So2 wine Calculator
Convert so2wine with our free cooking calculator. Get accurate measurements, scaling, and recipe adjustments instantly.
Formula
SO2 needed (mg) = (Target Free SO2 - Current Free SO2) x Volume (L)
The deficit in ppm (mg/L) is multiplied by volume in liters to get total mg of SO2 needed. This is then converted to the chosen addition form: Kmeta powder (divide by 0.576), Campden tablets (divide by ~253 mg SO2 per tablet), or 10% SO2 solution. Molecular SO2 = Free SO2 / (1 + 10^(pH - 1.81)).
Worked Examples
Example 1: Post-Fermentation SO2 Addition
Problem: You have 23 liters of red wine at pH 3.5 with 8 ppm free SO2. You want to raise it to 35 ppm. How much potassium metabisulfite is needed?
Solution: SO2 deficit = 35 - 8 = 27 ppm\nSO2 needed = 27 mg/L x 23 L = 621 mg\nKmeta = 621 mg / 0.576 = 1,078 mg = 1.078 g\nMolecular SO2 at 35 ppm, pH 3.5 = 35 / (1 + 10^(3.5-1.81)) = 35 / 49.95 = 0.701 ppm
Result: Add 1.078 g potassium metabisulfite | Molecular SO2: 0.701 ppm
Example 2: White Wine Pre-Bottling SO2 Adjustment
Problem: A 19-liter batch of white wine at pH 3.2 has 15 ppm free SO2. Target is 45 ppm free SO2 for bottling stability.
Solution: SO2 deficit = 45 - 15 = 30 ppm\nSO2 needed = 30 mg/L x 19 L = 570 mg\nKmeta = 570 / 0.576 = 990 mg = 0.990 g\nCampden tablets = 570 / 253 = 2.3 tablets\nMolecular SO2 at 45 ppm, pH 3.2 = 45 / (1 + 10^(3.2-1.81)) = 45 / 25.55 = 1.761 ppm
Result: Add 0.990 g Kmeta (or ~2.3 Campden tablets) | Molecular SO2: 1.761 ppm
Frequently Asked Questions
What is SO2 in winemaking and why is it added to wine?
Sulfur dioxide (SO2) is the most widely used preservative in winemaking, serving multiple critical functions. As an antioxidant, it prevents oxidation that causes browning and stale flavors in wine. As an antimicrobial agent, it inhibits the growth of unwanted bacteria and wild yeast that can produce off-flavors like volatile acidity or mousy taint. SO2 also helps preserve the fresh, fruity aromas and vibrant color of wine. Nearly all commercial wines contain some level of SO2, either added during production or naturally occurring from fermentation. The typical range is 20 to 200 parts per million total SO2, with legal limits varying by country and wine type.
What is the difference between free SO2 and total SO2 in wine?
Free SO2 is the portion of sulfur dioxide in wine that is not bound to other compounds and remains available to provide antimicrobial and antioxidant protection. Total SO2 includes both free SO2 and bound SO2, which has reacted with aldehydes, sugars, and other wine components and is no longer protective. Only molecular SO2 — a fraction of free SO2 determined by pH — is antimicrobially active. Winemakers primarily monitor and adjust free SO2 levels because it represents the active protective component. Over time, free SO2 decreases as it binds to wine compounds or is lost through oxidation and evaporation, which is why periodic testing and additions are necessary throughout aging.
How does wine pH affect SO2 effectiveness and dosing?
Wine pH has a dramatic effect on the proportion of molecular SO2 within the free SO2 pool. At lower pH values (more acidic), a higher percentage of free SO2 exists in the molecular form, which is the only form that effectively inhibits microorganisms. For every 0.1 unit increase in pH, the amount of free SO2 needed to maintain the same molecular SO2 level roughly doubles. At pH 3.0, approximately 6 percent of free SO2 is molecular. At pH 3.4, only about 2.5 percent is molecular. At pH 3.8, it drops to approximately 1 percent. This is why higher pH wines require significantly more free SO2 to achieve adequate protection against spoilage organisms.
What is the recommended molecular SO2 level for wine stability?
The widely accepted target for molecular SO2 in wine is 0.8 milligrams per liter (0.8 ppm) for adequate antimicrobial protection against most spoilage organisms. However, some winemakers target slightly lower levels of 0.5 to 0.6 ppm for wines with lower spoilage risk, while sweeter wines or those with higher residual sugar may require up to 1.0 to 1.5 ppm molecular SO2 to prevent refermentation. To achieve 0.8 ppm molecular SO2, the required free SO2 varies dramatically with pH — approximately 13 ppm at pH 3.0, 26 ppm at pH 3.3, 40 ppm at pH 3.5, and over 80 ppm at pH 3.8. Maintaining proper molecular SO2 levels is the single most important factor in preventing microbial spoilage.
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Is So2 wine Calculator free to use?
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