Term for liquid or solid chemical compounds containing hydrogen. The hydrogen ions cause the acidic taste of a solution. A distinction is made between inorganic and organic acids. In wine, mostly organic acids of the group carboxylic acids are present in free, bound and to a small extent also in volatile form. The term "acid" is not to be understood negatively, because without this important component a wine tastes flat and flat. Only then does it gain refreshing power and the sweetness is also shown to its best advantage. Wines from hot regions often have a lower content. Unripe grapes have a high proportion of each grape variety.
Acidity
Certain acids, such as malic acid and tartaric acid, which are mainly found in wine, are already contained in the grapes, while others, such as acetic acid and lactic acid, are only formed during fermentation. For reasons of conservation, acids are also added to must or wine. These are for example ascorbic acid and sulphur dioxide, from which sulphurous acid is formed in combination with the water in the wine. The acidity in wine describes the amount or concentration of acids. It is determined by titration and expressed in g/l.
Acidity level
Acidity, on the other hand, expresses something quite different. The acid taste of a liquid depends not only on the amount of acid but also on its degree of dissociation. The degree of dissociation of an acid or base depends on its acid constant (or base constant), its concentration or the existing pH value of a solution. The most acidic is tartaric acid, which is almost three times more acidic than lactic acid and one and a half times more acidic than malic acid. Succinic acid and acetic acid are even less acidic.
Acid types
Acids are divided into non-volatile acids and volatile acids, although the borderline cannot be drawn absolutely exactly (there are actually also medium volatile acids). The quantity of all acids results in the total acid. The three most common non-volatile acids in wine are tartaric acid (0.5 to 4 g/l), malic acid (0.5 to 6 g/l) and citric acid (0.1 to 0.3 g/l), which make up about two thirds of the quantity of all acids. Lactic acid (0.8 to 3.3 g/l) is mainly produced during malolactic fermentation by conversion of malic acid.
In smaller quantities there are also the acid types succinic acid, galacturonic acid, gluconic acid, glucuronic acid, glycolic acid, oxalic acid, mucic acid and cinnamic acid. The non-volatile acids are represented in total as tartaric acid (although there are several) in g/l. The most common volatile acid is acetic acid (0.15 to 0.5 g/l for healthy wine). As the name suggests, these do not remain in the wine but evaporate slowly. They are collectively referred to as acetic acid (although there are also several) and are expressed in g/l.
Total acid
The amount of total acidity is about 4 to 9 g/l for white wines and about 4 to 6 g/l for red wines. Higher amounts of acid contribute positively to the shelf life of the wine by repelling harmful microorganisms. Although EU law provides in principle for an acid correction for musts and wines, this depends on the wine-growing zone. In zone A(Germany except Baden) and B (Baden winegrowing area, Austria) partial deacidification is permitted, but acidification is prohibited in principle. Sulphurous acid is divided into free and bound acid. The two result in the total sulphurous acid, whose proportion in the wine is strictly limited. The acids are not broken down during ageing or bottle maturing. See a complete list of all wine ingredients under the keyword total extract.
further information
All aids, work and measures in the vineyard during the vegetation cycle can be found under the keyword vineyard care. Complete lists of the numerous vinification measures and cellar techniques, as well as the types of wine, sparkling wine and distillate regulated by wine law can be found under the keyword vinification. Comprehensive information on wine law can be found under the keyword wine law.
Graphic: By Mariana Ruiz Villarreal (LadyofHats), Public domain, link
edited by Norbert Tischelmayer, March 2019