This question is driving me crazy, and although there's a fair amount of general discussion out there on brett/bacteria and head space, I'd really appreciate some input that applies to my situation.
Based on my kettle size and stovetop heat source, all of my brews result in 4 gallons in a 5 gallon fermentor. I typically lose 1/2 gallon to trub, and net 3.5 gallons in bottles. Right now, I'm planning to brew a sour brown ale with ECY01. Based on my experience, I'll have 3.5 gallons eligible to go into secondary for a year's aging.
I only have two fermentors, both glass, both 5 gallons. If I rack my 3.5 gallons of sour to a 5 gallon carboy, that's a full 1.5 gallons of head space. Is that too much? Am I risking vinegar, even if I behave myself and keep the airlock topped off and never take samples?
The alternative doesn't sound very attractive--obtaining a 3 gallon better bottle for secondary, and either having NO head space, or else racking only 2.5 gallons over and losing some precious sour beer.
I'm willing to explore topping off with water or wort, but for the moment, let's discount that option. If you had to choose between the above two options (5 gallon glass secondary or 3 gallon better bottle) which would you choose, and how much or how little head space would you tolerate?