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.
The sulphurous acid or sulphur dioxide has an antimicrobial effect especially against Acetobacter (acetic acid bacteria), lactic acid bacteria and wild yeasts. The hydrogen sulphites bind aroma-impairing substances, including acetaldehyde (alcohol precursor). The sulphites react with the dissolved oxygen to form sulphates and have a reducing effect. The sum of free and bound sulphur dioxide (sulphurous acid) gives the total sulphur (also total sulphur dioxide or total sulphurous acid). The proportion in the wine is measured by iodometry (free) and acidimetry (bound) and expressed in milligrams per litre (mg/l). Too much sulphur in wine is harmful to health, which is why there are legal limits. Even if these limits are adhered to, improper dry preservation of empty wooden barrels or over-sulphurisation of the wine can lead to the wine defect sulphuric acid firn.
Sulfur is the most common component of the human body, along with water, salt and calcium. It is one of the most important functional carriers in the organism, is necessary for skin, hair and nails, keeps the tissue soft, relieves stress, is proven to help with asthma, arthritis, rheumatism, internal and external inflammation, back and muscle pain and all allergies. Sulphur baths are generally known as beneficial to health and are also used by many people. The body of an adult with an average weight of 70 kg contains around 150 g of sulphur. The daily requirement is estimated at just under 900 mg. Some sulphur compounds are toxic (poisonous) in higher doses. Sulphites can, for example, destroy the vitamins of the B group, inhibit the action of enzymes and increase the effect of carcinogenic substances. Foods rich in sulphur should therefore only be enjoyed in moderation.
The WHO (World Health Organization) has defined a safe health limit(ADI) for the daily intake of sulfur in the human body of 0.7 mg per kg body weight. Sulphur in food can cause allergies or other undesirable reactions. In the case of an allergy to sulphites, even much smaller amounts than those listed below can trigger the so-called "sulphite asthma". For this reason, since 25 November 2005 there has been an obligation to indicate on the label in accordance with the EU regulation if the sulphur content exceeds 10 mg/l (this value is exceeded for almost all wines). Permissible are the two texts "Contains: Sulphur dioxide" or "Contains: Sulphites" (the use of the formula "SO2" is not permitted, however). This provision applies to all products, i.e. grape must, wine, sparkling wine and vinegar (wine vinegar). The proportion of residual sugar is also relevant. The values since the EU wine market regulation valid since August 2009:
For the production of organic wine, significantly lower quantities up to a maximum of two thirds of these maximum quantities are assumed. Individual organic associations oblige their members to do so. Thus Bioland prescribes a maximum of 110 mg/l (red wine) and 140 mg/l sulphur dioxide (white wine) for red and white wines with less than 5 g residual sweetness per litre. Wines with more than 5 g residual sweetness per litre may not contain more than 140 mg/l (red wine) and 180 mg/l (white wine) sulphur dioxide. See also tabular lists under the keywords total extract (wine ingredients) and agents used in winemaking.
All aids, work and measures in the vineyard during the vegetation cycle can be found under vineyard care. Complete lists of the numerous cellar techniques, as well as the wine, sparkling wine and distillate types regulated by wine law are included under vinification. Comprehensive information on wine law can be found under wine law.