Minimum Fermenter Headspace?

[smyrnaquince]

What is the minimum headspace in a fermenter?

I do stovetop brews of half batches, typically 2.5-3 gallons into the fermenter. On Saturday I decided to push my system to the limit for the boil. I boiled 5 gallons of wort in a 6-gallon brewpot. I had 2-3" of headspace in the pot and kept the hot break from boiling over with a few sprays of Starsan. (Neat trick I read about on this forum.)

I boil off ~0.9 gallons in a hour and don't lose much to trub because I pour the boiled wort through a strainer into my fermenter. With this batch, I yielded 4 gallons of wort. I have a 4.5-gallon fermenter and there was only 1" of headspace above the wort.

In this particular case, it wasn't a problem because I was splitting this into two separate batches to try two different yeasts.

I'm guessing that, had I kept it all in the fermenter, 1" of headspace would not have been enough.

I would like to adjust the max size batch that I brew. What is a reasonable headspace that I want in the fermenter?

Thanks!

 

[Dixon9717]

In my experience which is limited your answer would simply depend on the yeast. Some are beasts that create a ton of krausen and some are more gentle with less krausen 1" of headspace is pretty small, a blow off tube I would definitely use in that situation. Today I racked 6 gallons into a 6.5 gallon carboy and I'm confident it'll be no problem using Pacman yeast.

 

[user 141939]

I agree. Other than dirtying up your blowoff tube, is there any problem with running small headspace and just using a blowoff tube to churn out all the extra krausen? I do it probably every second batch.

I think there could be a problem with that yes. For true top cropping yeasts, you're gonna end up losing your yeast.

Like for example a belgian triple. You're gonna want to keep the yeast in the carboy where it can help ferment.

 

[TurnipGreen]

I had a brew last year that I filled up to about three inches from the top. I don't recall the yeast off hand but it was pretty active. I really felt like I lost a lot of volume through the blow off on that. I don't have any hard science or even a huge experience base, but after that one I like to leave about six inches, so more of that yeast and beer can stay in the carboy.

I don't know how much of a real difference it make, but it sure seems like I'm not losing near as much as I did that time.

 

[pmaster]

I was pondering over that exact same question just a moment ago after finishing my brew day....hopefully it'll be OK with the blow off tube and fermcap...

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[user 141939]

I think it really depends on type of yeast, gravity of beer, ferm temp. I like having plenty if room for the yeast. But I know it can be hard with carboys. I just purchased a 8 gallon spiedel so I could have more room, especially for my belgian beers