Wine Sulfite Calculator
Sulfur dioxide (SO2) management is central to winemaking. The correct amount to add depends on the wine's pH: lower pH wines (more acidic) require less total SO2 to achieve the same antimicrobial effect because a greater proportion is in the active molecular form. This calculator determines the target free SO2 level for your wine's pH to achieve 0.6 ppm molecular SO2 (the standard antimicrobial target), then calculates how much potassium metabisulfite (KMBS) powder or Campden tablets to add, given your current free SO2 level and wine volume. Enter your wine's pH, current free SO2, and volume.
SO2 calculation formula
Molecular SO2 target = 0.6 ppm
Free SO2 target (ppm) = molecular_target / (1 / (1 + 10^(pH - 1.81)))
SO2 needed (ppm) = target - current free SO2
KMBS (g) = volume_liters * SO2_needed_ppm * 0.001 / 0.57
Campden tablets = volume_gallons * SO2_needed_ppm / 50
KMBS (potassium metabisulfite) is 57% available SO2 by weight. One Campden tablet = ~0.44 g KMBS per gallon = 50 ppm per gallon.
Sulfite addition safety notes
- Always dissolve KMBS in a small amount of water or wine before adding to the batch.
- Sulfites can cause adverse reactions in sensitive individuals, particularly those with asthma. FDA requires wines to label "contains sulfites" if total SO2 exceeds 10 ppm.
- Do not add sulfite during active fermentation. SO2 inhibits yeast.
- Test free SO2 every 3-4 months during aging and top up as needed.
- The legal maximum for table wine in the US is 350 ppm total SO2 (FDA/TTB).
Wine sulfite: frequently asked questions
Why do winemakers add sulfite (SO2)?
Sulfur dioxide (SO2) is an antimicrobial and antioxidant used in winemaking to prevent oxidation, inhibit wild yeast and bacteria, and preserve color and flavor. It is one of the oldest and most studied preservatives in food and beverage production.
What is free SO2 vs molecular SO2?
Total SO2 is the sum of bound and free SO2. Free SO2 is the biologically active portion. Molecular SO2, a subset of free SO2, is the antimicrobially effective form. The proportion of molecular SO2 in free SO2 depends on wine pH. Lower pH wines need less total SO2 to achieve the same molecular SO2 level.
What is the target free SO2 for winemaking?
Most winemakers target 0.5-0.8 ppm molecular SO2, which is the concentration shown to be antimicrobially effective. At pH 3.2, this requires about 19-30 ppm free SO2. At pH 3.6, it requires 50-80 ppm free SO2. This calculator targets 0.6 ppm molecular SO2 by default.
How many ppm SO2 does one Campden tablet add?
One Campden tablet (potassium metabisulfite) adds approximately 50 ppm SO2 to 1 US gallon (3.785 L) of wine. For 5 gallons, one tablet adds about 10 ppm. Always crush tablets fully and dissolve in a small amount of water before adding.
How do I test free SO2 in wine?
The Ripper test (iodometric titration) is the most common home winemaking method. Commercial wineries use the aeration-oxidation (A-O) method for more accuracy. Test kits are available from homebrew and winemaking supply stores.
Official sources
- FDA Code of Federal Regulations: 21 CFR 101.100 - Sulfiting Agents.
- Alcohol and Tobacco Tax and Trade Bureau (TTB): Wine Labeling Requirements.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.