Kennewick, Wash.—Does late-season irrigation degrade quality in winegrapes? Does a cold soak before fermentation increase quality in wine? Speakers debated these contentious issues and others this week during a heavy schedule of seminars running through the annual meeting of the Washington Association of Wine Grape Growers.

The session about cold soaks featured a researcher whose recent studies appear to contradict much of the conventional wisdom about the technique, while two of three winemakers who spoke said they believe cold soaking is good for their wine, even if they can’t explain why.

If that sounds like the same kind of debate that has been simmering over Biodynamic grapegrowing, then it’s no coincidence. A lively panel dissected this topic, too, during a full Wednesday morning program called Myth Busting in Vineyard and Winery Practice. (Editor’s note: For more on the Biodynamic vineyard issue, see the recent article by Jon Tourney on this subject, and Clark Smith’s column on the same.)

Cold soak claims tested
Cold soaks have become very popular among some makers of Pinot Noir and other red varietals, especially in small lots. These practitioners say that chilled grape must rest in the winery before fermentation gains more color, better aromatics and more intense flavors. But some enology researchers say that many of the benefits winemakers claim to get from the process are not proven out in their studies.

Federico Casassa, a graduate student at Washington State University, Prosser, has put cold soaks to the test in Argentina, both experimentally and with commercial winemaking. He has tested Malbec, Syrah, Pinot Noir and Cabernet Sauvignon, typically using three lots of must: 1) a control lot with no cold soak; 2) a cold soak with must chilled in a cold room, and 3) a lot chilled with dry ice.

Casassa  observed some benefits in the cold-soaked young wines. Merlot gained color, for example. But with Pinot Noir, the non-cold soaked control extracted measurably more anthocyanins, color, total phenolics and tannins than the lot cold soaked with frozen CO₂, according to Casassa. At pressing, the traditional cold soak without CO₂ had less color than both the control and the CO₂ lot.

He noted that many wines studied this way are measured after malolactic fermentation, and not retested when they are ready for consumption. So he took measurements with the three types of lots again after one year and finally after two years in the bottle.

At 12 months, the color enhancement effect had gone away in both cold soak lots. The control Malbec after two years had the most color the most red-fruit character, while the cold soak SO₂ lot was the highest in eucalyptus flavor, an unfavorable trait for many people.

Casassa and another speaker, James Harbertson, the WSU extension enologist, explained that one hazard of cold soaks is that yeast can work in temperatures down to at least 40°F. Many winemakers add between 25 and 75 ppm sulfur dioxide to cold-soaking must. Casassa said he has measured sugar being consumed at those temperatures and that indigenous, non-Saccharomyces cerevisiae yeast were doing the job.

Harbertson recommended a pragmatic approach for those who do cold soaks, including inoculating with a Saccharomyces strain so that a known yeast will do any sugar conversion that takes place. (Editor’s note: for more information on cold soaks see Tim Patterson’s column, June 2009.)

Why winemakers soak
Three winemakers talked about how they use cold soaks. Patrick Taylor, winemaker at Cana’s Feast Winery in Carlton, Ore., works a lot with Washington fruit and regularly uses cold soaking at about 38ºF. He stressed that unlike Casassa’s methods, his soaking wines get no stirring or other active oxidation. Over several years he has found no activity of yeast in lab tests, and has observed color and flavor enhancements that he likes.

Josh Maloney, the red wine winemaker for Chateau Ste. Michelle at Canoe Ridge, underlined that researchers disagree among themselves over the effects of cold soaking. “But I think it’s like saying black pepper makes food better. Well sometimes it does, but sometimes it doesn’t.”

He has experimented with cold soaks. And in 2010 he used a kind of modified cold soak, or slow warm up of must, with high-end grapes. He said the fruit comes into the winery at a very cool temperature, and rather than heating the tanks and doing pumpovers as in the past, he let the tanks slowly warm up on their own for a de facto cold soak.

“We do that now as part of our bag of tricks,” Maloney said. “To be honest I’m not really sure what it does,” he added. But he likes how the wine turns out.

Doug McCrea of McCrea Cellars in Ranier, Wash., said he appreciated the research but, “I’m not so sure how I can apply it in my own winemaking.”

Does late watering hurt?
While the cold soak controversy exists between academics and winemakers, the question of what effect late irrigation has on winegrapes is a matter of commerce between growers and the winemakers who buy their grapes—especially in Eastern Washington where rainfall averages 8 inches or less.

The assumption of this session was that some growers like to irrigate in the weeks or days just before harvest to keep their vines healthy and their grapes filled out. Some winemakers, on the other hand, think these growers are merely trying to up their tonnage to make more money while possibly diluting the flavors in the grapes.

Viticulture professor Markus Keller as WSU Prosser introduced the session by saying, “I must admit, I got tired of having these arguments with winemakers.” So he set about studying the fluid flow to the berries in detail.

He found that before veraison the berries are very responsive to water, which was accepted long ago. But in addition the studies showed that after veraison water can still flow into the berries, but it flows through the phloem not the xylem, through which it moves earlier in the season.

When the vines being studied were irrigated post-veraison, the water increased the plumpness and the sugar in the berries, Keller said.  He observed that the watering enhanced photosynthesis, which enhanced phloem flow, which enhanced sugar accumulation. “The more stressed they were, the more they recovered,” he said. “The story here is that irrigation of water-stressed plants does not decrease ripening, it increases it.”

Essentially the research showed that yes, post-veraison watering can send more water to the berries, but excess water doesn’t stay in the berries. It flows right back out to the other plant tissues. Keller observed that the berry skin stiffens during ripening and it becomes very difficult for it to increase in size, so it can’t take any extra water. The berry can shrink in size, of course, from dehydration, so moderate irrigation simply keeps the berry plumped up.

This argues in favor of growers who want to irrigate in the late season, but only to a point. Extreme irrigation late in the season when the berries are high in sugar can cause berries to crack from the water pressure. Cracking can also come from overhead irrigation (or in other regions, rain) because berries do absorb water through the skin. The cracking releases juice, and if water continues to fall from overhead it washes the (water soluble) sugar out of the fruit.

Keller concluded by emphasizing that more water before veraison increases berry size. To minimize berry size for quality reasons, growers should stress the vines early. More water after veraison decreases weight loss. Then he asked rhetorically, “If late irrigation before harvest dilutes quality, then why should watering back after harvest not dilute quality?”

Grower Jim Holmes, who moderated the session, added that there is no reason for growers not to understand their vines’ water status. “Proper instrumentation is all you need and you can tell to a dime how much water you have,” he said.

Big fans of irrigation
Winemaker John Freeman of Waterbrook Winery in Walla Walla, Wash., said “We are big fans of irrigation in general and have no problem with late-season irrigation.” He does have problems with flood irrigation, which is still in use in some Washington vineyards, because it creates a humid micro-environment and “pond scum” aromatics can show up in the grapes.

Freeman said that he has observed the same cracking of berries from overhead irrigation that Keller described. “Late in the season the berries absolutely do swell and absolutely do burst,” he said, and cautioned the substantial minority of growers in Washington who still use overhead sprinklers to be careful.

Gordon Hill from Milbrandt Vineyards Winery in Mattawa, Wash., said he thinks watering close to harvest is not a bad thing. “I can’t prove it but I believe it,” said the veteran winemaker. “We call it a grower fairness issue and we think both sides benefit.”

Hill said he doesn’t like watering back wine, so he likes to harvest grapes at a sugar level that will give an appropriate alcohol content without intervention in the winery. He added that frequent communication between the grower and the winemakers, especially as harvest approaches, can minimize disagreements about irrigation.

“It’s best to call the grower more than 24 hours before you pick,” Hill said. “I love to call the grower early and say, ‘Hey, you’re on the radar screen.’ Often the grower says, ‘I’m thinking about watering this week.’ That piece of communication really helps. Good communication and planning makes for a win-win situation.”

CURRENT NEWS INDEX »