Harvest 101: The Basics of Crush Season

Learn what goes on in the vineyard and winery during each stage of the annual harvest for wine grapes
Harvest 101: The Basics of Crush Season
Veraison, when grapes start to change color and soften, marks the beginning of harvest season. (ThinkStockPhoto)
Aug 31, 2011

Sports teams have playoffs. Students have finals. And for winegrowers, the big sink-or-swim moment—the event the whole year's efforts have led up to—is harvest.

The period culminating in grape crush begins when the grapes start to change color in mid to late summer. The actual picking of the grapes usually happens between August and November above the equator and February to April below. What happens in between is the greatest determinant of a wine's quality in a given vintage. Read on to learn about the processes—and perils—of harvest season.

The Metamorphosis—Veraison

Grape ripening begins with the growth period known as veraison, when the fruit hanging on the vines transforms from small, green, hard berries into what we recognize as grapes. Vines enter this stage about 30 to 70 days, depending on variety and climate, after fruit set (when fertilized flowers have fallen off and become tiny grape bunches)—typically in July or August in the Northern Hemisphere and January or February in the Southern.

During veraison, the grapes lose their bright green color and begin to take on mature hues—from greenish yellow for some white varieties to red, purple or almost black for red varieties. The grapes also soften and rapidly increase in size as the vine begins to pump sugars into the fruit, while acidity starts to decrease. Veraison doesn’t happen at the same time throughout a vineyard, or even for all grapes on a vine or within an individual bunch; those exposed to more sun and warmth get a head start on the grapes in shadier, cooler areas.

Striking a Balance—Controlling Crop Size

Unlike most farmers, top grapegrowers generally seek to limit their yields. That's right: They want less of the thing they're going to sell. Why? Because they believe that if the vine is carrying fewer bunches than it is capable of, those grapes will ripen more fully and be higher in quality.

If a crop looks to be too large at veraison, or if ripening has been delayed due to poor weather, a grower will sometimes thin the crop, or conduct a "green harvest.” Vineyard workers cut unripe bunches from the vines; in theory, each vine's resources are then devoted to the remaining bunches, speeding ripening.

On the other hand, a grower doesn’t want too many leaves per grape bunch. Leaves look pretty, but they can get between the grapes and the sun; too much shade can also promote rot and mildew on bunches. If the weather has been particularly cool, cloudy or damp, growers may remove leaves around the grapes to promote ripening and air circulation.

Pest Busting—Protecting the Crop

Along with the threat of poor weather, grapevines face harassment from various organisms—insects, mildew, rot, other fungi, bacteria and viruses—that can damage fruit, reduce yields or even kill the vines. And just as the grapes ripen come the birds—and deer, bear, wild boar, kangaroos and other hungry animals.

What can be done to protect the vines? Among other things, growers can apply pesticides and fungicides (ranging from copper and sulfur to synthetics, with green-conscious farmers eschewing the latter), control the canopy of leaves so that wind can dry moisture on the grapes and attract natural predators like bats, insect-eating birds and beneficial insects that eat the vine pests.

Strong fences can keep out four-legged animals, but not the airborne. For flocks of birds, who like a tasty Cabernet as much as anyone, the heavy artillery is wheeled out. Some vignerons shell out to cover all their vines with bird nets, or hire falconers to patrol vineyards with birds of prey. Others rely on bird bombs and bird cannons. Don't call PETA just yet: These devices don't actually blast the suckers out of the sky, they merely fire off loud booms that scare birds away.

Harvest Image Gallery

A visual guide to the different stages of the season; click to expand images.

Courtesy of ThinkStockPhoto, Frederic Hadengue - Collection CIVC, Alain Proust, Robert Anschutz, Jackson Family Wines

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Reaching Ripeness—Deciding When to Pick

Depending on the grape variety, region and wine style, the ripening process can last anywhere from 30 to 70 days after veraison. Some grapes, like Tempranillo—the name is taken from the Spanish for "early"—ripen quickly. Others, like Petit Verdot, ripen long after other varieties are being transformed into wine. As for regions, cooler climates, like Germany, typically have longer ripening cycles, while hotter ones, like California’s Central Valley, have shorter cycles.

During this period, growers closely monitor the development of the grapes. At the most basic level, as the berries ripen, they become sweeter. The acidity levels decrease and the sugars, which will be fermented into alcohol, increase; the more sugar in the grapes, the higher the potential alcohol level of the wine. In addition, in red grapes, the skin color begins to intensify in darkness. Flavor compounds develop, showing more fruit and fewer vegetal characteristics, and the tannins—compounds found in skins, stems and seeds that contribute to texture and structure—soften.

Winemakers may test grape juice, from a sampling of grapes across different parcels of a vineyard, in a lab to check pH and Brix (a measurement of sugar), to help them determine how ripe the grapes are. But they’ll also head into the vineyards regularly—sometimes daily—to taste and examine the grapes in the weeks leading up to harvest.

They’re checking for what's referred to as phenolic maturity or physiological ripeness—gauging the intensity and character of flavors and the quality of the tannins. They'll look at skin thickness, berry texture, seed color and texture and whether the stems have turned from green to brown. Ultimately, winegrowers are seeking a good balance between the sugars, acidity, tannins and flavor compounds.

As harvest nears, growers follow weather reports very carefully to stay ahead of sudden changes. Heat waves, excessive rain and even frost can ruin a crop. A year's worth of hard work can be wiped out by a hailstorm days before picking. Sometimes a grower is forced to pick early rather than risk losing his crop or needs to leave grapes hanging longer than expected to dry out and regain balance after heavy rain.

The date of harvest is rarely ever the same from one year to the next, so winegrowers must call it as best they can. Pick too early, and tannins may be "green," or bitter and underdeveloped. Pick too late and, along with the rising risk of fall rain or hail destroying the crop, the sugar levels may get too high, resulting in a flabby, unbalanced wine.

Finally, the style of wine being made also influences the time of harvest. In sparkling wines, high acidity is desirable, so the harvest is early. In dessert wines, by contrast, it's the sugar that counts and, thus, a late harvest.

Calling All Hands (or Drivers)—Harvesting the Crop

When a vintner decides the time is right, the harvest begins, though not all the grapes are brought in at once. In vineyards where varying sun exposure, altitude or soils result in different degrees of ripeness, workers may be sent out to pick individual parcels, or even just a few rows.

Traditionally, grapes have been harvested by hand, with vineyard workers deploying nothing more than a pair of well-sharpened shears and a basket or bin. When their bins are full, the workers empty them into a tractor or truck, which then delivers the grapes to the winery.

While hand-harvesting is more taxing, it is still the preferred method in many regions for high-quality wine production. Trained workers can identify properly ripened grape bunches and discard those that are underripe or show signs of rot or other damage. Hand-harvesting is also required on steep hillsides—such as those in Germany's Mosel region—where mechanical harvesters are unable to run.

Most mass-produced wines are now harvested mechanically, which is less expensive and speeds the process, but also increases the need to sort the grapes. Mechanical grape harvesters have been in use since the 1960s, and their effectiveness has greatly improved over the decades. However, they still cannot distinguish as well as humans between ripe, underripe or even rotten grapes, not to mention leaves, dirt, bugs and other things you wouldn’t want to drink. They are also less gentle than hand harvesting: They work by batting, shaking or stripping vines so the grapes fall onto a conveyor belt.

If the grape skins are accidentally broken during harvest, grapes can begin to prematurely ferment if they get too warm on the way from vineyard to winery, so many wineries elect to harvest during the night or at dawn, when it is coolest outside.

Depending on the size and diversity of the vineyards, harvest can require anywhere from a week to over a month of hard labor for a winery's temporary picking crew. When it's all over, many wineries host a grand harvest meal and party for the crew, highlighted by wine, music and the region's traditional dishes.

Only the Best—Sorting

As freshly picked grapes enter the winery, they have to be sorted for quality, a process commonly known as triage in French. Traditionally, the bunches were dumped on a sorting table, where sorters would look over the clusters and separate the good from the inferior, removing unripe, diseased or damaged grapes, along with any leaves that snuck in. Today, the grapes usually travel down a conveyor belt past a line of sorters making the selections. The belt often vibrates to shake out bad grapes that might sneak in under cover of the good ones.

Technology is taking the place of human grape sorters, however. Optical laser sorters are now in place at many top estates. As the grapes move down a conveyor belt, an optic sensor recognizes anything that doesn't have the desired size, shape and color and blows it onto another conveyor belt with a blast from an air cannon.

The Big Squeeze—Crush and Destemming

Once the best grapes have been selected, it's time to crush them so the yeast can quickly get to work fermenting. While foot-stomping used to be the way to go, it's unlikely that the table wines you purchase have had someone's feet in them.

Modern wineries typically use large, automated crusher-destemmers, which break the skins open, exposing the juice and pulp, but without crushing the stems and seeds, which contain tannins. These compounds contribute structure and texture to wines but also are responsible for the sensation of astringency or bitterness. Destemmers can remove stems before or after the grapes are crushed, depending on the winemaker's preference and the type of wine being made. The sooner in the process that the stems are removed, the less tannic the wine will be. Some winemakers want little-to-no influence of stems; others feel that "whole-cluster" fermentation fills out the wine's texture and flavor.

White grapes may go through a crusher-destemmer first or go directly into a press, which separates the juice from the skins so they don’t contribute color or tannins.

Now it’s time to start the fermentation, and that's when the steps of winemaking really begin.

Harvest Wine IQ

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