What Really Goes Into Making That Glass of Merlot

Harvest season is here, the time of year when oenophiles everywhere pile into cars and head to wine country for an up-close and personal look at their favorite wineries. While visitors may sample recent vintages, tour the vineyards and perhaps even indulge in a little ceremonial grape stomping, they aren’t likely to see much of the real action. Nor are they likely to know about the problems winemakers often face as they work to get that great glass of wine into consumers’ hands.

Broken sorting tables, rain, hail, the flock of birds that ate half the year’s grapes are just a few of the possible harvest mishaps. Things can go remarkably well or catastrophically wrong, and winemakers don’t always know which one it will be. With harvest, uncertainty is a given.

One of the few certainties is that the grapes will be picked. Choosing the harvest date is the most important decision a vintner makes every year, once he or she has determined that the fruit is ripe, with an ideal balance between sugar and acidity. Everything follows from this single decision. If the grapes are underripe, the wine might have a green note; if they’re too ripe, it might be too high in alcohol. So critical is the call that assistant winemakers have told me it’s the biggest difference between their position and the head winemaker’s job.

Once a date has been selected, speed is critical. The actual harvest, which can last days or weeks, is a full-court press to get the fruit off the vine and into bins as quickly and efficiently—and with as much care—as possible. Just-picked grapes are in a fragile state, and their juice can easily oxidize if the fruit is bruised or damaged.

Once a date has been selected, speed is critical. The actual harvest, which can last days or weeks, is a full-court press to get the fruit off the vine and into bins as quickly and efficiently—and with as much care—as possible. Just-picked grapes are in a fragile state, and their juice can easily oxidize if the fruit is bruised or damaged.

Although harvesting grapes with machines is faster and more efficient, many producers still choose to harvest by hand, either because their vineyards are too small, too steep or too narrow, or because they believe a human being, though slower, can do a better job of picking the best grapes.

Time of day is also key; grapes are often harvested late at night or very early in the morning to avoid high daytime temperatures. In Napa, where harvest can begin as early as August, days can reach 100 degrees. Picking grapes during the less-sweltering hours benefits not only the workers but also the grapes, as cooler temperatures preserve acidity and help sugar levels stay stable.

Even in the best conditions, though, harvest is an “endurance test and the ultimate cross-fit program,” said Morgan Clendenen, winemaker and owner of Cold Heaven Cellars in Buellton, Calif. She marked her 20th harvest this year. This may sound substantial, but in an irony that winemakers sometimes joke about, being in the business for decades like Ms. Clendenen translates to actually producing wine only a couple dozen times.

Of course, winemakers are making critical decisions long before harvest, such as when and how to prune vines, whether to irrigate and whether to perform a bit of canopy management, removing the green leaves that cover the fruit to ensure that it gets sun or that air circulates through the vines to prevent rot.

The next time you open a bottle of wine this fall you might want to raise a glass to all the people behind the scenes who helped bring it to your table. Here’s to a happy, healthy, hail-free harvest season!

By Lettie Teague, WSJ.com

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