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beer taste flat when keg is half empty

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pokerloict

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Hi,

Im a begginner with keg and I noticed something i dont understand with my try. I keg the beer and let it to 40psi for 4 days and the result is very good. Serve at 8-10 psi is perfect. After initial carbonation, let the keg to 8-10psi all the time, always connected.

One week later, when keg is half empty, the beer taste flat and almost no foam. I can serve at 20 psi without problem.

The thing I dont understand is that if the keg was unable to keep pressure, how the beer can be carbonated initially? I also made some test and if I fill keg the empty keg with 15 psi and purge it like 3 days later, the pressure is kept. Do this can be cause by the fact that the has space in it?

Thank
 

VikeMan

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What is the temperature of the beer?

Take that temperature and your 8 PSI and consult a carbonation chart to see what "volumes" of CO2 that corresponds to. In the absence of some of the data, my guess would be that your 40 PSI for 4 days is producing a higher level of carbonation than your beer is settling at later (at 8 PSI and whatever temperature). In other words, 8 PSI isn't high enough at your serving temp to maintain the initial CO2 level as beer volume is replaced with a larger headspace, which receives CO2 off-gassed from the beer. The beer off-gasses CO2 to the headspace because of the low-ish (8 PSI) pressure.

Again, this is just a guess, not knowing your serving temp.
 
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LittleRiver

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... 40psi...
...8-10 psi....
....20 psi...
...15 psi...
I recommend that you set your regulator for the recommended pressure (based on the temp of the beer), then leave it alone. It'll take about a week to carbonate to a decent level. It will stay carbonated till the keg kicks.
 
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pokerloict

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@VikeMan @LittleRiver

I made the test and carbonated the keg at 13psi for a week with a carbonation chart. All is perfect till the keg has some headspace in it. Even if I let pressure to 13psi, the beer more flat day after day.

Any other possibilities?

Thank
 

LittleRiver

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You may have unknowingly over carbed your beer initially, depending on how long you left it at the higher pressures you mentioned above.

If it was over carbed, and you now have it at a lower pressure, as the keg empties the carbonation level will slowly decrease until it reaches the equilibrium level for the temp/pressure you now have it set. That could explain a decrease in carbonation over time.

If a keg gets over carbed you can bleed off the pressure multiple times (over a period of time) to lower the carbonation in the beer. After that, set it to the pressure recommended for your temp, and give it some time to reach equilibrium.

Another possibility is that it's fooling you, it only appears that carbonation is decreasing. A first pour through a warm faucet can cause foaming, which can look like the beer has a lot of carbonation (or over carbonation), but in fact it's just the warm faucet causing CO2 to come out of solution. Subsequent pours through the now chilled faucet will look less foamy, though the carbonation level is exactly the same.

I find the best way to deal with a warm faucet is to initially pour only an ounce or two. While I dispose of that down my throat the faucet is being chilled because it's now full of cold beer. Then I fill my glass with no problems with excess foaming.

On your next brew try the "set and forget" method. Connect the gas at the pressure recommended for your temperature, and leave it alone for at least a week. You should get decent carbonation after that first week, but as more time goes by you'll notice that the foam bubbles get smaller and you get a better quality of head in your glass. It will stay that way until the keg kicks.
 
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pokerloict

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@Pkrd @LittleRiver The beer is not overcarbed. The foam is really good, not too much.... but there is less foam day after day. I tried the set and forget for 1 week at 13psi, same result.

The issues is not coming from the keg itself. My 3 kegs get same result.

Thank
 

LittleRiver

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@Pkrd @LittleRiver The beer is not overcarbed...
In your original post you said you had it at 40psi for four days (which can over carb it, and you've never mentioned bleeding off any of that excess), and by your account you've had the pressure all over the map since then.

That's not intended to sound harsh, just truthful.
 

Golddiggie

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@Pkrd @LittleRiver The beer is not overcarbed. The foam is really good, not too much.... but there is less foam day after day. I tried the set and forget for 1 week at 13psi, same result.

The issues is not coming from the keg itself. My 3 kegs get same result.

Thank
"Set and forget" method has always called out a two week (minimum) time span to infuse the beer with CO2 to the levels on the chart (PSI at temperature). IIRC, that's after the beer reaches the temperature (can take a couple/few days to get there). I've never had a keg that was on gas go from carbonated to flat. I printed out the chart and have it taped to the wall next to my regulators (both CO2 and nitro mix) for easy reference.

For reference, I've never put the kegs at a high PSI rating in order to attempt to shorten the time to carbonate. This way I don't need to jerk around with my regulators or have a separate regulator, and CO2 tank, JUST for that initial high PSI push.

Curious as to what regulator you're using. Also, how's the high pressure side gauge reading? Maybe you're running low/out of gas. Unless you have a 10# tank, and have only used it on a few kegs, you could be running low. Especially with pushing 40psi for days and all the other things you've mentioned.
 

yoop89

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How are you checking the pressure in the keg? If you are relying on your regulator you could have a faulty gauge? I have a separate gauge setup, 0-60 psi, that I use for checking pressures in kegs at various stages.

Are you using the correct regulator also? I dont bring this up often but when I first started kegging(got all my gear used in a fairly large lot) the first regulator I pulled out of the few that I received happened to be a MIG welding gas regulator. The numbers looked like they were in psi but it was actually in flow(cfm) when I took a second look after experiencing the same issue you are(on two different kegs as well). Flow regulators like the one I had usually operate at a very low pressure(3-10 psi).
 

Bobby_M

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If 40psi for 4 days did not severely overcarbonate the keg, I suspect that your pressure gauge is reading a lot higher than the actual pressure. That could explain why the keg starts going flat when you THINK you have 10psi in the keg. If it's actually 2psi, that would make sense.

One way to roughly check if the guage is OK is to purge the regulator down to zero, remove the plastic cover over the gauge and gently lift the point of the needle indicator so that it hops to the other side of the stop pin (at zero PSI). If the needle is still touching the pin but on the wrong side, you're probably OK. If however, it reads something like negative 5, 10 or whatever, then your gauge is out of calibration.
 

jseyfert3

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@Pkrd @LittleRiver The beer is not overcarbed. The foam is really good, not too much.... but there is less foam day after day. I tried the set and forget for 1 week at 13psi, same result.
By overcarbed, I believe they meant carbed beyond the equilibrium carbonation level for your serving temp and pressure. Since you said you were a beginner, let's back up and cover the basics quick:

Carbonation levels in beer are listed as "volumes of CO2" or more commonly just "volumes", where 1 volume is 1 liter of gas at atmospheric pressure dissolved in 1 liter of beer, 2 volumes is 2 liters of gas dissolved in 1 liter of beer, and so forth. A lot of beer is served around 2.4 volumes, but the ideal carbonation level depends on the type of beer and individual preferences.

Now, the volumes of CO2 depend on two things, pressure and temperature. At 38 °F, 10 psi gives 2.4 volumes, but at 50 °F you need 16 psi for the same 2.4 volumes. This is why at least one person asked what temperature your beer is at, since that affects carbonation levels just as much as pressure does.

The next thing to understand is equilibrium. Equilibrium is when the pressure and temp are held constant for long enough that the amount of dissolved CO2 in the beer stops changing. While pressure and temperature change the amount of CO2 in the beer, it's not immediate. It takes time for CO2 to dissolve into the beer, and more importantly, CO2 will come out of the beer if the pressure is reduced or the temperature increased, though this also takes time. In other words, this is a two way street. This is why your serving pressure has to be appropriate for the desired volume level of CO2 at your serving temp. If your serving pressure does not match the volume level of CO2 you desire, then the carbonation will either increase or decrease over time.

Okay, so let's put some pieces together here. It takes time to carbonate to equilibrium. The most basic method of carbonation is the "set and forget" where you choose your pressure based desired carbonation volumes and temp, then let it sit. This normally takes 2-3 weeks to become fully carbonated, or in other words reach equilibrium. If you tap off beer before this, it will be "undercarbed" as it has not yet reached equilibrium carbonation level. As time goes on it will become more and more carbonated until it reaches equilibrium carbonation at which point the carbonation will be the same until the keg is kicked, assuming the keg is left on gas at the same pressure and temp. Make sense?

So then the thing is people don't want to wait 2-3 weeks for beer to reach full carbonation. A common way to speed this up is "burst carbing". Burst carbing involves putting the keg at a much higher pressure than what would reach desired carbonation level if you did the "set and forget", but the idea is you don't let it go long enough to get that carbonated. For example, at 38 °F, if you set the beer to 30 psi and left it for 3 weeks, the beer would end up at 4.3 volumes of CO2, which is way too much for almost any style of beer. But if you leave it for a couple days, you may get it to say 2.4 volumes, then if you set your regulator to 10 psi and vent the excess pressure from the keg, the keg will maintain this 2.4 volumes until it kicks.

The problem with this method is that it's really difficult to reach the exact level of carbonation desired. Don't wait long enough before reducing the pressure, and the beer will be undercarbed, and will slowly increase in carbonation while on tap. Wait too long, and the beer will be over carbed, and will decrease in carbonation while on tap.

So, what does it appear happened in your case? Well, again I don't know your temp, so if I assume 38 °F, then 9 psi you served at will give 2.3 volumes of CO2. But you had the keg at 40 psi for 4 days. Likely you overshot this 2.3 volume mark, maybe your were at 2.6 or 3 volumes of CO2. And for you, that was a perfect carb level. But the problem is, 9 psi at 38 °F is 2.3 volumes of CO2, not 2.6 or 3 volumes. So as you let the keg sit at 9 psi, the carbonation started reducing. It won't reduce forever, just until the equilibrium of 2.3 volumes is reached.

I suspect to get the carbonation you desire, you need to increase your serving pressure. Try setting it at 12 psi for a week or two, then if not enough keep turning up until you find your sweet spot.

This was rather long, but hopefully it's useful for you to help understand what's going on here. Just remember that carbonation depends on both temp and pressure, and it takes time to reach equilibrium before things stop changing.
 

LittleRiver

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... I tried the set and forget for 1 week at 13psi...
With the excellent post from jseyfert3, hopefully you can see that you have not tried "set and forget". That method assumes you start out with un-carbonated beer (or at least carbonated to a level below your target).

On your next brew, look up the recommended pressure from a carbonation chart, set the pressure, and just leave it alone. In a week you'll have drinkable beer. If you leave it for another week you'll have better carbonation, with smaller bubbles and a better head in your glass.
 
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