Best practices for CO2 scrubbing of DMS

[iandanielursino]

Hopefully this is the right board. I figure carbonation at lagering temps goes under bottling/kegging. I have a batch that seems to have DMS issues.

I've heard about a process called "scrubbing" where if you run CO2 through a carb stone or something similar with a vent to allow gas to escape the vessel it will bring DMS out of the beer.

There doesn't seem to be much information about this online from a homebrew perspective, I'm curious about how long it would take, whether it's better to use an open vent or a PRV/spunding valve, and whether it matters what temperature and pressure you do it at. My naiive idea of how it do it is I just set the pressure of the CO2 regulator higher than I've set my spunding valve and sniff the gasses that it releases and hopefully they smell like DMS and then pretty soon stop smelling like it.

I would be doing it with a Spike CF10 and the matching carb stone. I'm also wondering if I raised the temp would it undo the lagering I've already done (3 weeks almost, I achieved a good hop separation using a mesh bag but have not dumped the yeast cake)

 

[hottpeper13]

I've only read where you can scrub sulfur with CO2 not anything else. Good luck.

 

[Broken Crow]

If I recall correctly, DMS vapourizes at around 90° or so but remains stable in solutions below that temp.
I could be wrong though, my brain is broken and I've lost most of my science..I can't even remember if that 90° is °C or °F...either way, not a temp you want to bring finished beer up to.
Was this one of those 'no-boil' brews?

 

[iandanielursino]

No just a 60 minute lager boil with weyermann pilsner malt. It was also overextracted because the mill was too fine and the mash took too long, and also we had a stuck sparge if that's relevant.

 

[hotbeer]

If it's not bottled yet, just leave it in the FV and make sure the temperature of the beer is over 64°F (18°C). I'd probably keep it about 69°F (20°C).

How long has it been in the FV at a temp over 64°F (18°C)?

Or am I confusing DMS with something else?

Raising the temperature doesn't undo the lagering process. It's part of the lagering process. Or so I think.

 

[IslandLizard]

No just a 60 minute lager boil with weyermann pilsner malt.

You know that boil is a bit short for Pilsner malts?
A 90 minute boil is the general guideline for those. It's also important the vapors (steam) can escape easily, so don't boil with a lid on it, or even partially (causing condensation and drip back).

 

[iandanielursino]

You know that boil is a bit short for Pilsner malts?

Yeah that seems to have been the reason.

If it's not bottled yet, just leave it in the FV and make sure the temperature of the beer is over 64°F (18°C). I'd probably keep it about 69°F (20°C).

How long has it been in the FV at a temp over 64°F (18°C)?

Or am I confusing DMS with something else?

Raising the temperature doesn't undo the lagering process. It's part of the lagering process. Or so I think.

I believe you're thinking of diacetyl and the lager fermentation process. I'm at the extended cold storage/cold crash or "lagering" phase.

As I understand DMS comes from the mash or from chilling too slowly and is typically reduced by the boil, hence why a lager is often boiled for 70-90 min or even longer.

 

[doug293cz]

As I understand DMS comes from the mash or from chilling too slowly and is typically reduced by the boil, hence why a lager is often boiled for 70-90 min or even longer.

No, DMS does not come from the mash. DMS is created from SMM during the boil. SMM starts to break down at temps above about 170°F. At 212°F, SMM has a half life in wort of 30 - 40 minutes, depending on pH. So, if half life is 30 minutes, then after a 30 minute boil, 50% of the SMM has been converted to DMS, after 60 minutes 75% has been converted, after 90 minutes 87.5% has been converted, and so on. DMS has a boiling point of about 100°F, so it readily evaporates during the boil, as long as there is some convection in the wort. A low boil provides more than sufficient convection in the wort to allow DMS to escape at a faster rate than it is created. A partially covered boil kettle will not hinder the dissipation of DMS, as DMS will not condense on a surface that is more than 100°F, and the boil kettle walls, and lid (if any), will be significantly hotter than 100°F.

DMS can also be formed during fermentation from DMSO in the beer (I don't remember off the top of my head where the DMSO comes from.)

SMM breakdown can be a problem during slow, sealed or covered cooling, as DMS will continue to be formed until the wort is below about 170°F. So, while the wort is above this temp, you want to make sure that any DMS formed can escape. Fast cooling minimizes the amount of time that the wort is above 170°F, so helps to minimize DMS if the system doesn't allow for efficient DMS dissipation during cooling.

Generally, the less kilned the malt, the more SMM is present in the malt. Pilsner malt being the lowest kilned malt, typically has more SMM, and therefore more potential DMS, than darker malts. This is why it is often recommended to boil longer when using large percentages of pilsner in a grain bill.

Reference

Brew on

 

[doug293cz]

Hopefully this is the right board. I figure carbonation at lagering temps goes under bottling/kegging. I have a batch that seems to have DMS issues.

I've heard about a process called "scrubbing" where if you run CO2 through a carb stone or something similar with a vent to allow gas to escape the vessel it will bring DMS out of the beer.

There doesn't seem to be much information about this online from a homebrew perspective, I'm curious about how long it would take, whether it's better to use an open vent or a PRV/spunding valve, and whether it matters what temperature and pressure you do it at. My naiive idea of how it do it is I just set the pressure of the CO2 regulator higher than I've set my spunding valve and sniff the gasses that it releases and hopefully they smell like DMS and then pretty soon stop smelling like it.

I would be doing it with a Spike CF10 and the matching carb stone. I'm also wondering if I raised the temp would it undo the lagering I've already done (3 weeks almost, I achieved a good hop separation using a mesh bag but have not dumped the yeast cake)

Scrubbing should work for DMS reduction, as DMS has a very low boiling point, and thus will have a significant vapor pressure at room temp. I would recommend scrubbing at room temp, rather than lagering temp, as the DMS vapor pressure will be higher, and thus be easier to remove.

Sniffing the exhaust gas might work for deciding when scrubbing is sufficient, but tasting the beer is probably a better determinant.

You should shoot for a low flow rate of CO2 whether you are exhausting at atmospheric pressure or spunding. This requires a fairly low differential pressure between CO2 input and exhaust - just slightly more than the threshold differential required to get flow thru the carb stone.

Be aware that stripping will also likely remove some of the hop aroma compounds from the beer.

Brew on

 

[iandanielursino]

Should I do it at standard pressure or can I leave the tank at its current pressure of ~7 PSI and just lower the spunding valves set point until it bubbles?

I'm guessing standard pressure, I assume that would result in a lower flow rate.

Still wish I had a ballpark of how many minutes to do it for before stopping the process and taste testing, and do I need to wait for some kind of equilibrium before tasting?

Will raising it to room temperature undo the lagering? should I perhaps dump some trub from the bottom to mitigate that?

 

[iandanielursino]

A low boil provides more than sufficient convection in the wort to allow DMS to escape at a faster rate than it is created.

If it escapes faster than it is created why is it important that we burn through all the SMM requiring a longer boil time?

 

[wepeeler]

I was under the impression scrubbing works for Sulfur, but DMS is in the beer for the long haul. I've scrubbed for Sulfur before with decent success.

 

[mac_1103]

If it escapes faster than it is created why is it important that we burn through all the SMM requiring a longer boil time?

I think it's because you have to burn through all of the precursors so that you don't create more after the boil is over.

 

[wepeeler]

Here's a scientific approach to reducing the DMS precursor. It's all about the boil!

https://scottjanish.com/how-to-prevent-dms-in-beer/

 

[iandanielursino]

I think it's because you have to burn through all of the precursors so that you don't create more after the boil is over.

Makes sense, I wonder if boiling time and cooling speed are confounded or independent. My cooling setup is an inline counterflow so its pretty fast, but I also did a flameout addition that I let steep for 10 minutes. It sounds like its a good thing I didn't have time to wait until 170F to do a whirlpool addition instead of a flameout one because that could have made it worse.

 

[wepeeler]

Makes sense, I wonder if boiling time and cooling speed are confounded or independent. My cooling setup is an inline counterflow so its pretty fast, but I also did a flameout addition that I let steep for 10 minutes. It sounds like its a good thing I didn't have time to wait until 170F to do a whirlpool addition instead of a flameout one because that could have made it worse.

They seem to be somewhat independent of one another. Boiling for X amount of time drives off most of the SMM, but any leftover from the boil can contribute to DMS, especially at elevated temperatures - like during whirlpooling/hop stands.

 

[iandanielursino]

Here's a scientific approach to reducing the DMS precursor. It's all about the boil!

https://scottjanish.com/how-to-prevent-dms-in-beer/

The other thing from there that might be relevant is that I spunded from the start, so from the start until somewhere around high krausen no vapors left the fermenter.

 

[day_trippr]

It's all about the boil!

I just read that linked Scott Janish article, and it's definitely not all about the boil!
So many ways to end up with noticeable DMS in the beer it seems impossible to miss all of them

Cheers!

 

[doug293cz]

The other thing from there that might be relevant is that I spunded from the start, so from the start until somewhere around high krausen no vapors left the fermenter.

Spunding does not prevent vapors from leaving the fermenter. 20 L of 1.050 wort fermented to 1.010 puts out about 440 L of CO2 (link). If you had 10 L of headspace, the pressure if no gas escaped during fermentation would be about 44 atmospheres, or about 650 psi. So, CO2 and misc. vapors get vented during spunding, not just with airlock fermentation.

Brew on

 

[doug293cz]

Makes sense, I wonder if boiling time and cooling speed are confounded or independent. My cooling setup is an inline counterflow so its pretty fast, but I also did a flameout addition that I let steep for 10 minutes. It sounds like its a good thing I didn't have time to wait until 170F to do a whirlpool addition instead of a flameout one because that could have made it worse.

If you whirlpool in the temp range 170°F to 212°F in an open vessel, most of the DMS formed should should escape due to the agitation of the wort. In a still hop hopstand on the other hand, there will be much less agitation of the wort, and DMS won't make it to the surface, and subsequently escape, as fast as with a whirlpool, so you could have more residual DMS.

Brew on

 

[doug293cz]

I was under the impression scrubbing works for Sulfur, but DMS is in the beer for the long haul. I've scrubbed for Sulfur before with decent success.

DMS is a volatile sulfur compound, so it can be scrubbed, just like any other volatile sulfur compound.

Brew on

 

[mac_1103]

If you had 10 L of headspace, the pressure if no gas escaped during fermentation would be about 44 atmospheres, or about 650 psi.

So I guess that not letting any gas escape isn't be a real good idea then?

 

[doug293cz]

Should I do it at standard pressure or can I leave the tank at its current pressure of ~7 PSI and just lower the spunding valves set point until it bubbles?

I'm guessing standard pressure, I assume that would result in a lower flow rate.

Still wish I had a ballpark of how many minutes to do it for before stopping the process and taste testing, and do I need to wait for some kind of equilibrium before tasting?

Will raising it to room temperature undo the lagering? should I perhaps dump some trub from the bottom to mitigate that?

The rate of DMS removal is going to be proportional to the CO2 flow rate (and some other parameters as well.) The CO2 flow rate is going to be a function of the difference in the input CO2 pressure and the headspace pressure - the differential pressure. The absolute values of the two pressures doesn't matter much - a 2 psig CO2 pressure with 0 psig headspace pressure will have the same flow rate as a 17 psig CO2 pressure and 15 psig headspace pressure. So, it's really dealer's choice.

Sorry, don't have any wisdom to offer on actual time scrubbing will take. I would suggest trying something like scrubbing for a minute, and then check to see if that made a significant difference in the taste/aroma of the beer. If yes, then maybe you only need 5 or 10 minutes to do an adequate scrub. If no noticeable difference, then try for 5 minutes, and check for improvement again. Repeat with 5x time increases as necessary to get a significant change, and then do 5X the minimum time it took to detect a difference. Check the result, stop when you are satisfied with the result, or continue longer if needed.

Just raising the temp won't undo the lagering, but if you stir up any yeast/trub while pushing CO2, then that will undo some of the lagering (the settling out of particulates) but won't undo any of the chemical changes that occurred during lagering.

Brew on

 

[wepeeler]

I just read that linked Scott Janish article, and it's definitely not all about the boil!
So many ways to end up with noticeable DMS in the beer it seems impossible to miss all of them

Cheers!

Well, it's mostly about the boil! The boil seems to be the most important factor in reducing SMM. Quickly chilling wort after boil is also a significant factor, but the boil seems to be the best way to reduce DMS in beer.

 

[iandanielursino]

I tried some scrubbing tonight.

I forgot I had changed the temp with the probe out so it was at 55F.

I did it for 1 min, then 5 min, then 25 x3 times so about 80 minutes total.

It tasted better at 5 minutes and 25 minutes and pretty much the same after so I gave up.

For a while while it was lagering I wasn't sure if the issue was scorching or DMS, until I took a larger sample that is, you see the head tastes really good but the liquid had a clear corn flavor. After the scrubbing, the hop and malt flavors seem more apparent, I think the remaining off flavor is actually scorch, instead of the cream corn its kinda like carbon with a hint of sweet, its just that the DMS was hiding it earlier. Bummer, but its drinkable now.

I'm going to drop it back to 32F, carb, and bottle.

 

[iandanielursino]

Was pretty successful. I forgot to chill my bottles which may explain why I had some inconsistencies in fill volume and carbonation but most of the bottles are well carbonated.

I notice that the less full bottles taste just like one out of three of the cans from a local micro from the Skagit region that shall not be named, I think that's oxidation, it actually mellows out the other faults so I don't mind. Overall it tastes more like a Mexican for some reason than a German, just how the faults bounce off each other.

I really need to get more knowledge about gas equipment, I feel like what the regulator gauge says doesn't matter and I have to just go with guess and check, but maybe that's just a self fulfilling prophecy. A system that is not in equilibrium is harder to predict after all. Spike says to aim for 4 PSI over but it seemed like in practice during carbonation to keep the tank gauge at 9 PSI it could be way over or way under 13 PSI on the regulator. Mind you both gauges are very cold so I don't expect them to be all that accurate.

I also kept getting beer refluxing into my gas lines which are super hard to clean, guessin' that's just cuz I need to set the regulator higher than the tank pressure before opening the valve to my carb stone.

 

[day_trippr]

I also kept getting beer refluxing into my gas lines which are super hard to clean, guessin' that's just cuz I need to set the regulator higher than the tank pressure before opening the valve to my carb stone.

Yup, that'll definitely do it. Might consider adding an in-line check valve to keep that from happening...

Cheers!