> > The level of pH when tartrates are forming is a factor for how
> > much it will change. The further away from the wines pKa (typcially
> > around 3.65) the more dramatic the change.
>
> Hi, Clyde -
> On another NG we had a similar discussion on the effect of cold stabilizing
> wines. IIRC, the pKa for potassium bitartrate mentioned was a lot lower
> than 3.65. It was more like 3.2 - and this data was from an organic
> chemist, who certainly should be a reliable source.
>

Hi TomS,

You know that I'm no chemist, but the way I understand this, the pKa
of KHTa is not the issue here, but rather the pKa of tartaric acid in
wine. Tartaric acid has a pKa of 3.5 in water, but because of the
buffering effects of wine (created by the various acids and salts
present) the pKa for tartaric in wine is slightly higher, usually
around 3.65, depending on the grape variety, growing season, location,
etc.

> > Sulfites at these elevated pH's is
> > virtually useless.
>
> I wouldn't go so far as to say that, but it's true that it takes a good deal
> more free SO2 to maintain 0.8 ppm molecular SO2 at pH 3.8 than it does at
> 3.2.
>

You differ from Clark Smith, who states that levels of 20 to 30 ppm is
all that should be maintained in wines of higher pH, and that the
purpose is only to bind acetaldehyde; not as a microbial disinfectant.
I don't go there, so cannot say from experience; just hearsay!!




clyde