Chapter 18

Sulfur Dioxide Use in Winemaking

Chemical Properties of Sulfur Dioxide

Today, the use of the additive sulfur dioxide is an almost universally accepted winemaking practice. Sulfur dioxide plays three important roles. Sulfur dioxide plays three important roles. First, it acts as an antioxidant, safeguarding the wine's fruit integrity and protecting it against browning. Second, it is an antimicrobial agent, and as such is used against acetic and lactic acid bacteria as well as against molds, preventing the wine deterioration and favoring its microbiological stabilization. Third, it inhibits the activity of oxidative enzymes, i.e., polyphenol oxidase (PPO) which cause the juice to turn brown.

Antioxidant

Sulfur dioxide (SO2) is used by winemakers to prevent oxidation; however, there is almost no sulfite ion present in solution at the pH range found in wine. Rather sulfur dioxide plays an important role against oxidation but not in a direct way, but with quinones and hydrogen peroxide. Phenols are the primary oxygen (O2) acceptor in wine.

Antimicrobial

Sulfur dioxide is a broad-spectrum antimicrobial agent that has an inhibitory effect on a wide variety of microorganisms. Sulfur dioxide prevents spoilage microorganisms such as acetic acid bacteria, most lactic acid bacteria, and certain wild yeasts. The level of sulfur dioxide at which the microbe, either yeast or bacteria, is affected varies widely by species.

Enzymatic Deactivation

Sulfur dioxide inhibits the activity of the polyphenol oxidase (PPO) enzyme. By suppressing the activity of PPO, sulfite ions limit the oxidation of phenolic compounds that serve as the primary substrates. The oxygen reacts with phenols and produces a compound known as quinone and in doing so causes browning reactions in juice.

Click on the following topics for more information on sulfur dioxide use in winemaking.