Sulphite naturally occurs in wine during the fermentation process. Every wine will contain at least some amount of sulphite. Sulphites are compounds that are made up of sulfur and oxygen. As grape juice slowly turns into alcohol, sulphites are often a by-product. There are other times when winemakers will actively add sulfur dioxide into grapes that have been freshly pressed in order to help preserve it. This is because there are times when bacteria and other natural elements are with the grapes as they are pressed and can potentially compromise the freshness of the wine.
Overall, sulphites in the bottle won’t do you any harm. They are simply involved so that wine remains as fresh as possible. Today, the winemaking process is more advanced than it used to be, so even less is needed. The United States does have regulations that require wines to have warning labels if sulphites are in excess of ten parts per million.