MOUSINESS | See wine faults.
Mousey aroma in wine was thought to be a Brettanomyces fault but is now known to be a Lactobacillus fault that can only occur when lysine is present in the wine (acetyl-tetrahydropyridines), says Tom Stevenson (2011). As many as 30% of all winemakers are apparently unable to detect this fault (Jancis Robinson MW, 02 June 2012). The following article on mousy taint is by the Australian Wine Research Institute.
The Australian Wine Research Institute
Mousy taint is an off-flavour reminiscent of caged mice or sometimes cracker biscuit, and in sensitive individuals renders the wine undrinkable. The taint is generally perceived late on the palate or after the wine has been swallowed or expectorated and usually takes a few seconds to build. It tends to linger and leave a most obnoxious taste in the mouth for some time. If you move quickly to the next wine in a line-up, you might miss a mousy wine. Mousy taint is rarely detected by sniffing because the compounds involved are not volatile at wine pH. Note that there is considerable variation in the sensitivity between individuals to the taint.
The compounds responsible for ‘mousiness’ are the N-heterocyclic volatile bases 2-acetyltetrahydropyridine (ACTPY), which is the main compound responsible, 2-ethyltetrahydropyridine (ETPY) and 2-acetylpyrroline (ACPY) (Grbin et al 1996).
Usually of microbial origin, most strains of lactic acid bacteria (LAB) being capable of producing the taint, particularly the heterofermentative species. These include Lactobacillus hilgardii, Lactobacillus plantarum, Lactobacillus brevis, and Oenococcus oeni (Cosello et al 2001) The yeast Dekkera/Brettanomyces may also capable of producing mousy compounds. In addition to microbial origin, empirical observation has shown that some wines develop mousy taint when exposed to air or oxygen. The mechanism by which oxidation enhances mousy taint is currently unknown. There is no satisfactory method to remove mousy off-flavour, which is more likely to occur in wines with low concentrations of SO2 and low acidity.
The AWRI observed an increased incidence of mousy wines during the 1990s when winemakers moved to a lower sulfur dioxide regime for the production of red wines in particular. Many red wines and some full bodied white wines had no sulfur dioxide added until the completion of the malolactic fermentation. Such a regime demands a fastidious approach to cellar hygiene to prevent unwanted microbial growth and the possible formation of ‘mousiness’. The AWRI has recommended to winemakers that they should work at between 50 and 75 mg/L total sulfur dioxide (more for wines of high pH) for red wine production if they have any doubts about their cellar sanitation.
Sources: Grbin, P.R.; Costello, P.J.; Herderich, M.; Markides, A.J.; Henschke, P.A.; Lee, T.H. Developments in the sensory, chemical and microbiological basis of mousy taint in wine. Stockley, C.S.; Sas, A.N.; Johnstone, R.S.; Lee, T.H. eds. Maintaining the competitive edge: proceedings of the ninth Australian wine industry technical conference; 1619 July 1995; Adelaide, SA. Australian Wine Industry Technical Conference Inc., Adelaide, SA: 1996: 57-61.
Jancis Robinson MW, ‘Those rival natural wine fairs’, www.jancisrobinson.com 2 Jun 2012.
Tom Stevenson, The Sotheby’s Wine Encyclopedia 5th Edition (Dorling Kindersley, 2011), p81.