Natural Carbonation In A Half Filled Keg

[BusinessTime]

I want to bottle half an 18L batch and keg the other, I was thinking I could bulk prime the lot then siphon 1/2 into bottles and the rest into a keg (say 9L in an 18L keg).

I'm guessing I will have to put some pressure in the keg as the carbonation created by the bulk priming will not have enough guts to carbonate the keg (given there will be 9L of head space ....).

Is there any way people have dealt with this before ? can i fill the keg to a certain PSI and just let the yeast do the final carbonation or will the PSI required to do that kill off the yeast.


Cheers,
Dave

Also apologies if I posted this in the wrong place

 

[MCT]

I want to bottle half an 18L batch and keg the other, I was thinking I could bulk prime the lot then siphon 1/2 into bottles and the rest into a keg (say 9L in an 18L keg).

I'm guessing I will have to put some pressure in the keg as the carbonation created by the bulk priming will not have enough guts to carbonate the keg (given there will be 9L of head space ....).

Is there any way people have dealt with this before ? can i fill the keg to a certain PSI and just let the yeast do the final carbonation or will the PSI required to do that kill off the yeast.


Cheers,
Dave

If it were me I'd keg half first and carbonate as normal, then bulk prime and bottle the rest.

 

[BusinessTime]

Thats a fair call, I wanted to try and get the keg and bottled stuff to be as similar as possible tho ... if you are bulk priming then the added sugar/yeast etc will change that so i figured I would try and take the same carbonation approach to bot hkeg and bottle, i guess the other way to look at it is to fill the bottles from the keg but that kills shelf life.

 

[drtomc]

Thats a fair call, I wanted to try and get the keg and bottled stuff to be as similar as possible tho ... if you are bulk priming then the added sugar/yeast etc will change that so i figured I would try and take the same carbonation approach to bot hkeg and bottle, i guess the other way to look at it is to fill the bottles from the keg but that kills shelf life.

I have never kegged, so flame away, but I have read in a couple of places that you typically need less priming sugar when kegging. I seem to recall it being discussed in Complete Joy, though I can't check because my copy is out on loan.

If I'm correct, then your kegged beer would be more carbonated than the bottled beer anyway.

T.

 

[Frank]

I don't keg, but here's my 2C. (Assuming you dont pressurize keg with CO2, to start with)
Carbonation of a full keg would give a specific pressure per cubic cm. Therefore to achieve the same pressure per cubic cm in less volume you would still need to add enough priming sugar to pressurize the whole vessel, including head space. (hope I haven't lost you yet)
1. Therefore if you normally prime with 6g/L, a full 18L keg would require 108g of sugar, to achieve pressue X.
2. Therefore to prime 9L of beer in the same Keg volume, you would still need to add 108g of sugar in the keg regardless of volume of beer. This would allow the head space plus beer to achieve the same CO2 pressure as the beer above in 1. (pressure X).
Disclaimer: no practical experience in kegs, all theory
Or have a go at force carbonation, follow the links in Wiki.

 

[buttersd70]

But isn't there less volume of co2 in the headspace than there is in solution? Discarding sugar priming for a second, and thinking of it in terms of bottled co2, doesn't it take less CO2 to dispense a keg than it does to carbonate? As there is for example 2.5Lco2/L in solution, but I thought that the co2 in headspace was closer to 1L per L of the container? Hard to verbalise what I'm thinking.....and I'm not entirely sure its right anyway.

 

[KGB]

If I'm correct, then your kegged beer would be more carbonated than the bottled beer anyway.

T.

No, you're not correct. As stated already the priming sugar will need to be sufficient to pressurise the (large) headspace as well as carbonate the beer. In a full keg there is not much headspace so it will pressurise quickly but not so when the is another 9L of headspace!

I'm not sure if Boston's theory is correct or not, its been a while since I studied gas partial pressures etc at uni and its too early in the morning...

I think the best bet is to dump 9L into the keg and bulk prime the rest before bottling. I know it defeats the purpose of trying to get them the same but maybe it would be a good comparison of natural carb'ing vs force carb'ing?