Carboy size

Currently do 5 gallon batches and I have a 6.5 gallon carboy and a 5 gallon MT. I'm considering doing more half batches so that I can have more types of beer more often. The MT should work great but, Do I need to buy a smaller carboy or will the 6.5 be ok for a 2.5 gallon batch?

 

yeah, You can do those smaller batches in there just fine.

 

Yep... head space is only a concern in a secondary. When there is a large head space in the primary, oxygen fills it at first... the yeast are totally cool with that. Then they fill it with Co2 and push the oxygen out. The reason it's bad in a secondary is because they are pretty much done producing Co2 and the oxygen stays in the head space and can oxygenate the beer.

Another option is to run by a big box retail store and pick up some 3 gallon buckets.

 

I brew all the time in half batches; don't Rack to a secondary and follow the 3/3 rule so you don't have any 02 by using a secondary w/big head space.

 

The whole larger head space thing I think is a myth. I've used a 6.5g carboy for secondary in 5 gallon batches 8 times now and have never had an issue. There will always be some head space in a secondary. Especially with the trub left behind from primary, secondary will never be completely full, thus leaving a similar head space regardless.

 

Thanks for the help.