Half-full fermentor not bubbling

[DasBrut]

I usually only brew about three gallons at a time, which is too much for my two-gallon fermentor, so I use a 5-gallon. But I’ve found that airlock activity stops within 24 hours. However, fermentation does eventually go to completion (checked by gravity). Any scientific explanation for this? Could the extra headspace allow for extra compression and thereby more gas retention? Btw the same recipes in a 2-gallon fermentor bubble like crazy for a long time.

 

[Snuffy]

I think a container with a lot of headspace would take longer to build up enough pressure to push bubbles out the airlock, but once that pressure was reached i imagine it would then bubble like normal. That would probably be seen as no activity for a while longer than usual and then a shorter period of bubbling since the brew is closer to the end of fermentation before the airlock starts.
Seems logical anyway, but there’s a good chance there’s a scientific reason it’s wrong.

 

[RM-MN]

it takes a certain amount of pressure for the airlock to bubble. When that threshold is reached, the airlock bubbles until enough pressure is relieved and then it stops while the pressure builds again. Instead of continuous bubbling you may see burst bubbling and then nothing as it builds pressure again. While the fermentation is vigorous, like it is at the beginning of the ferment, there is a lot of CO2 being produced and it can overwhelm a tiny leak and discharge the CO2 through the airlock but at some point the CO2 production slows enough that the tiny leak is all it needs to discharge the excess CO2.

 

[DasBrut]

it takes a certain amount of pressure for the airlock to bubble. When that threshold is reached, the airlock bubbles until enough pressure is relieved and then it stops while the pressure builds again. Instead of continuous bubbling you may see burst bubbling and then nothing as it builds pressure again. While the fermentation is vigorous, like it is at the beginning of the ferment, there is a lot of CO2 being produced and it can overwhelm a tiny leak and discharge the CO2 through the airlock but at some point the CO2 production slows enough that the tiny leak is all it needs to discharge the excess CO2.

I am shocked, dismayed, and offended that you would even imply that my 5 year-old brewers friend plastic carboy would have a leak

 

[DasBrut]

Just to follow up on this, it was fine:

2/2 OG: 1.056
2/5: 1.026
2/7: 1.017

So, for probably the thousandth time on HBT, don’t worry about the bubbling.

 

[ncbrewer]

When I scaled back and started using a 5 gallon bucket fermentor, I had the same issue. I checked the sealing area thoroughly and improved the sealing surfaces. Now the bubbling lasts almost as long as it did before since the leaking is reduced.