I have a few campden tablet left over from a mead I made 10 or so years ago. Are they still good? Do the lose efficacy?
Edit
When I google the subject, I find lots of links saying, Throw them out after 6 months. or They should be good forever. I'm looking for an answer that cites sources, or otherwise gives an empirical explanation as to why or why not.
if they have remained bone dry and away from air, they should be fine. If they've gotten moist or haven't been sealed properly in a right sized container, then they will have slowly gassed off their sulfites and just the starches will remain.
I was using some that were ~20 years old until they ran out and I had to buy some more, never had an issue with them.
Campden tablets consist of sodium metabisulphite (an inorganic salt used as a preservative with no expiry date) and a binder, typically lactose or starch which also doesn't go off. Normally lactose and starch could be subject to bacteria, mold or other organic deterioration, but the sodium metabisulphite will prevent that.
Bottom line: use them no matter what the "best before" date says.
Remember that a best before date is mandatory because this is a food grade product. Even CO2 used to serve beer on tap is required to have an expiry date, even though this is nonsense.
My stock is about 12 years old, and the tablets still do their job, removing chlorine and chloramines.
They should last at least 50 years, maybe hundreds. I've been using mine for 20 years.
David M. Taylor B.S. Chemical Engineering Michigan Tech Class of 1997
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