Campden tablets are mainly sodium metabisulphite, Na2
this chemical reacts with acid (such as wine or grape juice) to release
sulphur dioxide, SO2
, which is a common preservative, E220,
in many food stuffs. E223 is sodium metabisulphite itself.
Some campden tablets are potassium metabisulphite, E224.
Potassium sorbate is sold in most wine-making shops as "fermentation
stopper" and is a very common preservative in food listed as
E202. It is the potassium salt of sorbic acid
, E200, which is present in
edible Rowan (sorbus aucuparia) berries.
These "E numbers" are also used in much commercial wine-making.
Unfortunately, not all wine has its ingredients listed, but that's
slowing changing. If you wish to make an "organic" home wine, I'm
afraid that this is not the site for you.