Originally Posted by jakeman777
I've been searching for a while and I couldn't find a lot of information on this. How exactly does head space affect fermentation? I understand there needs to be some to contain the krausen or you need a blowoff tube, but is the optimum amount of head space just enough to contain the krausen and leave as little space as possible? I've also read that no matter how much head space your yeast will produce a layer of CO2 that will protect it from oxygen. So does it really matter?
I think this was proably answered by the thread, which is in a closed system, it doesn't matter if you have excessive head space during fermentation, but once racked you want as little as possible.
someone figured out (and I don't remember where I read it on line) that the average beer makes 60 gallons of CO2 at STP per gallon of wort (actually it was 300 gallons on 5 gallons, but it is the same thing). If you have 2 gallons of air mixed with 180 gallons of CO2, you pretty much have 2 gallons of CO2 in your fermentor- ok about 98% CO2 and 2% N2 and most O2 will have probably gone into solution our out by finish time.
If air can flow in, then the CO2 will mix out and negate the 'blanket' that everyone talks about.
Anyhow if you are only making a 1 gallon test batch and only have a 5 gallon bucket, by all means you can primary, but as soon as you want to rack, find a closely sized container.
One reason for the 30% rule was the 'do I need a blowoff'... more head space = less need for a blow off. But at some point, there are deminishing space returns, I mean if 30% is good, why not 70%... Wait I've got a 10 gallon bucket with 2 gallons of beer taking up space in my house/garage!! heck no, fill that sucker up!. Again your specific
situation will require you address this as you need.