Comments on: Aging Riesling

By: Thomas

Thomas — Sat, 04 Jul 2009 20:24:13 +0000

Thank you, Mitch.

By: Mitch

Mitch — Sat, 04 Jul 2009 17:47:19 +0000

According to Tom Stevenson (http://www.wine-pages.com/guests/tom/riesling-petrol-2.htm): “Riesling’s so-called petrol aroma has been identified as trimethyldihydronaphthalene or, to be precise, 1,1,6-trimethyl-1,2-dihydronaphthalene (Simpson, 1978). TDN is a C13 norisoprenoid, which some class as a terpene, but others do not. It is a moot point; a semantic argument upon which chemists continue to differ. TDN is rarely found in grapes or, indeed, young wine, although its precursors are, and they are primarily carotenoids (may chemists state definitely beta-carotene, others probably alpha-carotene, while some think quite possibly both). Beta and alpha carotenes (and lutein a by-product of alpha carotene metabolism) are all antioxidants. These precursors exist in all grape varieties, thus TDN can be found in almost every wine, although the ratio of lutein to carotene is usually low, thus the TDN potential for most wines will be well under the perception threshold level of 20ppb. However, the ratio of beta carotene to lutein is higher in Riesling than for any other grape variety. If ,as most scientists believe, beta carotene is the primary precursor for TDN, this may explain why, after lengthy bottle-maturation, the wines from this variety can accumulate as much as 200ppb TDN, ten-times the perception level. This is why mature Riesling is famed for its so-called petrolly aroma.
TDN can also be produced by the hydrolysis of two megastigma-3,6,9-triols linked to a sugar molecule (Strauss et al, 1986) and it has been theorised that the hydrolysis of a sugar molecule called 2,6,10,10-tetramethyl-1-oxaspiro[4,5]dec-6-ene-2,8-diol can create TDN (Winterhalter, 1991; Silva Ferreira & Guedes de Pinho, 2004)”

In short, TDN isn’t considered a phenol because it doesn’t possess a hydroxyl group (-OH) on an aromatic ring though it does possess an aromatic ring. TDN is a degradation product of carotenoids (think carrot pigments) and Stevenson notes other potential precursors.

By: Thomas

Thomas — Sat, 04 Jul 2009 17:09:18 +0000

Thanks, Mitch.

I had heard of this before, but have not seen data on it.

Is TDN considered a phenol?

By: Mitch

Mitch — Sat, 04 Jul 2009 14:40:28 +0000

Thomas,

Update according to Drs Richard Smart and Caroline Gilby (Wine Report 2009, p. 384): Nitrogen and TDN (trimethyl-dihydronapthylene) — It seems that increased levels of nitrogen fertilizer lead to lower levels of TDN, an important component of the kerosene-like aroma in Riesling), according to German research looking at various fertilizer treatments carried out over several vintages. Cheers !

By: Mitch

Mitch — Fri, 12 Jun 2009 15:26:55 +0000

Beserkers a fair amount and once in a blue moon MS’, e.g., Victor’s subprime thread or a tannin thread. The last few weeks have been real eye-openers for many casual readers

By: Thomas

Thomas — Fri, 12 Jun 2009 14:59:03 +0000

Thanks, Mitch.

Are you still posting on those sites???

By: Mitch

Mitch — Fri, 12 Jun 2009 14:29:45 +0000

Nice article Thomas.
Here’s a link to some info about petrol notes and “partial rootzone drying” I posted you know where:

http://dat.erobertparker.com/bboard/showthread.php?p=1984704&highlight=riesling+carotenoid#post1984704

Wikipedia covers it also.
Cheers!

By: Thomas

Thomas — Mon, 08 Jun 2009 20:51:41 +0000

In this economy, I’d bet the warehouse is in default!

So you left in the fifth grade or so. That means you probably remember something about the area. Of course, there were fewer than a dozen wineries then in the Finger Lakes region–it’s hovering 100 today.

Look up Keuka Lake on your Google map–Vinifera Wine Cellars. My home is about 1/4 mile from the winery. Keuka Rieslings are spectacular, and you cannot beat the beauty of this place, too (except in February).

I have a few near-extinct bobolinks nesting in my meadows behind the house. Got me some nice pics of them.

By: fredric koeppel

fredric koeppel — Mon, 08 Jun 2009 20:39:22 +0000

that would be a trip worth taking….. we’ll have to work it out sometime. i was born in rochester and haven’t been back since 1955, when my family moved to memphis. perhaps i could combine trips (though i see on Google Map that my boyhood home has been replaced by a warehouse!)

By: Thomas

Thomas — Mon, 08 Jun 2009 18:52:49 +0000

Fredric,

So true. There isn’t much to go around, and this isn’t much in the way of savvy promotion either.

I doubt the funded promotion arm of the industry does much to reach out to bloggers. Maybe you need to schedule a trip up north. I’ll be your guide.