Disinfecting with sulphite

Crashjack

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I made homemade wine for several years and learned that sodium/potassium metabisulphite was preferred by most winemakers as a disinfectant over bleach. The major reasons are that it rinses easily and is very effective. Sodium metabisulphite is a little more effective as a disinfectant than potassium metabisulphite but can cause off-flavors if used in wine as a preservative, which is why potassium metabisulphite is usually added to the wine, while sodium metabisulphite is usually used to disinfect equipment (obviously, nobody would use bleach as a wine preservative).

My question is, is there any reason not to use sodium or potassium metabisulphite as a disinfectant for QT equipment, filter socks, and other stuff I might want to disinfect? Also, after reading about bleach dosing in the General Forum, might there be other potential uses for a relatively safe disinfectant like sodium/potassium metabisulphite?
 

Randy Holmes-Farley

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I'm not aware of how well metabisulfite is able to kill the larger organisms that one is typically worried about in a qt disinfection. That is, pests like ich that are larger than bacteria. It may be fine, but I also see little reason to pursue it if you don't have the data (and won't readily know when using it) since concentration and time data is well known for bleach and such organisms.

FWIW, I do not see any reason to think the nature of the salt form (sodium vs potassium) makes a difference in the ability of metabisulfite to kill bacteria. They do not remain associated in water once dissolved. It may be important for other reasons in wine, but not for the disinfection aspect.
 
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Crashjack

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It has been a while so I don't remember the details. Just did a quick search and some claimed the sodium version contains slightly more sulfite than the potassium version. This might just be due to packaging standards or it might not be correct. Heck, the difference might just be cost... that the sodium version is cheaper than the potassium version making it more economical for sanitizing where larger quantities are used, than in preserving. My interest is based on simplicity and easy rinsing.

Of course as you state, we are trying to disinfect more than just fungi and bacteria, and that is where the big question lies. My major question here was in regards to safety for livestock. I wouldn't think there would be an issue as it does rinse very easily. It would likely wreak havoc on the display tank's biological filtration if exposed to disinfecting concentrations, but that wouldn't happen.
 

Randy Holmes-Farley

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Sodium metabisulfite will contain slightly more metabisulfite per unit weight since sodium weighs less than potassium. It's not a reason to pick one over the other. :)
 

Epicreefster

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I worked in a winery for a harvest season and routinely used metabisulfate for disinfection. Its nice because it seems less harmful than bleach. From what the head winemaker told me is it needs to be acidic to be really effective. We would mix about 1 cup metabisulfate, 1 cup citric acid and 50 gal of water to make a soak/dip. Supposedly this made a dilute sulfuric acid that did the disinfecting, maybe Randy can chime in on how true this is. These days I would recommend getting some high strength hydrogen peroxide, available at some pool or whole house water system stores. And dilute to .5-1%, soak a min or two and then you really don't even need to rinse as long as its nothing like a sponge. A little H2O2 is quite harmless.
 

Randy Holmes-Farley

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From what the head winemaker told me is it needs to be acidic to be really effective. We would mix about 1 cup metabisulfate, 1 cup citric acid and 50 gal of water to make a soak/dip. Supposedly this made a dilute sulfuric acid that did the disinfecting, maybe Randy can chime in on how true this is.

It wouldn't be sulfuric acid that was forming, but rather more likely SO2 (sulfur dioxide), which is a known preservative. It happens in water and is accelerated by acid:

https://en.wikipedia.org/wiki/Sodium_metabisulfite

Na2S2O5 + 2 HCl → 2 NaCl + H2O + 2 SO2

Any sulfate that did form will just be a bystander ion, not really doing anything, and it is much too weak of a base to protonate to form sulfuric acid:

2H+ + SO4-- _____ --/-->______ H2SO4
 
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Crashjack

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I never added acid to my sanitizing solutions. I would just add powered sulfite to a spray bottle filled with warm water and shake. I could then spray the inside of 5-6 gallon carboys, fermentation buckets, racking equipment, etc. A quick rinse was all it took and ready to go. The bottle was good for several months.

This is what entrigued me about using with QT equipment. Unfortunately, I couldn't find where sulfite was used for this sort of thing other than hatcheries spraying fish eggs, which was supposed to make them hatch better. I didn't read why that was.
 

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