SO2 Addition DetailsWhy adjust SO2?
It will keep your wine from turning into vinegar, that simple. If you want to make a wine without SO2 you will need impeccably clean conditions and probably a membrane filter nearby.
A winery is not usually a sanitary environment (barrels being the notable example), but it's not a problem if you use modest amounts of SO2. The low pH and high alcohol in wine will do most of the heavy lifting involved in keeping things from living in the wine, but there are still some nasties that can ruin wine if the SO2 is not managed effectively.
To understand what levels of SO2 you should have in your wine, you'll need to know your wine's pH. Knowing the pH will tell you what level of SO2 is required to achieve the holy grails (yes, there are two grails) of SO2: 0.5 ppm and 0.8 ppm molecular SO2.