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Issue # One - February 2013

Understanding the importance of molecular SO₂ in protecting wine

Sulfur dioxide is a universal additive in the wine production process. A column by Curtis Phillips directed at winemakers appearing in Wine Business Monthly – but of value to wine professionals generally – points out the importance of the accurate calculation of molecular SO₂, which the author says is “actually protecting your wine.” Sulfur dioxide exists in various forms: dissolved sulfur dioxide gas, or molecular SO₂; unbound or bound sulfite or bisulfite ions, termed free SO₂; and bound bisulfite. Added together, these constitute “total SO₂.” The writer says many winemakers overlook the fact that it is molecular SO₂, not free SO₂, “that provides protection from spoilage microbes.” Moreover, the molecular SO₂ in solution is governed by the level of free SO₂ and, critically, the wine’s pH. Phillips notes that it takes ten times as much free SO₂ to suppress microbes at a pH of 4.0 as compared to a pH of 3.0.

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