A side benefit of having a kegging setup is the ability to fill plastic bottles from the keg to take with you. And if you have Carbonator Caps, you can top the bottle off with CO2 to keep it well-carbonated. Even better, if the beer is not yet fully carbonated, you can use the Carbonator Cap to quickly force-carbonate the beer in minutes. To do this, you just blast the bottle with 30 psi, shake until the bottle becomes soft to squeeze, pressurize, shake, pressurize, etc. until the bottle stays firm after a good shaking.
Carbonator Caps are great, but they are expensive. At $20 each, having enough to take a few bottles with you really adds up quickly. That’s where the DIY Carbonator Cap comes in. I can’t take credit for inventing this. I merely copied something I found online. I’d link to the original source, but I’m not sure who or where that is.
Making a DIY Carbonator Cap is very easy. You need the cap from a 1 liter bottle, an automotive tire valve stem, a drill with a 3/8″ spade bit, and a 9/16″ wrench. Start by drilling a 3/8″ hole in the center of the bottle cap. Then just put the pieces together in the order shown in the picture above. Tighten the 9/16″ nut snugly. Don’t over-tighten. And that’s it.
To use the DIY Carbonator Cap, simply attach an air line tire chuck to your CO2 source and use it to fill the bottle with gas, just as you would to fill your car or bike tire with air. With the right NPT to 1/4″ MFL adapter, you can even thread the tire chuck into the MFL quick disconnects that you likely aready have attached to your gas-in disconnects on your kegs.
One advantage the commercial Carbonator Caps offer is that they allow you to attach your ball lock disconnects directly to the bottle without having to attach a tire chuck. That is a nice feature, but is it worth nearly eight times the cost of the DIY cap? Not to me.
A note about the valve stems: I used the chrome ones. I got them from Amazon where a pack of four cost $6.99. They have them at the auto parts store, but they’re significantly more expensive there. There are also rubber ones that you could buy. I have read that the rubber ones could cause your beer to smell or taste like rubber, so I went with the chrome ones. I haven’t confirmed that the rubber ones impart smells, so it might be worth investigating if you want to save even more money.