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MANY won’t be able to smell or see it until it’s too late, but the incidence of mousy off-flavour in wine appears to be on the rise, with a growing number of enquiries and requests for help coming across the AWRI helpdesk.

Australian Wine Research Institute (AWRI) senior oenologist Geoff Cowey says about 20 wines with mousy character, from large and small wineries, have been sent in to the helpdesk during the past three years, with about half of these now being white or sparkling wine.

“Previously you would be lucky to see it once a year, if at all. There is no seasonal trend as such but often it is picked up during wine ageing,” Cowey says.

“Some of the mousy character could be found in whites made with extended periods of lees contact and minimal SO2,” he says.

“The main chemical compound responsible for mousy off-flavour is 2- acetyltetrahydropyridine (ACTPY) – and its aroma is characterised as being ‘caged mice and cracker biscuits’.

“Generally, you can’t ‘smell’ the character as it is a basic compound, or is only aromatic at pH 7 (neutral) or higher.

“Wine is obviously acidic and in wine the mousy compound changes its chemical structure to one that is not aromatic.

“However when you put the wine in your mouth the pH increases and the compound returns to its normal aromatic form, allowing a taster to perceive it.

“The mousy flavour can be delayed – it might take more than 30 seconds to develop on your palate. So if you see it in a tasting line-up, it is important to identify the right wine as the culprit, and make sure what you’re tasting isn’t a carry-over effect from a previous wine.”

Cowey says the flavour can also persist for several minutes in sensitive individuals making it difficult to taste afterwards.

He says it is now believed as much as 30 per cent of the population are unable to detect this particular off-flavour at all, which can pose problems, particularly in small wineries, if the main tasters aren’t sensitive to the character.

‘Often it’s not until quite late when wines are almost ready for bottling, when someone might suddenly pick it up,” Cowey adds.

“Unfortunately in some cases the wine has already been bottled and it is only detected once consumers who are sensitive to the character complain about the wine to the winery,” he says.

There are two main origins of the off-flavour – microbial and chemical.

Full story in July’s Grapegrower & Winemaker.