Is there any practical difference between sodium and potassium metabisulfite?
I've been using the sodium variety because I was given a couple buckets of it. In my reading I never ever see reference to Na, only K.
NOW I ask the question -- two months into winemaking season!
Born Boozer Loser
Personally I don't think it makes much difference... the local shops only have Na-meta in tablet form, the bulk is always K-meta. I've heard the Na-meta is cheaper, but I think people use the potassium 'cos of the whole sodium-is-evil mantra that was big a few years back. HTH, but it's only my pet theory :^)
Sodium has received a bad reputation over the past few decades due to it's (alleged) association with hypertension (high blood pressure). For this reason, sodium metabisulphite is not permitted to be used by commercial wineries in the US. I have read that sodium metabisulphite can impart a bitter flavour to your wine, and for this reason I prefer potassium meta in my wine. However, I still use the (less expensive) sodium meta for sanitizing bottles and equipment, since the residual is rinsed or drained off.
There is also a very small difference in the amount of SO2 (which is what we really are trying to extract from these salts) per measured weight, but not enough to be significant.
Glad Heart,
Another consideration, and for me the main one, is that K tartrate will crystallize out of solution at cold temps, but not Na tartrate. This allows one to alter the pH and reduce the "mineral/salty" taste of a wine by cold stabilizing. I use K-meta. Somebody once gave me a 5 lb jar of Na-meta, and I wound up giving it to someone else. I wonder how many hands that jar passed through? ;)
Luck, Mike MTM
Either will work about the same in the small amounts required for wine stability, but there are a couple of factors to consider:
(1) The industry standard is potassium metabisulfite. The excess potassium, although small, can be chilled out of the wine as bitartrate. (2) It is very important to get your meta(bisulfite) FRESH! The stuff is reactive as hell, and degrades rapidly with air exposure to sulfate. It looks the same, but it's dead as a doornail.
Tom S
Thanks everyone.
Tom, my Na Meta is NOT fresh. I don't know how old it might be. Working with it, it still seems to have that characteristic harsh smell. Free SO2 levels seem fine in a couple wines I've tested. Maybe I'm lucky this time. Thanks for the alert.
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