Build Your Own Spunding Valve to Carbonate in the Keg

Having brewed on some large scale and pilot systems in breweries around the Portland area, I have been able to pick up some tricks that can be readily adapted to homebrewing. One of these techniques is the  capping of a bright tank for the retention of carbon dioxide (CO2) produced late in fermentation.  This produces naturally carbonated beer. For homebrewers, the most logical vessel for a sealed secondary fermenter is the Cornelius keg. The challenge becomes how to retain enough carbon dioxide pressure to provide for the right level of natural carbonation, but to vent any excess pressure.

Nine years ago, I sought to solve this problem. The best way I found was to build a version of the valve and gauge system, called a spunding valve, that is used in large commercial systems. An adjustable pressure relief valve and a 0–30 PSI gauge are the main two things needed. To connect these to the inlet side of a Corny keg, I used a brass Y adapter (one MPT “in” side and two FTP “out” sides), a standard ball lock fitting and a brass coupler (FTP on both ends) to connect the ball lock fitting to the Y adapter. All threads use plumbers pipe fitting tape to
prevent leakage.

To create your own naturally carbonated homebrew, simply transfer your beer into a sanitized Corny keg when your beer is 2–5 points above your estimated terminal gravity. For example, if your yeast is 80% attenuative and your starting gravity was 1.050, your target final gravity is 1.010. Thus, you should transfer your beer when a reading of about 1.015 is achieved. Place your pressure relief valve and gauge on the inlet tube side of your keg and keep the keg at normal fermentation temperatures. Check it daily and watch the pressure in the keg build.

To calibrate the adjustable pressure relief valve, you only need to monitor the pressure gauge. When it slightly exceeds your desired carbonation pressure (I generally shoot for  14 PSI) turn the top adjuster counter clockwise until pressure just starts to bleed off. Watch the gauge and when 14 PSI is indicated turn the adjuster back in (clockwise) until the pressure stops escaping.

After 4 or 5 days, turn the relief valve adjuster back in (clockwise) 1/2 turn and monitor the gauge for another day. If the pressure does not increase, you know that all secondary fermentation has ceased and the proper carbonation level has been retained.

An added bonus is that you need not transfer your beer again. It is well carbonated and ready to chill. Your secondary fermenter also doubles as your serving tank. Cheers!

Parts List:

  • Brass Y adapter and brass coupler
  • Pressure relief valve (the one I used is made by the Schrader Bellows Co. in Akron, Ohio. The part number is RV01A1N030SB)
  • 0–30 PSI gauge