Molecular SO2 Calculator

Why Molecular SO2 Matters in Winemaking

Free SO2 is what you measure in the lab, but molecular SO2 is the antimicrobial form that protects wine. You cannot measure molecular SO2 directly, so winemakers estimate it from free SO2 and wine pH. Related tools: Homebrew ABV Calculator and Alcohol Dilution Calculator.

Molecular SO2 Formula

$$\text{mol. SO}_2 = \frac{\text{free SO}_2}{1 + 10^{(pH - 1.81)}}$$

To hit a target molecular level, rearrange to $$\text{required free SO}_2 = \text{desired mol. SO}_2 \times (1 + 10^{(pH - 1.81)}).$$

Typical Targets

Many winemakers aim for about 0.5 mg/L molecular SO2 in red wine, 0.8 mg/L in white wine, and up to 1.5 mg/L in dessert wines. Lower pH means more molecular SO2 from the same free SO2 reading.