Sulphur: Does it need to off-gas

[Chupa LaHomebrew]

I brewed up this Belgian Blond a week ago, so it's still really young so obviously I am not expecting it to be mature yet.
I racked it to a keg today. There was still some yeast in suspension, but I'll just pour off the first yeasty pints so no problems there.
I did pick up, along with some nice fruity notes, a bit of sulphur in the sample. I assume that if it's really sulphur, it's just there because of it being very young, and the yeast will get rid of it. So I am keeping the keg out at room temp for a while.
Do I need to attach a blow-off tube to let the sulphur off-gas, or will it be reabsorbed wither way?
Thanks!

[BDawg]

Yes, the sulphur needs to escape into the atmosphere or it will simply build up in the keg and ultimately stop coming out when the partial pressure equalizes. Partial pressure can be thought of as a "balance" of molecules inside vs outside of the liquid within a closed container. The molecules will leave the liquid until the pressure due to the sulphur molecules in the airspace is equal to the pressure trying to escape from within the liquid.
They balance each other out, and stop transferring. If you drop the outside pressure, then the molecules will continue to come out of suspension until it balances against the normal air, which has a very, very low concentration.

HTH-

[siwelwerd]

Yes, the sulphur needs to escape into the atmosphere or it will simply build up in the keg and ultimately stop coming out when the partial pressure equalizes. Partial pressure can be thought of as a "balance" of molecules inside vs outside of the liquid within a closed container. The molecules will leave the liquid until the pressure due to the sulphur molecules in the airspace is equal to the pressure trying to escape from within the liquid.
They balance each other out, and stop transferring. If you drop the outside pressure, then the molecules will continue to come out of suspension until it balances against the normal air, which has a very, very low concentration.

So, if I had a keg full of sulfurous beer, I might just vent it, re apply CO2, vent it, etc. a few times and that would solve the problem?

[ajdelange]

This is what the Germans call "Jungbukett" often translated as "beer stench". No, you don't have to take any action because the yeast will eventually oxidize the hydrogen sufide to sulfate (which is wierd because you usually think of yeast as electron donors). Hydrogen sulfide (as are the other components of jungbukett) is volatile which means that it moves across the surface of the beer into gas readily and a low concentration of it in the beer results in a fair amount of it in the headspace. The trick to getting it out is to make sure the headspace is low in H2S and that is done by sweeping the headspace out periodically and replacing it. So a blow off tube isn't going to work because H2S will just build up in the headspace until the chemical potentials in gas are liquid are equal. Now if the yeast are still activve and producing CO2 the H2S will move into the CO2 bubbles and be swept out of the beer but this gas must be allowed to escape. This is exactly what happens in lagering (lager strains tend to proiduce more sulfur than ale ones) and lagering vessels are often fitted with a pressure relief valve to allow the gas to escape. If, after the yeast have stopped producing CO2, you open the lid of the keg and expose it to a draft then the released H2S gets swept away but you don't want to expose the beer to air (nor lose CO2). What you can do to speed it on its way is pressurize the keg and hold it for a week or more so the beer takes up some CO2 and then bleed off some of the pressure. This will result in bubbles forming in the beer which rise scrubbing the jungbukett volatiles out of the beer, just as the CO2 released by active yeast will, and into the headspace. Wait a day and then bleed the headspace again. The combination of scrubbing and yeast activity should have cleared things up and you should be able to set keg pressure to what you want for serving at this point but it may take more time and more cycles of scrubbing. Obviously, bleed gas which smells of hydrogen sulfide is a clue that Jungbukett is being cleared. When the bleed gas no longer smells of it you have cleared the beer. Whatever you do or don't do tincture of time is usually required.

[Chupa LaHomebrew]

OK I will make sure to attach a blow off hose or off-gas the keg periodically and refill it with CO2.
Thanks!

[SacoDeToro]

Lager yeasts are known for out-gassing sulfur during the primary fermentation - some more than others. WLP830 is my go-to lager yeast and in my experience, has a tendency to kick off large amounts of sulfur during primary fermentation. To combat this, I raise the temp of my lagers to 63-65 degrees for about the last 5-10 points worth of fermentation, which ends up being 3-4 days. This works twofold; it acts as a d-rest (although I don't have issues with diacetyl) and helps to out-gas the bulk of the sulfur that's produced during fermentation. The rest that's left gets absorbed during my lagering process.

[brewinhard]

Sean,

Which belgian yeast did you brew with? I have noticed sulphur production from the Safbrew T-58 dried yeast. When I smelled the sulphur, I simply let it age a bit longer before kegging or bottling and the smell went away after a few extra days.