UV Effect On Grapes??

WINE TALK
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In the latest Decanter, PeterMolnar, grower of ObsidianRidge in LakeCnty, comparing to NapaVlly, made the statement:

The UV light here is 50% higher here than in Napa and it ripens grapes quicker and sets the stage for flavor development at the top of the hillside and tannic structure at the bottom.

First, the 50% difference between Napa & ObsidianRidge strikes me as a little high.
Second, I’d never heard of UV being more efficient than visible wavelength light in ripening grapes. Any botanist types out there who can confirm that??
Tom

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Don’t have an answer to your second question, but there’s a good webpage from the National Weather Service on the relationship of UV radiation and altitude:
What is UV radiation and how much does it increase with altitude?

As stated on that page,

As mentioned earlier, UV radiation increases with altitude. This increase has been shown to be between 4-5% for every 1000 feet ascended. Thus, for the same day in June, the amount of UV radiation would be approximately 27% higher in Flagstaff than in Phoenix (about 6000 feet elevation difference). If you were going from Phoenix to the top of the San Francisco Peaks (approximately 12,000 feet), you would experience an increase in UV radiation of about 50%!

According to info I looked up on Obsidian Ridge Vineyard, the elevation there is 2,640 feet, so it sure looks like there’s no way the UV there could be even close to 50% higher than in Napa Valley.

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Could it also be affected by haze as well as simple altitude? Right around Clear Lake, it can be hazy and Napa is a narrow valley surrounded by high hills so it can trap things in the air. Perhaps on the ridge it’s clearer.

Or perhaps he’s a exaggerating a little.

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Tom:
UV light, though absorbed by leaves, is not used in the photochemical stage (photosynthesis). The plant uses several ways to protect from UV light and some of these increase phenolic compounds. So it depends on what you mean by ripening.
Did you listen to the last graperadio? Fukuoka is becoming popular…
Remember, you heard it first @ Castelli Vineyards…
Hope to see you soon.
E

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I’ve heard of UV light being beneficial for breaking down pyrazines, so higher altitude vineyards would be beneficial for getting rid of green aromas and flavors. But this is simply hearsay on my part. It’s not clear why UV would be more useful than visible light, though perhaps one might envision a reaction with an energy barrier that visible photons do not have enough energy to overcome. But again I’m speculating.

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Interesting question and for some reason I’ve been wondering about that so did a little research. More confused than ever now though.

Turns out that the southern hemisphere, like New Zealand gets 50% more UV than the equivalent northern latitudes, so they’re very interested in u.v. So Lincoln University in NZ is doing some studies right now on exactly that issue. And since I was kind of curious about it, I came across some of their work. They issued a press release a couple weeks ago on some of their work, stating:

"Specifically, UV causes accumulation of polyphenols (compounds that absorb the UV radiation and therefore protect the plant) in the grape skins and this may lead to changes in the properties of the wine, such as ageing and mouth feel. "

Then there’s this from another study, I think it’s also from NZ and possibly even from Lincoln, but saved it as Word so I don’t know for sure:

However, Hashizume & Samuta (1999) found light exposure had two opposite effects on the concentration of methoxypyrazines. Prior to veraison, IBMP concentration within berries was enhanced by berry light exposure; after veraison IPMP concentration decreased with exposure. They suggested that the production of methoxypyrazines might be closely related to the developmental stage of grapes, such that in the early stages the amount formed biologically exceed that degraded but in the later stages decomposition exceeded formation.

Increased levels of u.v. exposure increase the concentrations of quercetin in berries which makes this compound an excellent indicator of light exposure level . . . The flavour of quercetin has been characterised as generally being bitter and astringent. . . tasters described it as . . .sweet, sour, bitter, metallic, musty/dirty, viscosity, burn/alcohol, mouth coating, numbness/tingling, astringency and throat tightness. . . .Price et al. (1995) believe that quercetin can have powerful effects on red wine quality through its ability to co-pigment with other wine constituents and possess the potential to change, boost and stabilise anthocyanins. . .

(FYI - IBMP is 2-Methoxy-3-isobutylpyrazine, which is largely responsible for the bell-pepper flavors in the cab family and sauvignon blanc)

There was some study I remember where they used u.v. to irradiate wine with ladybug taint, because the bugs also add a lot of the bell pepper flavor to wine. Farmers have been trying to introduce them to eat aphids. They brought some from Asia and finally a colony took root in Lousiana and it’s moved west. We never learn because those ladybugs are stinkbugs and now they’re screwing the wineries. So people tried irradiating the tainted wine with u.v. but it didn’t seem to help. However, it turns out that the orange ladybugs have 10 times as much as their yellow cousins, but it’s hard to kill just one color of bug.

So I guess that the u.v. has a lot of influence on some things but it’s far more complicated than simply exposing a grape or not. It’s effects are also very much temperature-dependent. Sigh. Too much to learn.

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Thanks for doing the research, Greg. Like you…not sure it helps me understand things any more.
Not sure why the SouthernHemisphere would get 50% more UV than NorthernHemisphere. I would thing it would be primarily a function of the
amount of air between the sun & the vine. Maybe the higher humidity there & more water in the air would increase the UV absorption in the aiir I would think.
Tom

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Doesn’t help me understand either. I thought it was really easy and that more u.v. = less bell pepper flavor but it turns out it’s not nearly that easy. A good deal of influence on the grape bunch comes from the 2 closest leaves, so removing, exposing, or doing things to those can have a big impact on the wine. Also there’s a correlation between sandy soil and decreases in the methoyxypyrazine, vs an increase in clay soils, which can also be attenuated by leave exposure, irrigation, etc…

Hildegarde Heymann, who is a taste scientist, and Ann C. Noble, both at UC Davis have done a lot of research in this and I believe one or both have also done some work on the idea of basal leaf removal. Of course, a lot of people have done that but theirs relates to methoxypyrazine…

It’s completely complicated because timing, temp, and so many other things matter. It’s why I have so little patience for people who make broad simple comments about things like limestone, slate, minerals, old vines, natural wine and other things, basically stating beliefs w/out backing. The more you look into any of this, the less simple it is.

Incidentally, the Southern Hemisphere has more UV because of the ozone hole, which is in the south.

UV exposure has increased over the last 30 years, but stabilized since the mid-1990s -- ScienceDaily" onclick="window.open(this.href);return false;

And for something completely and utterly off topic, it seems that UV has a beneficial effect on preventing MS, which is perhaps why you never see symptoms in penguins:

http://www.sciencenews.org/view/generic/id/57542/title/UV_radiation,_not_vitamin_D,_might_limit_multiple_sclerosis_symptoms" onclick="window.open(this.href);return false;

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