Wine News Water and Wine: The Irrigation Equation

Water and Wine: The Irrigation Equation

The decision about whether to irrigate or not can have a massive effect on the grapes.
© Lodi Growers | The decision about whether to irrigate or not can have a massive effect on the grapes.
In a world where drought is an increasing threat to agriculture, what effect does irrigation have on terroir?
By Margaret Rand | Posted Sunday, 11-Oct-2020

Jean-Luc Colombo, of Cornas in the Rh?ne, states that irrigation gives fruity, marmalade flavours in Syrah, whereas non-irrigated Syrah has aromas of wild flowers and violets. Discuss.

But first, consider this: the argument about irrigation is an argument about terroir. It may be expressed as an argument over flavors, but it's about terroir, and what a proper expression of terroir should be. Winemakers are both the best people to ask about that, and the worst.

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The best because, obviously, they're the ones who deal with it. They're the ones who work their terroir, understand it, and have the most idea of what it's saying. But the worst because they're also the ones who can mess about with their terroir and change it to suit themselves. If you want the argument in a nutshell, just listen to a European winemaker saying "Why would you plant vines where there is no rain?" And then listen to an Australian winemaker saying "Why would you plant vines where grapes won't ripen and you have to add sugar to the juice?"

That's the subtext. In Colombo's case it’s also part of a wider concern about how we're using the planet, of which growing vines in deserts is only part. Consumers, even wine merchants, don't understand the effects of irrigation on wine, he believes; if wine is good enough, only a few people will ask questions, and then they will be questions about organics or biodynamics, not irrigation. He compares the differences between irrigated and non-irrigated wine to a Picasso by – well, Picasso – and a Picasso painted by you or me. The latter might fool enough of the people, enough of the time.

Let's leave aside the generous irrigation of industrial vineyards to produce a deluge of personality-free wine. There continues to be a market for this, just as there is a market for battery-raised chicken. But it's not what we're talking about here. We are talking about complex, elegant, serious wine from good sites, some of which might be short of water.

Does irrigation really change the flavor of Syrah from violets to marmalade? What do other growers think about this? Is Colombo over-simplifying?

Craig Stansborough, chief winemaker at Grant Burge Wines, emphasises that irrigation won't change flavor directly, but the availability of water is one of the main things that affects flavor.

Obviously, too much water means dilute flavors from big, fat grapes. The intensity of a non-irrigated grape is totally different, says Colombo; and you could argue that that principle has been adopted by a great many winemakers in arid regions who these days give their vines as little water as possible. Balance is the aim: vine balance, via stress management. If this is beginning to sound like boardroom-speak, don't be deceived: it actually means being in close touch with your vines, all the time.

Sixty per cent of Barossa vineyards now use soil moisture monitoring, says Stansborough. That does what it says: tells you exactly how much water is in the soil, at all times, so that you can avoid overwatering. Other methods can measure the amount of water in the leaves, and even the circumference of the vine trunk throughout the growing season; it expands until veraison, and then shrinks as all effort goes into ripening the grapes. Too much water stress means the trunk starts to shrink too early in the season, which means the grapes might not get everything they need. The vine trunk shrinks from night to day, as well, which complicates matters, or there can be sap flow sensors on vines.

Once a grower starts irrigating a vineyard, it can be hard to go back.
© iStock | Once a grower starts irrigating a vineyard, it can be hard to go back.

Or there’s partial root drying, in which you irrigate each side of the row in turn, which keeps the vine on its toes but stops it reacting to water stress by shutting the stomata in its leaves, which would stop photosynthesis, which in turn would stop ripening.

Nobody wants ripening to stop; nobody wants drought stress. Drought stress gives you green, bitter wines with unripe tannins and high alcohol. And defoliation, adds Stansborough, and pruney flavors.

Too much irrigation can give you green tannins, too, so it's not an either/or. Too much water means too much canopy, rocketing sugar levels, and phenolic ripeness that lags behind sugar ripeness. Which means – you guessed it – green tannins, unless you want enormous alcohol levels.

Does this sound like whatever you do, you're wrong? Could be. The trouble is that what all winemakers really, really want, is really, really difficult to achieve unless nature smiles on you – and she won't, not every year. The ideal is getting sugar ripeness as close as possible to phenolic ripeness. In hot climates that is difficult because the former comes with sun and warmth, and the latter with time. In hot climates you have to wait for tannins to ripen while sugar levels rocket. Cool climates traditionally didn't have this problem; but instead they could have some pretty feeble sugar levels. Hence chaptalization.

Colombo makes the point that irrigations tends to iron out vintage differences. The 2009 vintage in the Rhône was, he says, "a solaire year" – a hot, sunny one. "It's like California wine," he says. But 2007 "has more taste of Cornas: juniper, incense, violets, spice". Those differences are without irrigation, in a world where solaire vintages are increasingly frequent.

Like 2020 in the Douro Valley, for example. David Guimaraens, winemaker at The Fladgate Partnership, says that the Upper Douro suffered most from the dehydrating heat and, on his travels round the vineyards, "I cringed at the damage in some places". Would irrigation have stopped those grapes from raisining? Yes, it probably would. "But my big issue with irrigation is that once you start it's difficult to go back," Guimaraens says. "In viticulture in hot climates you have to match the right rootstock with the right vine in the right place. In more arid regions you have to be more selective when you plant. The old-timers were very selective about where they planted."

Those vines the old-timers planted are themselves old now. Old vines, we are told, have much deeper roots (although this can depend on soil structure: if the roots meet solid rock two feet down, they won't be able to go further). And those deeper roots are supposed to give better flavors – better balance, finer tannins, more complexity. It's hard to measure these things, but winemakers who work with unirrigated old vines, like Henschke or Ridge, will swear that it is so. But if you start irrigating an ancient, deep-rooted vine it will change its focus to its surface roots. The deep roots might even die back. And then you are dealing with a different plant. And, as Guimaraens says, it's difficult to change back.

Nobody would dispute that every vine, young or old, irrigated or not, gets nearly all its nourishment from the top few inches of soil. (Some new irrigation systems are able to deliver water to between one and four feet down, leaving an unirrigated zone on top, to encourage deeper root growth.)  But people like Henschke and Ridge are not given to delusions. They see a difference in umami flavors in the wine from old dry-farmed vines, in completeness, even though they can't measure it. The flavors, they reckon, are different.

There have been studies on the effects of irrigation, and they tend to find that less water equals smaller berries and more color and tannins, except when it doesn't (I précis). So let's return to Craig, who stresses the importance of irrigation at the right moment. Too much in the early part of berry development, when the cells are dividing, he says, will give you bigger berries. So you give the minimum from then until Christmas (he's in Australia). "After that the main aim, the only aim, is to keep the canopy healthy. There's a lot of research now that says that in a very dry winter, putting water in gives advantages. If you water in spring, it's too late."

What about flavors? Gary Jordan, of Jordan Wines in South Africa, says that "if the object of the irrigation is to stop the vine shutting down and grow in a less stressed optimal environment, then I believe that you can still produce wines showing floral, violet and peppery flavors, assuming microclimate temperatures aren't too high ... If the object of the irrigation is to increase yield, i.e. berry size, and not specifically to alleviate stress, then yes, the flavors will change more like Jean-Luc says." And those marmalade flavors can come from a warm climate; they might not be the result of irrigation. "Heat definitely produces more 'cooked/stewed' flavors too when taken to the extreme," says Jordan.

Will irrigation tend to even out the differences between vintages? Yes, it must do. Will it change flavors from what they would have been without water? Perhaps; but flavor is a complex matter. The best flavors from any given variety in any given vineyard come when the vine is in balance. Whether vines should be grown where that balance doesn't naturally exist is a bigger question. But if it's not, there won't be much to go round.

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