Wednesday, August 28, 2013

Fun with a Spunding Valve

Few if any homebrewers are familar with a spunding valve.  It's actually used commonly in commercial breweries, but only a small subset of homebrewers could consider using it as it requires a fermenter that can withstand 10 PSI or so of internal pressure (such as a Cornelius keg).  Since most of us use carboys or plastic buckets to ferment, a spunding valve is not an option.

A spunding valve is basically a pressure relief valve that is used on commercial bright tanks to carbonate the beer using the CO2 generated during the final stages of fermentation.

An adjustable pressure relief valve is the key to dialing in just the right amount of pressure, while allowing excess pressure to bleed off harmlessly.  This pressurized CO2 yields the same result as connecting a CO2 bottle to your keg....your beer gets carbonated!

Last year, I began fermenting in Cornelius kegs.  I can't recall why, but it was then that I found a thread on one of the homebrew forums describing how to build a spunding valve.  It allows you to get your beer carbonated as fermentation finishes using the CO2 produced by the yeast as it eats away at the last vestiges of sugar in the wort.  Some claim that you can go from pitching yeast, to drinking beer in 10 days on some low gravity beers by using this method.

After a few weeks of thought, and mulling over how to make a functional yet affordable version of a spunding valve I could live with, I ordered what I needed and assembled what you see below.

A standard gray gas fitting with barb is shown at the bottom connected to the keg.  I used hose clamps and a short piece of tubing to connect to a transition fitting that mates with the adjustable pressure valve (black body with round gray knob).  To the left of the valve is a pressure gauge that monitors pressure in the keg.

Cornelius kegs are rated to 140PSI, and they also have a built-in relief valve on the lid (at least mine do), so maintaining 10 PSI does not pose any danger.

The biggest challenge in using these is figuring out when to put them on the keg.  When I pitch the yeast, I remove the Gas In fitting and tube, and force a piece of tubing over the threaded nipple that sticks out of the keg.  The tubing (blowoff tube) feeds into a small jar of water.  If you fill the keg too much with wort, the krausen will push up into the tube and into the jar.  You need to wait until this settles down before putting the spunding valve on, or you'll end up with all of that in your pressure relief valve and gauge..yuck.

BYO has an article written in 2007 by Marc Martin describing the spunding valve and when to attach it.  He says that you should wait until you're within 0.005 of final gravity, but I usually don't wait that long. I just wait for the krausening to calm down, and then set the pressure to 10PSI and stick it on there.

Chris White's book about yeast discusses the effect of pressure on yeast, and he says that you should keep it under 15PSI.  If you set it to 10PSI, you should get good carbonation, and not hurt the yeast too much.  It's worked fine for me.

Once fermentation stops, I rack from one Corny keg to another using a short tube with liquid fittings on each end.  This transfers the beer without exposing it to oxygen (assuming you've purged the target keg with co2 prior too the transfer).  Just make sure you divert the initial burst to another vessel so you don't get all the yeast from the bottom of the fermenter keg into the target keg.

You'll need your CO2 tank handy to help force all of the beer over into the target keg. I usually set my regulator to 5 PSI or so...just enough to push it through the tubing.

Let me know if you have any questions or comments.  I'm writing this with a glass of Merlot sitting next to me, so I may have missed some details!


Very cool, man, thanks for sharing your experience, it was useful to me.

Hi, where did you get your adjustable pressure valve? Thanks for the build information.

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