Molecular SO2 calculator
The only sulphite number that matters. Free SO2 alone tells you almost nothing, because how much of it is actually protecting the wine depends on pH, and the relationship is logarithmic.
Molecular SO2 now
0.60 mg/L
Free SO2 needed
40 mg/L
Free SO2 to add
10 mg/L
Potassium metabisulphite
0.35 g
A share of any addition binds immediately to acetaldehyde and other carbonyls and never shows up as free SO2. Measure again after adding rather than assuming this figure landed.
Model used
Henderson-Hasselbalch on the sulphurous acid pKa of 1.81. If another calculator gives you a different answer, this is usually why. Neither is wrong; they are different published models of the same process.
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