This typical taste and smell, which is also generally referred to as "Alterston" or dialectally "Altl", is mainly found 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 tone should not be confused with UTA (atypical ageing tone), Böckser (Lagerböckser) or the related Petrolton. The cause for Altersfirne is primarily oxidation by atmospheric oxygen. This occurs through excessive oxygen uptake after filtration, as well as through high temperatures during storage, intensified by the high content of flavonoid phenols in the wine. This is also promoted by defective corks (closures). If stored in wooden barrels, firn can develop after only one and a half years; if stored in bottles, this usually takes much longer.
Firne is formed by caramelisation reactions between amino acids (proteins) and sugars. The typical bitter taste is expressed by the smell and taste of black tea, old straw, honey, resin, nuts, mushrooms and damp earth. The substances responsible for this are higher aldehydes (alcohol compounds). The tone can increase to an unpleasant camphor-like (after the tree) impression. The oxidation causes colour changes up to high colouring. Lovers of older white wines tolerate the Altersfirn to a small extent and even describe it positively as "noble firn". In more pronounced form it is in any case a wine defect. Other causes have the Schwefeläurefirn.