Ensure proper sulfite protection in your wine.
Only the molecular (undissociated) form of SO2 is antimicrobially active. The formula is: Molecular SO2 = Free SO2 / (1 + 10^(pH - 1.81)). At pH 3.0, about 6% of free SO2 is molecular; at pH 3.5, only 3%; at pH 4.0, just 1.5%. This means higher-pH wines need disproportionately more free SO2 to achieve the same protection — a wine at pH 3.8 needs twice the free SO2 as one at pH 3.5. The target molecular SO2 is 0.6-0.8 mg/L for dry wines (enough to inhibit Brettanomyces and other spoilage organisms). Wines with residual sugar need higher levels (0.8-1.0). The first pKa of sulfurous acid (H2SO3) is 1.81, which determines the equilibrium between molecular and bisulfite forms. Always measure free SO2 using the aspiration/oxidation method (Ripper is less accurate) and adjust based on pH, not a fixed ppm target.