Wine Sulfite Dosage Calculator
Determine how much potassium metabisulfite (KMBS) you need to reach your target free SO₂ level. Enter batch size, current and desired SO₂, and the purity of your sulfite powder to get a precise gram recommendation.
Why Add Sulfites?
Sulfites play several vital roles in winemaking: they inhibit wild yeasts and bacteria, prevent oxidation, and preserve flavor during aging. Potassium metabisulfite, often abbreviated KMBS, releases sulfur dioxide (SO₂) when dissolved. This active form of sulfur binds to oxygen and microbial enzymes, keeping wine stable. Without adequate additions, even small amounts of residual sugar can lead to refermentation, and oxygen exposure can quickly dull aromas or create unwanted off-flavors.
Using the Calculator
Start by measuring the current free SO₂ level with a reliable test kit. Enter that value along with your desired target, batch volume, and KMBS purity. Commercial KMBS is typically about 57% SO₂ by weight, but some winemakers adjust for 50–55% depending on brand or storage age. The calculator converts the difference between desired and current levels into grams of KMBS using the relationship
where is the KMBS dose in grams, is the volume in liters, is the target free SO₂ level, is the current level, and is the purity percentage. The factor of 1,000 converts mg/L into grams.
Example Dosage Table
| Volume (L) | Current (mg/L) | Desired (mg/L) | Purity (%) | Dose (g) |
|---|---|---|---|---|
| 20 | 10 | 30 | 57 | 0.70 |
| 23 | 15 | 35 | 57 | 0.81 |
| 50 | 20 | 40 | 55 | 1.82 |
Remember that only free SO₂ provides protection. If your wine has high residual sugar or a low pH, you may aim for the higher end of typical ranges: 25–50 mg/L for whites and 20–35 mg/L for reds. Always measure again after dosing to confirm the new level. Stir gently to distribute the solution without introducing excess oxygen.
Keep building your winemaking toolkit with the fruit wine ABV calculator, the wine fermentation schedule calculator, and the solar food dehydrator area calculator for preserving harvests alongside careful sulfite management.