Eucalyptus flavor in wine: what is it?

Isabelle Lesschaeve Author

Do eucalyptus trees planted near vineyards transmit the eucalyptus flavor found in many Australian red wines? Find out the answer in this article.

Date published July 28, 2021

Solving the mystery of eucalyptus flavor in Australian wines

It all started with a challenging question.

"Every time I taste an Australian Shiraz, I get a Eucalyptus aroma. My theory is that Eucalyptus trees transmit this character to the grapevines nearby, one way or another. Thoughts?"

Jim's theory reminded me of another idea I've read in a wine magazine. The writer stated that wines produced in the South of France, in Provence near lavender fields, expressed a lavender flavor typical of this region.

So the big question is: Can aromatic plants growing near vineyards transmit their aromatic components to the grapevines and then to the finished wines?

I turned to colleagues specializing in viticulture. Their answer was: Exchanges between plant systems are complicated.

But it might not be the case for the eucalyptus flavor in wine.

An Australian colleague shared an in-depth research conducted by the Australian Wine Research Institute in 2011-2012. Their findings lifted uncertainty about the the origin of eucalyptus flavor in Australian wines [1].

But first,

How to tell if you smell a eucalyptus flavor in your wine.

Eucalyptus aroma is part of the “Vegetative/Fresh” category in the Wine Aroma Wheel.

The aroma responsible for imparting the eucalyptus aroma is well known: 1,8-cineole. It’s also called eucalyptol, for obvious reasons.

What does it smell like? 

Eucalyptus flavor is often described as camphoraceous, medicinal, or spicy, with undertones of mint and citrus, with a peppery aftertaste. 

My advice is to buy a small flask of essential oil and memorize what this smell evokes in you.

How does the eucalyptus flavor end up in your glass of red wine?

What do we know about eucalyptol?

It’s a very potent compound

This aroma compound has a low detection threshold of 1.1 micrograms per liter of wine (1.1 ppb). It is pretty potent. 

Research showed that consumers don't mind experiencing eucalyptus flavor in wine, but to a certain level. Research showed that Australian consumers rejected a red wine containing more than 27.5 micrograms per liter of eucalyptol in red wine (27.5 ppb) [2].

 It’s mostly present in red wines

The AWRI study found that 40% of red wines contained 1,8 cineole at a level greater than 1.1 ppb. But, the aroma compound wasn’t found at a detectable level in white wines. 

Shiraz and Cabernet Sauvignon wines tended to be more affected than other red varieties.

Does the distance between eucalyptus trees and vineyards matter?

The Australian researchers evaluated wines from Western Australia and the Yarra Valley. Yes, the further the grapevines from the Eucalyptus trees, the lesser concentration of 1,8 cineole in the finished wines. 

So Jim's theory has some traction with this data. But what is the mechanism?

Testing a few scenarios.

Skin contact during fermentation

The Australian researchers showed that the eucalyptol concentration increased daily during shiraz red wine fermentation, but stopped once the wine was pressed off the skins.

So the grape berry skins or other matters are responsible for transmitting the eucalyptus aroma to red wine. 

So, how did it get there?

Grape skins, stems, leaves, or other matter than grapes?

First, the scientists showed that airborne transmission existed between eucalyptus tree leaves and vineyards by placing some traps at various distances to capture eucalyptol molecules.

The scientists also measured the culprit compound, three years in a row, in grape berries, leaves, and stems of these vineyards planted close to Eucalyptus trees.

They showed that grape leaves had the highest concentration of eucalyptol, not the berries. They found, though, that the berry skins contained more eucalyptus compounds than the pulp. So, this data explained the transmission of eucalyptol from the skins to the must; but, skin content is not high enough to reach the eucalyptol concentration found in finished wines.

While conducting their research in the vineyards, the scientists found many eucalyptus leaves and bark trapped in the vines' canopies. This finding raised new questions.

So the scientists compared wines made from hand-picked grapes and mechanically harvested grapes. 

Yet, they found more eucalyptol in the latter. The harvester picks more than the grape bunches, and other matters like Eucalyptus leaves can end up in the fermentors. Hence the higher concentration of Eucalyptus flavor in these wines.

Mystery solved!

What to say about Jim's theory?

Wines made from grapevines located near Eucalyptus trees have a distinct eucalyptus flavor

• Yes, the proximity of Eucalyptus trees to vineyards plays a significant role in imparting a Eucalyptus aroma to finished red wines.
• The aroma compound, 1,8-cineole or eucalyptol, can spread via air from the tree leaves to the grapevines. 
• Its highest concentration was found on leaves and stems. The berry skins didn't contain enough of the culprit compound to explain the high levels found in wines.

What’s the most plausible explanation?

The wind spreads dried tree leaves and barks on the vineyard canopies. This matter is un-distinctively harvested mechanically and ends up in the fermentors for skin contact fermentation. This matter (other than grapes) is the primary vehicle of the eucalyptus aroma in the wine.

The good news is that winemakers have remedial treatments to minimize the collection of this external matter before fermenting their red musts.

Train your nose to detect Eucalyptus flavor in wine

Are you living near eucalyptus trees and can enjoy their smells?

Yes. Great, smell the leaves next time you’re outdoors.

If not, there is another way to become familiar with the eucalyptus flavor. The easiest is to get eucalyptus essential oil at your pharmacy. Smelling a cloth on which you put a few drops of eucalyptus oil will enable you to smell the aroma. And it can help you prevent or heal a cold!

Let me know how it goes.

References

[1] Capone, D.L. Francis, L., Herderich, M. J., and Johnson D.L. (2012). Managing eucalyptus aromas. Wine & Viticulture Journal JULY/AUGUST 2012

[2] Saliba, A.J., Bullock, J., Hardie, W. J. (2009). Consumer rejection threshold for 1,8-cineole (eucalyptol) in Australian red wine, Food Quality and Preference, Volume 20, Issue 7, 500-504.

Categories: : wine aroma, Wine Language, wine style