Brainstorming about ways of recapturing CO2 from fermentation

[TNP]

Let's talk about this.
The easiest and stupidest thing that comes to my mind is to fix a bag, a normal shopping plastic bag, around the airlock with an elastic, very tight. The plastic bag may and probably would inflate.
Then, with due care, After fermention remove It and fix It to a keg: It should both carbonate and push the liquid outside while serving.

What do you Say?

 

[Clarence]

The bag will collect the CO2, but it won't carbonate or drive the beer out of the keg. For that you need the contents of the bag to be at a greater pressure than the beer in the keg.
One member used to use a system like you describe as a cask-breather so that his gravity fed beer didn't draw air into the void as the beer was drawn off. That sounds quite different to what you're looking for.

 

[TNP]

The bag will collect the CO2, but it won't carbonate or drive the beer out of the keg. For that you need the contents of the bag to be at a greater pressure than the beer in the keg.
One member used to use a system like you describe as a cask-breather so that his gravity fed beer didn't draw air into the void as the beer was drawn off. That sounds quite different to what you're looking for.

I would't mind Gravity feeding. Is that the only difference?

But why wouldn't it carbonate? Won't the CO2 mix with the beer (especially if kept cold)? Bear with me and my naive questions, I've (still) never kegged.

 

[Agentgonzo]

It will carbonate it to a very very small degree. To carbonate it to make it fizzy, you need to apply pressure, normally an atmosphere or two, which you won't get from a plastic bag.

I've thought similar thoughts. I had thought about a collapsible camping water container instead of a bag, or a plastic polypin. Apparently you can also use catheter bags (clean!!!) As a gas collection bag. Most of these are for allowing pure (enough) CO2 to be drawn into a cask when serving our cold crashing a fermenter

 

[Brew_DD2]

I would't mind Gravity feeding. Is that the only difference?

But why wouldn't it carbonate? Won't the CO2 mix with the beer (especially if kept cold)? Bear with me and my naive questions, I've (still) never kegged.

CO2 will only be absorbed under pressure.

 

[Agentgonzo]

CO2 will only be absorbed under pressure.

Not true. It will be absorbed under standard pressure... Just not a lot

 

[TNP]

Not true. It will be absorbed under standard pressure... Just not a lot

Could one reach at least British cask ale carbonation? Let's say, 1,3 or 1,5?

If not, one could at least carbonate the beer and still use the collected CO2 to serve by gravity without letting air touch the beer

 

[Sadfield]

CO2 from fermentation isn't pure. Why would you want to return off flavour volatiles, such as hydrogen sulfide and dimethyl sulfide (DMS), that gets scrubbed off through fermentation, back to the beer?

 

[Hoddy]

Unless you have the ability to compress, clean, cryogenically chill to be able to liquify and then compress again. It’s not possible at home brew level. Especially not with a plastic bag

The best option you have is to be able to use the highest point of fermentation to push out and purge a keg of sanitiser from one to another. But you can only do this if you have all of the prerequisite closed transfer equipment.

 

[Hoddy]

Could one reach at least British cask ale carbonation? Let's say, 1,3 or 1,5?

If not, one could at least carbonate the beer and still use the collected CO2 to serve by gravity without letting air touch the beer

Not with a carrier bag

 

[Brew_DD2]

Not true. It will be absorbed under standard pressure... Just not a lot

If you're wanting to be facetious, then yes. For the purposes of what the OP is asking, then no, it'll be no more carbonated than it is when it has fermented.

 

[TNP]

Not with a carrier bag

I can't trust if you don't explain me why.
I see that if I blow in a bag of plastic or paper It inflates. Why can't yeast do the same, when he's got better lungs than mine?

 

[Agentgonzo]

Could one reach at least British cask ale carbonation? Let's say, 1,3 or 1,5?

If not, one could at least carbonate the beer and still use the collected CO2 to serve by gravity without letting air touch the beer

Probably not even that. Cask ale is pressurised by a bit of residual fermentation in the cask (why you have to release pressure via the spile before you tap it). The best you can get at ambient pressure is probably a slight tingle on your tongue and increased acidity. As Brew_DD2 says, you won't get anything above the carbonation level at the end of fermentation.

 

[Brew_DD2]

I can't trust if you don't explain me why.
I see that if I blow in a bag of plastic or paper It inflates. Why can't yeast do the same, when he's got better lungs than mine?

Pressure differentials. If you blow lightly on a balloon, it won't inflate. If you create a seal and blow like ****, it will inflate.

If you attach a balloon filled with CO2 to a keg there is not going to be enough pressure to displace liquid inside. You need more pressure to do that.

 

[Agentgonzo]

I can't trust if you don't explain me why.
I see that if I blow in a bag of plastic or paper It inflates. Why can't yeast do the same, when he's got better lungs than mine?

Yes, yeast has better lungs than you (it can make bottles explode).
But it's more about the pressure that the bag can hold to force more CO2 into the beer. Think of trying to inflate a plastic bag you've duct taped over a tube to anything more than atmospheric pressure. Either it'll leak, or it'll burst once it gets ever so slightly above 'full'. It just can't hold the pressure needed to force CO2 into solution

 

[Leon103]

I would try with a condom first. Nice ans sterile and can be reused with a bit of a swill

 

[Agentgonzo]

I would try with a condom first. Nice ans sterile and can be reused with a bit of a swill

mmmm, that lovely latexy taste in your beer.

 

[CaptAwol]

I save some of my fermentation C02 into used and sanitised 20l polypin ale bags, they quickly blow up at the beginning.

These are connected to the gas post of a keg which I serve through a hand pull similar to cask but protecting the beer, although it tends not to spend to much time in the keg once opened.

 

[Agentgonzo]

For reference, a fully inflated balloon has an internal pressure (from a quick google search) of about 1.07 atmospheres. It's just not much more pressure than normal. And a balloon will hold in a lot more pressure than a plastic bag taped onto a tube

 

[Leon103]

mmmm, that lovely latexy taste in your beer.

If someone is using a carrier bag to carb their beer I doubt they will be giving Cloudwater a run for their money any time soon