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reductive expansion

Reduction (see there) is a complex chemical process. In winemaking, reductive ageing is understood to mean the complete exclusion of the oxygen required for the metabolism of microorganisms and thus the prevention of undesirable oxidation. This requirement is met by minimising transport routes and processing times for 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.

Effects on the wines

The colour, smell and taste, i.e. the overall aroma, are strongly influenced by reductive ageing. The wines are characterised by a typically tangy, fruity and pure taste with pronounced aromas (primary aromas) and a white to light yellow colour (the iron-containing pigments can be oxidised and lend a darker colour). These flavour and aroma impressions are known positively as reductive notes. The complex chemical changes that occur during the ageing of a wine in the bottle are sometimes also referred to as reductive ageing or reductive processes (see also micro-oxidation). In contrast to reductive ageing is oxidative ageing with dosed oxygen contact. This is usually carried out for red wines with barrel ageing.

Process

Reductive ageing is mainly used for white wines and sparkling wines. This is the rule in Germany and Austria. There are exceptions, mainly in more southerly regions such as Italy and Greece. However, the process must be carried out in a controlled manner, as an excessively rigorous, strong exclusion of oxygen can lead to the formation of volatile sulphur compounds such as hydrogen sulphide and thiols (mercaptans) with reductive notes. To a small extent, this may still be acceptable as a so-called "stink". At higher concentrations, however, these are negative flavours such as a musty note or the dreaded "Böckser " (sulphur booze) and constitute a wine defect. A wine can possibly be brought back into balance by aerate or decanting (see also reduction flavours).

Further information

For the production of alcoholic beverages, see Champagne (sparkling wines), distillation (distillates), spirits (types), winemaking (wines and wine types) and wine law (wine law issues).

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