Why is potassium metabisulphite preferred to sodium by some sources?
I have read a number of sources that recommend the use of potassium metabisulphite or potassium-based campden tablets in preference to their sodium-based equivalents (e.g. Jack Keller states that he doesn't recommend the use of sodium metabisulphite here), but I have been unable to find a clear explanation of why this is. And it seems that most American recipes that specifically call for one or the other suggest potassium. But here in the UK, it is by far easier to acquire sodium-based sulphites. As far as I can see, they are very similar and produce almost identical reactions in the wine, so is there any reason I should take the extra effort to acquire potassium-based sulphites?