Sodium Metabisulfite, (often referred to as SO2, sulfites meta, or meta-bi) has several uses in winemaking. It is used at the crush, to help control the spoilage bacteria and indigenous yeast that may already be present on the fruit or the equipment. The amount used is enough to stop most of the unwanted organisms but not enough to hinder a cultured yeast, which has a higher tolerance to sulfites. This effectively “wipes the slate clean” for the cultured yeast to step in and rapidly colonize the must.
Sulfites also help to inhibit the enzymatic browning of musts and finished wines. During storage and in the bottle, sulfites at the proper levels will protect a wine by continuing to inhibit spoilage organisms, as well as by scavenging oxygen.
Campden tablets are Sodium Metabisulfite in an easier to measure format. Adds 75 ppm of sulfites at the rate of one tablet per gallon. These must be fully ground-up prior to use. It is possible the sodium could contribute a very small salty flavor. Especially when making white wine it is preferable to add potassium over sodium since added potassium can later help with cold stabilization.
Potassium Metabisulfite in powder form, AD495 or AD500, is much easier to use if you have a scale and does not add sodium to your wine.
For more information refer to our MoreManuals! on Red or White Winemaking or one of the winemaking books that we offer for a complete explanation on how to properly manage sulfites.