As I understand it, what we're after is free molecular SO2. How much free
SO2 is generated by any given quantity of KMS (short hand for potassium
metabisulfite) is inversely influenced by pH. Meaning; the more acidic the
must or wine, the greater the free molecular SO2 generated. I use a simple
chart to help me determine the desired level of SO2 to add at crush time.
One chart for red wine, one for white. A good source for info by which to
determine these ratios is Margalit's book.

After crush, I test for free SO2 (recently switched from Ripper to
aeration-oxidation; life is MUCH better!) to determine if I need to add
more. Usually at racking time. Again, I try to keep the freee SO2 within a
range determined by the pH. Before bottling, I try to get free SO2 to 30
ppm.

Personally, I try to minimize the addition of KMS. By testing more
frequently, and only adding as necessary, I hope to keep sulfite additions
to the minimal necessary to protect the wine. I'm one of those 'sensitive
nose' types who can detect when there is too much sulfite in a wine.



> I've been told that every time I move the wine, add 50ppm of KSO2. This
> goes for crushing, pressing, racking and bottling.
>
> A) I've also been told that if you want MLF to keep SO2 under 30ppm,
> and in some cases seen it recommended that you only add so2 in the
> crush and not the press. I'd be interested in the range of comments
> capable of this board, as I plan on pressing tmw night.
>
> B) Should I just get a SO2 test kit and bring the free SO2 up to 50
> from wherever it is? - given that it probably doesn't go to 0.
> thanks
>