Riesling's Telltale

Have you ever taken a really good whiff of Riesling? Particularly Riesling with some age on it? What do you smell that you likely don't smell in any other wine (you might smell it in Chardonnay, but if you do that Chardonnay is really bad)? You smell petrol. Gasoline. Petrol sounds nicer than gasoline.

Before we get into what's going on with Riesling, we need a little wine encounter story about petrol and Chardonnay. Just to humor you because true funny stories are way funnier than made up ones. 

We were in southern Arizona. We're not talking near Tucson. Compared to where we were, Tucson is northern Arizona. We were close enough to the Mexican border that at one point, we encountered the border patrol driving, thankfully sober, in our rental car. That I recall, we were in the Arizona town of Nogales whose closest neighbor is Nogales, Mexico.

In any event, we did head north just a bit, not very much. Because within 15 miles of there, there are a bunch of wineries. One in particular was pretty good and another in particular had gotten really good reviews from the locals. We visitied the latter. Upon entering the tasting room that seemed more like a fiesta just south of the border, the smell was, shall we say, different. But, we decided to taste.

Four wines in, we  were afforded the not so rare opportunity to taste the wine that "all the local ladies love," their Reserve Chardonnay. It was grown in the severe heat and dryness of southern Arizona and aged 33 months in new American oak. Yes, 33 months. And, apparently, when you combine summer heat spikes with lots of new oak and Chardonnay in the hands of someone who has spent a good part of his live around fuel, you get the overwhelming smell of petrol. Ouph!

But, in detectable, but not overwhelming proportions, Riesling connoisseurs think this is a good thing. And, it is the telltale sign of Riesling in a blind tasting, particularly Riesling with a bit of age on it.

The petrol aromas come from something known as TDN and it's called TDN in the wine world because just as I had to, if you want to know what it is, Google is your friend. It turns out that TDN is actually 1,1,6, -trimethyl, -1,2 -dihydronapthalene (aren't you glaad you asked?).

TDN is found naturally in white grapes, at least pre-fermentation. Through a chemical process known as acid hydrolysis in which acidic wines serve as the acid, various aromatics, particularly TDN in Riesling emerge. And, as a wine ages in bottle, they show themselves more. Chemically, this occurs because Riesling has far higher carotenoid (yes, the same thing that creates that orangish color in very ripe tomatoes and of course in carrots) content than any other wine grape.

In particular, heavy sun exposure and summer heat spikes tend to increase the Riesling carotenoid level (common in the Mosel region growing season). And, lower yields, which usually means grapes with more concentrated sugars and flavors and therefore higher quality Riesling have higher levels of carotenoid and thus evolve into higher TDN concentration producing the petrol aroma particularly as the wine ages.

So, blind tasting, stron petrol, somewhat browned rim, equals aged Riesling.