- ATA (atypical aging) and the early emergence of petrol character are wine defects that may seem like winemaking issues, but they originate in the vineyard.
- ATA describes the emergence of off aromas--furniture polish, dirty dishrag--after some time in the bottle, in otherwise sound wines.
- Though the chemistry is still not clear, vineyard correlates for ATA have been established--notably heat-induced water stress around veraison and lack of nitrogen nutrients.
- Early petrol aroma, while a distinct issue, seems to arise from similar viticultural conditions
Great wines, we are told over and over, are made in the vineyard, and there's a lot of truth to that mantra. But some really crappy, problematic wines are made in the vineyard, too--a phenomenon that doesn't get quite as much press or marketing spin.
I'm not thinking here of the usual suspects: overcropped vines, moldy grapes, varieties suited to the Sonoma Coast grown near Bakersfield. I'm thinking more of subtle, slightly mysterious and decidedly irritating chemical malfunctions--like the stink of atypical aging (ATA), and the distinct but in some ways parallel problem of the too-early emergence of the petrol character in young Rieslings. These unpleasant aromatic flaws are rarely noticeable at bottling, showing up later when they're least expected--about the time the wines are released. You might well think somebody messed up the winemaking--but you'd be wrong.
Chances are good that something went awry in the vineyard. All the chemistry on these little time bombs hasn't been worked out, but there are some pretty well established vineyard correlates, some combination of heat and water stress and nutrient deficiency. All of this could happen in an off year in one of those vineyards where the afore-mentioned great wines are routinely made. ATA und UTA
Atypical aging often is associated with Riesling because the majority of research was conducted in Riesling sites like Geisenheim, Germany (above), and Cornell University in upstate New York.
I first learned about ATA three years ago, while visiting Dr. Thomas Henick-Kling at the Cornell University New York State Experiment Station during a trip to the Finger Lakes, where ATA had emerged as a concern for growers and as a research focus for the staff. Deciding to get back to the topic, I tried to look up his e-mail address in New Zealand, where he had gone after Cornell, only to discover he had repatriated to Washington state.
Atypical aging was Henick-Kling's coinage, a loose translation of the German Untypische Alterungsnote
("untypical aging note"), aka UTA. The syndrome was first diagnosed and characterized in German wines in the 1980s, though chances are good it has popped up now and then since time immemorial. As Henick-Kling observes, there was so much bad wine on the market 30 years ago, isolating particular flaws wasn't that easy.
And some people still aren't convinced that ATA/UTA is for real. Morten Hallgren, winemaker at Ravines Wine Cellars
on New York's Keuka Lake, says of his area, "Some people still deny it's a problem, some people accept it, but we definitely have it here."
The trajectory goes something like this: At bottling, the wine seems fine, stable--nothing amiss chemically or sensory-wise. After six to 12 months or more in bottle, the wine starts showing a bouquet variously described as dirty dishrag, furniture polish/varnish, floor polish or Linden blossom, often with some bitterness and a metallic aftertaste, and always with suppression of varietal character. It can arrive in varying degrees of off-ness--sometimes just nicking a wine, sometimes ruining it--and once it's in full flower, there's not much to be done.
Atypical aging has become identified with Riesling, likely because so much of the research has been done at Geisenheim in Germany and at Cornell, both in the heart of Riesling country. But the phenomenon has been identified in other whites and in reds, and on several continents. Estimates from people honed in on the problem run as high as perhaps 20% of wines sent into tastings. And no, it's not part of terroir
--at least not in the good sense. Chemistry and viticulture
Efforts to deconstruct the chemical pathways involved in atypical aging--at Geisenheim, Cornell and the Australian Wine Research Institute--have been less than conclusive.
The most commonly fingered alleged culprit is the bad spawn of amino acids, specifically 2-aminoacetophenone. Methyl anthranilate has also been implicated, though Henick-Kling thinks that's more of a foxy/Labrusca indicator than a true ATA component. Indole and skarole show up on some lists, and Terry Acree's Cornell chemical analysis team spotted peaks in gas chromatography for two as-yet-unidentified compounds, respectively producing "animal" and "urine" characteristics. (Beginning to see the problem here?) Some of the miscreants that show up in one study make no appearance in others, and it's quite possible the compounds operate in the rarefied parts-per-billion realm.
Chehalem winegrower Harry Peterson-Nedry says water stress is uncommon in Oregon, and that may be one reason Atypical Aging is not a common occurrence there.
In any case, no one has yet to nail the full chain of events--how precursor X morphs into compound Y--that eventually volatilize into the offending Z. And as for the disappearance of varietal character, we don't know if something in ATA neutralizes it or if it simply gets overpowered, which is too bad- -and not just because inquiring minds want to know. If the chemical trail could be tabbed down, there would be a possibility of testing in the cellar, knowing a problem is at hand, and perhaps taking some form of remedial action.
Meantime, researchers have had somewhat better luck in finding vineyard correlations. Tim Martinson at the Cornell Station headed up the viticultural side of a three-year study of conditions that promote or discourage ATA, and the chief problem areas turned out to be drought stress in hot years, especially during the period right around veraison, and a lack of nitrogen nutrients in the grapes headed for winery must. Similar patterns have been found at Geisenheim.
Avoiding water stress seems to be the most promising method of reducing the incidence of ATA. Drip irrigation during periods of unusual heat is one obvious precaution, but attention has also focused on the potential downside of cover cropping. One of the reasons Henick-Kling thinks the problem has emerged so strongly in recent decades has been the move, especially in traditional winegrowing regions like Germany, to the use of cover crops to combat erosion--bringing along the unintended consequence of greater competition for water. In Oregon, Chehalem winegrower Harry Peterson-Nedry says the problem is not common, but that may be in part because "serious white winemakers" in his area tend toward clean cultivation, no cover crops, and use of drip systems in prime white winegrape blocks.
If heat and water stress are key factors, odds are good that climate change--both higher temperatures and more temperature variability--will accentuate the ATA phenomenon, unless growers adapt to lessen the impact.
| Early petrol character vs. atypical aging
The early, premature emergence of the petrol/kerosene character in Riesling (and potentially other wines) is, in a sense, another form of non-standard aging--but at least in this case, Riesling fans want it to show up at some point. The issue is that a quirky strain of aromatics that is much prized in 10 and 15-year-old wines seems out of place in a young, fruity, summer picnic wine. I will confess that when I started this article, I had early petrol and ATA all mashed together in my mind--and that same conflation can be found in a lot of the literature on atypical aging.
Petrol has clearly been linked to the compound TDN (tri-dihydronaphthalene), and carotenoid precursors are involved, though there is still some guesswork about exactly how this works. While TDN can theoretically show up in any wine, the frequency with which it presents in Riesling stems from the relatively high carotenoid content.
What we do know about early emergence comes, again, from the vineyard. And the list is by now familiar: The more heat and sunshine, the more TDN and more chance of early petrol; the better the nitrogen level in the vineyard, the greater the production of other, good, Riesling-like aromas that keep any TDN in its place, at least for several years.
So, even though early petrol and ATA/UTA are different concerns, with their own sets of chemicals and sensory descriptors, both seem to stem from fruit that is stressed and malnourished in the vineyard. Next time you come across one of these wines, don't blame the winemaker.
The other technique that has shown some promise is foliar applications of nitrogen during the ripening period. The foliar part here is important: As Morten Hallgren notes, soil-based nitrogen additions would likely promote more vegetative vigor, postponing grape ripening, the last thing anyone needs in the Finger Lakes, with its narrow ripening window. And although the low nitrogen levels of incoming grapes can lead to a kind of mildly stuck fermentation, simply adding DAP to the must doesn't do the trick. ATA is not a fermentation byproduct, but rather a legacy of problems in the vineyard.
In the winery, the only prophylactic measure that has shown promise is addition of ascorbic acid--the earlier the better. According to Henick-Kling and growers in the Finger Lakes to whom he proposed the tactic some years back, ascorbic acid may only delay the onset of ATA for another two or three years, not conclusively remove it--but that may well be enough time for the wine to meet its fate in a glass with happy results.
One last complication: If the appearance of ATA is somehow an oxidative reaction (and lots of things are), there could conceivably be some connection to the bottle closure--the amount of oxygen ingress through various media or the quality of the bottling run itself. That part, at least, is the winemaker's responsibility.
Tim Patterson writes about wine and makes his own in Berkeley, Calif. Years of experience as a journalist, combined with a contrarian streak, make him interested in getting to th e bottom of wine stories, casting a critical eye on conventional wisdom in the process. Contact him through firstname.lastname@example.org.