Many of you may be familiar with a distinct minty, camphor aroma in certain Napa or Australian red wines. Heitz’ Martha’s Vineyard in the Napa Valley is one of the more famous for this character. Researchers in both countries have since established what many producers have known for a long time – that the minty aromas originate from the fragrant oils of nearby eucalytpus trees which are cast onto the grapes and leaves and then fermented with the skins. The compound is “eucalyptol” aka 1,8 cineole and the species e. globulus more commonly known as the Blue Gum contains among the highest levels. Like any aroma compound, its usually an excess that makes it a taint rather than adding character to the wine. The threshold of detection is around 1.1 micrograms (parts per billion), whereas the threshold of recognition is about 3.2 ppb. In recent research performed by the Australian Wine Research Institute, the level of eucalyptol measured in a sample of 146 Australian red wines reached as high as 20 ppb (same as the California research). When they measured the level of eucalyptol in finished wine based on the location of the grapes, those from the rows nearest the grove of eucalyptus trees – as close as 33 feet – measured the highest with a level of 9.6 ppb while those sourced from furthest away – 1400 feet – contained as little as .4 ppb. Pending further research on managing the compound in wine, producers can fell trees, remove vines or blend away as they wish to manage the levels of “mint” in their wines.
So what is the connection? Before California’s Gold Rush, there were no eucalyptus trees in California. Among all the men rushing to California seeking gold were Australians and with them came Eucalyptus seeds, the most common being Blue Gum. Blue Gum is a fast-growing species with a straight growing habit that would make it suitable for timber in an equally fast-growing population and shipments of hardwood from the East Coast were slow prior to the completion of the Transcontinental Railroad and the opening of the Panama Canal. It was also desireable for firewood, bio-fuel, ornamental purposes and as windbreaks. The first eucalyptus were planted in 1851 and in the 1880’s, were used to create a forest at the location of the then military base, The Presidio, which stands at the base of the Golden Gate Bridge next to the Pacific. Until the forest was created, The Presidio was a swath of wind-swept dunes that was un-inhabitable without the windbreak of the forest. Eucalyptus was planted throughout California as windbreaks to protect citrus groves and other agricultural crops. Because of its straight, tall and stately growing habit, they were used to border properties and line driveways, which is where you will still find them today. In “Illustrations of Napa County” (Smith & Elliot 1878), the Soscol Ranch, among the largest and most reputable of nurseries in all of the Bay Area at the time, was selling blue gum and a certain Mr. Charles Thompson of Rutherford was but one of many who lined the grand avenues leading to their estates with blue gum trees.