I made a few caps by simply drilling a 1/2" hole in the cap and cramming a plain ordinary tire valve through it. Tire valves are something like 2 for $5.
My store-bought carbonator cost $16, but leaks a little with the gas QD attached. It takes a little jiggling to settle it and stop the hissing.
You could probably make an all stainless version from a real gas port for not much more $$. A 1/4" pipe thread adapter for cornie posts costs $13 at Midwest.
The cost aside, everyone contemplating forced keg carbonation should play around first with a clear container to take the mystery and voodoo out of the process. Buy or make a carbonator cap, and fizz up some liquids in any old 2L bottle. Forget the agonizing and time-pressure graphs you've seen.
The short version is this:
- Fill the container about 2/3 or 3/4 full. You want a little head space at the top.
- Purge the atmospheric air with a brief burst of CO2.
- Seal the container; pressurize it to carbonation pressure. (See the pressure charts.)
- Shake the container and contents hard until it stops taking CO2. (Less than a minute.)
- Let the liquid settle for a few moments;
- ... then vent the excess pressure gently and slowly. Since you can see inside the bottle, vent it slowly and gently to avoid forcing the carbonation out of solution.
All that carbonation means is to dissolve CO2 into the liquid until it equalizes with the CO2 gas partial pressure in the sealed container. The variables are CO2 gas pressure, and liquid temperature. See this following chart for various CO2 volumes. (For what it's worth, BeerSmith's carbonation tool comes up numbers that very closely match the linked chart.)
http://www.kegerators.com/carbonation-table.php
Notice that time is not one of the variables. It doesn't matter if you shake the liquid to speed up the process, or leave it alone for weeks to seep it in slowly. The process is self-governing, for the given CO2 pressure and liquid temperature. Once they equalize, your liquid will have absorbed the tabulated volumes of CO2.
Carbonation is exactly the same process as decarbonation. From our childhoods, we know that shaking soda pop releases its carbonation quickly. It's exactly the same as letting it get flat by itself in an open container, only faster.
For me, fastest is bestest. Vigorous, or even violent, shaking does that fastest and best. We shake our wort to oxygenate before pitching, without qualms about brutalizing the precious liquid. Shaking fermented beer in a pressurized CO2 environment is equally harmless.
To recap the process:
- Vent the atmospheric air with a shot of CO2.
- Adjust the regulator to the tabulated carbonation pressure.
- Shake the container as hard or as little as you want.
- Your beer is done carbonating when it no longer takes CO2 from the tank.
- Disconnect the gas line until you're ready to serve.
- Vent the keg gently to dispensing pressure to serve.
Assuming your keg holds pressure properly, the sealed container will hold its carbonation just as any sealed can of beer holds its carbonation. Let it get warm; let it get cold. Chill it before serving, or open it warm; it all comes out the same. This is worth repeating: Store the carbonated keg sealed and disconnected from the gas line. The carbonation level and gas pressure is self-regulating in the sealed container, just like any other can or bottle of beer.
If you carbonate in 2L bottles, you can swap out the carbonator cap for its original cap. Vent out the excess gas pressure slowly and gently first, of course. (BTW, this was all I set out to say when I started to post. I just got carried away with my frustration at the superstitions and myths surrounding carbonation.)
There are some remaining uncertainties, concerning storage. Should you store the beer carbonated? Or can you just (re-) carbonate immediately before serving?
Carbonation forces CO2 into solution, and forms carbonic acid in proportion to the dissolved CO2 volume. Thus, carbonation lowers the pH of your beer. My experience is that it changes the flavor profile somewhat. More empirical data is needed, but my impression is that beers stored warm and flat have slightly more hop flavor and aroma than those stored carbonated.
