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WINEMAKING Eucalyptus Aromas: A Mystery Researchers confirm source behind minty characters By Dimitra L. Capone, I. Leigh Francis, Markus J. Herderich and Daniel L. Johnson A s an investigative story, the hunt for what causes eucalyptus character—and the origin of its aroma compound 1,8-cineole—in wine has the makings of a classic whodunit. The search for the culprit or ally, depending on your preference for or against eucalyptus characters, has thrown up false leads and an unexpected ending. Studying the origin of 1,8-cineole, the Australian Wine Research Institute (AWRI) found that the location and leaves of eucalyptus trees play a direct role in the concentration of 1,8-cineole and occurrence of the "eucalypt," "fresh" or "minty" characters in wine. Native to Australia, eucalyptus trees have been planted throughout the world, with large populations of the species now growing in California as well as China, India and Brazil—they live on every continent apart from Antarctica. Hardy and resilient, they grow in a range of different climates and environments, providing raw timber and wood pulp as well as large supplies of eucalyptus essential oil. It is the oil that matters most to winemakers. Most species of eucalyptus tree contain essential oils in their leaves and, depending on the species, the main component of the oil is a volatile compound called 1,8-cineole, commonly known as eucalyptol. Used as a flavoring agent in a wide range of foods and beverages—as well as being present in a range of therapeutic products—1,8-cineole can also be found in red wine, where it is Highlights • t has long been assumed that natural oils from eucalyptus I trees drifted onto grape bunches to cause the distinctive eucalyptus aroma. • group of researchers from the Australian Wine Research A Institute has determined that assumption to be incorrect in identifying the main cause. • heir work over three vintages with many experimental wine lots T revealed more potent sources and how to manage them to limit or increase eucalyptus character. 52 W in e s & V i ne s F E B R UARY 20 13 1,8-Cineole Concentration 1,8-cineole concentration decreases further from eucalyptus trees Concentration of 1,8-cineole (μg/L) (Editor's note: This article is reprinted with permission from the Wine & Viticulture Journal of Australia and New Zealand, where it appeared in the July/August 2012 issue.) 10 16 8 14 Western Australia 6 Victoria 12 10 4 8 2 4 0 6 2 11- 15 18.5 27 50 77 Meters from trees 230430 0 0-50 50175 Meters from trees responsible for characters described as "eucalypt," "camphor," "fresh" and "minty." For some winemakers these characters are a selling point. Some red wines are well known for their "eucalypt" sensory properties, and the compound responsible is considered a help, not a hindrance to the winemaker's craft. For other wine producers, however, "eucalypt" characters are something they prefer to avoid—or at the very least limit through effective management strategies. Discovering the source of 1,8-cineole and understanding how it gets into wine has become a detective story: a case that wine scientists have been determined to solve. Early evidence For some time, the origin of 1,8-cineole in wine remained a mystery. Scientists had theories, but none were verified: Some researchers believed that "eucalypt" characters were associated with the proximity of vineyards to eucalyptus trees;1 others proposed that there were compounds in grape berries that acted as precursors for 1,8-cineole.2 Further investigations revealed, however, that the precursor proposal did not account for most of the 1,8-cineole found in wine. Research at the AWRI showed that the precursor compounds were unable to generate high enough levels of 1,8-cineole to reach sensory threshold concentrations.3 Once this potential source was discounted, the AWRI researchers continued to focus on the proximity of eucalyptus trees to vineyards (historically planted as windbreaks) and whether the