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)
References:
http://www.bcawa.ca/winemaking/so2use.htm
http://www.nandinichemical.com/online_journal/dec03_nandini_chemical_journal.htm