Trefethen Dry Riesling - petrochemical nose?

[pickypicky]

Last night we were served two rieslings by a young sommelier, who is a bit raw but talented. ( It's been fun to watch his learning process.) One of the rieslings was a Trefethen dry. I don't remember the vintage, but the nose was flatout petroleum or gasoline. The taste was lovely, although my husband says he found it slightly oily in the mouth. Is this a characteristic? I can't believe it isn't a flaw or that a jug of transmission fluid didn't fall into the barrel. The sommelier couldn't explain it and accepted the strangeness without question.

Help.

[pickypicky]

Once again, CHOW pulls through. I learn almost as much about wine here as I do by drinking it. I have enjoyed many off smells and flavors in wine (cat pee, dirty hair, burning tires) but the petrol nose of the Trefethen seemed to be too much. Thank you, Maria Lorraine and others, for clearing up my mystery. I learned something!

[kaysyrahsyrah]

I love PETROL in reisling!!!!!!

[chrisinroch]

Petroleum is fairly common on the nose of German Rieslings. Its more common as bottles age, but I had an 04 jj prum last week that was really really strong. It is usually a turn off for folks who do not expect it.

[carswell]

Kerosene (the Brits say petrol) aromas and even flavours are often found in Riesling, especially in bottles with some age on them. It's due to a hydrocarbon, TDN. Like cat pee aromas in Sauvignon Blanc, a little can add an appealing complexity while high concentrations can be unappealing.

For more information, see http://en.wikipedia.org/wiki/Riesling...

[pickypicky]

thanks, carswell! yes, while drinking, I'd thought of the cat pee analogy and a south african wine I had a few years ago that was absolutely burning tires. While I drank the riesling, I thought that a little would be a nice complement to the wine, but this was more than a little. AND it did not diminish over the course of the meal. (I saved a bit to keep tasting.)

[maria lorraine]

carswell, hello...

I thought TDN was a function of at least five years of aging, whereas fusel -- which can also have a petrol aroma -- can appear in a very young wine since it is formed during fermentation.

My guess -- though I'm not certain -- is that the petrol aroma in the the Trefethen Dry Riesling is fusel, since it has appeared so quickly after the bottling of several vintages. The 2005 reeked of petrol early on, as did the 2007.

[carswell]

Hi, Maria.

TDN is generally acknowledged to be associated with aging, though this is the first time I've seen a figure (five years) assigned to it.

Fusel, on the other hand, I've always understood to be more of an issue for distillates of wine than for wine itself (though, dog knows, fusel is often used as a tasting note descriptor for Riesling). Oxford Companion to Wine (3rd edition): "Fusel oils are of only minor importance to the wine drinker since they represent such a small proportion of wine, except in the case of some red wines made from Cabernet Sauvignon and Zinfandel grapes in which a hint of isoamyl alcohol can sometimes be deteced (aromas sometimes likened to whisky or malt or described as burnt)."

A cursory Google search of *riesling fusel* sheds little light. Unfortunately, many of the more scientific articles are hidden behind subscription firewalls. Will continue searching as work permits, but meanwhile (and without spending undue amounts of time) can you provide citations, pointers or anecdotal input?

[Melanie Wong]

TDN is associated with aging, but also with climate that is too hot for riesling. I have no cites for this, but German vintners have said to me that riesling grown in warmer new world climates (such as Napa Valley) will develop the petrol prematurely.

[maria lorraine]

I have a citation:
"TDN is linked to the famous ageing flavour of Riesling, which is described as petroleum, kerosene, diesel, Band-Aid or the German expression Firne. Especially in wines made from Riesling grapes grown in warm climate areas such as Australia or South Africa, evolution of this ageing flavor is accelerated and may impart the wine quality as soon as 6 months after harvest...While TDN is generally absent in grapes or young wines, it may develop up to up to 200 μg/L in aged wines."

Excerpted from "Flavours and fragrances: chemistry, bioprocessing and sustainability," by Ralf G. Berger, 2007:
http://books.google.com/books?id=ax1O...

So, Melanie is right about the possibility of TDN appearing without years of bottle aging when wine grapes are grown in a hot region. TDN also increases with ripeness.

The number of years TDN usually takes to appear is dependent on how long the molecule needs to become unbound (so it can then volatilize). But aging, a warm growing climate, or very ripe grapes do not guarantee the formation of TDN; there must be a chemical precursor.

I'm not certain of the source of the Trefethen "petrol" aroma yet but I'll continue to gather info over the next few days. When I was in Alsace, I heard much about fusel being formed during fermentation, but will have to check that info for accuracy. I have calls in to a few UC-Davis wine chem geeks, and one to Trefethen. Will report back.

[maria lorraine]

Sorry for the delay in responding. It's a busy time in the wine industry.

I talked to two winemakers at Trefethen -- David Whitehouse and Zeke Neeley -- and their answer is that they don't know what the petrol component is. Their guess is that it's TDN, due to Napa's warm climate for growing Riesling. They say the petrol appears about a year after bottling.

All this points to a larger confusion about the cause(s) of the "petrol" aroma and flavor in wine, and its proper identification. I've heard petrol in Alsatian and Austrian wines described a great many times as fusel by the winemakers themselves, who also said that the petrol component appeared during or shortly after fermentation. That seems at variance with the formation of TDN.

To explore the accuracy or lack thereof of that fusel description, and if there might be several causes of petrol, I called and emailed a few wine chemistry professors at UC-Davis. Got the brushoff by one, and haven't yet heard back from the others. It's harvest now, and the wine chemists are extremely busy, as am I, so I haven't been able to hound them sufficiently to get answers. But I hope to do that in the next few weeks.

If it's not obvious, I find the chemical underpinnings of a wine's sensory components fascinating. It's like breaking a code. I can never learn it all.