"ab" > wrote in message
om...
> Let me see if I understand what you are saying:
>
> The bound SO2 is pretty well irrelevant to wine protection. It is the
> Moleclar SO2, present in the Free SO2, that does the protecting.

That's pretty close.

> The Molecular SO2 that is required to protect is based on the PH and
> this gives you the free SO2 level that you should be aiming for.

Not quite. The amount of molecular SO2 needed to protect the wine is
constant at about 0.8 ppm. The amount of free SO2 required to produce 0.8
ppm molecular SO2 depends on the pH. If the pH is 3.2 e.g., it takes about
20 ppm free SO2 to produce the "magic" 0.8 ppm molecular SO2. If the pH is
3.6, it takes closer to 60 ppm free SO2 to produce 0.8 ppm molecular SO2.

A good rule of thumb is to set the free SO2 to the two digits to the right
of the decimal of the pH. IOW, at pH 3.50, set the free SO2 to 50 ppm; at
pH 3.35, set it at 35 ppm, etc. That'll get you pretty close for wines in
the normal pH range, and it's easy to remember.

Tom S