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sulphurous acid

Medium strength acid (international name dihydrogen sulphite), which is formed when sulphur dioxide is introduced into water. Especially in a warm environment, it tends to change into the much more toxic and stronger sulphuric acid by oxidation. The salts and esters of the sulphurous acid are called Sulphites or also neutral or secondary sulphites, as well as hydrogen sulphites or formerly bisulphites or also primary or acid sulphites. When sulphur dioxide is added to mash, must or wine, most of it is converted into sulphurous acid, only a small part remains as sulphur dioxide. The sulphurous acid immediately begins to split into sulphites and hydrogen sulphites. Both enter into compounds with different substances in the wine. Only when these processes are complete is the so-called free sulphurous acid present. The amount depends on the temperature and the pH value, but is usually about 20%. This means that the major part of the sulphurous acid, around 80%, is present in wine in bound form.

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