The Draft Beer Flashlight Test

If you are not quite certain as to your draft beer’s carbonation level, there is still hope in determining keg pressure. A flashlight can be used to determine if your beer’s gas content is staying put with the applied CO2 pressure to the keg.

You’ll need a bright flashlight to test a keg’s carbonation.

It is not an exact science although you will be surprised to how accurate it can be. It will not correct a warm tower issue or an air leak in your line.

This test works best on a fresh keg that has acclimated to your cooler. A risk would be to go overboard and increase the pressure too far, causing over-carbonation of your beer. A dim flashlight will not cut it.

Follow these steps:

  1. After turning your secondary regulator’s shut-off valve to the off position, reduce your pressure to a low 5 to 6 psi(pounds per square inch).
  2. Tap your keg and then relieve the keg head pressure using the coupler’s safety relief valve (the “key ring” on side of coupler).
  3. Turn the regulator shut-off on — you should hear the rush of gas entering the keg and pressurizing the vessel.
  4. Open the beer faucet for one second and close (you may need an assistant to do this if you are inside the cooler). Immediately shine your flashlight through your beer line just above the coupler. You may see a couple of large bubbles rising. Do not pay much attention to these. Look for very fine, small bubbles that are rising out of the top of the coupler through your line. This is the actual gas in the beer breaking out.
  5. Raise your pressure one to two pounds and and after a few minutes, repeat step four. You should notice that the break out of the gas bubbles are becoming less frequent. You are becoming close to what is called “gas equilibrium”. But if you still see the bubbles, you are not quite there.
  6. Repeat step five and continue this procedure until gas bubbles no longer rise out of the top of the coupler. Be careful not to raise the pressure too high. Once the gas bubbles disappear, you can be assured that the pressure you are applying to the keg is keeping the beer’s carbonation where it belongs — in the beer!

You should find that — for most beers — you will stop raising pressure right around 12 to 14 psi if your beer’s temperature is 38º Fahrenheit and you are working with a 2.6 gas volume beer.

As always, the keg must be acclimated to your system (38º and never before tapped) before you perform this test. Be aware that it can take hours for a keg’s temperature to drop by even a couple of degrees. It will take a 15 gallon keg of beer about 24 hours to reach the ideal temperature.

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