1,8-cineole (eucalyptol) in commercial Australian wine
Background
A recent study in California has shown that eucalyptol (1,8-cineole) could play an important role in the sensory perception of ‘eucalyptus’ character in some wines. The characteristic aroma of eucalyptol was described as ‘eucalyptus’, ‘fresh’, ‘cool’, ‘medicinal’ and ‘camphoraceous’. It was suggested that the eucalyptol in the wines might have been derived from nearby Eucalyptus trees. Subsequently, an Italian study showed that at least some of the eucalyptol in wine could also be derived by acid catalysed transformations of grape metabolites.
This project aims to explore the extent of eucalyptol's abundance in grapes obtained from Australian vineyards known to display the characteristic aromas of eucalyptol. We also endeavoured to understand what impact Eucalyptus trees and winemaking processes had on the amount of eucalyptol found in the finished wine.
Progress
To study the presence and relevance of eucalyptol in Australian wines, we developed a simple and rapid analytical method using synthesised deuterium-labelled analogue, d6-eucalyptol and used this to determine the amount of eucalyptol present in a broad cross section of commercial Australian wines. We also investigated whether eucalyptol could be transferred to grapes in the vineyard from nearby Eucalyptus trees.
As part of this study, we analysed 146 commercially available red wines: Shiraz (43 samples), Cabernet Sauvignon (45 samples), Merlot (25 samples), Pinot Noir (17 samples), Cabernet Sauvignon and Merlot blends (10 samples) and Durif (6 samples). Of the commercial wines analysed, 40% contained eucalyptol above the reported aroma detection threshold of 1.1 µg/L and several contained relatively high amounts (between 5-20 µg/L). The highest level of eucalyptol found was 19.6 µg/L in a Shiraz wine. The vineyard that produced this wine had Eucalyptus trees in close proximity.
For the 44 white wines (12 Rieslings, 10 Sauvignon Blancs, 10 Semillons and 12 Chardonnays) analysed, eucalyptol was not detected above 0.8 µg/L. The low concentration of eucalyptol found in all white wines examined might be because this compound accumulates in the skins and is thus only extracted during maceration of skins.
Highlights
- A method was developed for the analysis of eucalyptol in ferments and wines
- Eucalyptol ‘traps’ were devised to assess transfer of the aerosol from Eucalyptus trees to grape vines
- Eucalyptol levels in ferments and wines were determined and related to the proximity of Eucalyptus trees to the vineyard
- Red wines had higher levels of eucalyptol than white wines, presumably due to maceration of skins in a red wine ferment
Project leader: Dr David Jeffery
Project team members: