Talk to me about "Off Gassing"

So I have a NB kit of Irish Draught and Denny’s Wry Smile (5 gal batches). Both went through primary ferment in plastic for two weeks (F.G. steady), and then I racked into cleaned, sanitized, and CO2 purged kegs for the remainder of their “scheduled secondary” ferment.

I did the EXACT same thing to an Irish Red, at the same time. While in the kegs, I periodically check the pressure relief valve to vent any excess pressure (I know there will be SOME off gassing…) The Irish red did its two weeks in the secondary, and stopped creating pressure inside the keg, so in the fridge it went and is being carbonated. However, the Draught and WryPA are STILL creating a noticeable amount of gas pressure every couple of days; pull up on the relief valve and a consistent amount of “pssssht” is released. It has been almost six weeks since pitching, and almost four weeks in secondary.

Now for the “Hmmmmmm…” part for me…

On BOTH of those batches, I inadvertently started at a mash temp of about 160, and ended up at about 152 at mash out (started high, then drifted low). On the Irish Red, I started mashing at 150, and slowly brought it up to 153/154. …oh, and I used Irish moss on the Red and the Draught but not on the WryPA (just an FYI). Ferment temp from start, until now, has stayed in mid-60’s (house temp, the best I can do for a constant temp).

Why are these two both still producing gas/pressure? I know the kegs were clean and sanitized properly, and I don’t think they could have been contaminated/bad. Should I continue to let them do their thing until they stop gassing, or should I just throw them in the fridge and force carb? What causes off gassing when it’s been racked to a secondary?

Thanks for any input!

I can think of two possible physics causes, one chemistry cause and two biology causes. Your issue might be caused by a combination of these though.


  1. What temperature are the kegs at? If you allow them to warm up, the beer will out-gas.
  2. How full are the kegs? If there is less head space, the beer will outgas less, meaning there is more excess gas still in the beer when you release the pressure. Thus, the smaller head space can pressurize again, where as a keg that is less full will have already outgassed more so it doesn’t have enough reserve to outgas and fill the headspace again.

Chemistry: When you started by mashing high, you denatured enough of your beta amylase that a significant amount of the converted sugar was in longer, harder to metabilizes fragments. That might lead to a much longer fermentation, though I’m speculating here. The conventional wisdom is that simply more of the sugars are non-fermentable and you just have a more full-bodied beer, but I wouldn’t be surprised if it is in reality a little of both. If so, you kegged too early before the yeast was done.


  1. Good sanitation doesn’t eliminate the chance of infection, it just reduces it (a lot). The beer could be infected and thus the microbes are still producing gas. But if your beer tastes ok, you can probably eliminate this as the cause.
  2. You kegged too early before the yeast was totally done. This might have nothing to do with the mash issue; it could have been weak or too small a pitch of yeast, too cool fermentation temperatures or some other issue. Some yeast strains are faster than others. But if there is still sugar present that the yeast can consume, it will. Confirm stable gravity readings before you assume the fermentation if finished.

It would be great if you figure out why this is going on if you let everyone know.

So as you pull the pressure relief pin what does it smell like? Was it funky, er nothing really noticeable? I wouldn’t pull the pin anymore as the off gassing is more than likely CO2, just what you want to carb yer brew! Lay them on their sides and roll them gently a few times a day and take a sample after few days. That is the old way of tending to green beer waiting for them to mature, CASK CONDITIONING! Sneezles61

160° is a little on the high side but nothing to worry about. Could have slowly added cold water and stirred to bring it down. Most everything that happens in the mash happens in the first fifteen minutes. It will take some time before you dial in your system and know what temp strike water works but AG is much more forgiving than you would think and you will still get great beer.

Could have left the 150° alone. It would make for a very fermentable wort so your beer may be more dry than you like. Ramping it up to mid 150’s could not hurt.

Rebuilt gave the perfect rundown on the scientific stuff. Here is my less than scientific. Get your mash close to what you are shooting for. Don’t even think about a step mash yet. It’s not needed with almost all modern malt. Take an OG reading and let it ferment. Be patient. Start checking the gravity when you think it is finished. Three days running of the same reading and it is done. Keg it and forget it.

Your chemistry postulation was what I was wondering as well. Hmmm…

But, based on ANOTHER batch that is not “going as expected” I’m wondering if, in fact, my two F.G. readings were “really close” but not “exactly” the same - I usually just give them a quick check. Maybe my yeast was acting really slow/temp was lower than it liked (mid-60’s) and it is just slowly chewing its way through. …might try sneezles61 suggestion of rolling.

I thought this post was about that guy that was still complaining about the new forum format.

hopefully he went away after off gassing his opinion! :laughing: I think that HDFmark is close to why its still fermenting. Seems that the actual saccrifination process does start quickly and at a higher temp the longer the chains are of sugar and less enzymes to help break down the chains of sugar. So that requires a long ferment stage. And now that its in a bit cooler temp range, add a bit more time fer it to finish up… So try CASK CONDITIONING! You may enjoy the way its carbonated! Whew! Sneezles61

If I had to pick one cause, I’d vote for Rebuilt’s Physics explanation.

Of course, letting it sit for a couple of weeks should cover all the bases. If the problem is really sanitation, it should be obvious by then.

@sneezles61 - Oh no, I’m still here - I’m just embracing my “gassing” now, as opposed to “venting it” throughout the house. :smile:

Going to cask condition, and go from there.

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