Fermenter Headpsace

Is there a problem with having too much head space in a fermenter?
I have this 50 gallon stainless steel conical fermenter.
Can I use it to ferment 20 gallons?

 

If properly sanitized the only issue I see with head space is oxidation or cooling issues (if you have glycol coolant.) During active fermentation the beer will release CO2 that mixes with the air already in the headspace and then vents as a air + CO2 mixture, with the head space increasing in CO2 content and decreasing in air content over time..... with 30 gallons headspace you MAY not get the O2 concentration in the headspace decreased enough. You could help this out by purging the headspace a couple times with CO2 after the yeast have been pitched.

I would avoid opening the conical for anything other than a hop addition.

 

These guys seem to do fine with more headspace than you are describing.

 

This is from a veteran member of the BeerSmith Forum (Dec. 2014) that I found helpful:

"Your answer is in the MBAA Practical Handbook, Volume 2, Page 92.

Your range of 20 to 40% would just about cover it.

All fermenter freeboard (the term of fermenter headspace) is going to depend on gravity, pitching rate, fermentation temperature and yeast strain. The design or type of fermenter you use will depend on your brewing process. That's probably something you already knew.

I ferment under pressure and need only 8% headspace. The same gravity beer at atmosphere can fill 20% headspace and still yield 6% blowoff. So, the process change allows 10% more wort in the fermenter with no blowoff, for an increased yield of 16%.

High gravity ales are anything over 1.055, by brewing science standards, which is to say, nearly every craft and homebrew. A properly pitched and aerated ale, at just 4 F degrees above optimal fermentation temperature can create 50% more krausen. So, it's a sliding scale: higher gravity = more krausen.

On the other end of the scale, a properly pitched and fermented lager may only need 12 to 15% headspace at atmosphere and less than 5% under pressure."

Good luck!

 

They are likely only doing active fermentation here. If OP is like most homebrewers they will also use the conical as a "brite tank" where O2 uptake is a concern because the beer is no longer actively releasing CO2