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Building an Airlock to Ferment in a Corny Keg

I was lucky enough to take part in a small group that obtained a Bourbon Barrel for the use of aging beer. For our first batch, we brewed an Abbey Dubbel and I contributed 10 gallons to fill the 55 Gallon Barrel. The beer aged in the barrel for about 4 months until we pulled the Dubbel and replaced it with a Russian Imperial Stout. This left me with 2 5gallon corny kegs full of Abbey Dubbel.

Since I had 2 kegs of the same beer, I wanted to do something different in one of them. I decided to blend two types of Brettanomyces. I chose one package each of White Labs Brettanomyces Bruxellensis and Wyeast Brettanomyces Lambicus. I’ve used Brett B before and really like the taste. I decided to play around with a blend. The hope is to get some of the flavors I loved of the Brett B and add to them the more potent flavors and aromas Brett Lambicus.

To do this, I didn’t want to have to take the beer that was already in a corny keg and transfer it again into a carboy just to referment with the Brettanomyces. So I threw the two wild yeasts into the corny keg. In about a week, once the Brettanomyces grows a little, I will add some D2 Dark Candi Syrup to build some more complexities to the flavor. Since I am not trying to prime the beer with the sugar, I needed a way to vent any of the CO2 that gets built up in the keg. To do this, I built a small homebrew gadget to fit a 3-piece airlock to the gas side of a corny keg. This is how I built it.

Parts List for Corny Keg Airlock:
1 – White ball lock (Gas Side)
1 – Stainless steel hose barb for the gas line
2 – Stainless steel hose clamps
1 – 2” Piece of ¼” OD soft copper tubing (used for water lines to fridge)
1 – 5” Piece of ½” OD vinyl tubing
1 – 3-Piece airlock

Step 1
Screw the hose barb to the ball lock and tighten. Place the piece of copper tubing inside the hose barb.

Step 2
Place the vinyl tubing over the copper and onto the hose barb. Secure tubing with 1 hose clamp.

Step 3
Bend the soft copper tubing to angle the tube straight up and down.

Step 4
Cut the tubing to allow enough room for the airlock to fit in snug up against the copper tubing with leaving enough vinyl around the airlock. Secure the airlock with the second hose clamp.

Step 5
Place the ball lock on the gas out of the corny keg and fill the airlock with water/sanitize/vodka. Happy Fermenting.

Bonus Tips
  • While there is no reason this can’t be used as a primary fermenter, keep in mind the headspace. You would have to ferment less than 4.5 gallons if used as a primary. Beware of blow off too.
  • I am using a keg with about 1 ½” of the dip tube was cut off. This is a good idea to leave behind any of the fallen yeast or tub. Since I am using this as a secondary, I will throw in a fining agent like gelatin or sparkolloid before I am ready to transfer to clear the beer. With a shorter dip tube, I don’t need to worry about sucking that stuff off the bottom of the fermentation keg and into the serving keg.
  • Fermenting in a keg has benefits. It is completely dark inside and has a pretty air tight seal. Once the fermentation is done, the beer is easily transferred from keg to keg in a closed system flushed with CO2. There is less chance of oxidation transferring in this closed system.
  • Since corny kegs are metal, there is no scratching like in plastic buckets or breaking like in glass carboys.

Views: 16885

Comment by Eivind Sandstrand on March 7, 2010 at 11:05am
Great write-up, Jeff. I've been wanting to do this for my secondaries. Just need more kegs... With 1 1/2" of the dip tube cut off, how much beer to you think is left behind?

Comment by Jeff Louella on March 7, 2010 at 11:42am
I'm guessing about 2 pints.

Comment by Jeff Louella on March 7, 2010 at 11:55am
I just updated the article. Missed a photo and the photos didn't line up. They do now.
Comment by Brother Benny (aka Carl) on March 7, 2010 at 8:14pm
Hey Jeff, this last batch for the RIS barrel project I did 30 gallons, and split among 8 corny kegs, I used just the gas ball lock and tubing running from each of the 8 kegs to a bucket of sanitizer. Sounded pretty good when all 8 of them were bubbling away happily. :)

Comment by Jeff Louella on March 7, 2010 at 10:43pm
I agree, that is the easiest way to do it. I wanted something a little more elegant and portable. With this setup, I can easily pick the keg up and move it anywhere. The airlock can be swiveled directly above the lid so it is out of the way. And mostly, I had an idea for a gadget that I didn't see many people doing and thought it looked cool. :)
Comment by Brother Benny (aka Carl) on March 13, 2010 at 12:52am
I like your idea Jeff. Currently where I run my ferments is under a plywood box, I don't have enough headroom to put a bubbler on top of a keg, but as I found out, I do have enough room to run 8 kegs at one time. So looks like I need to get brewing more. :)
Comment by Don Gravatt on March 13, 2010 at 10:23am
Any issues with using cornies for primary fermentation? I'm curious on if the ball lock would clog during a vigorous fermentation.


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