Prevention is best option for mousy off-flavour in wine

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.

The Australian Wine Research Institute (AWRI) senior oenologist Geoff Cowey said about 20 wines with mousy character, from large and small wineries, had been sent in to the helpdesk over 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. Some of the mousy character could be found in whites made with extended periods of lees contact and minimal SO2’, Mr Cowey said.

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’, he said.

‘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 over 30 seconds to develop on your palate. Thus 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! The flavour can also persist for several minutes in sensitive individuals making it difficult to taste afterwards’.

Mr Cowey said it’s believed 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. Unfortunately in some cases, the wine has already been bottled and is only detected once consumers who are sensitive to the character complain about the wine to the winery’, he said.

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

‘If it’s microbial, it comes from the strains of lactic acid bacteria (LAB) including Lactobacillus hilgardii, Lactobacillus plantarum, Lactobacillus brevis, and Oenococcus oeni  and also the yeast Dekkera/Brettanomyces,’, Mr Cowey said.

‘Historically this issue occurred in old style winemaking, such as high pH wines, minimal SO2, unfined and unfiltered. The result was high pH red wines with mousy character, but also Brett and some VA faults too.

‘But much of this has changed as preventive hygienic measures introduced by wineries to control Brett have also controlled mousiness and VA’.

If its origin is chemical, it’s linked to the process of hyperoxidation, when hydrogen peroxide is used to remove SO2 from juice or wine.

‘The mechanism by which oxidation enhances mousy off-flavour is currently unknown, but has been responsible for several sparkling base wines going mousy when treated to remove SO2 before secondary fermentation’, he said.

‘This highlights the importance of performing SO2 removal steps carefully. A recommended method for removing SO2 is available on the AWRI website’.

At this stage, Mr Cowey said, there were no routine methods for measuring the level of mousiness in wines, and detection was still reliant on the known tasters, sensitive to the off-flavour, in the AWRI tasting panel to help confirm mousy character for helpdesk clients.

‘There’s also no verified ways to remove the character, other than blending away the affected wine. As the character often comes from microbiological sources it is important to sterile filter the wine to make sure no more mousy character will be produced’, he said.

‘High additions of SO2, particularly in white wines, can mask the character, but once the SO2 drops below a certain level over time, the character can be observed again.

‘Simply, prevention is best of course, for both origins listed above’.

More information regarding mousy off-flavour is available on the AWRI website here or by contacting the AWRI helpdesk during business hours on 08 8313 6600 or by email: winemakingservices@awri.com.au.

The AWRI help-desk service provided to levy payers is funded by the GWRDC. For urgent afterhours queries, Con Simos, AWRI’s Group Manager for Industry Development and Support, is available on 0448 889 432.

Like its namesake, mousy off-flavour in wine is difficult to get rid of once found. The AWRI suggests prevention is the best option.
Like its namesake, mousy off-flavour in wine is difficult to get rid of once found. The AWRI suggests prevention is the best option.