🍷 Potassium metabisulfite

Potassium metabisulphite is a white crystalline powder. In winemaking it is dissolved in water or must, and then it releases sulphur dioxide, SO2. This gas protects wine from spoilage and oxidation, which is why the powder is so widely used.

Where does it come from? It is a chemical made in a factory, not in the vineyard. About half of its weight turns into sulphur dioxide, so it is convenient for dosing the desired amount of sulphites. On packaging and in reference lists it is known as additive E224.

Potassium metabisulphite replaced the old method of fumigating barrels with burning sulphur. The powder is easier to dose and store. It is also used to wash and sanitise barrels, hoses and bottles.

For the consumer, what matters is that it supplies sulphites. If a wine has more than a certain threshold, the label says contains sulphites. For some people, especially asthmatics, this can matter.