Whether you’re smart enough to not finish that second growler — or just have several growlers of different ales and lagers going at once, sometimes it’s just not possible or smart to drink all the beer on hand. The unused beer is usually pretty dead by the the next day.

As a chemistry problem, keeping beer carbonated is a pretty easy issue to solve — pressurize the beer with a gas that won’t oxidize or interact with whatever is in the growler. Getting that done is a little tricky. Custom valves, gauges, fixtures, hoses, containers, and questions like: “What pressure?” and “Where can I get an easily available and affordable source for CO₂?” come to mind.

A few kickstarted projects came and went that promised customs caps and other setups to keep growlers fresh, but the best I can tell they were undone by liability insurance on the way to market. They do exist, or did at one time, but you can’t buy them for whatever reason. A few products have made it market, but seem overwrought. One of the most interesting is the “GrowlerTap” — but after using it, the solution seemed unwieldy. It basically turns a growler into a keg with a dispenser. Maybe I wasn’t smart enough to use the thing properly, but I couldn’t keep from over pressurizing (FOAM!!) the growler. Your results may vary.

Keeping it Simple 

There is the start of a pretty cool solution over at instructables.com: Just use the existing growler setup and modify the metal cap with a custom bike valve. Use a step drill to put a hole in the cap and assemble a custom valve stem with a food-grade rubber seal — replacing the existing seal packaged with the stem.

 

Assemble the valve and food-grade seal into the cap and you’re done — all you need after that is a CO₂ source and a way to regulate the pressure. (And some rough idea of what psi the beer needs to be kept carbonated.)

I asked one of the owners of the local microbrewery at what pressure beer needs to be kept — his answer was “just under 10 psi; nothing over that.” (I immediately wanted to find a time machine and warn my 19-year-old self; saved a boatload of bad keg experiences.)

Making it Work

Without going overboard with custom hoses and regulators, a pretty common solution on the Web was to use a hand-held bike tire inflator to pressurize the growler. Pretty cheap and the canisters use CO₂. I thought about rigging some sort of high-end bike inflator and monitor the pressure as I pressurized the beer but opted for a cheap tire gauge. You have to get a feel for what pressure you’re applying. I usually end up going over a bit and just checking the pressure until I get it down to 10psi. You can also leave the cap loose and “purge” the air out first, and then tighten it and bring it up to pressure.

The Setup

It’s a bit of a cave-man solution: There are NO safety factors here, nothing to release extreme pressure if you get carried away. With the right “expertise” or beer googles I’d imagine someone could blow up a growler, end up in the ER, or worse.

But there it is — it’s worked pretty well thus far.