1. What is a Molecular SO₂ Calculator?

Definition: This calculator estimates the molecular SO₂ concentration in wine based on free SO₂, pH, and other factors.

Purpose: It helps winemakers determine the effective antimicrobial concentration of sulfur dioxide in their wine.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( [SO₂] \) — Molecular SO₂ concentration (mg/L)
• \( k \) — Conversion factor (typically 1)
• \( FSO₂ \) — Free SO₂ concentration (mg/L)
• \( pH \) — Wine pH
• \( pKa \) — Dissociation constant (~1.81 for SO₂ at wine pH)

Explanation: The formula calculates the equilibrium between molecular and bisulfite forms of SO₂ based on pH.

3. Importance of Molecular SO₂ Calculation

Details: Molecular SO₂ is the active antimicrobial form. Maintaining 0.5-0.8 mg/L provides microbial stability in wine.

4. Using the Calculator

Tips: Enter free SO₂ (measured by titration), wine pH (measured by pH meter), and adjust pKa if needed (default 1.81).

5. Frequently Asked Questions (FAQ)

Q1: Why is pH important for SO₂ calculation?
A: The proportion of molecular SO₂ decreases exponentially as pH increases. At higher pH, more free SO₂ is needed for the same antimicrobial effect.

Q2: What's a typical pKa value?
A: The pKa of sulfurous acid is ~1.81 at wine pH and temperature, but can vary slightly with temperature.

Q3: When would I change the conversion factor (k)?
A: Normally k=1, but some models may use slightly different values to account for temperature or other factors.

Q4: How much molecular SO₂ do I need?
A: 0.5 mg/L inhibits most yeasts, 0.8 mg/L inhibits most bacteria. Higher may be needed for problem wines.

Q5: Does this account for bound SO₂?
A: No, this calculates only the molecular portion of free SO₂. Bound SO₂ doesn't contribute to antimicrobial activity.