Campden Tablets - Best Before Date?

[CrownCap]

Have had a pack of Campden tablets for a couple of years used to remove the chlorine from my water and noticed on my last brew at the weekend that they had a best before date back in March of this year.

Anyone know is they are an unstable compound that deteriorates over time or is that best before date just there to placate the health and safety police?

PS and yes, I am trying to be a cheap skate before you ask

[harry_mac]

I didn't know they had a shelf life until I checked after reading your post. Mine expired 02/08 .

According to http://winemaking.jackkeller.net/wineblog9.asp:- "Campden tablets degrade over time, so after a year - certainly after two - they should be discarded and new ones obtained."

There's no explanation as to why they degrade - maybe it's to do with sulphur dioxide gas being produced after reacting with moisture in the air?

Anyway, at 1 fresh tablet per 20 gallons for chlorine/chloramine treatment (which equates to < 1/2 tablet for a final volume of 5 gallons), it wouldn't do any harm to bump up to 1 tablet to allow for some degradation.

As it happens I don't use the campden tablets for water treatment in brewing - I use powdered sodium metabisulphite instead, at a pinch at a time per 10 litres from the combi boiler. I got the tablets for winemaking as most instructions referred to using one or 2 campden tablets at a time, and it's easier using them rather than try to measure the right amount of powder. The strange thing is that the powdered sodium metabisulphite doesn't have a shelf life shown on the label, even though it's the same chemical as the campden tablets I've got. Maybe it's to do with campden tablets being used in foodstuffs (i.e. wine), rather than being just a chemical.

[OldSpeckledBadger]

Metabisulphites aren't totally stable and will break down to give off sulphur dioxide leaving a sulphate salt It's actually this reaction which gives them a certain amount of sanitising effect.