Dry hop creep / Diacetyl in IPA

[Jesse93]

Hi all!

Sure, this topic has been up before. Even dug deep into with scientific articles etc.
Still some things aren't quite clear to me.

Spoiler: For you who does not know about hop creep:

Hop Creep is a phenomenon that occours due to enzymes being present in hops. These enzymes do break down long chained sugars into short chained sugars, which then is metabolized by the yeast. Thus, a secondary fermentation will occour. A bi-product of this is yeast related off-flavours such as noticable presence of Diacetyl. The more hops you add in, the more likley you are to suffer from this refermentation

So, a couple of hours of googling, reading articles, listen to podcasts etc. I have a good understanding of what "Hop Creep" acutally is, and why it occours. But this doesn't actually tell me any practices of avoiding it.

You guys who brew heavily hopped beers such as NEIPA, DIPA or just IPA. How is your process to avoid the dry hop creep?

Spoiler: My dry hop process, with room for improvements

Notes: Different grain bills and yeasts has been used. I still suffer from the same problem.
I usually ferment at 68F / 20 C. I do rehydrate the yeast (I always use dry yeast), and I areate the wort. I have never had an infection, so sanitation process is fine.
For the yeasts I have tried, S-04 has the biggest problems and Belle Saison the least. Although, almost all of Swedens breweries that makes IPA / NEIPA / DIPA do use S-04...

Method 1: I let my beer fully ferment, controling the temperature. This usually takes 2 weeks. I then dry hop in the primary with loose pellet hops during the D-rest. Normally around 6g/l (1 ounce per gallon) finished beer. I let the hops sit for 3-4 days then package the beer. All beer gets over carbonated, and tastes like diacetyl

Method 2: I "dry hop" using a french press, making a hop tea, and add to the bottling bucket prior to botteling. I use same amount of hops as above, and infuse the tea at 70 degrees celcius (158 F). I do get the hop creep.

Method 3: I dry hop during mid-fermentation. 1 ounce per gallon finished beer. I then let my fermentation continue for 1,5 weeks. Then I package the beer. A lot of hop aroma is lost, but precievibly less diacetyl than in method 1.

Method 4: I let the beer be in the fermentor for 2 weeks, then I transfer it to secondary over loose hops and let the beer sit for 3 days. Strong notes of diacetyl and increadibly strong gushers.

I have also tried the methods above using a hop bag with no different results.

Any ideas?

 

[bierhaus15]

Well, first off, if you are using dry yeast, you should not be aerating the wort for most applications. That residual 02 is forcing the dry yeast to stay aerobic longer than necessary, producing diacetyl. That beer then needs longer to remove the D than you are likely giving it time. I would bet this is why you are seeing elevated D levels in your DH beer.

Per hop creep, my experience is that most people cannot taste 100-200ppb of diacetyl in highly hopped beers. Remove the hops and that same amount is overwhelming for many. It likely goes unnoticed in yeast-heavy, murky, hop bombs.

A way to limit this is to DH when the beer is 2-3 plato from terminal gravity and then give the beer 5-7 days warm on the hops. Healthier fermentations will breakdown D faster than sluggish ones, so yeast health, pitch rate, ect is a big part of the equation as well. Ensuring the beer has largely finished D rest before dry hopping can be a big help as well.

 

[Jesse93]

Well, first off, if you are using dry yeast, you should not be aerating the wort for most applications. That residual 02 is forcing the dry yeast to stay aerobic longer than necessary, producing diacetyl. That beer then needs longer to remove the D than you are likely giving it time. I would bet this is why you are seeing elevated D levels in your DH beer.

Per hop creep, my experience is that most people cannot taste 100-200ppb of diacetyl in highly hopped beers. Remove the hops and that same amount is overwhelming for many. It likely goes unnoticed in yeast-heavy, murky, hop bombs.

A way to limit this is to DH when the beer is 2-3 plato from terminal gravity and then give the beer 5-7 days warm on the hops. Healthier fermentations will breakdown D faster than sluggish ones, so yeast health, pitch rate, ect is a big part of the equation as well. Ensuring the beer has largely finished D rest before dry hopping can be a big help as well.

Thank you for the information Bierhaus, I didn't know dry yeast shouldn't be aerated. I really like to make processes stream lined, and if skipping shaking the bucket is part of the solution then I am more than happy to avoid it.

Next time I will try to dry hop after 3-5 days, should be sufficient time for the beer to be around 2-3 plato from original gravity then dry hop for 5 days.

Maybe the fermentation time will be extended as I suspect the hops will start a refermentation, so one week of D-rest might be in place after hitting terminal gravity.

Cheers!

 

[couchsending]

are you fermenting at 68 ambient or 68 controlled? What temp are you pitching at? How many packs of S04 are you pitching? Are you using yeast nutrient? What is your pH going into the fermenter?

It sounds like your issues could
be fermentation related or at least partially created by a less than ideal fermentation.

I would never ferment S04 at 68 personally. It’s much better at 64 and then ramping to 68 or 70 at the tail end while you still have activity. Yeast clean up diacetyl much better when they’re active.

You can easily do a forced diacetyl test. Take a sample, shake the piss out of it and heat it up to 160 or so for 10 minutes then cool it down to 40-50f and smell/taste it.

If you want to use the same process I wouldn’t crash the beer until it’s negative for diacetyl in a forced test.

Better option would be to:

A: not aerate dry yeast
B: don’t overpitch (1 pack should be more than enough)
C: make sure your pH is close to 5-5.1 going into the fermenter
D: Use a yeast nutrient
E: ferment colder and start raising the temp after say 50% attenuation.

Do a diacetyl test before you add dry hops and then do one after say 4 days of dry hops. If you get Diacetyl wait a little longer.

You’re bottling? Chances are good you’re getting a lot of O2 pickup if that’s the case. This can exacerbate the diacetyl issue as well.

 

[Jesse93]

are you fermenting at 68 ambient or 68 controlled? What temp are you pitching at? How many packs of S04 are you pitching? Are you using yeast nutrient? What is your pH going into the fermenter?

It sounds like your issues could
be fermentation related or at least partially created by a less than ideal fermentation.

I would never ferment S04 at 68 personally. It’s much better at 64 and then ramping to 68 or 70 at the tail end while you still have activity. Yeast clean up diacetyl much better when they’re active.

You can easily do a forced diacetyl test. Take a sample, shake the piss out of it and heat it up to 160 or so for 10 minutes then cool it down to 40-50f and smell/taste it.

If you want to use the same process I wouldn’t crash the beer until it’s negative for diacetyl in a forced test.

Better option would be to:

A: not aerate dry yeast
B: don’t overpitch (1 pack should be more than enough)
C: make sure your pH is close to 5-5.1 going into the fermenter
D: Use a yeast nutrient
E: ferment colder and start raising the temp after say 50% attenuation.

Do a diacetyl test before you add dry hops and then do one after say 4 days of dry hops. If you get Diacetyl wait a little longer.

You’re bottling? Chances are good you’re getting a lot of O2 pickup if that’s the case. This can exacerbate the diacetyl issue as well.

Hi,

Good that you also can confirm the aerate topic. pH is something I already control, but I have not used yeast nutrient or stepping up the temperature during primary fermentation.

I really appreciate these tips, for me, continious improvement is as important as enjoying the hobby

 

[bw7hb]

Jesse93 - did you get this sorted? I'm having major diacetyl issues with dry hopped beers and I'd appreciate any update you may have on this

 

[couchsending]

If you have constant diacetyl issues with hoppy beers try using 1007. It doesn’t produce diacetyl. As soon as you reach terminal with it you can crash it. Local huge brewery near me uses it for everything. They have to filter cause it doesn’t flocc for ****. I think it’s the strain Pizza Pint uses as well although I’m not 100% sure on that.

 

[Jesse93]

Jesse93 - did you get this sorted? I'm having major diacetyl issues with dry hopped beers and I'd appreciate any update you may have on this

Hi,

Yes, sort of. Atleast better on the 1 brew I have made with my method so far. Still had precievable amounts of diacetyl after botteling due to bottle conditioning. But swirling the bottles 2 times to rouse yeast cleaned it up.

Summary below:
instead of fighting the enzymes and the yeast, I decided to work together with them as I could not prevent this secondary fermentation.

Three elements seemed to be essential to change my processes:
1. Temperature controlled fermentation
2. Yeast variety
3. Dry hop schedule

Let's start from bottom up. We know that we can not prevent the enzymatic- and the fermentation activity. So lets take advantage of this. I used to dry hop after the fermentation was completed, this is ofcourse a no-no. My new process is to dry hop at yeast pitch. Why? Because it gives the yeast more time to work with the break down sugars in an earlier stage. This might extend the primary fermentation stage by a day or two, but over all shortening the conditioning time.
- how about escaping aroma compunds? Well, hop oils weight more than air/co2. They will not get scrubbed out Do a 3-5 day long DH.

Yeast variety depends, too. You definately want a yeast that is not prone to produce big amounts of diacetyl to begin with. Let's say I prefer US-05 over Ringwood for these purposes. Yeast is one important parameter, so select the strain with care. You can also enhance the enzymatic activity by using a var. diastaticus strain to really break down the complex sugars.

Finally, managing the yeast with controlled fermentation temperature is the final, and important step. You don't need a fancy system to controll it degree by degree. Moving your vessel to a warmer place after primary fermentation will help. Example, moving the vessel from a 18C basement to a 22C room could be enough. This will help the yeast to clean up diacetyl produced by the yeast. Always peforme a diacetyl test before botteling the beer.

Besides for these actions, the input (the wort) into the fermentation vessel does matter too! Try avoiding malts that has long and complex sugar chains, such ss caramel malts, to reduce the possible magnitude of the hop creep. Less complex sugars to convert, the less effect of the hop creep will occour.

 

[Jesse93]

If you have constant diacetyl issues with hoppy beers try using 1007. It doesn’t produce diacetyl. As soon as you reach terminal with it you can crash it. Local huge brewery near me uses it for everything. They have to filter cause it doesn’t flocc for poopy. I think it’s the strain Pizza Pint uses as well although I’m not 100% sure on that.

I will order that yeast when I am out of dry yeast. Sounds very interesting. Floccing is not a problem for me, I'll just fine it with gelatin thank you!

 

[bw7hb]

If you have constant diacetyl issues with hoppy beers try using 1007. It doesn’t produce diacetyl. As soon as you reach terminal with it you can crash it. Local huge brewery near me uses it for everything. They have to filter cause it doesn’t flocc for poopy. I think it’s the strain Pizza Pint uses as well although I’m not 100% sure on that.

According to Wyeast it produces "low or no detectable diacetyl" - I think it must clean it up really fast due to staying in suspension.

Might give this yeast a go if I can't make my usual S-04 or US-05 work.

 

[Amadeo38]

Just thought I’d chime in that in your Method 1, over-carbonation in combination with diacetyl could point to infection. This is further supported by your use of belle saison yeast in your brewery at times, which is a diastaticus strain and can leave a biofilm that will result in an over-carbonated beer, and potential off flavors.

Have you written down which fermenters you used for each batch to try to track down a potential infected equipment source?

 

[Vale71]

- how about escaping aroma compunds? Well, hop oils weight more than air/co2. They will not get scrubbed out Do a 3-5 day long DH.

Right, because we all know that gases never mix. Oh wait...

 

[jjw5015]

If you dry hop below ale yeast temps, hop creep won't happen.

 

[stickyfinger]

D: Use a yeast nutrient

I actually read a paper showing that adding yeast nutrient can increase levels of diacetyl in the final beer. I can't remember the reasoning at the moment - something to do with the yeast getting lazy if they have too much of most of the nutrients they need. Anyway, I tried supplementing my wort with valine on a few brews, but it didn't remove the VDKs once the beer was dry hopped - the idea being that if the yeast have valine around, they won't need to produce acetolactate (the precursor that is oxidized to diacetyl in beer when it is aged) which then can be converted into valine inside of the cell. But, I think in general some yeast nutrient additions will help some with diacetyl reduction within reason. More might not be better though...

 

[stickyfinger]

If you have constant diacetyl issues with hoppy beers try using 1007. It doesn’t produce diacetyl. As soon as you reach terminal with it you can crash it. Local huge brewery near me uses it for everything. They have to filter cause it doesn’t flocc for poopy. I think it’s the strain Pizza Pint uses as well although I’m not 100% sure on that.

I can absolutely confirm this. I was struggling with diacetyl in my dry hopped beers for a long time. One of the things I tried was usying WY1007. There were no diacetyl precursors or diacetyl in the beer at any point when I tested it that I could detect at least. It must produce a very low amount of acetolactate or not need much valine to ferment well. However, I didn't really like the flavor that it gave my IPA - seemed kind of lagery tasting to me. I think it had some sulfury character that didn't really age out very well. I could have kegged it too soon though, worth experimenting more.

Another yeast that I found eliminated the problems with diacetyl was one of the Kviek strains. I didn't detect any diacetyl precursors or diacetyl in a couple beers I did with it. I think it was the Hornindal or the Voss yeast from Omega. I also fermented them at like 95F, which may have been hot enough to speed up the oxidation of acetolactate so much that it just blew away all of the precursors and diacetyl in a short amount of time.

 

[stickyfinger]

Honestly, the huge breakthrough for me that I know worked for reducing diacetyl in dry hopped beers is fermenting in a closed system with spunding. I started fermenting in kegs with a clear beer draught system. Dry hop b/w 24-36 hrs, seal up, purge headspace and then spund it at like 70F @ 30 psi for 5-6 days. I've never had any diacetyl in my IPA using this method. I then either drink from the primary or transfer to a fermentation-purged keg. I may have diacetyl precursors, but they just don't seem to oxidize to diacetyl when using this method. I think if I warmed up the kegs and let them sit for a week or two after chilling them they might start to show diacetyl though. But why would I do that?

Anyway, I think part of my early problems with diacetyl could have also been from not sealing my glass carboys well enough when cold-crashing. I used to ferment in glass, dry hop at like day 2-5 or so, and then cold crash at like day 10-14 or so after putting a rubber bung into the hole. I think the bung must have been coming out a bit or something or leaking a bit when I cold crashed and caused oxidation to diacetyl in the wort that would come forward pretty quickly after kegging. I switched to keg fermenting right around the time I realized this, so I haven't explored if that was my real problem or not.

I've let IPAs rest a pretty long time trying to eliminate all precursors that I could detect, but it seems you'd have to wait an eternity to get rid of them all! I'm also super sensitive to diacetyl I think when comparing with my brewing buddies, so a very small amount ruins a beer for me. On the other hand, I don't seem to mind DMS as much as some. I guess it's different for everyone's taste!

 

[Vale71]

You don't need oxygen to turn acetolactate indo diacetyl. It's a spontaneous reaction and its speed depends only on temperature, concentration and PH. Even in a closed unitank system diacetyl will develop given enough time if precursors are present.
BTW I too am oversensitive to diacetyl, good thing I like diacetyl-laden beer styles.

 

[stickyfinger]

You don't need oxygen to turn acetolactate indo diacetyl. It's a spontaneous reaction and its speed depends only on temperature, concentration and PH. Even in a closed unitank system diacetyl will develop given enough time if precursors are present.
BTW I too am oversensitive to diacetyl, good thing I like diacetyl-laden beer styles.

it's possible that oxygen enhances the oxidation of acetolactate. in addition, there are other precursors that form other VDKs when oxidized. I'll have to see if there are any studies on the impact of oxygen on beer at terminal gravity vs fermenting beer.

 

[Vale71]

Here's a paper on the topic:

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1978.tb03843.x/pdf

 

[mediant]

I actually read a paper showing that adding yeast nutrient can increase levels of diacetyl in the final beer. I can't remember the reasoning at the moment - something to do with the yeast getting lazy if they have too much of most of the nutrients they need. Anyway, I tried supplementing my wort with valine on a few brews, but it didn't remove the VDKs once the beer was dry hopped - the idea being that if the yeast have valine around, they won't need to produce acetolactate (the precursor that is oxidized to diacetyl in beer when it is aged) which then can be converted into valine inside of the cell. But, I think in general some yeast nutrient additions will help some with diacetyl reduction within reason. More might not be better though...

That's a contradictory statement, as usually yeast nutrients contain BCAAs, and valine is one of them. Anyway, here's the paper. Among other things, there are few points worth mentioning:

• Malt modification impacts valine content (lager malt has the highest)
• Dry yeast has lower valine uptake capabilities, supposedly resulting in higher VDK

it's possible that oxygen enhances the oxidation of acetolactate. in addition, there are other precursors that form other VDKs when oxidized. I'll have to see if there are any studies on the impact of oxygen on beer at terminal gravity vs fermenting beer.

The point is, if a beer has alpha-acetolactate present, it must be left on yeast for D-rest until acetolactate is decarboxylated into diacetyl, which only then can be reduced by the yeast. When a beer is packaged with acetolactate, the latter will convert to diacetyl (no matter how - with oxygen or without, but eventually it will!), but there'll be no yeast to reduce it to 2,3‐butanediol.

 

[stickyfinger]

That's a contradictory statement, as usually yeast nutrients contain BCAAs, and valine is one of them. Anyway, here's the paper. Among other things, there are few points worth mentioning:

• Malt modification impacts valine content (lager malt has the highest)
• Dry yeast has lower valine uptake capabilities, supposedly resulting in higher VDK

The point is, if a beer has alpha-acetolactate present, it must be left on yeast for D-rest until acetolactate is decarboxylated into diacetyl, which only then can be reduced by the yeast. When a beer is packaged with acetolactate, the latter will convert to diacetyl (no matter how - with oxygen or without, but eventually it will!), but there'll be no yeast to reduce it to 2,3‐butanediol.

yea, the paper was a surprise to me. perhaps not all nutrient contains valine or adequate valine


i cant explain why spunding stopped the diacetyl issue other than oxygen. cold temps must be enough to keep the conversion rate low enough enough that it is below taste threshold for at least a few months

 

[maltyboy]

ALDC enzyme anyone?

 

[Vale71]

Thanks, but no thanks. I don't need to drink my lagers two weeks after pitching yeast.

 

[stickyfinger]

ALDC enzyme anyone?

i’ve wanted to try it for sure but it’s pretty expensive with limited shelf life. seems like the ideal fix

 

[stickyfinger]

This is a review article I was looking at when I was worrying about diacetyl more. It might have some useful info. for someone:

https://onlinelibrary.wiley.com/doi/full/10.1002/jib.84

 

[Comfort_Zone]

Dry hop just as fermentation is finishing up, and just be patient. It only takes a couple days for the diacetyl to be cleaned up anyway. I've just accepted that hop creep is going to happen and so I take advantage of it.

 

[lupulinaddict]

ALDC enzyme anyone?

Have you found a source for it on the homebrew scale?

 

[maltyboy]

Have you found a source for it on the homebrew scale?

I'm in Australia, but a few stores sell it. I bought 250ml through a commercial supplier.

I've never had a real issue with diacetyl at home, but appreciate it's use as one more thing I don't have to worry about. Has worked particularly well in lager production as well.

 

[porter1974]

Hi,

Good that you also can confirm the aerate topic. pH is something I already control, but I have not used yeast nutrient or stepping up the temperature during primary fermentation.

I really appreciate these tips, for me, continious improvement is as important as enjoying the hobby

Stepping up the temp to 70ish for a few days after your beer is mostly fermented will clean it up.

 

[Jesse93]

Now,

I did an IPA with the method mentioned above.
Straight out of the fermenter, it was the best beer I have made so far with bright citrusy charachter and aroma.

After 9 days in primary only, and dry hopped at yeast pitch - the beer passed the forced diacetyl test.

I proceeded with bottling straight from the primary using a spigot and wand. 6 days later I tried two of the beers... horrible.
I could not simply pick out any hop flavours, and I went heavy on the mosaic on this one.

What I can confirm is:
* Diacetyl forms due to refermentation in the bottle
* Some oxygen will always be introduced when bottling, I did spot acetaldehyde in the beer
* New yeast are formed and consumes the hop oils
Hop aroma fades due to the three observations above, leaving you with muddeled hop taste.

Conclusion: You can not bottle condition home brewed IPAs with results that is compareable to commercial top range IPAs. You either have to keg and force carbonate the beer and serve from the keg - or bottle using a beergun.

Further more, I have contacted two local breweries to see how they manage packaging.

 

[Jesse93]

Right, because we all know that gases never mix. Oh wait...

Oils are not gases though.

 

[Vale71]

Oils are not gases though.

Everything turns to gas when it evaporates. I've never seen oils leave a fermenter in liquid form when the fermenter is opened.

 

[Jesse93]

Everything turns to gas when it evaporates. I've never seen oils leave a fermenter in liquid form when the fermenter is opened.

You will need quite high temperatures for that to happen, maybe this is a problem if you ferment at 35 celcius, but should not be a problem at 16 celcius for exsample.

 

[couchsending]

Now,

I did an IPA with the method mentioned above.
Straight out of the fermenter, it was the best beer I have made so far with bright citrusy charachter and aroma.

After 9 days in primary only, and dry hopped at yeast pitch - the beer passed the forced diacetyl test.

I proceeded with bottling straight from the primary using a spigot and wand. 6 days later I tried two of the beers... horrible.
I could not simply pick out any hop flavours, and I went heavy on the mosaic on this one.

What I can confirm is:
* Diacetyl forms due to refermentation in the bottle
* Some oxygen will always be introduced when bottling, I did spot acetaldehyde in the beer
* New yeast are formed and consumes the hop oils
Hop aroma fades due to the three observations above, leaving you with muddeled hop taste.

Conclusion: You can not bottle condition home brewed IPAs with results that is compareable to commercial top range IPAs. You either have to keg and force carbonate the beer and serve from the keg - or bottle using a beergun.

Further more, I have contacted two local breweries to see how they manage packaging.

Sure you can. Have you tried reyeasting when bottle conditioning these beers? Adding yeast that isn’t already tired and covered in alpha acids. You could also krausen the batch which would probably be the best route. There’s a krausening calculator on Brewer’s friend.

 

[Jesse93]

Sure you can. Have you tried reyeasting when bottle conditioning these beers? Adding yeast that isn’t already tired and covered in alpha acids. You could also krausen the batch which would probably be the best route. There’s a krausening calculator on Brewer’s friend.

I have not tried to krausen / add more yeast, but I have read about it but it leaves me with some further questions.

(Before moving on and changing an unknown parameter, I need to know the root cause for fading hop aroma; yeast management or bottling process. Could be both, which is indicated if brewers who keg do not need do krausen.)

Then 1/2 package of dry yeast should be sufficient for 3 gal / 11 l of normal strength beer, and adding the last 1/2 when bottling?

 

[couchsending]

I have not tried to krausen / add more yeast, but I have read about it but it leaves me with some further questions.

(Before moving on and changing an unknown parameter, I need to know the root cause for fading hop aroma; yeast management or bottling process. Could be both, which is indicated if brewers who keg do not need do krausen.)

Then 1/2 package of dry yeast should be sufficient for 3 gal / 11 l of normal strength beer, and adding the last 1/2 when bottling?

Root cause of fading hop aroma is Oxygen pickup. Impossible to avoid if you’re trying to bottle off say a bottling bucket. You’d need at least a keg/beer gun/Co2 I’d think. I don’t ever bottle condition anything that isn’t sour/wild/mixed ferment. When I do I use a beer gun to try to keep everything as O2 free as possible.

1-2g of dry yeast is all that’s necessary for reyeasting 5 gallons of beer for bottling. For 3 gallons I’d probably go .5g.

 

[moreb33rplz]

Wait, why is aeration bad for dry yeast and not liquid? That doesn't make sense to me. Is there a source for this?

 

[Gravitysucks]

Wait, why is aeration bad for dry yeast and not liquid? That doesn't make sense to me. Is there a source for this?

There's a lot of information in this thread.
https://www.homebrewtalk.com/forum/...on-and-also-does-not-require-aeration.665957/

 

[Jesse93]

Root cause of fading hop aroma is Oxygen pickup. Impossible to avoid if you’re trying to bottle off say a bottling bucket. You’d need at least a keg/beer gun/Co2 I’d think. I don’t ever bottle condition anything that isn’t sour/wild/mixed ferment. When I do I use a beer gun to try to keep everything as O2 free as possible.

1-2g of dry yeast is all that’s necessary for reyeasting 5 gallons of beer for bottling. For 3 gallons I’d probably go .5g.

Thanks for the solid info Couch! [emoji869]

Then I'll better be off doing saisons for example, untill I live in a more spacy place where I can have a keezer.

Cheers [emoji16]

 

[couchsending]

Thanks for the solid info Couch! [emoji869]

Then I'll better be off doing saisons for example, untill I live in a more spacy place where I can have a keezer.

Cheers [emoji16]

You might be able to bottle spund, although I’d use some heavy glass if you’re not 100% sure of your FG. You’d have to bag the hops and add them at say 3 plato before FG, transfer to bottles with 1 plato to go. Without Co2 that might be the best way to mitigate O2 pickup.