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CORVALLIS, Ore. - While it might make it difficult for gardeners to ripen backyard fruit, the cool weather this season could be an advantage to Oregon wine grapes, according to researchers at Oregon State University.

"Often the most challenging weather conditions produce some of the finest wines," said Steve Renquist, an OSU Extension horticulturist who works with the wine industry in the Umpqua region.

In monitoring heat units--a calculation involving time and temperature--Renquist pointed out that most wine growing regions in Oregon are about on schedule with last year for ripening, and the northern Willamette Valley is a bit ahead of 2010. In areas where heat units are fewer, less sugars develop. But the complexity of wine comes from many attributes of the fruit, not simply sugar content.

"In cool years similar to this in the past, the wines have developed delicate, crisp flavors because they've retained some of the acid in the fruit," Renquist said. "Of course, we won't know about this year until the grapes are harvested and the wine is in the bottle," he added.

Wine grape growers are accustomed to dealing with challenging weather, according to Patty Skinkis, an OSU professor and viticulture specialist. Cool temperatures this spring delayed flowering in the vineyards, she said, so everyone expected a late harvest. However, Skinkis's research has quantified that fruit set was significantly higher than normal for most of the region's wine grapes, resulting in big clusters of grapes.

"The growers prepared well for the season. They thinned fruit and pulled leaves to open the canopy in order to maximize grape quality, hasten ripening, increase fruit color, and reduce the potential for Botrytis bunch rot." Skinkis said.

Furthermore, results of her fruit quality research in 2010 indicate that last year's cool season led to higher than normal development of phenolic compounds and other quality parameters, despite being lower in overall sugar accumulation.

Unlike sweet table grapes, the quality of wine grapes relies on development of a complex array of flavors as well as the balance between sugars, acids and phenols, according to James Osborne, the Extension enology specialist at OSU. This is especially true of the cool season varieties that are iconic of the Willamette Valley.

"Pinot noir, for example, can develop more complex flavors and aromas with a longer, cooler season that often results in lower sugar levels," said Osborne, whose research focuses on how microorganisms impact flavor development during the wine-making process. "It's always a matter of balance, and some of the best vintages come from cooler years."

"The challenge and the attraction of Oregon wines are that they are not easy to make, but the potential for excellence is always there," Osborne said.

Neil Shay, director of the Oregon Wine Research Institute, sees potential for excellence in this year's vintage. "I've visited vineyards all around the state, and the fruit that's hanging now looks excellent," he said.

The harvest is now underway in parts of southern and eastern Oregon, Shay said. The wines will take months or years to develop. But like a good wine, he expects a fine finish for this year's grapes.

For more information about vineyard and wine research at Oregon State University, see http://owri.oregonstate.edu/