Reduction (see there) is a complex chemical process. In winemaking, reductive vinification is understood to mean the complete exclusion, as far as possible, of the oxygen required for the metabolism of microorganisms and thus the prevention of undesirable oxidation. This requirement is met by the shortest possible transport routes and processing times for the grapes, must and wine with cool ambient conditions during pressing, must treatment, fermentation, ageing in hermetically sealed containers (steel tanks) and bottling.
This is also supported by measures such as sulphurisation, fining and filtration. Reductive ageing strongly influences the colour, as well as the smell and taste, i.e. the entire aroma of a wine. The wines are characterised by a typically tangy, fruity and pure taste with pronounced aromas (primary aromas) as well as a white to light yellow colour (the iron-containing pigments can be oxidised and give a darker colour). These taste and smell impressions are called reductive notes in a positive sense.
Reductive ageing is mainly used for white wines and sparkling wines. In Germany and Austria, this is the rule. Exceptions are mainly found in more southern regions such as Italy and Greece. However, the process must be carried out in a controlled manner, as too rigorous, strong oxygen exclusion can lead to the formation of volatile sulphur compounds such as hydrogen sulphide and thiols (mercaptans) with reductive notes. In small amounts, this may still be accepted as a so-called "stinker". At higher concentrations, however, these are negative taste directions such as mustiness or the dreaded Böckser (sulphur boil) and signify a wine defect. Such a wine can possibly be brought back into balance by means of aerate or caraffing (see also reduction aromas).
The complex chemical changes that occur during bottle age ing or ageing of a wine are sometimes also referred to as reductive ageing or reeductive process (see also under micro-oxygenation). In contrast to reductive ageing is oxidative age ing with dosed oxygen contact. This usually takes place in red wines with frequent barrel ageing.
A complete list of the numerous vinification measures and cellar techniques, as well as the various types of wine, sparkling wine and distillate regulated by wine law, can be found under the heading " Winemaking ". Comprehensive information on wine law can be found under the heading Wine Law.