June 26th, 2005

Summary: 1)eucalyptus aroma is produced by at least one grape variety.
2) a common monoterpene found in grapes is a precursor to eucalyptol, indicating that this aroma could be an indication of age in certain wines.

What is the liklihood that eucalyptus trees near your vineyard are going to impart eucalyptus aroma to your wine? Certainly it is not difficult to smell eucalyptus when several trees are around and it seems logical that if you can smell it in the air than the volatile compound could potentially settle on grape skins. Fair enough? As far as I can find, no study has been published demonstrating that this occurs at levels which would impact wine aroma, thus bolstering opinions in either camp. But not finding something to be true does not make it false and vice versa. One recent study (published in In Proceedings of the VIIe`me Symposium International d’OEnologie. Actualites OEnologiques 2003. Bordeaux, Francia, 2003; i.e. limited peer review, cited from study below) found Eucalyptol in wines from vineyards surrounded by Eucalyptus sp. trees, though it was not shown that the aroma came directly from the trees.

Before cutting down some of these beautiful giants, look at this recent study that demonstrates the production of eucalyptol (1,8-cineole, threshold of about 2 ppb) in Tannat grapes. Furthermore it was shown that limonene (an apparently common grape monoterpene giving citrus - orange, grapefruit, lemon - aromas and used in bergamont) can undergo reaarangement in acidic media to form eucalytol (slow reaction, white wine pH). Of course this doesn’t mean that the aroma cannot come from trees, but it does mean if your wine smells of eucalytpus, it could have come from the grape itself.

Naturally this begs the questions: how does our viticulture impact the formation of this compound? The aforementioned study shows its concomittant increase with sugar after veraison. Light can increase monoterpenes in general suggesting this may also increase eucalyptol or at least its potential to form after ageing. We’ll just have to wait. Finally, I will note that Tannat wines are purportedly well known for this characteristic and I was unable to find reports on the amount of eucalyptol or limonene in other varieties.

One Response to “Eucalyptus”

  1. Tyler Says:

    Instead of looking at glycosylated compounds, why aren’t people looking directly at flavor compounds such as limonene or eucalytptol as a fucntion of ripening level. Then we could see what is happening to acutal (as opposed to putative) flavor compounds due to extra hang time.

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