Chemistry Quiz: Star San + NaMeta = ?

[Brooothru]

Alright all you chemistry majors. What bad things can happen if you mix, say, 1 tbsp of sodium metabisulfite into 5 gal of water/Star San?

I ask this because I really got interested in closed transfer brewing about a year ago after reading and studying up on the Low Oxygen thread topics. I've incorporated LoDO techniques into my brewing processes and I've noticed a marked improvement in my beers, especially with kegs that have been sanitized with Star San and then purged with CO2, then stored until use with a 15 psi CO2 charge and later filled with finished beer from the fermentor under pressurized transfer.

Beers seem to stay "fresher" longer. I recently tapped an IPA that had gotten pushed to the back a few months ago and I figured it was probably a dumper by now, but the hop flavor and aroma was still bright and very intact. Pleasantly surprised.

Yesterday I was cleaning a cannonball keg after it 'kicked' and the thought occurred to me: since the objective is to scavenge O2 from the keg, and since NaMeta is both a sanitizer and a strong O2 scavenger, why not add a tsp/gallon to my Star San solution before purging with CO2? I haven't come across anything in the literature that indicates it's either beneficial or dangerous, so I thought I'd bounce the idea off the brain trust on this forum to get some insight that I can add to my knowledge base.

Bueller...? Anyone..Bueller?

Brooo Brother

 

[Robert65]

Don't add NaMeta to iodophor. It scavenges iodine the same way it does its cousin, chlorine. (It's fun, though, to drop a pinch into a keg of iodophor and watch it instantly turn clear.)

As for any ill effects with Star San, I don't know. I'll caution, though, that NaMeta is not a sanitizer at all. Just slowly inhibits some things, hence the way winemakers use it. That said, Star San is definitely not a broad spectrum antimicrobial either. It does not kill yeast, wild yeast, fungi, any spores, or some bacteria, it only kills many bacteria. Therefore, I use iodophor, which is stone cold killer, and don't worry about the minuscule amount of 02 left after pushing it out (I too brew low oxygen.) Seems a fair trade off for good sanitation, and I hope my beer has enough residual reducing power of its own to compensate.

I did at one point have the same thoughts as you, though. Good question.

 

[RPh_Guy]

You can make a sanitizer solution with sulfite and citric acid. That's what I would use for purging if I kegged.
No need for the Star San.

@Robert65 In fact, both star san and sulfite are broad spectrum antimicrobials when used correctly.

 

[Robert65]

You can make a sanitizer solution with sulfite and citric acid. That's what I would use for purging if I kegged.
No need for the Star San.

@Robert65 In fact, both star san and sulfite are broad spectrum antimicrobials when used correctly.

Thanks, @RPh_Guy. That leads to, what is "correctly," particularly in the case of sulfite? It's dirt cheap and I need a supply on hand for low oxygen brewing anyway. What "recipe" would you recommend?

 

[RPh_Guy]

Half an ounce of each metabisulfite and citric acid per gallon works well. Adding more of either/both will increase how long it lasts.
Oxygen inactivates the sulfite, as you know, but you can determine that it's still effective by the odor.

It's a potent sanitizer and the gas it produces also sanitizes.

You probably could add sulfite to Star San; I don't see any potential chemical interaction ... But it's untested as far as I know so I can't really recommend it.

Cheers

 

[Brooothru]

Half an ounce of each metabisulfite and citric acid per gallon works well. Adding more of either/both will increase how long it lasts.
Oxygen inactivates the sulfite, as you know, but you can determine that it's still effective by the odor.

It's a potent sanitizer and the gas it produces also sanitizes.

You probably could add sulfite to Star San; I don't see any potential chemical interaction ... But it's untested as far as I know so I can't really recommend it.

Cheers

Thanks for the suggestion. I never thought about combining NaMeta with a simple acid to make a sanitizer that also scavengers O2. Of course, Star San is a food acid based sanitizer. But citric acid + NaMeta might be just the ticket while also saving some $$$. What about an iodophor soak (12.5 ppm titration) followed with a citric/NaMeta wash and CO2 purge? Might cover all the bases.

Brooo Brother

 

[Robert65]

Thanks for the suggestion. I never thought about combining NaMeta with a simple acid to make a sanitizer that also scavengers O2. Of course, Star San is a food acid based sanitizer. But citric acid + NaMeta might be just the ticket while also saving some $$$. What about an iodophor soak (12.5 ppm titration) followed with a citric/NaMeta wash and CO2 purge? Might cover all the bases.

Brooo Brother

Unless you are worried about your water supply (on a well maybe)* is the acid in the rinse necessary? Iodophor followed by a purge with water that's been deoxygenated, dechlorinated, etc. with metabisulfite might be all that is needed if you simply are concerned with what chemical residue might remain in the keg. All that would remain is water with some assortment of sulfate, chloride, etc. I used to filter my beer, and used just that procedure to sanitize everything with an iodophor run and then purge the keg and flush the filter in one operation with water with NaMeta. But I really don't worry about the immeasurable film of iodophor that might coat the inside of a keg since abandoning filtration. Maybe I should? Insights welcome. Interesting topic.

*Even if there might be some bugs in the water, it still isn't an environment likely to support beer spoilers, is it?

 

[RPh_Guy]

What about an iodophor soak (12.5 ppm titration) followed with a citric/NaMeta wash and CO2 purge? Might cover all the bases.

You don't need a separate sanitizer. Iodophor isn't any more effective than sulfite.

@Robert65
Low pH increases the effectiveness of the sulfite as a sanitizer. This eliminates the need for a separate sanitization step.

The small amount of residue after a sanitizer rinse is not concerning.

 

[Robert65]

@RPh_Guy,
What is the contact time required for the meta/acid solution?

 

[Bilsch]

Half an ounce of each metabisulfite and citric acid per gallon works well. Adding more of either/both will increase how long it lasts.
Oxygen inactivates the sulfite, as you know, but you can determine that it's still effective by the odor.

It's a potent sanitizer and the gas it produces also sanitizes.
Cheers

I'm guessing the intention is to create sulfur dioxide gas however I thought the method was to mix sulfuric acid with metabisulfite to give you SO2.
Does citric really work the same? I cant seem to balance the equation with those two and get SO2. Either way I'm not sure I'd want that stank round my house.

 

[RPh_Guy]

@RPh_Guy,
What is the contact time required for the meta/acid solution?

That's a difficult-to-answer question for every sanitizer. Anecdotal evidence suggests a couple minutes is good.

I cant seem to balance the equation with those two and get SO2.

Metabisulfite releases SO2; most of it forms a bisulfite ion. Low pH shifts the equilibrium towards higher SO2.

 

[Robert65]

I'm guessing the intention is to create sulfur dioxide gas however I thought the method was to mix sulfuric acid with metabisulfite to give you SO2.
Does citric really work the same? I cant seem to balance the equation with those two and get SO2. Either way I'm not sure I'd want that stank round my house.

Good point on the stank. I just got a fresh gallon of iodophor, and looking up some prices, it looks like at best I'd only save a few bucks mixing up the recipe given here. But if anyone can verify that it would work, it would be good info to file away. I like to learn something new every day. Maybe I have.

 

[RPh_Guy]

Good point on the stank. I just got a fresh gallon of iodophor, and looking up some prices, it looks like at best I'd only save a few bucks mixing up the recipe given here. But if anyone can verify that it would work, it would be good info to file away. I like to learn something new every day. Maybe I have.

The sulfite also scavenges oxygen, which is beneficial while purging a keg. It is necessary? No. Worthwhile? Maybe.

 

[Robert65]

The sulfite also scavenges oxygen, which is beneficial while purging a keg. It is necessary? No. Worthwhile? Maybe.

I don't think the oxygen potentially contained in that residue of iodophor or other sanitizer on the inside of a keg is where I should be worrying when it comes to TPO. That's been my assessment for some time. But you have at least presented a potential way of dealing with that issue if anyone sees it differently. Thanks.

 

[Brooothru]

Unless you are worried about your water supply (on a well maybe)* is the acid in the rinse necessary? Iodophor followed by a purge with water that's been deoxygenated, dechlorinated, etc. with metabisulfite might be all that is needed if you simply are concerned with what chemical residue might remain in the keg. All that would remain is water with some assortment of sulfate, chloride, etc. I used to filter my beer, and used just that procedure to sanitize everything with an iodophor run and then purge the keg and flush the filter in one operation with water with NaMeta. But I really don't worry about the immeasurable film of iodophor that might coat the inside of a keg since abandoning filtration. Maybe I should? Insights welcome. Interesting topic.

*Even if there might be some bugs in the water, it still isn't an environment likely to support beer spoilers, is it?

We are on a well, however the water quality is quite good. The aquifer is supplied mainly from an undeveloped forested hillside watershed into an agricultural valley of mostly agrarian crops (little livestock). Our well is nearly 500' deep, even though multiple water sources were available at several lesser depths starting at 80', and filters through soil and rock beds typical of ancient Atlantic Coast seabeds.

Ward Labs reported no elevated levels of harmful bacteria. pH is 7.3, so mostly neutral acidity. We do not use water softening, however all water passes through a primary filtrate bed and a carbon block whole house filter before entering the distribution plumbing. For brewing I also run the water through an in-line KDF filter like the ones used on RV water inlet hoses. I do run an analysis using Bru'in Water for every brew session based on beer style and grain bill, correcting with water salts and lactic acid for pH, anions and cations.

I use iodophor for cleaning most of my non-plastic equipment and fittings, but I do worry about iodine or medicinal smells so I usually perform a quick rinse with water just before using to get rid of any residual iodine-based chemical residues. I'm probably destroying the sanitized protection, but I'm really sensitive to the iodine smell. And that's what concerns me most about the iodophor soak. After you soak your kegs, do you do a full volume rinse with only NaMeta treated water and then purge with CO2? Is that sufficient to get rid of any iodine smell? Are you able to get rid of all the 'leftover' iodophor and NaMeta water, since either one could adversely affect the taste of the final beer, and NaMeta can leave a ton of sodium behind if you don't purge all of it.

Lots of questions, but I think you're probably on to something with your procedures and I'm anxious to give it a try. Citric acid and NaMeta sound appealing, but iodophor followed by an NaMeta water rinse is probably more thorough for sanitizing as long as I can eliminate the smell and any residual liquid with the CO2 purge.

Thanks for sharing,

Brooo Brother

 

[RPh_Guy]

I don't think the oxygen potentially contained in that residue of iodophor or other sanitizer on the inside of a keg is where I should be worrying when it comes to TPO.

The amount is sanitizer left in the keg isn't the issue.

Oxygen diffuses not just into, but out of solution, to reach equilibrium. So if you purge a keg with a sanitizer that is saturated with oxygen, oxygen will be diffusing into the CO2 while it's being purged.
The significance of this? Not sure, but it is very easy to scavenge the oxygen with sulfite. (I'm not advocating this practice, just presenting facts.)

@Brooothru
Question: why are you using iodophor if you're afraid of leaving a residue? You may as well not be using it at all since you're rinsing.
Iodophor is a sanitizer, not a cleaner. You don't need to soak anything with it. A rinse with kill any residual microbes on a surface that's already been appropriately cleaned.

No, a sodium metabisulfite rinse won't leave behind "a ton" of sodium. Each tablespoonful of sanitizer adds 3ppm of sodium to 5 gallons (if my math is correct). If that bothers you, you can just as easily use potassium metabisulfite since the potassium is flavor neutral.

 

[Robert65]

@Brooothru,
I use iodophor at the 12.5ppm titratable concentration (I occasionally confirm the dilution with test strips as my gallon jugs of concentrate age,) for almost of all my sanitizing operations and for liquid/CO2 purge of kegs, and I don't rinse at all. I used to. I used to be worried, in theory, about anything residual that might affect flavor higher than the chlorine concentration in my municipal water supply, which I rinsed with. But I've tried to streamline processes, eliminating unnecessary steps, and, apparently unlike you, I am fortunate enough to be oblivious to residual iodine at this level (I can just about smell it on a sanitized surface, but detect nothing in the beer. I've only recently become aware that some people are so sensitive; I fully sympathize, being one of the genetically cursed cilantro averse.) I only thought the flush of the iodophor with NaMeta-deoxygenated water was absolutely necessary when filtering, because the system could retain a fair bit of solution that would get mixed into the beer, containing both iodine and oxygen. The whole filtering operation is another thing I've weaned myself away from as it probably doesn't win in a cost/benefit analysis. But if you're concerned about residual iodine, try the flush and let me know how you think it works. I never measured carefully, but dosed NaMeta to the rinse water using what was clearly overkill for oxygen scavenging, but realizing that very little sulfite/ sulfate would end up in the beer.

 

[Robert65]

@RPh_Guy, actually iodophor can be a very effective cleaner. It functions just like chlorine bleach, which is of course quite effective on glass and other materials that can tolerate it, but is less corrosive of metals. A good soak in iodophor is my go to cleaning method for a stainless oxygenation stone that needs some extra attention, as it doesn't risk leaving a deposit like standard alkaline cleaners can. Just a side tip.