Technically a type of salt added to the must in winemaking 12 hours before the yeast is pitched (added to the mix). Potassium metabisulphite is also used in larger concentrations to sterilize brewing equipment.

Metabisulphite comes in a powdered form, or in tablets called campden tablets (named for the location they were developed in). The tablets are used to add potassium metabisulphite to wine must in an easy to use formula (approx. 1 tablet to 1 gallon of must). A concentration of 10% or less of potassium metabisulphite is good for sterilizing must. Using p. metabisulphite to sterilize must leads to traces of sulphites in the resulting wine. If this is undesirable, do not use p. metabisulphite to sterilize your must. Some brewers avoid using this due to many people's sulphite allergies or low sodium diets.

Potassium metabisulphite is used to kill wild yeast strains in must, and also to stabilize wine before bottling, so the bottles do not explode because of a slow continuing ferment. These days, people also use potassium sorbate to stabilize alcoholic beverages before bottling. Some people prefer to use potassium metabisulphite when racking wine because of the stifling effect that it has on oxidation.

The action of potassium metabisulphite on must is that of releasing sulphur dioxide (a choking gas that sterilizes) throughout the container. This process takes 12 hours. That is why winemaking/brewing yeast is added 12 hours after the potassium metabisulphite is.

Other uses besides brewing for Potassium Metabisulphite:

  • Photographic industry: Reducing component in formulations and for acidify fixation baths.
  • Food industry: As a preservative (this application is restricted)

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