crash than in keg. Use liquid to liquid and gas to gas with a height difference and then you'll have perfectly carbed beer cleared into your keg and some gas in the fermenter to use to draw off the first few pints with.

I believe that plants need oxygen at night, so either leave the lights on in your greenhouse or turn the CO2 off at night.