Wine Sulfite Addition Calculator
Wine SO2 addition in grams and solution mL from volume and ppm gap.
What it does
Sulfur dioxide protects wine twice: free SO2 blocks microbes and oxidation while pH decides how much of it stands in the active molecular form. Additions therefore start from measured free SO2 and a pH-aware target, not from habit.
The tool above takes batch volume with current and target free SO2. It returns metabisulfite grams with 10% solution milliliters and the rise.
The default 20 liters rising 10 to 40 ppm needs 1 g KMBS (10.4 mL of 10%). The imperial mirror of 5.28 gallons reads the same.
Math follows Iowa State extension practice with Virginia Tech enology formulas and PubChem stoichiometry behind them. All three agree on the addition equation used here.
How to use
- Pick liters or gallons.
- Enter the batch volume.
- Enter current free SO2.
- Enter target free SO2.
- Read powder grams first.
- Read solution mL beside it.
Formula
- rise
- Free SO2 rise in ppm (mg/L).
- liters
- Batch volume in liters.
- 576
- KMS SO2 fraction from molar masses.
- x10
- 10% w/v solution strength.
The 576 divisor is stoichiometry (K2S2O5 at 57.6% SO2); Iowa State field factor 0.00175 matches it. Gallons convert first (x 3.78541). Already at target adds nothing; retest after racking, cold work, or MLF.
Worked example
Example: 20 liters, 10 to 40 ppm
Metric defaults: 20 liters, current 10 ppm, target 40 ppm.
- Rise: 40 - 10 = 30 ppm.
- Volume: 20 liters.
- SO2: 30 x 20 = 600 mg.
- KMBS at 57.6%: 600 / 576 = 1.0 g.
- Solution: 1.0 x 10 = 10.4 mL of 10%.
- Check: Iowa 0.00175 factor gives 1.05 g, same within rounding.
- Tool shows 1 g potassium metabisulfite, 10.4 mL of 10% solution, 30 ppm rise.
Reference table
| pH | Free needed | Note |
|---|---|---|
| 3.0 | 13 ppm | Low pH needs little |
| 3.2 | 21 ppm | White table zone |
| 3.4 | 32 ppm | Mid zone |
| 3.6 | 50 ppm | High zone |
| 3.8 | 79 ppm | Very high zone |
Limits
- Cellar estimates; assays rule.
- Binding varies with wine chemistry.
- Legal totals cap near 350 ppm US.
- Sorbate and pH work need own plans.
Common mistakes
- Dosing powder dry into wine.
- Skipping the retest.
- Targeting free without pH.
- Stacking totals past legal caps.
- Using stale opened KMBS.
Try it yourself
Quick checks. Answers sit tucked under each question.
100 liters, 15 to 50 ppm?
Rise 35: 35 x 100 / 576 = 6.1 g (60.8 mL).
Current 45, target 40?
Rise zero or less: 0 g, 0 mL, already at target.
Where does 576 come from?
About 57.6 g SO2 per 100 g KMBS from K2S2O5 molar masses.
Questions
What chemical adds SO2?
Potassium metabisulfite, 57.6% SO2 by stoichiometry. Dissolve in water before adding.
What is the addition formula?
Grams = rise ppm x liters / 576. A 10% solution needs grams x 10 in mL.
Does pH change the target?
Higher pH needs more free SO2 for the same 0.8 molecular shield; check the table before targeting.
How much at crush?
25 to 75 ppm at crush per Iowa State, tuned to fruit condition and pH.
Does all added SO2 stay free?
No. Only part stays free; the rest binds aldehydes and sugars. Retest free SO2 after a day or two.
Is there a legal ceiling?
Yes, near 350 ppm total in the US. Track totals across additions, not just free readings.