Critics of natural wines are wont to describe issues with faults. I have said many times on this blog that I believe that they exaggerate and that I find as many conventional wines faulty as natural wines. However, I must be truthful and say that one fault does seem to emerge from time to time. On Wednesday I opened a bottle of 2009 Rhone wine from one of my favourite producers. There was a slightly funky nose but the wine was lovely, liquorice and dark fruit flavours, it went well with food too. A couple of hours later the last glass was full of mouse.
Mousiness is a fault to which I am sensitive, about 30% of wine drinkers apparently are not at all. They are fortunate, because when encountered it leaves a nasty taste in the mouth. Usually described as like a mouse cage and cracker biscuits, it also fills the senses with unpleasant aromas resembling that cage which has not been cleaned for a long time. Once tasted the effects linger making it hard to taste other wines afterwards.
The cause of the problem lies in bacterial infection probably from grapes which were rotten. Other origins might be dirty equipment or exposure to oxygen. The wine becomes affected when it is made, but it is hard to diagnose the problem as it shows little, if any, aroma. The high acidity of wine masks the mousiness and it is only when it comes into connection with saliva that the problem is obvious to most people. Saliva lowers the acidity of the wine in the mouth so the mousiness is no longer masked.
I have only knowingly come across mousiness in red wines but, apparently, it can occur in white and sparkling wines. It is a real problem, I have had bottles from a number of natural producers which were mousy including by some favourite vignerons (not Jeff Coutelou I hasten to add). Why are they more vulnerable than conventional producers? The answer lies with SO2. Sulphur Dioxide masks the Lactobacillus bacteria when it releases chemicals (such as 2-acetyltetrahydropyridine) which cause mousiness. It disguises the flavour and aroma problem without removing it. Even 10mg per litre would achieve that, though as SO2 dissolves in wine over time the problem might re-emerge.
However, many natural producers are determined to avoid adding any sulphites and therefore must take a risk. The closest attention must be made to hygiene, exposure to air and, above all, to the quality of grapes which enter the cellar and the wine; rejecting bad grapes, sorting table work and cleaning, cleaning, cleaning.
It is pointless hiding the issue of mousiness. It is a potential problem for natural producers and it is capable of ruining wines. As so many people do not notice it (including some producers) the wines need to be checked before entering bottle and the marketplace. Even then it can emerge later, as with the 2009 Rhone wine I tasted last night, very good for the first two glasses, undrinkable for the last. There is no wand to wave to magically remove the problem. It is an unpleasant trap for all involved.