Term (also aldehyde clay) for a wine defect caused by oxidation, especially in white wines. It manifests itself by a typical honey-spicy and tart to bitter taste, an aroma of fresh bread and a discoloration up to the extreme of brownish tint or high colouring. The substance responsible for smell and taste is the alcohol precursor acetaldehyde. Small amounts of it remain in the young wine after fermentation. If sulphurization does not take place in time, this missing tone is formed. Such wines are also called rahnig. Similar causes and effects have the firn (age firn), which however only forms after long bottle storage. In the production of sherry and Madeira, the formation of acetaldehydes is deliberately encouraged and the sherry tone desired in this case is produced.