Most commonly Sodium Metabisulfite is used as an additive to preserve and stabilize wines and ciders, but sometimes it is also used in beers.
When it is added to wine or cider it will prevent most wild microorganisms and yeast from growing and it will work as an antioxidant that will not only protect the color but the delicate flavors.
It can also be used as a sanitizing rinse.
Usage: 1/4 tsp per 6 gallons of must
Sanitization: 2 oz per 1 gallon of water