Vineyards in the mist

They refresh sunbathers by the pool in Las Vegas.

They bring relief to overheated firefighters.

They even keep the lettuce crisp in the produce aisle.

Now, cooling misters are being installed in some of the nation's finest vineyards to protect prized wine grapes from damaging heat waves. The systems spray a fine mist of water into the air around the vines, helping to reduce the temperature in the vineyard.

At Beaulieu Vineyard, one of the Napa Valley's oldest wineries, managers are experimenting with a variety of misting systems to see which do the best job of keeping their prime cabernet sauvignon vineyard cool.

"The basic premise is vine cooling is going to improve wine quality," said Brian Shepard, general manager of the Napa-based Walsh Vineyards Management.

When it gets too hot, the grapes ripen too quickly, reaching maturity before the rich, complex flavors winemakers crave have fully developed, Shepard explained.

Concerned about increasingly unpredictable heat spikes in the Napa Valley, Beaulieu winemakers asked Walsh in 2006 whether a cooling system could help them control the rate of ripening and protect the grapes from damage.

Whether global warming is behind the recent spate of hot weather in Wine Country is a hotly debated topic. Some say a pattern of more heat and temperature variability is clear, while others say heat spikes in Napa are nothing new.

Either way, winemakers are closely watching Beaulieu's misting experiment as the prospect of global warming threatens to change how and where fine wine grapes can be grown.

"I think it's in the back of people's minds," Shepard said.

A new way to cool down

The Beaulieu vineyards in Oakville lack the type of overhead sprinkler systems that double as frost protection in the spring and vine cooling in the summer at many North Coast vineyards. Beaulieu, like many vineyards in the Napa Valley, uses massive wind machines for frost protection. They can blow out the frost, but they can't cool down the vines when the temperature soars past 100 degrees.

So Walsh hired Edwards Engineering of Napa to help design a system that would cool the vines, use little water and be easy to manage.

Grape growers have a good handle on their frost protection and irrigation systems, but know far less about the effects of vine cooling, Shepard said. The industry has used a seat-of-the-pants approach to vine cooling. Traditionally, growers have turned on sprinklers when it gets around 100 degrees, soaked the vines for a few hours and hoped for the best, he said.

Cooler grapes, better wine?

Little research has been done about how heat damages grapes, how it affects wine quality and how using sprinklers or misters helps, if at all, Shepard said.

So the goal of the Beaulieu experiment last year was to see whether the misters could cool the grapes. Four different systems were installed in the Oakville block, two dispensing water near the base of the vine and two misting over the top canopy.

The goal was not to soak the grapes with water, but rather create a "microclimate" around the vine that would reduce the air temperature.

The results showed that when two misters were sprayed over the top of each vine, the average temperature dropped 7 degrees in the interior area of the vine. The misters used about 22 gallons a minute, less than half of what overheard sprinkler systems use.

The experiment also found that the higher the air temperature, the greater the apparent cooling effect. Similarly, the lower the humidity, the greater the cooling effect, because evaporation increased.

This year, the experiment has been narrowed to the two most effective mister systems, but will be taken one step further: Wine will be made from the grapes in each group, to determine whether the cooler grapes make better wine.

"That's the real test," Shepard said.

If it turns out that misters help winemakers make better wine, they will still need to decide if the difference is good enough to justify the additional costs, which could run in the neighborhood of $200 an acre.

"This is not something that is going to be used by someone making a $5 bottle of wine," said Brent Edwards, owner of Edwards Engineering.

The natural solution

Sonoma County grape growers are already using such a system.

Kendall-Jackson founder Jess Jackson has about 200 acres on his Alexander Mountain estate east of Geyserville fitted with misters. For him, the cost-benefit analysis was easy. The wines off the estate run as high as $200 a bottle.

Vineyard manager Tony Viramontes said he used the misters regularly several years ago, but rarely turns them on these days.

By increasing irrigation, strengthening the vine's root system through deep tilling, and adding compost, Viramontes said the vineyards stand up better to the heat than they used to.

Viramontes also makes sure enough leaves remain on the canopy to shade the fruit, naturally protecting the grapes from being scorched, he said.

"These vines can tolerate a lot of heat," Viramontes said.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat

.com.