Name for a wine defect, which is derived from the unpleasant to disgusting sound of ammonia and the smell of mouse urine. It is also expressed by a dull, oxidative, musty and vinegary smell. Depending on its intensity, however, the missing tone is often only recognisable in the finish (aftertaste), where it is expressed by a long-lasting, scratchy taste impression that lingers unusually long on the palate.
It occurs mainly in young wines with residual sugar, especially also in fruit wines (strawberry and currant). Particularly at risk are low-acid(pH 3.5 to 4), warm fermented wines which have been stored in a cloudy state for a long period of time or which have not been sufficiently sulphurised. Long periods of heat during the ripening period are favourable.
The causes are lactic acid bacteria (Lactobacillus brevis and Lactobacillus cellobiosus) and the yeast species Brettanomyces bruxellensis. As a result, metabolism (chemical metabolic reactions) produces acetic acid ethyl ester (ethyl acetate) and acetamide, among others, which cause the typical mouse-like impression. The olfactory perception threshold for some of these metabolic products is in the millionth of a gram range with 0.1 to 1.6 µg/l. Mice are often confused with a light buckser (Hefeböckser). Not infrequently, the off-tone occurs together with the wine defect horse sweat, which is also caused by Brettanomyces bruxellensis or its metabolites. In the case of slight expression, strong sulphurization with subsequent filtration (disinfection) brings an improvement. Other possibilities are activated carbon or a blend with a wine rich in acid. With strong expression the wine is to be regarded as spoiled.