Harvesting CO2 from Big Mouth Bubbler

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Monmouth00

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Hello all,
I’ve seen other threads about harvesting CO2 from fermentation to purge a corny keg, but my question is specifically about harvesting from a Big Mouth Bubbler.
Can I run a hose directly from the top of my BMB lid to the gas port of a star-san filled corny? Do I need a spunding valve in between?
Will it produce enough pressure to push the sanitizer out of the liquid port into an over flow bucket?
Will I need a weight on top of the BMB lid to ensure it doesn’t pop off? (This has happened using only an airlock)
Is enough CO2 produced to fully purge the keg?
What happens if there is vigorous fermentation and it pushes krausen into the gas off tube?
Can I just leave the overflow tube connected after the sanitizer is pushed out, or should I disconnect and replace with an airlock?
Is there anything else I haven’t thought of with this setup?
After completing, I’ll connect the liquid tube to the spigot and gravity fill the keg, looping the gas line back into the headspace.
Sound like a good plan or am I setting myself up for failure?
Thanks so much for your thoughts.
 
Well, I'm interested to hear other people's thoughts, but I also ferment often in a BMB and my instinct is that it's 1) not airtight enough to let any real pressure build and 2) definitely not pressure rated. So if I understand correctly putting a spunding valve between the BMB and the corny keg would be to allow some build up, and I'm pretty sure that would be unsafe. If you just ran a tube directly to the keg from the top of the bubbler I do think the pressure would just push up on the top and probably get out. But I haven't experimented much with pressure transfer and could be wrong.
 
You can’t but don’t really need to do it with pressure. Simply sanitize the keg, dump out the sanitizer, and seal it back up. Then you can purge the keg with CO2 at atmospheric pressure. Attach a blow off at the keg’s gas port.
 
Sorry to bump this thread, but I'm really looking for answers before either screwing up a batch or somehow harming either my fermenter or keg.

Anyone have any experience displacing a keg full of star san with the CO2 from a fermenting Big Mouth Bubbler?

Will it work?

Thanks so much!
 
See post #3. Sorry I missed your follow-up question. The answer is yes. I have never used fermentation gas to push out StarSan, but I have read about others doing it. However it's just not necessary, since the CO2 will entirely displace the keg's air contents if left connected during fermentation. You don't need to have liquid in the keg to "prove" that the contents have been entirely evacuated.

It's not that the CO2 is heavier; it's that it's being pushed into the keg with more pressure than the static air inside the keg. So air is forced out. The best way to do this is to run your fermentation gas into the liquid port, so it enters the keg from the bottom. Then the blow-off goes from the gas port on top into a jar.
 
Thank you for your reply! I greatly appreciate it.

I'll try to do it dry, with a previously flushed and sterilized keg.

Fingers crossed!
 
Fear not! It's very easy and you'll wonder why it's not talked about that much.

Here's an epic thread showing some math that supports the theory that there's plenty of CO2 in fermentation to purge a keg.

Here's a pic of one of my setups, using an Anvil fermenter and a 2.5 gallon keg. In this example I'm feeding CO2 into the gas port, but normally I'd use the liquid port for that.

UNADJUSTEDNONRAW_thumb_163.jpg
 
That's pretty much the plan.
Instead of a metal pressure fermenter though, I'll be using my plastic Big Mouth Bubbler. Fingers crossed that it can hold enough pressure to push the CO2 into the keg. I've had some problems keeping the lid on when just fermenting, so I bought some clips to put on it to make sure the lid stays on.
Thanks again!
 
FYI, the Anvil is not pressure-rated. The bung on top would pop out in half a second if there was any pressure. Same as the BMB.

Some common sense: Your BMB has no problem pushing CO2 into an airlock full of water, or into tubing feeding a blow-off jar full of water. You'll be asking it to push CO2 into tubing and an empty keg. No issue whatsoever. It doesn't even "see" the keg on its way out the gas port into the blow-off.
 
No experience with a big mouth bubbler, but it takes less than .5psi, yes half of a psi to push liquid out of a keg, albeit pretty slowly. I used to pressure transfer out of my glass carboys using as little gas as my regulator would push. I recently went stainless out of fear my carboys would explode at some point. I'll stop rambling now.
 
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