© Bob Campbell

Eucalyptus trees planted next to a Western Australian vineyard

A distinctive eucalypt smell makes Australian reds easy to spot in a blind tasting. But how does it get into the wines?

Would you like some mint in your cabernet? Or perhaps a dash of eucalypt in your shiraz? If so, you’ll need a vineyard near eucalyptus trees and Australia has plenty of those on offer, endowing the country’s red wines with a distinctly minty character.

The aromatic compound that causes this character is called 1,8-cineole. First identified by a German scientist in 1884, it is the main component found in the oil from the leaves of the eucalyptus tree. But to this day, nobody has quite fathomed out its journey from tree to bottle.

There have been conflicting theories. A French study suggested that the compound originated in eucalyptus trees surrounding vineyards and was airborne, while an Italian group proposed that aromatic compounds in grapes, known as terpenes, were the creators of 1,8-cineole.

In an attempt to get to the heart of the issue, the Australian Wine and Research Institute (AWRI) in Adelaide set out to confirm just why so many of the country's cabernet sauvignon and shiraz-based wines are affected. In a study of 190 wines, it found that the existence of eucalyptus trees near grapevines can influence the concentration of the compound. The closer the trees, the higher the concentration of the minty smell.

Digging deeper, the AWRI then discovered that the machine harvesting of rows close to eucalyptus trees was likely to result in leaves from the trees being mixed in with the bins of grapes. Among their key findings, the scientists reported that even hand harvesting could "result in a surprising number of eucalyptus leaves in the picking bins.” From their experiments, they concluded that the “presence of eucalyptus leaves and, to a lesser extent, grape-vine leaves and stems in the harvested grapes" were the “main contributor to 1,8-cineole concentrations in the wine.”

But that didn’t explain how even meticulous producers, who remove the eucalyptus leaves from their grapes before processing the fruit, still end up with a minty smell in their cabernets. The answer, it appears, can be found in the grape skins, which contain 80 percent of a berry’s 1,8-cineole. How it gets there is still up for debate, but the results of the AWRI study “tended to indicate the airborne transfer of 1,8-cineole, which was pronounced within 5 meters of the eucalyptus trees and seemingly limited to within 20 meters of them.”

The presence of the compound in the skin explains why the eucalypt notes are found in Australian cabernet and shiraz, but not white wines. The study’s author, Dimitra Capone, explains that this is because white wines are separated from the grape skins before fermentation, while reds are fermented in contact with their skins.

“Where skin contact time is negligible, no significant amount of 1,8-cineole is found in the finished wine,” explains Capone.

© iStock

The skins of red grapes can bring a eucalypt character to the resulting wines

Bearing these findings in mind, it’s up to the Australian wine industry to decide whether or not it wants the minty taste in its wines. Eucalypt is certainly a divisive aroma. Earlier AWRI testing found that while most Australian consumers preferred a wine sample spiked with 1,8-cineole, 30 percent of respondents said they did not like wines with the compound added.

Capone notes that the issue of mint – or not – splits winemakers. “For some producers who have vineyards which give wines with higher cineole levels, they definitely consider it a positive character that buyers have come to appreciate and seek out in the wines,” says Capone.

She adds: “There are many gold-medal wines that contain quite high amounts of 1,8-cineole, and some very well regarded, premium wines commanding a high price have a minty character.”

Nevertheless, the eucalypt aroma is not viewed so favorably by some wine producers. For example, The Age newspaper reported that fruit from Yarra Valley vineyards which regularly produced eucalypt characters was being downgraded or rejected.

"Once we smell that sort of character we feel it's a problem, particularly with pinot noir," De Bortoli's chief wine maker, Steve Webber told The Age. "We like seeing fruit character, not gumleaf character."

Unfortunately, some Australian vineyard owners don’t have much choice when it comes to having mint in their wines. Sometimes, neighboring landowners have established commercial eucalyptus plantations near vineyards, with predictable results. In some cases, the plantation owners are rapped over the knuckles and warned to keep clear of the vineyards; in others, the wine producers have to adapt.

For vineyard owners who have eucalyptus trees on their own properties, a simple solution would be to cut them down. But Capone is not impressed by that suggestion.

“Australian wine producers are sensitive to their local environment, and being good custodians of the land is important to the wine industry,” she says.

The take-home message, then, is that producers with a eucalypt problem must be extra careful about any leaves finding their way into the picking bins, or plant their vines further away from those troublesome trees.