How much is too much ullage???

[ColonelForbin]

For example, if i have a 6 1/2 gallon carboy with 4 gallons of beer am I going to risk oxidation for having too much ullage? What is the maximum amount of headspace that I can get away with without the chance of seeing negative side effects?

 

[ColonelForbin]

If anyone knows a percentage that would be even better incase i ever need to scale it up for a 30 gallon batch of beer. How long would it take for the beer sitting on too much headspace to start oxidizing?

 

[devilishprune]

Primary fermentation=not important. CO2 is produced and will quickly fill the headspace in there. You want more head room so that you have room for the krausen.

Percentage? I don't know, it really depends on the shape of your fermenter also. Seems like people put 5 gallon batches in 6.5 gallon carboys, so greater than 20% seems to work alright.

 

[Cheaton]

I recently fermented a 2.5 gallon batch in a 6 gallon better bottle. To date it is one of my best brews. I wouldn't worry about it.

 

[ColonelForbin]

I recently fermented a 2.5 gallon batch in a 6 gallon better bottle. To date it is one of my best brews. I wouldn't worry about it.

WOW. Did you leave it in there the whole time after fermentation or only during fermentation?

 

[Cheaton]

6 weeks.

 

[Zamial]

The way I understand this is in 2 parts and NOT scientific.

Part 1: Primary fermentation: There is no such thing as to much. There IS such thing as to little. Better have a blow off tube just to be sure! I do try to fill it with as much wort as possible within reason. I would REALLY suggest stopping a ways before the neck. I will also add that most of my beers have "sized" themselves.

Part 2: Secondary fermentation: You want as little as possible, up to or as close to the neck as possible.

The reasoning is that the fermentation causes Co2. The Co2 forms a "blanket" over the beer as it ferments, protecting it. This is ONE reason why the air lock bubbles, the co2 is escaping. There are some instances where there can be a "suck back" but these seem rare or related to picking up an Ale Pale or plastic bucket.
The "blanket" keeps O2 from oxidizing your beer. In secondary much of the fermentation is over and as such it will make a smaller "blanket" or a less dense one. O2 can get by it easier.

All that being said, most people will have a hard time oxidizing their beer if they are careful. Even fewer will even notice the off taste since it builds over time (aka new beers gets consumed pretty quickly most of the time.) This does not mean use the racking cane as a "pump" (I did this, as have others here...) or just pour it from the fermenter into the bottling bucket; but do it the way it is supposed to be done and you will be just fine!

Many people here do not even use a secondary so it becomes even more so of a moot point. I am sure there is a formula to determine this space but I do not know what it is.

 

[pjj2ba]

I would say that, if you have CO2 available, size doesn't matter. Whenever I move beer from vessel to vessel, I always first purge with CO2. Then when I move the beer, it is always covered by a blanket of CO2. It doesn't matter how much head space there is as it is filled with CO2.

This is a non-issue during active fermentation and the yeast will clean up any O2 around and they will easily fill the vessel with CO2.

 

[moti_mo]

+1 on what pjj2ba said. If you secondary and you have a kegerator, simply purge the headspace of your secondary that you're racking to for a few minutes after the transfer.

As others said, for primary I wouldn't worry about it at all. So if you're going to only do a primary with this beer, and you know you have a good air-lock seal on your carboy (should be a no-brainer if its a glass carboy), then just let-er-go and don't worry about keeping it in the primary for weeks after fermentation's done if you like.

I just split a 5.5 gallon batch into 2 equal aliquots out of necessity (only 5 gallon carboys available, no 6 or 6.5's) so I fermented each with ~2 gallons of head space and then combined them after a ~4 week primary in the keg. No oxidation as far as I can tell.