Use a keg as a co2 vessel?

[Carolina_Matt]

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.

https://www.morebeer.com/products/duotight-inline-regulator-gauge.html

 

[day_trippr]

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]

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]

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

 

[GoodTruble]

@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.

 

[SanPancho]

Champagne yeast and cheapest sugar you can get.

 

[day_trippr]

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

Cheers!

 

[DuncB]

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.

 

[renstyle]

Champagne yeast and cheapest sugar you can get.

Another, more recent thread which linked me here thankfully has opened my eyes to another option for experimentation...

Ironically, I am well stocked in CO2 supply: I have (2) 10lb CO2 tanks and a 20lb I offered to "dispose of" when a convenience store building was due to be demolished... the idea of creating CO2 locally, if only for dispensing purposes, is intriguing!

 

[DuncB]

Now if I could capture the nitrogen from the exhaust of an oxygen concentrator that would be handy as well, Nitrogen is more expensive than CO2. Something else to ponder.

 

[doug293cz]

Now if I could capture the nitrogen from the exhaust of an oxygen concentrator that would be handy as well, Nitrogen is more expensive than CO2. Something else to ponder.

The the "waste" coming from an O2 concentrator is not very pure - still has lots of O2 in it.

Brew on

 

[doug293cz]

One thing that needs to be considered if using a fermenter as a source of "pure" CO2, is that you have to purge the fermenter headspace to an acceptably low O2 concentration, before you start collecting the CO2. I think there is probably a way to calculate how much fermentation needs to take place to do this, or you could use a mass flow meter to measure how much gas has been pushed out of the fermenter (still requires some calculations.) The calculation would be similar to those done here.

Brew on

 

[Dland]

I use fermentation gas to purge kegs, of course.

Beyond that, without specialized equipment, the only way I've come up with to provide higher pressure CO2 to dispense or displace is to intentionally over spund kegs for semi high pressure CO2, albeit in limited volumes.

If one is going to do this, one should leave plenty of head space in keg, since the gas is part of the harvest, not just the beer.

I've mainly done this as a preparedness experiment, to see if I could keep enjoying dispensing nicely carbonated beer if CO2 was not easily available. Maybe a shortage not likely to happen, but if it does, I've worked out a way to dispense beer without oxidizing it.

Also, if one over spunds by accident, one can use the gas to dispense more mature beers, and not have to worry about "de carbing".

 

[AlexKay]

I would worry about the other gaseous products of fermentation: for starters, H2S and DMS. I’ve definitely had some (e.g. 3068) yeasts where I’m very glad that the gas output from fermentation is going far, far away from any beer I’m going to drink.

 

[doug293cz]

I would worry about the other gaseous products of fermentation: for starters, H2S and DMS. I’ve definitely had some (e.g. 3068) yeasts where I’m very glad that the gas output from fermentation is going far, far away from any beer I’m going to drink.

Any such contaminant gases only off gas to the headspace if the concentration in the beer is already above the saturation level (otherwise, they would remain in the beer.) If you're just purging kegs with the ferm gas, you will be venting most of it to the atmosphere anyway when you fill the keg. You might have to worry if you pressurize the ferm gas significantly above atmospheric pressure, as that will increase the amount (but not the concentration) of trace gases in the storage vessel. The higher partial pressures of the trace gases would tend to push some of the trace gases back into the beer. But, then spunding will do the same thing.

I have not seen any reports of purging kegs with ferm gas leading to off flavors in beer.

Brew on

 

[DuncB]

The the "waste" coming from an O2 concentrator is not very pure - still has lots of O2 in it.

Brew on

I suspected as much, will keep saving for one of these for the stout serving.

https://nitrobrew.com/nitrobrew-tabletop/
Can't quite work out how this doesn't contaminate the whole keg of beer.

 

[AlexKay]

Any such contaminant gases only off gas to the headspace if the concentration in the beer is already above the saturation level (otherwise, they would remain in the beer.) If you're just purging kegs with the ferm gas, you will be venting most of it to the atmosphere anyway when you fill the keg. You might have to worry if you pressurize the ferm gas significantly above atmospheric pressure, as that will increase the amount (but not the concentration) of trace gases in the storage vessel. The higher partial pressures of the trace gases would tend to push some of the trace gases back into the beer. But, then spunding will do the same thing.

I have not seen any reports of purging kegs with ferm gas leading to off flavors in beer.

Brew on

No, I’ve come around to agree that purging with fermentation gases won’t be a problem. But what’s being proposed here is collecting a lot of gas and (maybe I’m making an assumption here, but if you’re going to be collecting this much) doing it early in fermentation. You’re going to end up with partial pressures of problematic gases proportional to their concentrations in solution, and early in the fermentation these concentrations are too high. (Smell a Hefeweizen early on…). Reintroduce those gases to a new brew and — assuming the volume of the storage keg is large enough; the CO2 pressure is irrelevant — you’ll reach the same concentrations in the beer you’re trying to carbonate/push.

On a separate note, the OP proposed collecting 40-50 psi. Do this without a compressor and it seems like this level of dissolved CO2 would be detrimental to yeast health. I’m not a pressure-fermenting or spunding pro, but isn’t this several times what you’d use in those situations?

 

[DuncB]

@AlexKay
Viewing the video in Post 8 the yeast seems to work for gas production at very high pressure. I wouldn't want to drink a sugar wash fermented at low or high pressure.

 

[Dland]

No, I’ve come around to agree that purging with fermentation gases won’t be a problem. But what’s being proposed here is collecting a lot of gas and (maybe I’m making an assumption here, but if you’re going to be collecting this much) doing it early in fermentation. ...

On a separate note, the OP proposed collecting 40-50 psi. Do this without a compressor and it seems like this level of dissolved CO2 would be detrimental to yeast health. I’m not a pressure-fermenting or spunding pro, but isn’t this several times what you’d use in those situations?

Fortunately, carbonation by spunding takes place near the very end of fermentation.

Normally I spund to about 30 PSI at 60F, which translates to about 12 PSI at 32F.

Have never detected off flavor gasses in my beers, but I'll admit I only use clean "normal" yeasts, so I would not know if some of the more "flavorful" yeasts produce off flavored gases.

 

[mashpaddled]

I mentioned this in the other thread going on with the same subject but even if you get a keg filled with CO2 at 30 PSI you're not getting 30 PSI of CO2 back out to push beer. Once your CO2 keg reaches the pressure in the serving keg there is no more pressure differential to push out beer (unless you're willing to let CO2 come out of solution and slowly push a little more beer). You need at least two or three of these kegs to push a single keg of beer to the end. I just don't see how you can buy sugar for every run through this (assuming you already have kegs and connections to donate to the cause) and spend less than a CO2 tank refill. I suspect your costs to match the same amount of beer you can push with a CO2 tank will be astronomical by comparison.

Somebody with a spunding valve and an in-line regulator should hold on to a blown keg and top up the pressure to 30 or 40 PSI. When the spunded beer is ready hook up the gas keg to the spunded vessel with the regulator set inline at serving pressure. See how much of the spunded beer you can jump between kegs before you lose beer flow. (You can use a scale on the empty keg to measure the volume transferred.)

 

[McMullan]

I start off by pulling the PRV on the receiving keg to get a pressure difference for transfer. I think I'll try it combined with the gravity assisted method next time to see if I can get away with not using any exogenous CO2 to complete the transfer.

 

[Red over White]

I mentioned this in the other thread going on with the same subject but even if you get a keg filled with CO2 at 30 PSI you're not getting 30 PSI of CO2 back out to push beer. Once your CO2 keg reaches the pressure in the serving keg there is no more pressure differential to push out beer (unless you're willing to let CO2 come out of solution and slowly push a little more beer). You need at least two or three of these kegs to push a single keg of beer to the end. I just don't see how you can buy sugar for every run through this (assuming you already have kegs and connections to donate to the cause) and spend less than a CO2 tank refill. I suspect your costs to match the same amount of beer you can push with a CO2 tank will be astronomical by comparison.

Somebody with a spunding valve and an in-line regulator should hold on to a blown keg and top up the pressure to 30 or 40 PSI. When the spunded beer is ready hook up the gas keg to the spunded vessel with the regulator set inline at serving pressure. See how much of the spunded beer you can jump between kegs before you lose beer flow. (You can use a scale on the empty keg to measure the volume transferred.)

As the keg used to generate co2 loses pressure, some of the contents can be removed and counterpressure filled with syrup and nutrients if your game is on point. A simple carbonation tee and a 2 liter bottle could feed it many times after the intial generation oxygen free. This could be done for emergency situations or strictly for purity of the co2, unlike what we buy that does contain trace amounts of oxygen. It's there if we need it though.