Napa GrapesDear Wine Witch: I visited Napa this summer for the first time and was surprised by the afternoon breezes and cool nights. One day it was even overcast, and we thought it would rain. Tasting room employees said that the weather was exceptionally cool and were worried that the grapes wouldn’t ripen properly. Do you know if they did? – Cold and Curious

Dear Cold and Curious: Afternoon breezes and cool nights are common throughout California wine regions and definitely desirable. Cooling influences slow the maturation of the grapes, which become more flavorful when they can hang on the vine for longer periods. Climates that are consistently warm would ripen the fruit too quickly, which is fine for raisins but not premium wine-grapes.

But the downside of a typically long growing season is the risk that cold weather and rain could arrive prematurely in the fall before grapes are sufficiently ripe. This may be one of those years although it’s still too soon to know. California vintners are saying that this summer has been the coolest in forty years, and the fall continues to be cooler than normal.

White grapes are picked first at lower ripeness levels so that the crisp quality that we enjoy in white wine is protected. So white grapes will be fine regardless of cooler temperatures. But red grapes need to ripen to a greater degree because, unlike white grapes, they are fermented with their skins, which give red wine its characteristic color. And the skins contain tannins, which impart texture to red wine. But if red grapes are not sufficiently ripe, they can be too tannic and not as smooth as we like them to be.

Of all the reds, Cabernet Sauvignon takes the longest to ripen. In the absence of warmer weather this fall, farmers will wait to pick and will probably develop stiff necks as they continually look to the sky, fearful of rain. A downpour would activate molds and diminish the quality of the fruit, but harvesting the crop before it fully ripens also lessens quality. In exceptionally cool years, Cabernet is harvested as late as November if rains don’t fall. Dismal as the decision may be, farmers are adept at trying to out-smart nature. If they’re not up to the task, they find desk jobs.

There could be a silver lining for this vintage. Some people feel that California wines have become too alcoholic. During the last decade, winemakers have allowed grapes to ripen to very high sugar levels, which convert to alcohol during fermentation. This year that may be impossible. Because of cool weather, the taste profile of California wine may be closer to Italian, French, and Spanish wines, which are generally lower in alcohol and higher in acid. Europeans and at least some Americans prefer this style.

But check back with me in November. Until then, we won’t have a definitive answer on the quality of this vintage. And remember to bring a warm sweater when you visit California in the summer. Evenings and nights are typically cool along the entire coast.

And by the way, Mark Twain never said, “The coldest winter I ever spent was a summer in San Francisco,” even though everyone says he did, especially San Franciscans.