Ask The Brewmasters

We do this when we centrifuge our hard seltzer using the same in-line carb stone we use for carbonation, just at a much higher flow rate.  It is a very efficient way to blow off volatile aromas.  We also tried it once with a small batch lager that had just a touch too much sulfur with good effect.  It does have an impact on head retention and hop aroma, but depending on the beer and your time constraints, it might be a worthwhile compromise.

Head retention reduction, the loss of desired aromatics and the CO2 usage are all downsides or potential downsides that I was concerned with.  However, there must be a technique to mitigate the loss of head retention and preferred aromatics because high quality lagers are made using this process.  

Questions I have are:

1. Is this done under pressure?  I am assuming a spunding valve would be used to maintain a steady head pressure and reduce foaming in the tank.
2. What kind of flow rate would be used for the CO2?  A slower flow rate would give you more time to be sampling and deciding when you have reached the proper level however, there must be some sort of minimum flow rate needed to push out the sulfur.
3. At what temperature would this be best performed? 

CO2 rousing is definitely an effective way of reducing some sulfur compounds in your beer. I've seen it done/done it just before filtration (not just in lagers). Flow rates are going to be so variable based on your batch size, tank size and sensory load that you're probably best trying it out yourself. 'Vigorous' is what I would suggest.

I do agree with many of the downsides listed by others here, but Janelle Harmon did a very interesting presentation on the weighted impacts of 'positive' vs. 'negative' compounds on lager beer regarding consumer preferences at the ASBC meeting in Providence last year. It suggested that consumers are more sensitive to negative compounds (I think mercaptan and H2S were the ones cited) than positive ones (isoamyl acetate), so re a CO2 scrub, you're probably winning more than you're losing by getting rid of some of those sulfurs.

More than anything, I worry about the cost/sustainability (not as big a concern if you have CO2 recovery as Alex says) and establishing a consistent rousing process may be a challenge. A day-long rouse seems extreme to me, and begs the question of whether it takes a day to get everything out of the beer or whether the SOP errors on the side of overkill just to be sure. In either case, I feel like Phil's points re looking at other process inputs are well-founded instead of sending CO2/money out the window and creating a potential safety hazard if it's not monitored well.

Hi folks,

Could anyone, maybe Daniel or Nassim, expand on the idea of CO2 containing significant levels of oxygen? Do you mean as a result of impurities from your supplier or CO2 recovery system? That should not be the case, or if it is you would want to rectify it asap, no? That issue would be adding to DO pick up across your entire cellar and packaging operation even if you're not scrubbing. Personally I've never seen O2 pick up after adding CO2 (carbing or scrubbing) to beer. 

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880
------------------------------


Original Message:
Sent: 12-11-2023 17:03
From: Daniel Carey
Subject: Co2 scrubbing with lagers to reduce sulfur levels

Hi Francesco, great question! Before I get to my thoughts, I want to clarify my initial comment: in light of what Dan had said, I merely wanted to highlight that the positives to be gained by CO2 scrubbing could come at the expense of oxidation. Regardless, I'd also love to hear more from Dan.

Here's what I've found from a little bit of research: beverage grade CO2 isn't going to be 100% pure (even research grade is only 99.999% pure). In the US 99.9% pure seems to be pretty standard for beverage grade CO2. This leaves 0.1%/1000 ppm for other compounds. Typically oxygen isn't the only compound that makes up that other 0.1% and it seems that the typical max level of O2 in beverage grade CO2 is 20-30 ppm. 

20-30 ppm O2 isn't a lot in general, but let's consider the target DO levels for packaged beer: 150 ppb or less (ideally much less). For context 20-30 ppm is the equivalent of 20,000-30,000 ppb. In other words, CO2 scrubbing has the potential to add meaningful levels of oxygen to finished beer depending on how much CO2 is used.

The next question that comes to my mind is "So what? When we force carbonate we have to use CO2 and so we're necessarily adding some O2, so why does adding a little more via CO2 scrubbing matter?" I don't have measurements to form an answer, but my initial thought would be that problems arise from the additive nature of carbonating and scrubbing: sure, you're only adding a little more O2 from scrubbing, but you're adding it on top of the O2 you will be adding at the point of carbonation.

To be clear, this is just my thought process on this issue--I could be off base. I'm just kind of thinking aloud here.

(Side note: the presence of oxygen in beverage grade CO2 seems to be one more reason to use spunding valves!)

------------------------------
Nassim Sultan
Brewer/Free Agent
nassimsultan@gmail.com
------------------------------


Original Message:
Sent: 12-14-2023 04:52
From: Francesco Mayell
Subject: Co2 scrubbing with lagers to reduce sulfur levels

Hi folks,

Could anyone, maybe Daniel or Nassim, expand on the idea of CO2 containing significant levels of oxygen? Do you mean as a result of impurities from your supplier or CO2 recovery system? That should not be the case, or if it is you would want to rectify it asap, no? That issue would be adding to DO pick up across your entire cellar and packaging operation even if you're not scrubbing. Personally I've never seen O2 pick up after adding CO2 (carbing or scrubbing) to beer. 

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880
------------------------------

Hi Francesco, great question! Before I get to my thoughts, I want to clarify my initial comment: in light of what Dan had said, I merely wanted to highlight that the positives to be gained by CO2 scrubbing could come at the expense of oxidation. Regardless, I'd also love to hear more from Dan.

Here's what I've found from a little bit of research: beverage grade CO2 isn't going to be 100% pure (even research grade is only 99.999% pure). In the US 99.9% pure seems to be pretty standard for beverage grade CO2. This leaves 0.1%/1000 ppm for other compounds. Typically oxygen isn't the only compound that makes up that other 0.1% and it seems that the typical max level of O2 in beverage grade CO2 is 20-30 ppm. 

20-30 ppm O2 isn't a lot in general, but let's consider the target DO levels for packaged beer: 150 ppb or less (ideally much less). For context 20-30 ppm is the equivalent of 20,000-30,000 ppb. In other words, CO2 scrubbing has the potential to add meaningful levels of oxygen to finished beer depending on how much CO2 is used.

The next question that comes to my mind is "So what? When we force carbonate we have to use CO2 and so we're necessarily adding some O2, so why does adding a little more via CO2 scrubbing matter?" I don't have measurements to form an answer, but my initial thought would be that problems arise from the additive nature of carbonating and scrubbing: sure, you're only adding a little more O2 from scrubbing, but you're adding it on top of the O2 you will be adding at the point of carbonation.

To be clear, this is just my thought process on this issue--I could be off base. I'm just kind of thinking aloud here.

(Side note: the presence of oxygen in beverage grade CO2 seems to be one more reason to use spunding valves!)

------------------------------
Nassim Sultan
Brewer/Free Agent
nassimsultan@gmail.com
------------------------------


Original Message:
Sent: 12-14-2023 04:52
From: Francesco Mayell
Subject: Co2 scrubbing with lagers to reduce sulfur levels

Hi folks,

Could anyone, maybe Daniel or Nassim, expand on the idea of CO2 containing significant levels of oxygen? Do you mean as a result of impurities from your supplier or CO2 recovery system? That should not be the case, or if it is you would want to rectify it asap, no? That issue would be adding to DO pick up across your entire cellar and packaging operation even if you're not scrubbing. Personally I've never seen O2 pick up after adding CO2 (carbing or scrubbing) to beer. 

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880
------------------------------

Hi folks,

Could anyone, maybe Daniel or Nassim, expand on the idea of CO2 containing significant levels of oxygen? Do you mean as a result of impurities from your supplier or CO2 recovery system? That should not be the case, or if it is you would want to rectify it asap, no? That issue would be adding to DO pick up across your entire cellar and packaging operation even if you're not scrubbing. Personally I've never seen O2 pick up after adding CO2 (carbing or scrubbing) to beer. 

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880
------------------------------

Hi folks,

Could anyone, maybe Daniel or Nassim, expand on the idea of CO2 containing significant levels of oxygen? Do you mean as a result of impurities from your supplier or CO2 recovery system? That should not be the case, or if it is you would want to rectify it asap, no? That issue would be adding to DO pick up across your entire cellar and packaging operation even if you're not scrubbing. Personally I've never seen O2 pick up after adding CO2 (carbing or scrubbing) to beer. 

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880
------------------------------


Original Message:
Sent: 12-11-2023 17:03
From: Daniel Carey
Subject: Co2 scrubbing with lagers to reduce sulfur levels

Beverage Grade CO2 can contain 50 ppm O2, according to Matheson Gas.

Hi folks,

Could anyone, maybe Daniel or Nassim, expand on the idea of CO2 containing significant levels of oxygen? Do you mean as a result of impurities from your supplier or CO2 recovery system? That should not be the case, or if it is you would want to rectify it asap, no? That issue would be adding to DO pick up across your entire cellar and packaging operation even if you're not scrubbing. Personally I've never seen O2 pick up after adding CO2 (carbing or scrubbing) to beer. 

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880


Original Message:
Sent: 12-11-2023 17:03
From: Daniel Carey
Subject: Co2 scrubbing with lagers to reduce sulfur levels

Thanks for your responses Dan, Nassim, Alexander!

And apologies to the OP for sidetracking this discussion, but the potential ramifications of O2 impurity in brewery CO2 has piqued my curiosity! I agree that scrubbing beer to remove unwanted volatiles is not ideal as an SOP for the reasons already mentioned (blowing off other aromatics, foam stability, even clarity issues from collapsed foam) and is better addressed by adjustments in the fermentation stage. I would reserve it for "emergency" situations. 

As far as O2 pickup however, even accepting that beverage grade or recovered CO2 will contain oxygen in the 30ppm range, does anyone have any empirical evidence that this oxygen will dissolve into the beer? Even if Henry's law tells us that the gas will equalize across the gas/liquid interface, as I recall oxygen is way less soluble than CO2. 

Consider this example from my brewery. We carbonate in-line using a carbstone and T-bar at the outlet of the centrifuge. We add about 2g/L of CO2 (carb levels in FV pre-transfer being around 3g/L. We tend to see 5-10ppb O2 pick up from FV to BBT. 

If we transfer 10,000L, we are adding 20kg of CO2 to about 10,600kg of beer. If the CO2 contains 30ppm O2, that means we are injecting 60g of oxygen at high pressure into the beer stream in a high turbulence low pressure zone, encouraging gas solubility. If all the O2 was dissolved into the beer, we'd be talking about 60g in 10,060,000g of beer, or 59.6ppb. But like I said, we're seeing 5-10ppb pick up, and that's including pick up from the centrifuge and the BBT as well. 

Let me know what you think, and thanks again for your input!

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880
------------------------------


Original Message:
Sent: 12-14-2023 14:24
From: Alexander Kopf
Subject: Co2 scrubbing with lagers to reduce sulfur levels

Beverage Grade CO2 can contain 50 ppm O2, according to Matheson Gas.

Hi folks,

Could anyone, maybe Daniel or Nassim, expand on the idea of CO2 containing significant levels of oxygen? Do you mean as a result of impurities from your supplier or CO2 recovery system? That should not be the case, or if it is you would want to rectify it asap, no? That issue would be adding to DO pick up across your entire cellar and packaging operation even if you're not scrubbing. Personally I've never seen O2 pick up after adding CO2 (carbing or scrubbing) to beer. 

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880

Thanks for your responses Dan, Nassim, Alexander!

And apologies to the OP for sidetracking this discussion, but the potential ramifications of O2 impurity in brewery CO2 has piqued my curiosity! I agree that scrubbing beer to remove unwanted volatiles is not ideal as an SOP for the reasons already mentioned (blowing off other aromatics, foam stability, even clarity issues from collapsed foam) and is better addressed by adjustments in the fermentation stage. I would reserve it for "emergency" situations. 

As far as O2 pickup however, even accepting that beverage grade or recovered CO2 will contain oxygen in the 30ppm range, does anyone have any empirical evidence that this oxygen will dissolve into the beer? Even if Henry's law tells us that the gas will equalize across the gas/liquid interface, as I recall oxygen is way less soluble than CO2. 

Consider this example from my brewery. We carbonate in-line using a carbstone and T-bar at the outlet of the centrifuge. We add about 2g/L of CO2 (carb levels in FV pre-transfer being around 3g/L. We tend to see 5-10ppb O2 pick up from FV to BBT. 

If we transfer 10,000L, we are adding 20kg of CO2 to about 10,600kg of beer. If the CO2 contains 30ppm O2, that means we are injecting 60g of oxygen at high pressure into the beer stream in a high turbulence low pressure zone, encouraging gas solubility. If all the O2 was dissolved into the beer, we'd be talking about 60g in 10,060,000g of beer, or 59.6ppb. But like I said, we're seeing 5-10ppb pick up, and that's including pick up from the centrifuge and the BBT as well. 

Let me know what you think, and thanks again for your input!

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880
------------------------------


Original Message:
Sent: 12-14-2023 14:24
From: Alexander Kopf
Subject: Co2 scrubbing with lagers to reduce sulfur levels

Beverage Grade CO2 can contain 50 ppm O2, according to Matheson Gas.

------------------------------
Alexander Kopf
Brewer
Northwoods Brewing Company
alex@northwoodsbrewingcompany.com
------------------------------


Original Message:
Sent: 12-14-2023 10:28
From: Daniel Carey
Subject: Co2 scrubbing with lagers to reduce sulfur levels

Original Message:
Sent: 12/14/2023 4:52:00 AM
From: Francesco Mayell
Subject: RE: Co2 scrubbing with lagers to reduce sulfur levels

Hi folks,

Could anyone, maybe Daniel or Nassim, expand on the idea of CO2 containing significant levels of oxygen? Do you mean as a result of impurities from your supplier or CO2 recovery system? That should not be the case, or if it is you would want to rectify it asap, no? That issue would be adding to DO pick up across your entire cellar and packaging operation even if you're not scrubbing. Personally I've never seen O2 pick up after adding CO2 (carbing or scrubbing) to beer. 

Cheers,

------------------------------
Francesco Mayell
Lead Brewer
Brixton Brewery
London
02036098880