Carboy Bung Retainer

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Empty Calorie Connoisseur
HBT Supporter
May 31, 2011
Reaction score
Stow, MA
"I was bored, so..." šŸ˜

Year ago I started cold-crashing my 6.5g glass carboys under light CO2 pressure - provided by a standard primary regulator which was touchy AF to dial in an acceptably low pressure (like, under 1 psi). Plus said regulator had a propensity to drift in either direction. My "solution" to maintaining safety was to equip carboy caps with gas posts and balloons, with the latter acting as "pneumatic fuses". Here's the setup:


Eventually these were proven to work :oops: but after the third time finding a blown balloon I decided to add BBQ grill regulators as "secondary" regulators to provide a fixed 0.4 psi. This proved to be highly reliable (zero issues to date) but I still was using the carboy caps, which require band clamps and are very difficult to remove from a post-crashed 36Ā°F carboy as the rubber seriously stiffens. Plus removing them post-soft-crash to add dry hops is another pita for the same stiff-rubber reason.

I've been thinking of just using carboy bungs with push-in PTC stems, but had not come up with an easy way to ensure the bungs didn't back out and dump a tank of CO2. I thought of duct taping the bungs, or making something from copper wire, but neither seemed likely to provide an easily implemented and ideally reusable solution.


Today as I was setting up four carboys for a soft-crash prior to dry hopping I was thinking of a different way to use wire to make a retainer when something clicked and I set about making a simple device that took advantage of the carboy neck geometry. After taking some measurements I came up with this piece of 1/4" MDF with a 1-5/8" rounded slot carved in it..


Which works like this:


After messing around with this to understand how much pressure it can exert on the bung I'm pretty confident it's going to work.
So I outfitted all four carboys with them.


Much easier to deal with and there'd be no problems popping the bungs out when needed for dry hopping and then post-cold-crash kegging. I'll see how well these work over the next handful of days as these beers get finished and kegged. If they work well enough I may see if my youngest son the mechanical engineer can crank out a bunch from a 3D printer...