Use a keg as a co2 vessel?

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Carolina_Matt

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There are a few threads about using co2 from fermentation. I'm wondering if it you can capture the fermentation co2 in an empty keg, then hook it up to the kegerator instead of using a co2 tank with a regulator? It would be something like this:

Start off by filling a keg with 40-50 psi of co2 from fermentation. You can start off with a keg of Star San and push it out, to ensure there's no residual o2 in the keg. You'd be left with a keg full of co2.

Then you attach an in-line regulator (like below), and set it to your serving pressure. In my case, that would be about 10 psi. So anytime you pull a pint, it would push a little bit of co2 from the co2 keg into the dispensing keg to get it back to serving pressure. A couple weeks later (or however often you brew), you can disconnect the keg and hook it up to the fermentation vessel to top it off to 40-50 psi.

My assumption is that a 5 gallon keg can hold enough co2 to top off the kegs, because it doesn't take a whole lot to push beer out of the kegerator. I could be wrong though.

And if you wanted to, you can set up a spunding valve before the inline regulator, then set it to serving psi. That would essentially show you how much more co2 is in the keg.

 

day_trippr

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Interesting posit. Using your pressure range you'd end up with a keg with ~3-4 volumes of CO2 to dispense one volume of beer.
Which seems like it should work - especially if you started with a fully carbonated keg of beer.
What I don't know is if one can actually pressure-ferment at those pressure levels.

Let's see what the Gas Guru @doug293cz has to say :)

Cheers!
 

DuncB

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I have managed to pressure ferment to 30 plus psi and some where there is a keg king video of a pressure fermenter being tested to failure and it was over a 100psi.
I have just done a pressure ferment of some ginger beer and that was warm and at 30psi and I flushed and filled a keg to the same pressure.
So a 20 litre keg with 30 psi . So that should be able to serve the beer as @day_trippr says if it is already carbonated.
I'd be tempted to just have a keg with sugar, water yeast nutrient and yeast and use that as the engine for the CO2 in your system. Then you could just add more sugar as needed.
You'd be able to work out the amount of CO2 per sugar gram somewhere @doug293cz has worked this out and shows the maths but I can't put my finger on the relevant thread.
Note you would need an alcohol tolerant yeast for the engine and perhaps dump some of the "alcoholic " liquid for dilution periodically.
 

doug293cz

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Let's assume you need a 2 psi differential for the regulator to work. Then to serve a single keg at X psi, you need X + 14.7 psi absolute in the emptied keg, and X + 2 + 14.7 psia in the pushing keg at the end of serving. All of this CO2 has to start out in the pushing keg, so that works out to 2X + 31.4 psia to start. The gauge pressure would be 14.7 psi less, or 2X + 16.7. To serve at 10 psig, that works out to 36.7 psig in the pushing keg to start.

Whether or not the yeast would tolerate that kind of pressure during fermentation is for someone else to answer.

Brew on :mug:
 

GoodTruble

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@DuncB - The idea of keg fermenting beer simply to keep generating CO2 is fascinating. Almost tempting to ferment 4 gallon batches in kegs at a time, just to see if I could keep rotating in new fermenting beers at a rate that keeps the kegerator pressured indefinitely.
 

day_trippr

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lol!
Forget "free" captured CO2, is that actually cheaper than bottled CO2? :)

Cheers!
 

DuncB

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Seems ideal for real ale that that I serve with the beer engine and just needs enough CO2 to replace the volume loss from the keg and a few psi.
Regarding the ability of yeast to ferment under pressure this video gives a few clues.

Given the pressure rating of a corny keg the 35psi seems well in the safety range.

 
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