I'm thinking about switching from fermenting (primary and secondary) in glass carboys to using Cornelius kegs. Specifically, I'd ferment a 5.5 gallon batch in a 10 gallon keg.

My goal is to ferment under pressure -- around 10 or 15 psi. Why? There's some anecdotal evidence that fermenting under pressure reduces ester production which could help with lager fermentation. But mostly, the pressure would a) let me remove yeast and trub after a few days of fermentation, and b) let me transfer the finished, carbonated beer to a serving keg under pressure

How can I regulate the pressure of fermenting beer in a Cornelius keg?

I can image a setup where the gas in line (with the tube removed, perhaps) is connected to a blow-off tube with an in-line pressure regulator. The regulator would need to be adjustable, so I could dial in different pressures for different beers, and at different stages in the fermentation.

I'm not sure if such an in-line regulator exists. I also expect it would need to be resilient to moisture. Fermenting 5.5 gallons in a 10 gallon vessel, there's not much chance that liquid will end up in the blow-off tube, but I want to be prepared for it if it does happen.

Has anyone ever put together a setup like this? Can anyone foresee technical difficulties I haven't thought of?

  • 1
    Interesting idea. But is hydrostatic pressure at the bottom of a 200bbl conical the same type of effect as gas pressure of built up CO2?
    – brewchez
    Commented Feb 9, 2013 at 12:20

2 Answers 2


Look into "spunding valves", either to buy or DIY. Often used for natural carbonation, but it could be used to control primary fermentation pressure, as you suggest.


I've done just this for my last 30 batches or so. It's lovely, and I see no reason to go back. I fill the corny to the weld line, bubble some oxygen up through the liquid diptube, and then connect my spunding valve to the gas connect.

The spunding valve is just a pressure gauge and an adjustable pressure relief valve attached to a 1/4" stainless tee. To prevent its getting clogged with blowoff, I use an empty water-filter housing as a water trap. It sits between the corny and the release valve to catch any liquid that comes out the top.

Good luck! It's a great way to ferment.

  • 2
    Great idea about the water filter as a trap. Are you using a 10gal or 5gal corny to ferment in?
    – mdma
    Commented Feb 7, 2013 at 13:57
  • 1
    Just a five gallon. I use fermcap and usually get a small amount of blow-off. A ten gallon would give me a bit more breathing room, but I still end up with just a smidge under five gallons of finished product.
    – MalFet
    Commented Feb 7, 2013 at 16:23
  • Could you post a picture of the setup? Commented Jan 23, 2015 at 14:51

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