Purging Keg Through Fermentation - Not Working

[chieftain]

So I'm taking my first stab at spunding, aiming to dry hop under pressure. My problem is that I tried to harness the C02 from my carboy fermenter to purge the serving keg, but it did not work.

I brewed an NE IPA variant last Wednesday, the 21st. Temp controlled fermentation at 66 for first 3 days. Using 1318, had a vigorous ferment that required a blow off tube. Yesterday I replaced the blow off tube with basically a keg jumper from the carboy to the liquid in post on the serving keg. I did this by inserting a barb into a drilled bung, then screwed one end of the jumper onto the barb and inserted it into the carboy cap (using a BMB).

I've used this same bung-barb set up to push beer out for closed transfers, so I know it works for that purpose. But it doesn't seem to be pushing much, if any, C02 into the keg. I attached a spunding valve onto the gas in post on the keg to monitor pressure and it never budged off 0. When I released the PRV after 12 hours, it let out just a faint hiss of gas. I've pressurized the keg using my regular C02 source, so it is not leaking.

Any ideas as to what I'm doing wrong?

 

[Smellyglove]

If I'm reading this correctly you used a jumper between the fermenting beer and a keg?

The pressure from a fermenting beer isn't very great, and the keg is a solid keg (it's not a plastic bag). So you can't push much co2 into a sealed keg.

What's happening is all the pressure build-up is being equally distributed between your fermenter and the keg, and also being diffused into the beer. So you're basically just carbonating the beer with a big headspace. To harvest the gas I'm guessing you should use some kind of flexible container. If you'd use a balloon or such, the ballon would inflate, then any excess co2 would be absorbed into the beer in the fermentor, unless the pressure is so big that the ballon would burst in the end.

 

[vtipsy]

1) You're too late and and the beer had already fermented out
or
2) There is a leak

 

[chieftain]

1) You're too late and and the beer had already fermented out
or
2) There is a leak

I put a 3 piece airlock on the carboy this evening and it's bubbling still, but not much. Fermentation definitely more vigorous yesterday when I had the jumper on it. I guess I needed to get those first 2 days worth of C02. Will double check all seals to be safe.

 

[chieftain]

If I'm reading this correctly you used a jumper between the fermenting beer and a keg?

The pressure from a fermenting beer isn't very great, and the keg is a solid keg (it's not a plastic bag). So you can't push much co2 into a sealed keg.

What's happening is all the pressure build-up is being equally distributed between your fermenter and the keg, and also being diffused into the beer. So you're basically just carbonating the beer with a big headspace. To harvest the gas I'm guessing you should use some kind of flexible container. If you'd use a balloon or such, the ballon would inflate, then any excess co2 would be absorbed into the beer in the fermentor, unless the pressure is so big that the ballon would burst in the end.

Thanks for the feedback. Yes, you've got it right. I think I overestimated how much C02 would be generated at the tail end of ferment.

 

[Smellyglove]

Thanks for the feedback. Yes, you've got it right. I think I overestimated how much C02 would be generated at the tail end of ferment.

It's just not about how much co2 is being produced. (A noticeable amount is being produced, even after initial krause). But also where it ends up. As I said you're distributing the co2 between the fermentor, the keg, and into the beer. Since the keg can't expand the excess co2 is going into the beer as carbonation.

 

[mongoose33]

I've tried to pull CO2 back into my fermenter when I cold crash. It worked one time, the other times it does not. My only guess about why is that there's a tiny leak that relieves the partial vacuum formed when the headspace cools. That is, the headspace isn't cooling fast enough to create a strong enough partial vacuum to pull the CO2 back. That minute leak, I theorize, simply fills the headspace.

I wonder if you have a similar issue going on.

 

[chieftain]

It's just not about how much co2 is being produced. (A noticeable amount is being produced, even after initial krause). But also where it ends up. As I said you're distributing the co2 between the fermentor, the keg, and into the beer. Since the keg can't expand the excess co2 is going into the beer as carbonation.

The keg had barely any C02 in it, based on the lack of hiss when I pulled the PRV. Is there a way to change the set-up so that C02 flows into the keg?

Edited to add - this was the post that got me thinking about this idea: https://www.homebrewtalk.com/forum/threads/keg-purging-with-active-fermentation.628658/#post-8004741. I missed the part where the author described using an airlock on the gas-in post as part of purging the keg. I assume a tube into a jar of sanitizer would serve the same purpose, since I don't have an airlock fitting for my keg (yet).

 

[vtipsy]

There are two things going on here:

- Purging a serving keg with c02 from fermentation.
- Carbonating the beer with c02 from fermentation (spunding).

Your carboy + bung to keg set up will purge the keg but it wont carbonate it by spunding. The bung won't hold the required pressure.

If you want to spund, what you need to do is this. As soon as the blow off tube stops spewing krausen hook up your carboy to the liquid keg post. Run a piece of tube from the keg gas post to a cup of sanitizer. It will bubble away while fermentation continues and will purge the keg with pure c02; each bubble that escapes will have diluted the amount of oxygen in there.

Then when there are 4 to 6 gravity points of extract remaining, transfer the beer to the keg and seal it up. Attach the spunding valve to the gas post, set the valve to achieve your desired level of carbonation and let the beer ferment to completion. Be mindful that spunding valves can get very leaky (don't assume otherwise).

 

[murphyslaw]

I've tried to pull CO2 back into my fermenter when I cold crash. It worked one time, the other times it does not. My only guess about why is that there's a tiny leak that relieves the partial vacuum formed when the headspace cools. That is, the headspace isn't cooling fast enough to create a strong enough partial vacuum to pull the CO2 back. That minute leak, I theorize, simply fills the headspace.

I wonder if you have a similar issue going on.

So you purged the keg with fermentation gas, left it hooked up, and when you cold crashed it didn't just pull that co2 back in? That's really disappointing. I plan to try the fermentation purge and hoped it would also let me cold crash without o2 suck back.

 

[mongoose33]

So you purged the keg with fermentation gas, left it hooked up, and when you cold crashed it didn't just pull that co2 back in? That's really disappointing. I plan to try the fermentation purge and hoped it would also let me cold crash without o2 suck back.

No, I've used the two-jar system to try to draw CO2 back. They're two different approaches, but when I tried the 2-jar system I couldn't get it to work right except once.

There has to be a tiny leak in my setup somewhere to prevent it from working, and I was suggesting a similar situation here, i.e., tiny leak that is releasing some pressure during the active fermentation, preventing there being enough pressure to purge the keg.

BTW, I use those jars from time to time as an airlock as one of my ferm chambers isn't large enough to allow for an airlock; I pass the fermentation gases out of the ferm chamber into the jars as airlock, or into a keg to purge. The interesting thing is that I can feed that gas into a 1- or 2-jar system as an airlock, use it to purge a keg, or whatever.

Here's what the 2-jar approach looks like, the one time it worked on cold crashing. The left jar has the CO2 line from the fermenter going into it. It pushes the air out of that jar into the second, which is filled with star-san. During active fermentation, the left jar is empty, the right one is bubbling away.

When crashing, the partial vacuum created in the headspace draws the CO2 in the left jar back into the fermenter; it's replaced by pulling the star san from the right jar into the left jar, maintaining the air seal.

As I noted, it only worked correctly once; the rest of the time, there's a leak somewhere that relieves the partial vacuum preventing the drawing back of liquid from right jar to the left jar.

 

[murphyslaw]

No, I've used the two-jar system to try to draw CO2 back. They're two different approaches, but when I tried the 2-jar system I couldn't get it to work right except once.


View attachment 559854

Gotcha. Thanks!

 

[chieftain]

There are two things going on here:

- Purging a serving keg with c02 from fermentation.
- Carbonating the beer with c02 from fermentation (spunding).

Your carboy + bung to keg set up will purge the keg but it wont carbonate it by spunding. The bung won't hold the required pressure.

If you want to spund, what you need to do is this. As soon as the blow off tube stops spewing krausen hook up your carboy to the liquid keg post. Run a piece of tube from the keg gas post to a cup of sanitizer. It will bubble away while fermentation continues and will purge the keg with pure c02; each bubble that escapes will have diluted the amount of oxygen in there.

Then when there are 4 to 6 gravity points of extract remaining, transfer the beer to the keg and seal it up. Attach the spunding valve to the gas post, set the valve to achieve your desired level of carbonation and let the beer ferment to completion. Be mindful that spunding valves can get very leaky (don't assume otherwise).

Thanks, I missed the window to spund this one, have plans to do so next time.

 

[MSK_Chess]

We really need to be careful not to miss the spund window. While most of the advice is fine for Lager yeasts it must be noted that they have a tendency to stay in suspension longer than ale yeasts, especially British ale yeasts and I have learned to my detriment that ts best to err on the side of caution rather than rely purely on gravity readings. In other words if using a British ale yeast I transfer probably just after high krausen as it has a tendency to drop fast. I also make sure to 'catch', a little of the yeast during transfer to facilitate the fermentation of remaining sugars.

 

[chieftain]

So you purged the keg with fermentation gas, left it hooked up, and when you cold crashed it didn't just pull that co2 back in? That's really disappointing. I plan to try the fermentation purge and hoped it would also let me cold crash without o2 suck back.

Quick question - did you try this for cold crashing? Because I was planning to do it in a couple of days.

 

[Fictional]

We really need to be careful not to miss the spund window. While most of the advice is fine for Lager yeasts it must be noted that they have a tendency to stay in suspension longer than ale yeasts, especially British ale yeasts and I have learned to my detriment that ts best to err on the side of caution rather than rely purely on gravity readings. In other words if using a British ale yeast I transfer probably just after high krausen as it has a tendency to drop fast. I also make sure to 'catch', a little of the yeast during transfer to facilitate the fermentation of remaining sugars.

I think I ran into this problem exactly. I missed my window and now it's in my keg not doing anything. I planned to send some sugar solution in there later today to jump start some extra fermentation but do you think there is even enough yeast to do this? If that doesn't work I can always carbonate with my co2 tank but I didn't want to do that because I don't think my tank is very pure.

 

[murphyslaw]

Quick question - did you try this for cold crashing? Because I was planning to do it in a couple of days.

No, I dont think that would work. as the fermenter cools and pulls co2 from the keg, what replaces the co2? When racking, the beer flowing into the keg replaces that volume.

 

[4of7]

Beer troll saying...If you ferment in a keg...with another keg as a water lock...primary ferment keg gas line out to water lock keg liqud in and gas with spud set to 20psi ..water lock keg will pressurize to 20 psi which can be used..