Meta bisulphite

When mixed with water, sodium meta bisulfite releases sulfur dioxide (SO₂), a pungent, unpleasant smelling gas that can also cause breathing difficulties in some people. For this reason, sodium meta bisulfite has fallen from common use in recent times, with agents such as hydrogen peroxide becoming more popular for effective and odorless sterilization of equipment. Released sulfur dioxide however makes the water a strong reducing agent.

Sodium metabisulfite or sodium pyrosulfite (iupac spelling; br. E. Sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula na₂s₂o₅. The name is sometimes referred to as disodium (metabisulfite, etc). It is used as a disinfectant, antioxidant and preservative agent.

It is commonly used in homebrewing preparations to sanitize equipment. It is used as a cleaning agent for potable water reverse osmosis membranes in desalination systems. It is also used to remove chloramine from drinking water after treatment.

Potassium metabisulfite, K₂S₂O₅, is a white crystalline powder with a pungent sulfur odour. The main use for the chemical is as an antioxidant or chemical sterilant. It is a sulfite and is chemically very similar to sodium metabisulfite, with which it is sometimes used interchangeably. Potassium metabisulfite is generally preferred out of the two as it does not contribute sodium to the diet.

Potassium metabisulfite is a common wine or must additive, where it forms sulfur dioxide gas (SO₂). This both prevents most wild microorganisms from growing, and it acts as a potent antioxidant, protecting both the color, and delicate flavors of wine.

Typical dosage is 1/4 tsp potassium metabisulfite per 6 gallon bucket of must (yielding roughly 75 ppm of SO₂) prior to fermentation, and 1/2 tsp per 6 gallon bucket (150 ppm of SO₂) at bottling.

Potassium metabisulfite is sometimes used in the brewing industry to inhibit the growth of wild yeasts, bacteria, and fungi. This is called 'stabilizing'. It is used both by homebrewers and commercial brewers alike. It is not used as much for brewing beer, because the wort is almost always boiled, which kills most microorganisms anyway.