Carbon Dioxide Purity And Off Taste

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There are numerous discussions on HomeBrewTalk about off-flavors from CO2. Some are non-believers and insist that CO2 is CO2, while others claim to have experienced these off-flavors first-hand. I am primarily a soda brewer, and I'm a firm believer now that CO2 can have a significant impact on flavor. It is not about 99% vs 99.95% purity; it is about what the impurities are.
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Co2 Can Have A Significant Flavor Impact
Our senses are exceptionally sensitive to certain compounds, having the ability to smell or taste it in the orders of parts per million or billion. A good example of this is gas odorants in flavor infused water. The additives are in the orders of several PPM, yet we're able to detect these odors as a hint of peach or rose in water, even though the essential oils are in such a small amount that they're not easily measured.
I have a Sodastream machine, and there are only two main components to it. Water and CO2. I've modified it to accept bulk tank and at first it worked great. The line goes up to the machine unregulated and as temperatures change, CO2 condenses in the line. One time I left the main valve open and came back to use the machine a few days later, and immediately noticed a nasty chemical odor from the escaping CO2. Trying a sip, the carbonated water had a nasty chemical taste to it.
Suppose you mark a piece of paper with water soluble ink. It stays nice and clean even in humid air, but as soon as it gets wet, the ink will run. Same thing happens with CO2. CO2 is a good solvent for various oil-soluble components, and even if the gas is pure, it can leach out chemicals such as plasticizers and bring them out to surface, which can then get injected into beverage as an oil mist. Unlike water, CO2 becomes super critical above 88F, so instead of CO2 exiting only in a gaseous phase, it gains the ability to diffuse whatever is dissolved in it in a "fog" like fluid.
CO2 is handled as liquid in transfer, and it will dissolve oils used in process equipment such as the machining oil residues used in fittings and such.
I tested my 2.5 lb aluminum tank which has been filled numerous times, and sure enough, it contained quite a bit of residue. It was rinsed internally with petroleum ether which was collected. The rinse was collected and solvent was allowed to evaporate. The residue was allowed to dry at 180F, which gave off an odor of oil. The residue is a mixture of viscous oily liquid mixed with metal shavings, and it was weighed out to 61 milligrams on an analytical balance. Even if this was all soluble, it would only amount to 54 PPM in 2.5 lbs of CO2.
I believe that the difference between "beverage grade" and "industrial grade" CO2 is the filling process, and measures are taken to ensure PPM level residues with toxicity or objectionable flavor/odor are not introduced.
After experiencing this off-flavor, I think the most worthwhile solutions are an oil mist filter to remove the bulk of the impurities and an absorbent filter such as charcoal to grab the last bit of contaminants. Once the system has been contaminated, I would replace the plastic lines and clean the regulator, and disassemble and solvent-wash all metal parts. I would also replace the diaphragm, as once absorbed, you can't remove trace amounts of residues from rubber parts.
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A Picture Of The Residues I've Found
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The View Inside Of A Co2 Tank
The inside of an aluminum tank looks like this. It sort of looks like cast iron. It doesn't have the nice and shiny look that the outside does. It wasn't the easiest thing to photograph, so please excuse the quality.
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What about that? Should solve the problem.
http://www.micromatic.com/draft-keg-beer/gas-equipment-pid-770SG-L1300.html
 
This is super helpful. I wonder what kind of junk is in those paint ball tanks. Great article
 
You "believe" the difference between beverage and industrial grades is in filling method? Do you have anything to support that?
 
@MikeSkril I wonder if the CO2 filter will work for O2 tanks as well?
 
@241There isn't one. The only difference is the certification needed to sell food grade C02.
The dude at my local shop says both tanks are filled off the same large co2 tank at his shop. Only difference is he charges more for the food grade as he had to pay for the certifications. You also have to bring him a food grade tank to have him to fill and say it's food grade.
FYIW if you have a clean tank, doesn't matter.
 
Something to read http://www.foodsafetymagazine.com/magazine-archive1/december-2000january-2001/international-society-of-beverage-technologists-carbon-dioxide-guidelines/
 
Much better price for what appears to be the same filter.
http://co2purifier.com/co2-filter/
 
Also very interesting:
http://www.weldingandgasestoday.org/index.php/2015/03/a-primer-on-food-safety/
 
@oldion3
And there is a lot of info on this site. Cool!
 
I wouldn't blame the CO2. Unregulated gives me the thought it overcarbed for whatever reason and you got a carbon taste.
 
Better once seen... Thanks for posting up the images. I knew CO2 is a crappy thing and needs to be handled with attention to its purity but man I never supposed it could be _so_ filthy. I'm going to get myself a real good filter right NOW.
 
@beskone This is incorrect from what Ive been told. a number of gas manufacturing companies are customers of mine and one of them (Praxair) did warn me that their welding gas is handled differently than their food grade gas. They cited the their is contaminants and oils from the storage and transfer systems used and that they strongly recommended against me buying any used welding/industrial tanks for this reason. That being said perhaps not all companies handle the gases differently but are you sure who does and doesn't?
 
This article (as many that make the front page here) is half finished and extremely light on details.
You "believe" the filling process is different? Find out and put the answer in the article.
It mentions all these things the author did and gives zero detail on how to accomplish them: How do you clean a tank? Where do you get food grade gas?
If the point of this article was to start a conversation, it worked well as there is much more information in the comments than in the article itself.
Just saying... If you're going to make these articles a front page post and drop an email in my inbox about them, make them complete. Otherwise, leave them as a post in the forum like all the others. I'm not pointing at this article as the only example here, it's just the one that pushed me to post about it.
 
Further reading:
CocaCola's CO2 Quality guide: http://www.cokesolutions.com/Pages/DownLoadFile.aspx?DocID=1274
Draught Quality (specifically pg. 14) - http://www.draughtquality.org/wp-content/uploads/2012/01/DQM_Full_Final.pdf
International Society of Beverage Technologists Fountain Carbon Dioxide Quality Guideline: http://co2.ir/pdf/Fountain_Guideline.pdf
 
$130 and replace every 12 months?? I'd like some better product details than that...
 
@theonetrueruss Might not be able to withstand the pressures associated with carbonation... clogging? Micron issue?
 
In the US CO2 is produced from refining oil and natural gas. Benzene is very close in size and contaminates beverage grade CO2. In the EU beverage grade CO2 is made from fermentations. In order to remove benzen pass the CO2 through activated carbon blocks.
 
I have a diffrent frame of refrence to this issue than most on here - im new to home brew but have been scuba diving for almost 10 years.
I have had one 'bad' air fill where the filter somehow got oil within it and even people a few feet a way could smell it when i breathed from the reg - impuritys as rare as they are do happen and i have no doubt you would taste it - my mouth certainly tasted like oil for a good while after and that was only from a single breath - it was immediantly noticeable
It not always to that level but problems do occur and ive no doubt that this is no myth
 
I actually grilled a guy at Praxair over the phone today, (kind of felt bad, he didn't know some of the answers, had to walk back to the "plant" to ask someone)about purity rating, foodgrade Co2, etc. He basically said the same thing someone else posted above. He confirmed their Co2 is 99.9% pure, and that the only difference between food grade and "non-food grade," is the certification as such. I looked at Praxair's site last night, and their MSDS, and I didn't see where they listed the benzene content. From another link I found, the concentration should be no more than 20ppb. I didn't even ask him about the impurities profile, figured I had run him around enough for one day.
 
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