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Cracking Chemistry In Cold Climates

September 2010
 
by Tim Patterson
 
 
I spent my high school, college and grad school years avoiding science classes. I wasn’t anti-science, I just had other things on my mind -- the kinds of academic interests that make you nearly unemployable. Then I took a couple of computer programming classes at a community college, total cost about $25, and found myself quite gainfully employed doing a sort of science thing. When I got hooked on wine, I started wondering how it worked, and here I am.

My idea of a good time now is listening to smart people give lectures about chemistry and biology, which I did for four days in June in Seattle. This year the annual meetings of the American Society for Enology and Viticulture hosted back-to-back gatherings for the International Cool Climate Symposium. What follows are quick passes at several ideas that got presented there, the kind of tantalizing stuff that makes you (or me, at least) want to go back for more.

The ICCS, not surprisingly, spent a good deal of time discussing the Cool Climate part of its organizational name -- specifically how climate change might be redefining the new cool. What struck me about the string of presentations and posters touching on this theme was the scant amount of time spent on gloom, doom and dire predictions, and the generous amount of time spent on what growers, winemakers and researchers can do and already are doing to deal with the problem. Grapevines and humans are both adaptive species.

Perhaps the most indicative sign of the times in this regard was a presentation by a marketing consultant about the rosy future for bubblies from the UK. We all know that the Brits did a great deal to establish international standards for fine wines -- including claret worship -- in the era when they had more money than anyone in the world but no way to ripen their own grapes. Now they’re becoming players with seriously high-quality sparklers.

Riesling chemistry
One of the high points of the ICCS for me was a paper about Riesling aroma chemistry presented by Gavin Sacks from Cornell and co-authored by a number of researchers there. The question was: What makes Riesling Riesling? Sacks quoted several sources that claimed monoterpenes (linalool and such) are Riesling’s signature. However, he pointed out that Riesling monoterpene levels are down near or under the sensory threshold -- nowhere near as elevated as, say, Muscat. Norisoprenoids? Sure, but not in the same league with Gewürztraminer. Thiols? Got some of those, too, but no match for Sauvignon Blanc. And so on.

“If monoterpenes are what makes Riesling smell like Riesling,” Sacks said, “then why can’t I make a good facsimile of Riesling by blending Pinot Grigio with Muscat, the latter which has 10x the monoterpenes found in Riesling?”

The only place Riesling leads the pack, Sacks argued, is in TDN, the basis of the “petrol” aromas in mature Riesling. Part of the presentation was devoted to discussing how vineyard sun exposure affects TDN levels.

But what struck me (and Sacks) was that in every category of aromatic compounds, Riesling showed up at “peri-threshold” levels -- different from the profiles of other aromatic grapes, which tend to specialize. The upshot: Riesling is particularly sensitive to growing conditions and to winemaking, both of which can easily alter the aromatic mix. Riesling, with more arrows in its quiver, has the best shot at complexity. We already knew those two things about Riesling; for me, at least, getting the guided tour of the distinctive chemistry was one of those light-bulb moments.

Norisoprenoids also were involved in my favorite bad news/good news presentation: University of California, Davis, researcher Mark Krasnow’s tale of the silver lining in berry shrivel. Berry shrivel, which Krasnow prefers to call SAD (Sugar Accumulation Disorder), is an unexplained condition that affects Cabernet Sauvignon. In random years and places, berries stop accumulating sugar, stop developing anthocyanins and just shrivel up. Most of the affected fruit is discarded, but Krasnow & Co. used some of this damaged fruit in test fermentations, anyway.

Lo and behold, the partially SAD wines turned out to show more fruitiness and less vegetal character, the result of unusual levels of ß-damascenone, the poster compound for norisoprenoid volatility. Other samples of SAD fruit showed the same presence of this rose-petal compound. Krasnow didn’t exactly endorse berry shrivel as a viticultural strategy, but it does seem like a better route to enhancing Cabernet aromatics than the old-school habit of dumping a can or two of Muscat concentrate into Cab fermentations.

The quest for wimpy yeast
In the recent period of high-Brix, high-alcohol wines, people have often attempted to shift the blame to modern commercial yeast strains, allegedly capable of producing more units of alcohol per unit of sugar than the old-timers. This is mostly wishful thinking, since yeast metabolism cannot remap the underlying chemistry of alcoholic fermentation, in which one molecule of sugar yields two of ethanol, two of carbon dioxide and a few bits of other stuff. There simply aren’t enough atoms around from the sugar to make 2.5 molecules of ethanol, whatever that would mean.

But Dr. Linda Bisson’s lab at UC Davis, which took the lead in critiquing the “super-yeast” notions, is exploring an alternative that might offer actual help to high-octane winemakers: inefficient yeasts that produce less ethanol. One presentation coming from this research, given by Yeun Hong, analyzed metabolites produced in a number of Chardonnay fermentations using different yeast strains ranging in final alcohol from 11.1% to 13.8%.

Another paper, presented by Vidhya Ramakrishnan, explored the role of two aldehydes -- furfural and hydroxymethyl furfural -- in inhibiting ethanol production during fermentation. Some yeast strains adapt to one or both of these inhibitors better than others, and research continues to identify easily intimidated yeast.

For sheer chemical intrigue, the work coming out of Dr. Andy Waterhouse’s lab about oxidation mechanisms has plenty to offer. Waterhouse and his grad students at UC Davis are exploring a maze of pathways, during and after fermentation, through which oxygen is used, bound, scavenged or allowed to run riot, involving interactions with all manner of other compounds. The oddest coupling among these reactions is the fact that, as Waterho use has explained on other occasions, in certain situations oxygen can be an effective anti-oxidant.

In Seattle, the news from this research dealt with polyphenols and their roles as anti-oxidants -- the value of tannins, for example, in barrel and bottle aging of red wines. Waterhouse explained, in the course of an overview presentation at the ICCS, that the longstanding view of what phenolics bring to the anti-oxidant table is their phenol-ness -- the benzene rings with hydroxyl groups hanging off them that show up in so many wine chemistry chicken-wire diagrams. True enough, but what the Waterhouse lab has found is that other flavors of phenols besides the usual suspects -- known as vicinal diphenols -- can play a similar role; he offered cinnamates as one quick example.

Later, during the ASEV sessions, Nick Gislason from the Waterhouse lab went into more detail about how the “unsaturated sidechains of hydroxycinnamates” join in the oxygen-bashing. To translate this into terms I had at least heard of -- and perhaps you have, too -- forms of caffeic, ferrulic, coumaric and cinnamic acid often indulge in “radical trapping” alongside the better known oxygen cops. This research won’t likely translate into a packaged fermentation additive by the next harvest, but it certainly does expand our understanding of the amazingly complex role played by oxygen in winemaking.

The anti-bentonite conspiracy
Among the posters at ASEV, two that caught my eye had to do with reducing or eliminating the use of bentonite in removing protein from juice and wine. (Maybe I was sensitized by having bentonite finings under way in my own garage wines that very week.) One from Rachel Fanning at Texas Tech continued that institution’s forays into the use of phytic acid (rather than clay) for protein stabilization in wine; other results have been published in the American Journal of Enology and Viticulture. One limitation of this approach is that, at the moment, phytic acid is not a permissible wine additive, but that doesn’t make the research any less interesting.

Another poster from Tymari LoRe of Cal Poly revisited a longstanding discussion about the pros and cons of bentonite additions before or after fermentation. This bit of research indicated that, contrary to much past work and opinion, using bentonite at the juice stage does not adversely affect fermentation, the resulting wine chemistry or the eventual sensory evaluation. What it does is greatly reduce the amount of bentonite needed to do the job; one test wine needed only a small post-ferment dosage; another, none at all.

With the money you save by replacing or reducing bentonite, you could buy some norisoprenoids for your Cabernet. Just a thought.

Finally, it was good once again to hear that work continues on the trail of that ever-elusive wine attribute: “minerality,” whatever that is. Dwayne Bershaw, working with sensory specialist Hildegarde Heymann at UC Davis, gave a presentation focused on use of a particular sensory panel methodology that proved to offer a shortcut way to identify wines displaying this mysterious trait.

The study did not, as Bershaw made clear, focus on what minerality is or might be. In a burst of creativity, the researchers devised as a reference sample a cocktail of pea gravel, soapstone and a pinch of benzyl mercaptan -- a sulfur-containing fermentation by-product identified in one French study as the “smoking gun” behind minerality.

I’m putting the money I save on bentonite into benzyl mercaptan. And now, if I can just find a way to get to Tasmania in 2012 for the next Cool Climate Symposium...

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 the bottom of wine stories, casting a critical eye on conventional wisdom in the process. Contact him through edit@winesandvines.com.

 
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