[sambrewer]

I plan to brew a 2 1/2 gallon batch of ale but I only have equipment for a full 5 gallon batch. 

I would like to know if I would be ok in formenting this 1/2 batch in a 6 gallon bucket an 6 gallon carboy.  I was hoping to try this before I invest in new equipment to see if I am successful with this 2 1/2 gallon batch. 

I am concerned about how much extra space in the fermentation vessels and any oxygen that might still be in the vessels.

[Steve Ruch]

Go ahead, you'll be fine. Just don't age it with that much head space.

[erockrph]

I've done it many times over the years without a problem. Oxidation in the fermenter isn't a concern until fermentation is completely finished. Yeast consumes available oxygen during active fermentation, and will easily take care of any oxygen even if the headspace is a few times larger than the volume of fermenting beer.

And while we're at it -  it is generally best to minimize oxygen exposure whenever practical, but a bit of oxidation isn't normally going to make a batch of beer undrinkably bad even if it does happen.

[Bob357]

Shouldn't be a problem, but I would forget transferring to secondary unless you have a good reason. The transfer will cause more oxygen exposure that the extra space in primary.

[reverseapachemaster]

I routinely brew 2-4 gallon batches in a brew bucket without problems. As Steve said, I wouldn't age beer for a long time in those circumstances but a regular 2-4 week turnaround shouldn't be an issue.