Just curious as I've never really put too much thought into this until now. What are (if any) the negative effects of putting 4 gallons of your 5 gallon batch into a glass 5 gallon carboy for secondary? The reason I am asking is because I sometimes put 1 gallon into a 1 gallon glass jug to play around with (i.e. oak, fruit). Is the ~1 gallon head space in the 5 gallon carboy enough to start being concerned with having any negative effects on the beer? More oxygen, more surface area, etc..
I personally would not put 4 gallons of beer in a 5 gallon carboy for conducting a secondary; I would be concerned about oxidation. 1 gallon of head space is a lot. Do you have the ability to purge your carboy with CO2? That could potentially mitigate the concern of oxidation of placing 4 gallons of beer in a 5 gallon carboy? Cheers!
Do you suppose there will be enough residual fermentation going on to fill the headspace with CO2? I think there might be. Honestly I wouldn't worry too much about it. Cheers!
You are correct. Without off-gassing CO2, the area in the headspace increases the risk of oxidation. However, if you're not actually doing a secondary fermentation (e.g. adding fruit, adjuncts or other yeasts), you might as well just bottle or keg the remaining 4 gallons and let them age out in the bottle, or even leave them in the primary. Otherwise, purge the carboy with CO2 if you can. If you have access to regular pure glass marbles, you could try filling the remaining space up with those to reduce headspace.
You all just confirmed what I was afraid of. Crap. I believe I will let it rest in the primary for 3 weeks or so, take a gravity reading and if I'm at my target FG then I will rack off the 1 gallon to secondary and immediately bottle the other 4 gallons. Cheers!
That's an interesting question, and I suppose it could be a 'cheating' way to get around purging the carboy with CO2 if you don't have the ability to do it the real way, but you'd probably have to do it right after peak fermentation. Has anyone ever tried this?
I normally don't secondary but I have (for maybe 1 week max) and not noticed any staling. I suspect that you'll get enough CO2 coming out of the beer either from continued fermentation of from out-gassing that it's not worth freaking out about. However, if you do have the CO2 handy (I don't keg) then by all means purge that secondary!
