Rotten egg smell after switching to pressure fermentation

Brewing Processes
1

Persistent sulfur / rotten egg smell after switching to pressure fermentation — looking for ideas

I’m trying to solve a recurring sulfur problem in my homebrew. I’m not very good at sensory evaluation, so I’m trying to approach this from a process/fermentation perspective.

Ever since I switched from bucket fermentation to pressure fermentation in Cornelius kegs, I started getting a sulfur character in the finished beer — mainly rotten egg / sewage / drain-like.

I never had this problem when fermenting in buckets.

It happens mostly with lagers, but occasionally with ales too. I’ve had maybe two completely sulfur-free batches, but when I repeated the same process afterwards, the sulfur came back.

Equipment

  • 45 L Coobra brewing system
  • Immersion chiller
  • Whirlfloc 15 min before the end of the boil
  • 18 L Cornelius kegs
  • Usually 13–14 L of beer in the keg, maximum ~17 L

Fermentation

My typical lager process:

  • 10–12°C during primary fermentation
  • Previously I used 10 psi throughout fermentation + diacetyl rest
  • Then changed to 10 psi during primary and 2 psi during the diacetyl rest
  • Currently I use ~2 psi throughout fermentation
  • When fermentation reaches roughly 60% attenuation, I raise the temperature to 16–18°C
  • Hold until FG, then another 4–5 days
  • Soft crash to 10–12°C
  • Remove the spunding valve
  • After another 3–4 days, transfer to a second keg
  • Lager at 1–4°C for about two weeks

I used to transfer some yeast sediment as well; now I try to leave as much sediment behind as possible.

Oxygenation

Previously:

  • 0.5 µm stone
  • inhalation device
  • ~10 minutes of aeration

Currently:

  • pure O₂
  • 1 bar
  • 1 L/min
  • 1 minute
  • 0.5 µm stone

Nutrients / additives

Previously I used:

  • ~1 ml/10 L of a 1% ZnSO₄·7H₂O solution
  • Yeast Side Labs FAN, ~0.5 g/10 L

Now I use:

  • Yeast Vit, ~0.5 g/10 L

I also add a few drops of Fermcap to the keg before oxygenation.

For hoppy beers I sometimes use vitamin C (~2 g/10 L).

I previously used potassium metabisulfite (~0.1 g/15 L), but stopped using it because I was concerned about sulfur.

Yeast strains and sulfur

This is where things get interesting:

  • NovaLager — little sulfur
  • WLP833 — little sulfur
  • WHC Blitz — a lot of sulfur
  • WHC Saturated — a lot of sulfur
  • WHC Haze Heaven — little sulfur
  • K-97 — little sulfur
  • US-05 — variable, depending on the batch

So there seems to be a significant difference between strains, but I can’t figure out why switching to Cornelius fermentation made the problem much more noticeable.

What I’m trying to understand

What could cause this?

Could pressure fermentation change how much H₂S is retained vs. stripped from the beer?

Could the timing of the temperature increase matter?

Could removing the beer from the yeast after fermentation make the problem worse?

Could this be related to nutrients, oxygenation, water chemistry, or something specific to certain yeast strains?

Or should I be looking more seriously at contamination or something in the Cornelius kegs?

I’m looking for mechanistic explanations and ways to systematically troubleshoot this, rather than simply “use a different yeast”. I’d especially appreciate input from anyone who has experienced sulfur problems after switching from open/bucket fermentation to pressure fermentation.

2

Yeast is alive and doesn’t like pressure. It’s not trained to do what you are asking it to do. Stop fermenting with pressure! Pressure fermentation is mostly a fad that cannot fade away quickly enough in my opinion. Anyway… quit pressuring your yeast and enjoy cleaner fermentations without pressure.

6 Likes
3

But now, i ferment in max 2psi (It ferments under minimal pressure so it doesn’t suck anything back in) and still i have sulfur in finished beer.

4

Try 0 to 0.5 psi and see how that works for you.

3 Likes
5

100% agreement

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6

I’ll give it a try, but please tell me: what’s the deal with brewers who write online that they ferment lagers at room temperature under high pressure and the beer turns out clean?

7

That, sir, is one of the biggest brewing questions of this decade.

EDIT: What thousands of homebrewers including myself are now finding is that we get clean results with lager yeasts fermented close to room temperature WITHOUT any pressure.

3 Likes
8

Could pressure fermentation change how much H2S is retained vs. stripped from the beer? Absolutely! H2S is a normal product of fermentation. In an open fermenter, it readily gasses off, as do other volatiles. Plus the CO2 bubbling further strips the wort of volatiles.

Under pressure, volatiles are unable to escape, and so they remain in the finished beer. And because the human palate is exquisitely sensitive to sulfur-containing molecules, it takes only a tiny extra bit of H2S to be noticeable.

When you raise the temp at 60% attenuation, you should release all the pressure and let the beer vent (with an airlock of course) for many days. What your process is missing is time spent venting all that H2S that has accumulated in the beer during fermentation.

Sample the beer before soft crashing. If you taste H2S, note that it will not dissipate after crashing. If you still taste it, you can try gently scrubbing with beer by bubbling CO2 thru the bottom.

But the best advice is, just go back to using buckets.

3 Likes
9

I have only ever heard of fermenting under pressure at room-ish temp. It’s sort of a cheat, i.e. you don’t have to ferment cold if you ferment under pressure.

Pressure or not, a warmer temp allows the yeast to more quickly metabolize the H2S (it is an intermediate in the production of two amino acids). It makes sense to me that fermenting under pressure, but at warm temp, would be fine.

But you are fermenting both cold and under pressure, which I think is the issue.

1 Like
10

I ferment under pressure at lager temperatures and it’s a game changer for me. Lager yeasts are well known for fruity esters and the combination of lager temperatures (52-55F) and 7.5 psi produces extremely clean beers.

The sulfur problem you have can have a number of sources, but I doubt pressure is the main problem. I have not noticed an increase in sulfur with pressure, but lager yeasts will produce sulfur in a normal healthy fermentation. With 34/70 the sulfur peaks around day 3 in a 7 day fermentation. I found that it’s important to get the fermentation as vigorous as possible to scrub off the sulfur compounds (healthy yeast pitch). Secondly, I add the yeast nutrient to the fermenter, not the boil. Protein acts as a chelation agent and drops most of the zinc the yeast needs. By adding it to the fermenter, the zinc is available for the yeast and can help to reduce sulfur production.

If you are convinced it’s related to pressure, switch back to ambient pressure. The other suggestion is that ales should be fermented at ambient pressure, there’s no good reason to pressure ferment an ale, at least in my opinion.

As a side note, not all yeasts do well under pressure, some just don’t produce good beer while pressurized.

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11

I’ve heard that copper will remove the sulfur from finished beer, just by adding a small piece of copper tubing.

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12

Didn’t Keith try that and confirmed it worked?

13

Maybe pressure is not significantly impacting the beer and lagers fermented warm taste clean without pressure?

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14

I think the head pressure may be trapping sulfur in solution instead of letting it off-gas like it would during a pressureless fermentation.

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15

To the OP, does your brewing system have ANY copper in contact with the wort or is everything stainless steel? Just a little bit of copper is all that’s needed. While its not ideal with respect to LODO and the potentially degrading introduction of copper ions to your wort, it may be worth it if your beer isn’t improved by just venting the beer near the end of fermentation.

16

I wonder also if the OP is just in a bit of a hurry? A good 3 to 4 weeks of lagering will typically eradicate most or all of the sulfur regardless of any action or inaction on the part of the brewer. Time is our friend.