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I tasted the beer when it came out of the fermenter and it was great. I cooled it to 4 degrees then I racked it into the keg and force carbonated - about 1 minute at 300kPa, a good few minutes of vigorous shaking later it dropped to 140kPa so left it for an hour. I then tapped the keg and it was all foam - very overcarbonated... my regulator is a bit dodgy so will go for less CO2 next time.

The thing is, when I tried the beer after the foam settled the flavour was completely different - very astringent, almost plastic-like, flavour. This is the first time I've use the lines and the CO2 cannister.

What could the off-flavour be caused by? Could it be bad gas? Or bad lines (heat-resistant PVC, only about 30cm long)? Would chlorine in the water be doing something bad with the CO2? Or just the fact that it's over-carbonated so there's excess carbonic acid?

Also, is there any way to resolve the situation? I guess just periodically release the CO2 from the head space to solve the over-carbonation issue, but is that also likely to resolve the flavour issue?

Thanks

  • Did you purge the head space in the keg before you shook it? If not, then you likely oxidized the beer. It's also possible that the excessive carbonation is affecting the flavor. – bughunter Dec 22 '14 at 13:13
  • What did you use to clean the keg or lines? If I'm reading the timeline correctly, this all took about an hour- too fast for oxygen to matter, I would think. – Pepi Dec 22 '14 at 14:45
  • @bughunter yeah I purged first – Darryl Snow Dec 23 '14 at 13:39
  • @Pepi I used oxyclean to clean the keg and the lines and then sanitised with iodophor. – Darryl Snow Dec 23 '14 at 13:41
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    If I'm reading this correctly, your pressure is way too high and your beer lines are way too short. I'll use my system as an example, even though it might not be perfectly balanced. My kegs sit at about 38F (3C), my regulator is set to 11 PSI (76 kPa), and my beer lines are 5 feet (153 cm) long. All of these factors (and others, such as the beer line inner diameter and material) do matter. Read more about balancing your draft system here: byo.com/grains/item/… – bughunter Dec 23 '14 at 14:55
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Carbonation can have a dramatic effect on beer flavor. I suspect your beer is overcarbonated and that's the cause of the off flavor. You can reduce the carbonation by allowing the keg to warm up to room temperature and periodically venting the keg as the CO2 comes out of solution. As suggested by @Pepi, use this chart to determine what you should set your regulator to: http://www.kegerators.com/carbonation-table.php

If you suspect the beer lines might be to blame, you can depressurize the keg, open the top, and dip some beer out with a sanitized ladle or something. That will allow you to taste the carbonated beer before it comes into contact with the beer line.

All that said, there are examples out there where people conclude that "bad gas" was making their beer taste funny. E.g., http://www.homebrewtalk.com/f39/could-bad-taste-co2-247914/

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It's quite possible you're just tasting the dregs from fermentation. A little bit tends to come through, even with careful racking, and it'll precipitate to the bottom of the keg. It compacts well, so it's not really a problem, but the first pint out of a keg will suck up the dregs from around the end of the dip tube, giving a cloudy appearance and a yeasty or phenolic taste. (I don't know if I'd describe it as "astringent", but who knows.)

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To minimize foaming:

  • consider a lower pressure, 140kpa is on the high end of the range: http://www.kegerators.com/carbonation-table.php
  • keep the keg as cold as possible when serving
  • keep the lines cold too - it'll foam until the beer cool them off
  • set up the CO2 at a lower pressure for a slow pour when serving, cold beer won't lose its gas too quickly
  • Somebody disagrees! What did I get wrong? – Pepi Dec 23 '14 at 5:06
  • The question is about an off-flavor that appeared after kegging, not about how to minimize foaming. – Graham Dec 23 '14 at 13:27

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