Sulfites are produced naturally during fermentation, but they are also added to the wine in order to stop the fermentation process (for example, the delay of malolactic fermentation in the presence of sulfites is well-known). A good part of sulfite is reversibly linked to other compounds such as sugars or polyphenols. The free sulfite (either in the form of SO₂, HSO₃ or H₂SO₃), on the other hand, acts as a preservative to prevent deterioration both due to its antioxidant capacity and its antimicrobial action. Free sulfite has been associated with different allergic reactions, so its specific determination is a legal requirement in many countries.