This typical taste and smell, also commonly referred to as " Alterston " or "Altl" in dialect, occurs mainly in older white wines. The name is derived from the Old High German "firni" for "previous year" or "old". However, this most common type of ageing hue should not be confused with UTA (atypical ageing hue), Böckser (Lagerböckser) or the related Petrolton. The cause of ageing varnish is primarily oxidation by atmospheric oxygen. This occurs due to excessive oxygen uptake after filtration, as well as high temperatures during storage, exacerbated by high levels of flavonoid phenols in the wine. This is also promoted by faulty corks (closures). In the case of storage in wooden barrels, firns can develop after only one and a half years, whereas in the case of storage in bottles, this usually takes considerably longer.
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