Mousy off-flavor: a review

Although mousy off-flavor occurs infrequently in wine, it can be economically disastrous to the wine producer as, at worst, it can render the wine unpalatable or, at best, decrease the quality of the wine resulting in a lower sale price. Wines infected with either lactic acid bacteria (LAB) (particularly heterofermentative strains) or Dekkera/Brettanomyces yeast can potentially produce mousy off-flavor. There are three known compounds that cause mousy off-flavor: 2-ethyltetrahydropyridine, 2-acetyltetrahydopyridine, and 2-acetylpyrroline. Dekkera/Brettanomyces have been shown to be capable of producing at least two of these compounds, whereas LAB are capable of producing all three. The reason as to why mousy off-flavor forms in some wines and not in others is still not fully understood. The issue is further complicated by the fact that the compounds that have thus far been identified as necessary for off-flavor formation are all potentially available in wine (e.g., ethanol, L-lysine, L-ornithine, and metal ions). For these reasons, the microbe's metabolism probably plays a key role in mousy off-flavor formation. In the case of Dekkera/Brettanomyces-induced mousy off-flavor, it appears that oxygen may play a key role. Thus, a wine infected with Dekkera/Brettanomyces in the absence of oxygen may not become mousy unless exposed to oxygen via a processing or handling procedure.