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Using 7.5 gallon carboy to ferment 5 gallon batch

Hey everyone, I’m new into brewing and I’ve got access to a 7.5 gallon glass carboy. I’m wondering if that would be ok to use as a primary fermenter for a 5 gallon batch? I currently also have a 5 gallon carboy I plan to use as a secondary fermenter as I understand it’s necessary to have no headspace during this stage. Any thoughts are greatly appreciated!

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I use and 8 gallon fermenter for 5 gallon batches with no issues. But as you state I too never use it for a secondary.

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You will be happy to have that much head space some day. No blow off tube and no mess with a violent fermentation. Once fermentation starts the O2 will be pushed out your air lock by the CO2 produced. I’m sure there is a limit to how much head space but IMHO that is not too much.

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Should be fine. If you’re never used glass carboys be aware that they are quite fragile even though they feel pretty solid.

I used them for years and scoffed at the horror stories I heard or horrible injuries from breaking carboys. Then a couple years ago I lightly bumped one agains the edge of a granite counter top while cleaning it in the kitchen sink. I didn’t get cut at all but man the huge jagged chunks of glass that thing just fractured into were pretty damn scary!

I still have a few in the basement but haven’t used them for years since I never use a secondary vessel for most of the beers I brew.

Just be careful.

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I’ve never had an issue with headspace in my glass carboy. I have a 6-6.5 (can’t remember) gallon one that I only use for secondary when needed. I still use a bucket for primary. It’s sort of backwards, I know, but it has always worked.

The only beer I’ve ever oxidized was with a conical that I misused and also had a leaky butterfly valve. Then again, I never use a secondary as merely a waiting vessel, I always add something for extra flavors that usually starts the fermentation again slightly.

This is exactly what I do. I actually mark a line with tape on the primary fermenter at about the 5 and 1/2 gallon mark so that when I siphon out of that bigger carboy and into secondary it comes out about perfect every time. That way there might just be one glass left over for tasting. In secondary there is a small amount of headspace, maybe just an inch or two. It basically gets filled up to the neck…

So I have the same question. I need to brew three different batches and only have one 5 gallon carboy for a secondary. I always use a secondary fermentation/conditioning stage…I was a wine maker long before doing any brewing. I do have several 6 gallon carboys and would like to use those for secondaries. Will a gallon of headspace hurt anything?
Thanks,
Ken

probably if you purge the head space. I would maybe put a balloon with a pin prick hole over the airlock to monitor the pressure. You could just scale up and brew 6 gallon batches

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