Name: Mike R.
This is a simple but important question. Mainly because potassium metabisulfite is responsible for doing so much throughout the wine making process. A home winemaker relies on it heavily. If you are blindsided with some potassium metabisulfite that is old, it could cost you a batch of you precious wine.
The problem with old potassium metabisulfite is not that it will directly ruin the wine. It doesn’t change into something that is harmful. It just loses its sanitizing power. It becomes weaker and weaker as time passes on. Eventually, it will come to a point that it is not doing it’s job successfully.
Unfortunately, there is no practical way to tell if the potassium metabisulfite you have is old or not other than by age. You can try smelling the granules to see if you can smell any sulfur coming off, but this won’t even tell you if it is strong enough to protect your wine. Time or age is the best predictor.
If you purchased the potassium metabisulfite within the past 12 months, it should be fine. The only exception would be if humidity or moisture got to it. This would cause sulfites to leave the potassium metabisulfite as a SO2 gas, leaving you with a weaker powder. If the potassium metabisulfite has become hard, this could be the case.
If it is older than one year, you should be cautious, but it is most likely to still be okay to use, especially if it was stored in a cool, dry place. If you purchased it more than 3 years ago, then without question, throw it away. It’s not worth even trying or taking the risk.
If you are not sure when you purchased the potassium metabisulfite and you got it from us, you can call and we will be able to tell you when you purchased the potassium metabisulfite. We keep all your purchases on file.
The ultimate way to know the strength of your potassium metabisulfite is to test it with an SO2 testing kit. By doing this you can know the exact strength of your sulfite. There are certain situation where this may be necessary.
My thought on this is the cost of buying fresh potassium metabisulfite is nothing compared to loosing a batch of homemade wine. Your time along with the cost of other the ingredients being on the line, I say just keep the potassium metabisulfite fresh.
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.