Potassium Or Sodium Metabisulfite? Which Should the Home Winemaker Use?
New home winemakers often get confused between potassium metabisulfite and sodium metabisulfite. Some winemaking guides only refer to sulfite and it’s up to the reader to try to understand which form of sulfite the author was referring to. What’s the difference? And does it really matter?
Both potassium and sodium metabisulfite are used as sanitizing agents and as additives to wine to protect it from oxidation and to inhibit bacteria growth. When used in a solution with water, both can sanitize winemaking equipment and the workspace where wine is being made. When added directly to wine in small amounts, it releases sulfur dioxide (SO2) gas which is what protects wine from oxidation and micro-organisms.
Potassium metabisulfite, which is sometimes abbreviated as KMS, K sulfite, and K-meta, comes in a powder form. The sodium version is available in powder as well as tablets which are usually referred to as “Campden Tablets.” Some suggest that KMS and sodium metabisulfite are exactly the same, however this is not completely true.
Although they can be used interchangeably for the same purposes of sanitizing and preservation, those on a restricted sodium diet should try to use only potassium metabisulfite in their wine. Another difference is that the sodium version can contain a slightly smaller amount of sulfur dioxide.
When purchasing a wine kit, the type of sulfite that is included which is to be added to the wine after it has completed fermentation is potassium sulfite. It is best to follow the directions exactly and add this to your wine in order to protect it during the degassing stage, prior to clarifying and bottling. If you are planning on aging your wine for a couple of years or more, you may want to consider adding an additional amount of KMS prior to bottling or while it is bulk aging in the carboy.