Collecting CO2 From Fermentation

[cactusgarrett]

I recently gave a listen to the Brulosophy podcast episode on reducing cold side oxidation, and in an effort to improve my processes, I keep coming back to one of their suggestions on collecting fermentation CO2 for later use in kegging or cold crashing. I'm hung up on one aspect, however, and I was hoping someone had some experience with it.

One of the guys' suggestions for reducing oxidation at kegging, was to package into a CO2-filled/purged keg. To do this without wasting a ton of purchased gas each time, they suggested collecting CO2 from fermentation by means of first filling a keg of star-san, then having fermentation push that out, thus filling the keg for later use.

The issue eating at my brain is this: can the pressure of fermentation actually move 5 gallons of liquid from a keg somewhat easily? If it can, how much back-pressure would 5 gallons of liquid generate and would it have an impact on fermentation? I would imagine some yeast strains are more susceptible to back-pressure (can't remember if it was a specific saison strain, Denny's Fav, etc.), as i know there are a number of accounts of people needing to ferment without an airlock to prevent a stall.

 

[Vale71]

A 5 gal keg ist about 0,56 meters tall, this will generate a pressure of about 0,05 bar or 50 millibar. However this will only last until all liquid has been purged, once CO2 starts being released the pressure will go down to near zero depending on how you set up your blowoff.
BTW you don't need a ton of bottled CO2 to purge the same keg, at 1 bar overpressure you'll need only 3.9 g/l or 74 g for a 19 liter keg, hardly a ton...
An airlock on the other hand will generate only about 1-2 millibar of pressure, the idea that this might cause a fermentation to stall is pure, unadulterated bullcrap.

 

[bracconiere]

The issue eating at my brain is this: can the pressure of fermentation actually move 5 gallons of liquid from a keg somewhat easily?

depends on your fermenter.....but the yeast can....they can blow up bottles, i'm sure they can push a keg, as long as your fermenter can hold the pressure

 

[cactusgarrett]

the idea that this might cause a fermentation to stall is pure, unadulterated bullcrap.

Appreciate the math, but easy, man. I was just throwing out some ideas/thoughts and asking if it would have an impact. Considering people have commented that certain yeast strains benefit from not using an airlock during fermentation, it would stand to reason that 50 millibar > 1-2 millibar is worth some consideration.

 

[bracconiere]

Appreciate the math, but easy, man. I was just throwing out some ideas/thoughts and asking if it would have an impact. Considering people have commented that certain yeast strains benefit from not using an airlock during fermentation, it would stand to reason that 50 millibar > 1-2 millibar is worth some consideration.

i hope no one bottle's with these yeast strains?

 

[LittleRiver]

Filling a keg with StarSan and pushing it out is one way, but it's not the only way.

There's no need to completely fill the keg with StarSan. Just give it a normal sanitizing rinse of SS, drain it all out, then let fermentation purge the keg. This post shows my rig for doing that (& preventing suck back of air during cold crashing).

@doug293cz did the math to show that fermentation does indeed produce enough gas to effectively purge an empty keg in this post.

 

[kevink]

To do this without wasting a ton of purchased gas each time, they suggested collecting CO2 from fermentation by means of first filling a keg of star-san, then having fermentation push that out, thus filling the keg for later use.

I don't see the point as CO2 is so freaking cheap. One 20lb tank, which costs around $25, lasted me through 19 10 gallon batches. With that one tank, I purged all 38 kegs prior to filling, pressure transferred every batch, crashed every batch under CO2 pressure, partially carbonated all 38 kegs, purged growlers, and probably did other things with it that I can't remember during that time period. It is totally not worth the hassle of trying to use CO2 from fermentation in my opinion. It seems like it's a solution to a problem that does not exist.

Even if I ONLY purged the 38 kegs with that one tank, it only would have cost 65 cents per keg to purge. Is that worth trying to save?

 

[LittleRiver]

... It is totally not worth the hassle of trying to use CO2 from fermentation in my opinion. It seems like the solution to a problem that does not exist.

I've done it both ways. I no longer use pressurized gas for purging kegs, because capturing fermentation gas is LESS hassle.

To purge a keg I just pop the airlock onto the gas post of the keg, and pop the line coming from the top of the fermenter onto the other post. That's it -- that's all there is to collecting fermentation gas in a keg.

To transfer beer I pop off the airlock, move the line coming from the top of the fermenter over to the gas post, and connect a drain hose from the fermenter spigot to the keg beer post.

This truly is less hassle than messing with a CO2 tank, etc.

 

[cactusgarrett]

Thanks guys. Yeah, cost isn't the issue, as much as taking the time to get it filled.
LittleRiver - yeah, i saw that post on the LODO website, and my takeaway was that just having fermentation blow off into the keg wasn't sufficient, since O2/CO2 will mix too much. Maybe I misread that, though. However, I'm likely overthinking it since I'm not running LODO-dedicated, and just trying to minimize oxidation in my hoppy beers to begin with.

 

[cactusgarrett]

i hope no one bottle's with these yeast strains?

Stalled fermentation and bottle conditioning are different issues.

 

[bracconiere]

Stalled fermentation and bottle conditioning are different issues.

high FG, or flat beer?

 

[RPh_Guy]

The pressure from an airlock is negligible and has absolutely no effect on fermentation.
What removing the airlock does do is introduce oxygen, which is why some people report more success with it for certain finicky stains prone to stalling.

 

[cactusgarrett]

high FG, or flat beer?

You're essentially suggesting whenever someone has a stalled fermentation they won't be able to bottle condition without re-yeasting, and I'd hardly consider this to be the norm. Please stay on point with this discussion, though.

 

[cactusgarrett]

The pressure from an airlock is negligible and has absolutely no effect on fermentation.
What removing the airlock does do is introduce oxygen, which is why some people report more success with it for certain finicky stains prone to stalling.

Good point. I thought, though, it had more to do with some next-level physical property like off-gassing the CO2 more readily. But i digress.

 

[bracconiere]

You're essentially suggesting whenever someone has a stalled fermentation they won't be able to bottle condition without re-yeasting, and I'd hardly consider this to be the norm. Please stay on point with this discussion, though.

lol, that's why i came back so soon....if your fermenter has a tight enough seal, i'm sure the yeasties can push 5 gal of star san out the port.....they can build enough pressure in a bottle to carbonate it so, i wouldn't be worried about any of that other stuff...

 

[kevink]

To purge a keg I just pop the airlock onto the gas post of the keg, and pop the line coming from the top of the fermenter onto the other post. That's it -- that's all there is to collecting fermentation gas in a keg.

You are not guaranteed that's going to fully purge the keg of O2, so we're talking apples to oranges here.

This truly is less hassle than messing with a CO2 tank, etc.

Not for me as I have a dedicated tank near my fermenter. There is no "messing" with it. We are both just attaching hoses.

 

[LittleRiver]

...LittleRiver - yeah, i saw that post on the LODO website, and my takeaway was that just having fermentation blow off into the keg wasn't sufficient, since O2/CO2 will mix too much....

Read the last section of Doug's post I linked to above. He addresses the mixing, and found that the volume of gas produced is sufficient to reduce O2 to 5 parts per billion.

It works. I've been getting great aroma/flavor stability with kegs that have been purged with fermentation gas.

 

[Vale71]

Again, this "my airlock caused my ferment to stall with yeast strain XYZ" is just nonsense. Unfortunately some people are so attached to it that they will invent all sort of pseudo-scientific explanations to support something that simply does not exist.
And of course primary fermentation and bottle carbonation are exactly the same, you have the same yeast stalling because of 1-2 millibar overpressure on the one hand and on the other hand the same yeast eats away the priming sugar although pressure in the bottle easily reaches 3000 millibar or more. Please...

 

[cactusgarrett]

And of course primary fermentation and bottle carbonation are exactly the same

So show me the correlation of every stuck fermentation to failed bottle condition attempts.

 

[Vale71]

Are you serious?? There is no correlation because there is no correlation at all between pressure in the vessel and stuck fermentation, it's all just a stupid myth born out of utter ignorance.
Those who claim that "my fermentation would have gotten stuck had I not left the FV without an airlock" and then think nothing of the same yeast performing bottle conditioning flawlessy at pressures that are thousands of times higher than what they would have experienced in primary with an airlock on are simply as clueless about what they're doing as the next piece of rock. If what those people claim were even remotely based on actual facts then bottle conditioning with these yeast strains would have to fail each and every time, which is obviously not the case...

 

[Gnomebrewer]

If what those people claim were even remotely based on actual facts then bottle conditioning with these yeast strains would have to fail each and every time, which is obviously not the case...

I'm not disagreeing with you about the concept (I can't see an airlock making a difference or causing a stalled ferment) but there are differences between primary ferment and bottle conditioning that may potentially cause a difference - primary fermentation includes a range of sugars (glucose, maltose, maltotriose etc.) that make the yeast work harder, while bottle conditioning is typically only sucrose or glucose. So there is a possibility (until I see a study proving otherwise) that a small amount of oxygen in primary could help the ferment while it's not needed for bottle conditioning. Also, a significant amount of oxygen gets into bottles during bottling - probably more than an open hole on a fermentor allows in. To study this fairly, one would need to bottle in a completely purged environment (very difficult) using malt extract for priming to see if full carbonation still occurred.

 

[LittleRiver]

You are not guaranteed that's going to fully purge the keg of O2, so we're talking apples to oranges here.

Beverage grade bottled CO2 is 99.9% pure, or .1% impure. Doug's calculation (even if it's only a close approximation) definitely puts purging by fermentation gas in the same league. It's an apples to apples comparison.

Not for me as I have a dedicated tank near my fermenter. There is no "messing" with it. We are both just attaching hoses.

You're leaving out some things. Sure, we're both moving hoses, but I only have hoses between my two vessels (fermenter & keg), I don't have a need for the third vessel of CO2. Since I don't need it, I don't have to buy it, buy a regulator for it, get it filled, fix leaks, etc.

There's definite advantages to using fermentation gas to purge kegs.

 

[kevink]

And it all seems to be about saving pennies. That's why big breweries harvest CO2. If I had to worry about how little to spend on this hobby it would suck all the fun out of it!

You can believe whatever you would like to believe, but until someone actually tests the purity of the CO2 in a keg purged with fermentation CO2, there is no way in hell I'm trusting the math in that other thread (No offense to doug. I just have no desire to check it, which is what I would do if I cared to use that method).

After a quick skim of it, I didn't see anything about the fact that the fermenter headspace originally contained air. Was that taken into consideration? Maybe I missed it, but again, I have no desire to use that method for a number of reasons, so I didn't go through it in detail.

 

[wstumper]

After a quick skim of it, I didn't see anything about the fact that the fermenter headspace originally contained air. Was that taken into consideration? Maybe I missed it, but again, I have no desire to use that method for a number of reasons, so I didn't go through it in detail.

It's hard to believe that the out gassing occurring during fermentation is pure CO2...as opposed to what comes out of a CO2 bottle. Surely the CO2 generated during fermentation is picking up some other particles or molecules.

Of interest regarding CO2 reuse:

CO2 Recovery System Saves Brewers Money, Puts Bubbles into Beer

https://spinoff.nasa.gov/Spinoff2016/cg_3.html

 

[LittleRiver]

And it all seems to be about saving pennies. That's why big breweries harvest CO2. If I had to worry about how little to spend on this hobby it would suck all the fun out of it!

For me it's not about saving pennies. As I stated earlier, I've done it both ways. After trying out harvesting fermentation gas I stopped using bottled gas for that purpose. Harvesting is easier, and to me it's actually more fun -- I enjoy the elegant efficiency of it.

You can believe whatever you would like to believe, but until someone actually tests the purity of the CO2 in a keg purged with fermentation CO2, there is no way in hell I'm trusting...

Nobody is asking you to trust anything. Nobody is asking you to harvest fermentation gas.

I'm just stating that harvesting gas works, and it works well. Well enough that I stopped using bottled gas for purging kegs.

 

[kevink]

It's hard to believe that the out gassing occurring during fermentation is pure CO2...as opposed to what comes out of a CO2 bottle. Surely the CO2 generated during fermentation is picking up some other particles or molecules.l

You would sure think so. Even if it was pure CO2, the fermenter headspace would have to be completely purged of O2 before what was coming out of your fermenter was pure CO2.

But like you said, the CO2 is probably picking up other stuff on the way up through the beer. Is it just speculation that the CO2 produced during fermentation is pure or has someone actually tested it? Before that's done, I see no reason to believe it's any more pure than bottled gas.

 

[doug293cz]

...

After a quick skim of it, I didn't see anything about the fact that the fermenter headspace originally contained air. Was that taken into consideration? Maybe I missed it, but again, I have no desire to use that method for a number of reasons, so I didn't go through it in detail.

Sorry, but skimming my post on purging with fermentation CO2 will cause you to miss important details. The math assumes both the headspace and keg contain air at the beginning, and also assumes that the CO2 coming out during fermentation completely mixes with the gas in the headspace and keg (which is the worst case situation.) In reality, there will not be complete mixing, and the purging will be even more effective than the calculation shows.

Yes, there are surely other gases that come off during fermentation, but remember, all those other gases started in the beer, and were off-gased because the concentration in the beer and the partial pressure in the headspace were not in equilibrium (there was excess concentration in the beer.) Because of that, you will not get reabsorption of the contaminant gases into the beer during kegging.

Brew on

 

[Bilsch]

It's hard to believe that the out gassing occurring during fermentation is pure CO2...as opposed to what comes out of a CO2 bottle. Surely the CO2 generated during fermentation is picking up some other particles or molecules.

Might be hard to believe but still true. In regards to oxygen contamination, fermentation derived CO2 is far superior to bottled gas. Industrial ethanol production is the best/cheapest source for low O2 carbon dioxide.

 

[Vale71]

So there is a possibility (until I see a study proving otherwise) that a small amount of oxygen in primary could help the ferment while it's not needed for bottle conditioning.

With the same logic you could say that you firmly believe that dragons could exist until someone publishes a study proving otherwise. Sorry, but that is not how science works. Until you have proof a hypothesis is nothing more than an unproven idea.
Incidentally, there are tons of studies measuring O2 levels during beer production and levels during fermentation are always extremely low, regardless of fermenter type. That's a good thing too as the only thing you would get from oxygen exposure is staling of the beer. There are also a ton of studies on the different causes for stalled fermentation and not one of them mentions ridiculously low pressures or lack of O2 as being responsible.

 

[Vale71]

And it all seems to be about saving pennies. That's why big breweries harvest CO2.

Actually, saving fermentation CO2 is on average more expensive than buying it bottled. For small breweries it's even prohibitively expensive as the gear requires an investment upwards of a million dollars.