Eucalyptus

Australian red wine is noted for often having minty aroma and flavour. This can express itself in many ways, from blatant crushed gumleaf smell to peppermint to garden mint and spearmint. Tasters in other countries, who don’t see our wines as often, notice the mint more keenly, suggesting it’s so common in our wines that we are de-sensitised to it. For many overseas wine professionals, mint is a distinguishing trait of Aussie red wines. Winemakers are divided over whether it’s desirable, and if not, how it can be minimized.

There’s no doubt some lay wine-lovers enjoy this aroma … when was the last time you tried a Wolf Blass Grey Label (tastings), Orlando Lawsons Shiraz (tastings) or Lake Breeze red (tastings), that didn’t have some mint? Some wines have it so regularly you might assume the winemaker actively seeks it. But most experts seem to agree mint or eucalyptus character is not desirable if it’s too domineering.

There’s also an ongoing debate about how this aroma gets there in the first place. Is it caused by windborn eucalyptus oil, is it in the soil, or is it nothing to do with gum trees? Some winemakers think it comes from oak-maturation.

A researcher at the Australian Wine Research Institute, Dr Dimitra Capone, presented a most illuminating talk on this topic at the recent Australian Cabernet Symposium in Coonawarra. Her work focuses on a compound called eucalyptol, more correctly named 1,8 cineol, which is responsible for this aroma. She presented evidence – as yet unpublished – that eucalyptus trees are responsible, and the closer the vines are to the gumtrees the more eucalyptus character in the wine.

Some winemakers whose vineyards don’t have gum-trees nearby believe mint could come from the soil – which may have sustained gum trees before being cleared – and a residue in the soil is taken up by the vines. But Dr Capone said 1,8 cineol is not translocatable: in other words, it is not transported through the vine’s system, so its presence in grapes cannot occur in this way.

Others believe mint comes from eucalyptus oil transported onto the grapes by air currents, and Dr Capone’s work confirms this is one route. Air samples from the vine canopy contain increasing quantities of 1,8 cineol the closer the vines are to gum trees.

However, her work also shows the most significant source of 1,8 cineol in wine is the direct presence of eucalyptus leaves, twigs, bark and other material that goes into the fermentation along with the grapes.

She sampled this material, known in the jargon as MOG (matter other than grapes) in bins of grapes and found astonishing quantities. In a 500kg sample of hand-harvested grapes, she counted no less than 33 gumleaves. “Imagine what mechanically harvested fruit might contain,” she said. Machine harvested grapes tend to have a lot more MOG than hand-harvested, as the machine shakes the berries off their stalks and a lot of rubbish falls into the collecting bin along with the berries.

She also found that only tiny amounts of MOG are needed to introduce mint aromas into wine. The problem doesn’t affect white wines because they are fermented without the skins and other solids. She found much higher concentrations of 1,8 cineol in the skin of the grape than the pulp (in fact, four times as much). This tallies with the theory that the compound does not come through the vine’s sap system.

And there is much more 1,8 cineol on grapevine leaves and stems than skins.

Dr Capone prefaced her talk with the information that an AWRI tasting panel preferred wine that contained some 1,8 cineol to wines that contained none. The preferred level was 38 micrograms per litre. But her samples from vine canopies closest to gum trees contained as much as 213 micrograms per litre!

Dr Capone purchased 146 bottles of Australian red wine, and found that 40 per cent of them contained 1,8 cineol above the threshold (a threshold is the smallest amount at which the human palate can detect something.) Out of 46 Coonawarra cabernet sauvignons, 70 per cent contained 1,8 cineol at or above the threshold level.

Dr Capone also showed that 1,8 cineol is leached out of the skins and MOG in the ferment: the longer the fermentation proceeded, the higher the level of 1,8 cineol, until the wine was drained off and the skins pressed. At that stage, the skins and all other solid matter are separated from the liquid and no more 1,8 cineol is extracted. This further demonstrated that the cineol was moving from the solids into the liquid.

Dr Capone also suggested to winemakers that a 50-metre distance seemed to be a good separation from gum-trees, and that wine from closer trees could be kept separate for later back-blending, in order to achieve a controlled amount of mint in wines.

What is yet to be shown from further research is whether gumleaf and the various mint expressions are all derived from the same 1,8 cineol – or are there several substances at work?

*The most famously minty Australian wine of all time is undoubtedly ‘Peppermint Pattie’ – the 1963 Mildara Coonawarra Cabernet Sauvignon, which also happens to be famous because it’s a great wine.


 

The mintiest red wines

Regions

  • Padthaway
  • Langhorne Creek
  • Wrattonbully
  • Coonawarra
  • Pyrenees
  • Bendigo
  • Clare Valley

Makers


First published in Sydney Morning Herald, Good Living – 30 October 2012.

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