As the California wine grape harvest draws to a close, three to four weeks later than normal, one thing is perfectly clear: Vintage 2010 has been the most unusual in memory, more Bordeaux than Napa.

It is a crop that will challenge winemakers conditioned to dealing with the certainty of perfectly ripe grapes each year.

The summer of 2010 was unseasonably cool and wet all along the California coast. California's finest vineyards populate the east-west valleys along this corridor, where they thrive on the cooling maritime influence.

The combination of hot days and cool nights is good for wine grapes. But the lack of sunshine and the potential threat of autumn rain pose a risk to the California wine industry's money grape, Cabernet Sauvignon, which can take the heat (indeed, it needs it) and ripens late even in the best of conditions.

"I'm thinking about grafting my Cabernet over to Pinot Noir," winemaker Gary Eberle quipped on an August afternoon in Paso Robles, in the heart of California's Central Coast. "This time of year it's usually around 95 degrees by mid-afternoon. We'll top out today around 73 degrees. We haven't had a single day all summer when it's hit 100.

"I'd say our Cabernet Sauvignon is at least three weeks behind schedule, maybe four; never seen anything like it around here."

Eberle has been making wine in Paso Robles for nearly 40 years. Other California vintners have similar thoughts.

Winemaker Cathy Corison is a veteran of nearly 30 harvests in the Napa Valley. Corison has taken note of the dramatic drop in temperatures throughout Vintage 2010 and relishes the rare opportunity to work with grapes from a cool growing season.

"I always prefer the cooler vintages," she said. "I love the structure. They're fabulous with food."

The fact that 2010 has turned out to be a Corison kind of vintage presents an interesting question on the matter of taste and style. California wines, particularly the reds, have been made in a bolder, riper style over the past decade, with soaring levels of alcohol by volume that some wine enthusiasts find alarming.

Winemakers have taken this direction in many cases to please the handful of influential wine critics whose reviews routinely give tremendous weight to power and ripeness while being dismissive of nuance and elegance.

It is widely believed within the industry that bold, blockbuster wines will get higher scores from the most important critics.

Advances in viticulture and science also have contributed to rising alcohol levels. Research in rootstock and grape clones has given vintners plant material that is virus free and more efficiently produces sugar in wine grapes. Combined with new yeast strains that that are also more efficient at converting sugar to alcohol during fermentation, the result has been a generation of California wines that easily surpass 15 percent alcohol by volume, when the norm used to be 12.5 to 13 percent.

"The pendulum will swing back the other way," Craig Williams predicted a few years back, while still the chief winemaker at Joseph Phelps Vineyards in the Napa Valley.

"It has to. Given the prices people are paying, they deserve wines that have the structure to improve with age."

So perhaps in the vintage of 2010, nature has performed the job mortal men could not or would not do, delivering grapes that have higher levels of acidity and lower levels of sugar, which will serve to bring down the percentage of alcohol by volume in the finished wines, if only for one year.

The camp that has embraced the bolder, more powerful style of red wine seen in California in recent vintages will no doubt complain the grapes weren't "ripe" when picked, and thus flavor was sacrificed. That is a legitimate point of view. Yet it is hardly the only point of view.

You only need look back as far as 2003 - another cool growing season - to find a California vintage roundly trashed by the ripeness crowd among the wine media. This is one of my favorite California vintages, particularly in the Napa Valley. The Napa Valley wines I find most exceptional from the 2003 vintage all share the same characteristics: good acid, firm tannins and complex red and black fruit aromas. These wines are universally fresh and scintillating on the palate.

Those who prefer red wines that taste like blackberry jam, with enough alcohol to numb the olfactory, probably won't like them. Fair enough. They most likely won't like Vintage 2010, either. No worries. There's always gin.