"michael" > wrote in message
...
>I have some particularly promising white wine(Schonburger)which tastes
> beautiful now.The grapes were harvested in October 2007,racked in
> November and 30ppm sulphite added.It is now clear in a 1 gallon
> glass demijohn and I wish to make sure that it lasts into the
> summer.Will adding some more sulphite (another 30ppm) protect it,and
> should I put it somewher cool to keep it in best condition.I live in
> England (we do make good wine here!)and the summer temperatures rarely
> exceed 80F.Should I also keep it out of the light.I know that this is
> a small quantity,but I do wish to develop good practise.
> Michael

Conventional wisdom is that about half of the first dose becomes
"bound" (used up). But - having once reacted with all of the available
"sites", subsequent additions will remain as all free SO2.

Campden tablets are based on the assumption that 50ppm free SO2
will provide "adequate but not excessive" sulfite in any wine that has
a pH in the "typical" range of 3.2 to 3.6.

Thus, if I were unable to test my wine, I would assume that I only
had about 15ppm free remaining after the first dose and that I should
add about 30ppm to get it back up_near_that 50 ppm free (without
exceeding that amount.) All of this of course based on the
assumption that the wine has a typical pH.

Joe is right. It is always better if you can test things to better control
outcomes, but in a pinch you can use the above procedure. HTH

Frederick