3 gal of beer in a 5 gal keg?

[wyobrewer1]

I'm considering getting into kegging my beer and had a few questions. I typically only brew 3 gallon batches for a number of reasons. What I've found though is 5 gallon kegs are cheaper and easier to find. Any issues with using a 5 gallon keg and adding just 3 gallons of beer? I'm wondering about the extra head space and oxygen exposure. Thanks for the advice!

 

[cjhammel]

Yes you can put 3 gallons in a 5 gallon keg. You will end up using more CO2 to purge your kegs. What you want to do after you fill the keg is put about 30PSI of CO2 on the keg check for leaks. Turn off the gas and pull the pressure release on the keg if a ball lock or remove the gas in and depress the pop-it if a pin lock. Do this about 3-5 times to purge all the O2 from the Keg once done set the pressure on the CO2 to 10-12PSI and refrigerate under pressure for 7-14 days. With that much head space you might be able to slosh the keg around once the keg is at temp to speed up carbonation. I start testing carbonation levels after about a week.

 

[Pipelovejoy]

I do this quite often. You use more CO2 than you would with smaller kegs but like you I find 5 gal cheaper to acquire. Also, I like the option to brew more if I wanted and use the same kegs.
I haven't run into any issues with oxidation as long as purge as cjhammel stated above.
If purged correctly, starting with 3gal of beer in 5gal keg = starting with 5gal of beer and drinking 2gal.