Weather is the fickle catalyst for poor or great wine vintage

In the process of making great wines, the most unpredictable element is also the biggest contributor.

The whole issue of the weather and its effect on winemaking is about a wine's overall quality, flavor, richness, age-ability, complexity and even cost. A bountiful harvest could mean an abundance of wines at great value. A spoiled crop may mean increased prices and limited availability of good wines. There are always exceptions, and it is very possible to find great wines from not-so-great vintages, and vice versa.

First, winemakers speak of climate zones, which are geographic regions differentiated according to the average amount of warmth above 50 degrees each year. This part of the weather equation is steady, with minor variation over the long-term. Therefore, knowledge of climate zones helps a grape grower determine which types of vines to plant. For example, cooler zones are known to be best for growing chardonnay and pinot noir grapes, while warmer zones have proved beneficial to syrah and zinfandel.

The other side of the weather story is the one that can stress the winemaker as much as the grapes — the weather conditions in any given year, regardless of the climate zone. No two years will have an identical number of days of sun, rain, fog, mist, hail, frost and wind. What's more, the timing of these unpredictable events throughout the growing season of March to October can mean the difference between a "perfect" vintage and a horrible one. Thus, wines are identified with the vintage year — information critical to wine buyers.

With the help of Vintage Charts, you can compare vintages of any major wine-growing regions, which, in effect, is comparing the weather from year to year. If you buy your wine at wine specialty shops, vintage charts are normally available for reference, if you ask. When it comes to wines from California, our wine region weather is fairly good and consistent. In dry periods we irrigate the vineyards. But European vineyards depend more on the weather and wines from France especially can vary greatly from year to year.

So what kind of weather will produce a "perfect" vintage? It starts with rain in March, but as of April, is practically rain free. The days are warm, the nights are cool, and the summer is long and mild. If the days get too cold, the grapes will ripen too slowly, sometimes never fully maturing. This will increase the tartness and acidity in the wines. If the weather is too hot, the wine tends to be flat and heavy.

But the real devastator is rain during, or nearing, harvest time. This excess moisture will dilute the juice in the grapes and may even cause rot to form on the grapes. The period from mid-August to October is critical to grape growers and winemakers, as they must continually measure the ripeness of the grapes in making their decision on when to pick them.

They hope for continued warm weather and will shudder at even the threat of rain, as heavy rain at harvest time can ruin an otherwise great growing season.

— Len Napolitano is certified in wine by the Society of Wine Educators, Wine & Spirits Education Trust, and Chicago Wine School. Wineology is a registered trademark of Len Napolitano.