Bartles & Jaymes, like many wine coolers and wine products in general, uses the maximum amount of sulfur dioxide permitted by FDA regulations as a preservative. SO2 is one of the most effective antimicrobials on the planet and is highly antagonistic to growth. In its gaseous form, SO2 can be lethal to any air-breathing creature and is in fact the leading cause of death in a volcanic eruption. It’s the poison gas that gets you, not the lava.
But in liquid form, and in the right concentration, SO2 can be quite helpful. It not only prevents invasive microbial growth in human digestive systems, but it can actually clean and preserve a glass wine container itself, during both the fermentation and the storage process.