Kegging 2.5 gal batch in 5 gal corny keg

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leeeroy

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Novice homebrewer and new to the forum here.

Are there any downsides to kegging smaller batches in a larger corny keg? I have acquired some 5 gallon corny kegs but only have the equipment to mash and boil smaller batches. I think the only downside is that it would take more CO2 to force carb.

I apologize if this has already been covered somewhere, thanks for reading!
 
You are correct: it would take more CO2 than if you were using a smaller keg.

The only other downside is that all else being equal, you'll be starting with more O2 in the headspace, leading to faster staling. You'd have to do more purging to get the total headspace O2 down to the same mass.
 
I'd go for the double batch method too. All that extra head space full of CO2 isn't going to be good for the kegged beer in the long run. For a 2.5 gallon batch I'd bottle it instead, IMO.
 
I'd go for the double batch method too. All that extra head space full of CO2 isn't going to be good for the kegged beer in the long run. For a 2.5 gallon batch I'd bottle it instead, IMO.

It's not the extra CO2 that can be an issue. It's the extra O2. Perhaps that's what you meant?

Corny kegs have an internal volume of about 5.3 gallons. When filled with 5 gallons of beer, there's about 0.3 gallons of headspace. When filled with 2.5 gallons of beer, there's about 2.8 gallons of headspace; over 9 times as much, meaning 9 times as much O2. Virtually all of that O2 eventually reaches the beer. First, it seeks equilibrium with the O2 in the beer. As the O2 in the beer is used up in oxidative reactions, the equilibrium breaks, and more O2 gets into the beer. There will be continuous oxidation and rebalancing until almost all of the headspace O2 has been dissolved in the beer and oxidized it.

A way around this would be to start with a "completely" purged keg and do a true closed transfer. (There's really no such thing as a completely purged keg, but we can get close.) Or, one could use significantly more CO2 when purging the keg before and after an open transfer.
 
No problem... But I'd suggest purging the keg with CO2 first. I do this by filling the keg with StarSan and then use CO2 to push it out into my storage keg. This gives you a sanitized and purged keg, ready for your homebrew. If you can do a closed transfer, all the better!
Then put your 2.5G in, seal the keg and give it a few more purge's (fill with gas, vent, repeat).

The extra CO2 headspace does not hurt your beer in any way, especially if you purged the O2 prior.

The only drawback is the amount of CO2 wasted from this "overhead".
 
The only drawback is the amount of CO2 wasted from this "overhead".
I agree this is the only real drawback, but I buy 20 lb CO2 tanks for about $30 and they last me well over a year, so it's not really a significant expense. Others who make significantly more beer may feel differently.
 
I agree this is the only real drawback, but I buy 20 lb CO2 tanks for about $30 and they last me well over a year, so it's not really a significant expense. Others who make significantly more beer may feel differently.

I'd love to know the source of $30 20lb CO2... :D
 
Are there any downsides to kegging smaller batches in a larger corny keg? I have acquired some 5 gallon corny kegs but only have the equipment to mash and boil smaller batches. I think the only downside is that it would take more CO2 to force carb.

I agree with most of the other responses...biggest issues seem to be using extra CO2 and more concerns about purging out oxygen. A positive of something like the 10L Torpedo kegs is that you can stack two of them in about the same space as a single 5-gallon keg, but those small kegs are $$$.

Another great option is to ferment in your kegs. Plenty of people have good luck fermenting and serving from the same keg, usually with help from a floating dip tube. That would help to ensure your keg was fully purged of all oxygen. With a spunding valve, you could end up using less CO2 as well.
 
Thanks for all the feedback! I’ll definitely be looking into a closed transfer for my next batch. Fermenting and serving from the keg is a great option too once I get a floating dip tube.
 
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