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What defines cold and warm climate grapes

Altitude and latitude are just some of the factors that determine where grapes grow best.

America (Country Appellation)

The Coolness Factor:
Rethinking Where Varietals Grow Best

When cool climate grapes grow in a warm climate area and produce spectacular wine ostensibly atypical of that area, the question arises: “So just what defines a so-called cool climate?” Dan Berger runs hot and cold on the answer.

by Dan Berger
August 7, 2008

DropCap A48 scheduled breakfast meeting in August 1986 with wine makers in Washington’s Columbia Valley created a fascinating awakening for me. Over the last few years, that moment has come back to me in three dimensions, and from this I think I understand an aspect of terroir that was missing until now.

My trip to Washington 22 years ago had begun a few days earlier when I drove into Seattle well past 9:30 in the evening. As I was parking the vehicle behind a hotel, I glanced west and saw the rays of the sun splayed across the sky, remnants of a gorgeous sunset. I asked the hotel desk clerk what time sunset was. He said about a quarter past nine.

And I realized that this far north in the United States sunlight hours on grapevines are greater during the summer months than they are in California. That affects things such as veraison, sugar accumulation, and most critically, flavor development in wine grapes. More sunlight equals a different sort of development of the grapes. That was where my thinking ended.

Days later the second revelation occurred. Overnight it had been cold enough in the Columbia Valley that I had to turn on the heat in my motel room. The next morning at about 10 A.M., as I left the Richland, Wash., motel and headed for my
Riesling grapes do best in cool climates so why do they shine in the warm Clare Valley of Australia?
meeting with wine makers, the temperature was already 96 degrees! Wow, I thought, the heat really rises quickly down here in the southeast part of the state. Again, I didn’t think beyond the episode.

But these two factors have led to some recent revelations about what constitutes a cool growing climate for wine grapes. I was spurred to think more seriously about this following a wine column I penned not long ago in which I wrote of the Clare Valley in Australia, calling it a cool-climate region that was perfect for growing Riesling.

An old friend who writes for a major wine magazine wrote to correct me. “Clare is not a cool region,” he wrote. “It’s warm.” He added, as proof, that some of the gutsiest red wines in Australia come from the Clare.

That brought back to mind a visit to the Clare two years ago in which the noon temperature was pretty hot (I’d guess it was above 90°). So, sure, I know that’s not a cold climate. And neither is Columbia Valley. And yet both regions are famed for their classic Rieslings, and it is well known that Riesling doesn’t make classic wine in a hot region.

But a number of factors enter the picture. As a starter, here’s a case example. I have long judged at the Mendocino County Fair wine competition in “cool” Anderson Valley, that gorgeous side valley of Mendocino County. That event almost always takes place in early August outside Boonville, and the temperature there at that time of year almost always gets close to the century mark. It is hot. Really hot, and stays so for many days.

Anyone experiencing this is likely to ask, “Cool climate?” and answer it, “No way!”

Yet proof that it is cool enough comes from the fact that despite high daytime temperatures, such superb wines as Riesling and Gewurztraminer do brilliantly, as do the cool-preferring Chardonnay and Pinot Noir. They can’t be grown terribly successfully in a hot climate.

Back to the rest of the story of my recent visit to the Clare: Following the searing heat of mid-day, the afternoon experience was a major turnaround. Cool breezes from the north raced south through the vines. And by 5 p.m., I was racing to the rental car for a jacket. By 7 p.m., it was so cold a fire was started in the fireplace! And this was summer.

A Growing Degree Days System That’s Too Simplistic

So it is apparent that, decades ago, when UC Davis developed a five-tier system for determining the appropriate places to grow wine grapes (and additional data showing temperature zones for table grapes and raisins), it was using a premise that worked reasonably well for that time. But it had drawbacks. One was that it was too simplistic.

Then that system was refined with the use of Growing Degree Days (GDD), which looks at accumulated temperature units throughout a season. This relates
climatechange 275.jpg
Between now and 2100, the climate will change drastically, which will alter growing seasons no matter where you live. But for now, there’s no guarantee that cool climate grapes can’t fare well in warmer regions.
to the diurnal temperatures of a region – that is, the high of day compared with the cold of night. GDD is often used by gardeners to help determine flower development. In viticulture, knowing the GDD of an area helps growers to fine tune how grapevines should be grown and how they will develop ripe fruit, varietal to varietal.

As a result, we now know that the Carneros area in south Napa and Sonoma counties is cooler (less than 2,500 GDD) than are both counties’ upper valleys, and, as such, it is better suited for Pinot Noir, Chardonnay, Merlot, and sparkling wines. We also know that grapes like Syrah can ripen in Carneros and other cool regions, and indeed, in Australia, the cool regions of northern Victoria make some of the most prized cool-climate red wines.

By contrast, the central valley areas of California, with GDD readings of 3,500 or greater, usually produce low-acid, high-sugar grapes that produce wines that can be soft and lacking in much character.

Worldwide, the higher you go in altitude the cooler you get, based on lower average temperatures. So, for instance, the Eden Valley of Australia may be within the bounds of (warm climate) Barossa, but its altitude makes it a superb place to grow Riesling. It’s a lot cooler than the rest of the surrounding region.

However, there are curious exceptions. One of them is the Mendocino Ridge appellation in Anderson Valley of Mendocino County. Much of Anderson Valley, like the Russian River appellation, gets overnight and morning fog that keeps nighttime temperatures very low. And unlike Columbia Valley, which warms quickly from the cold nights, Anderson Valley remains cool until 11 a.m. or so.

Above the fog layer, however, there are mountaintop mesas that are actually a bit warmer on average than the valley floor in accumulated warmth. The Mendocino Ridge appellation was created just for those properties located at least 1,200 feet above the valley floor, thus appearing like islands in the sky above the fog line. Despite the altitude, they are warmer areas than is the valley floor, but still cooler than some areas because of the maritime and altitude impacts.

Much of the above material now is part of formal climate research in Australian and Canadian viticultural circles. (The Australian Journal of Grape and Wine Research just published a scientific paper called “Climate drivers of red wine quality in four contrasting Australian wine regions.” And an entire department has been established at Brock University in Canada called the Cool Climate Oenology and Viticultural Institute.)

A key factor in this quest to define “cool climate” viticulture relates to the coldness of the nights in a region and how wide a day-night swing is the temperature range. In the Clare, for instance, daytime summer temperatures well above

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Reader Feedback

Reader Comments... [11]

Arthur , Founder & Publisher
redwinebuzz.com, So Cal

VARIETALS don't grow any where. They are poured out of bottles.

That distinction aside, I agree that there is a trend to grow whatever is chic and not what does best in a particular region.

All the best.

Kent Callaghan , owner/grower
Callaghan Vineyards, Elgin, AZ
It always amazes me when the assumption is made that any grape variety is best suited to the area it "originated" in. Clare isn't cool.

TAPAS is doing a tasting right now at COPIA with Iberian varieties. Are we really stupid enough to (still) believe that the "best" places for any given variety are their (historically accidental) places of origin?

Bobby Cox , winegrower
Lubbock, TX
Great article, but I do not understand the temp. map. Seymor is in a cooler area than Lubbock? Seymor has the most 100 degree temps in Texas and might hold the record for high TX temp. The High Plains at high altitude are much cooler than most of Texas.

Alan Schwarz , Proprietor
Little Brampton Wines, Clare, South Australia
Dan, a great article and you have got it right. Clare is an inland area, and at 520m (1600ft) above sea level, our warm autumn days turn into chilly evenings. This high diurnal temperature variation is what brings the great fruit intensity and natural acid balance to Clare wines, and why Clare wineries have a high percentage of medals and trophies in their cabinets!

Marlene Rossman
ManhattanWineSeminars.com, Southern California
Marvelous piece!

Shae Cooney , Business Development/PR Manager
Old Bridge Cellars, Napa, CA
Dan, just wanted to say nice article on cool climates. Provided much needed clarification of this term to an oft-confused audience!!

Peter Fanucchi , Wine Grower -- ALL HATS
Fanucchi Vineyards, RussianRiver, Sonoma County, CA
Cool Article!
Very through too. I was taught that grape vine stomata start closing @ 90F.

Sadly, I think I will go out of business trying to not get caught up in that current sad mode of today's homogenized wine making...

Another extreme factor that is plaguing the vines around here is 100% sun exposure with total leaf removal around the clusters! I believe the flavors are baked out of the fruit. (I started noticing more roasted coffee flavors in some wines that I later discovered were so exposed.) But more on the topic – in a vine canopy that dose have a leaf layer or two it can be substantially cooler under the shade of the leaves & at least take longer to heat up. I also was taught that a leaf catches ~75% of the sun's energy so after the 3rd layer there is no sun & there shouldn't be any leaves in 100% shade. Oh well, --- just another angle.

Jeff Del Nin , Winemaker
Burrowing Owl Estate, Oliver, BC
Cool climate is most easily described as less than 1500 Celsius degree days (about 3000 F GDD). Anything above this is warm. Having spent 7 years in South Australia and 10 years total in Australia, I have come to know all of the regions extremely well. Clare has slightly more GDD than Barossa, but it is further from the ocean, so the diurnals are higher. Research says that the maximum flavours develop when the overnight temps during ripening are between 12-15C. The longer you can keep the grapes in this band, the more flavour will develop. I think this is why Clare Riesling (very good) is better than Barossa Riesling (rubbish). The real challenge is to understand why, in general terms, Margaret River wines, despite having similar GDD to Barossa, taste thinner and don't have the depth, power and concentration of their South Australian counterparts (there are exceptions, but in general, Margaret River wines have more red fruit character and tend to have an under-ripe sourness that is a result of a general lack of sweet fruit esters and fruity flavour compounds). I think that it also has to do with sunlight hours. Based on my own observations of quality in different Australian regions, the better predictor of big, deep, powerhouse wines is the sum of GDD plus sunlight hours. When you add them together, then South Australian Quality can be explained. Of course, once GDD above around 2000 Celsius degree days (about 4000 F degree days) then we are no longer talking about a quality scenario and we would be better off making fortified wines with these grapes.

Steve Snyder , Grower/Winemaker
Hollywood Hill Vineyards, Woodinville, WA
In my conversations with Dr. Greg Jones he said he is working towards a more accurate way to assess a region's climate to grow a particular variety and the way he measures that is through the average temperature of the growing season (April-October). I think the old Growing Degree System is outmoded and cannot accurately predict what you can grow. I think we are a prime example of that here in the Puget Sound AVA where critics have told us for years we can't grow wine grapes, but I've been doing it successfully for eleven years.

Albert Lewis
Julian, CA
Great article, although it may have raised more questions than it answered. Can anyone tell me how they would characterize the climate of Julian, CA in the mountains of San Diego (actually we're located a bit lower in Wynola, just outside of Julian)? What grape varieties would you grow there? My particular place is at about 3650' in elevation and has summer season (June-Sept) average temps of about 87 high and 57 low. 25+ degree daily temperature fluctuations are the norm.

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