How Wine Is Made

The Crush

The process of turning grapes into wine generally starts at the crush pad, where the grapes are brought in from the vineyards. Good winemakers carefully monitor their grapes throughout the year, but their presence is critical at harvest, when ripeness determines the proper day for picking. Once that day arrives, the crush begins.

Wineries pick their grapes by machine or by hand, depending on the terrain and on the type of grape. Some varietals are harvested at night with the help of powerful floodlights. Why at night? In addition to it being easier on the workers (daytime temperatures often reach 90°F [32°C] or more in September), the fruit-acid content in the pulp and juice of the grapes peaks in the cool night air. The acids—an essential component during fermentation and aging, and an important part of wine's flavor—plummet in the heat of the day.

Grapes must be handled with care so that none of the juice is lost. They arrive at the crush pad in large containers called gondolas. Unless the winemaker intends to ferment the entire clusters, which is generally done only for red wines to strengthen the tannins or add flavors or aromas, they are dropped gently onto a conveyor belt that deposits them into a stemmer-crusher, which gently separates the grapes from their stems. Then the sorting process begins. At most wineries this is done by hand at sorting tables, where workers remove remaining stems and leaves and reject any obviously damaged berries. Because anything not sorted out will wind up in the fermenting tank, some wineries double or even triple sort to achieve higher quality. Stems, for instance, can add unwanted tannins to a finished wine. On the other hand, winemakers sometimes desire those tannins and allow some stems through. A few high-end wineries use electronic optical grape sorters that scan and assess the fruit. Berries deemed too small or otherwise defective are whisked away, along with any extraneous vegetal matter.

No matter the process used, the sorted grapes are then ready for transfer to a press or vat.

After this step, the production process goes one of four ways, depending on whether a white, red, rosé, or sparkling wine is being made.

White Wines

The juice of white-wine grapes first goes to settling tanks, where the skins and solids sink to the bottom, separating from the free-run juice on top. The material in the settling tanks still contains a lot of juice, so after the free-run juice is pumped off, the rest goes into a press. A modern press consists of a perforated drum containing a Teflon-coated bag. As this bag is inflated like a balloon, it slowly pushes the grapes against the outside wall and the liquids are gently squeezed from the solids. Like the free-run juice, the press juice is pumped into a stainless-steel fermenter.

Press juice and free-run juice are fermented separately, but a little of the press juice may be added to the free-run juice for complexity. Because press juice tends to be strongly flavored and may contain undesirable flavor components, winemakers are careful not to add too much. Most white wines are fermented at 59°F to 68°F (15°C to 20°C). Cooler temperatures, which develop delicacy and fruit aromas, are especially important for Sauvignon Blanc and Riesling.

During fermentation, yeast feeds on the sugar in grape juice and converts it to alcohol and carbon dioxide. Wine yeast dies and fermentation naturally stops in two to four weeks, when the alcohol level reaches 15% (or sometimes more). If there's not enough sugar in the grapes to reach the desired alcohol level, the winemaker can add extra sugar before or during fermentation in a process called chaptalization.

To prevent oxidation that damages wine's color and flavor and kills wild yeast and bacteria that produce off flavors, winemakers almost always add sulfur dioxide, in the form of sulfites, before fermenting. A winemaker may also encourage malolactic fermentation (or simply malo) to soften a wine's acidity or deepen its flavor and complexity. This is done either by inoculating the wine with lactic bacteria soon after fermentation begins or right after it ends, or by transferring the new wine to wooden vats that harbor the bacteria. Malo, which can also happen by accident, is undesirable in lighter-bodied wines because it overpowers the flavor from the grapes.

For richer results, free-run juice from Chardonnay grapes, as well as some from Sauvignon Blanc grapes, might be fermented in oak barrels. Barrel fermentation creates more depth and complexity, as the wine picks up vanilla flavors and other harmonious traits from the wood. In many cases the barrels used to make white wines, especially Sauvignon Blanc, are older, “neutral” barrels previously used to make other wines. These neutral barrels can add a fullness to a wine without adding any wood flavors. Sometimes, though, the winemaker uses a percentage of “new oak” (the term for the first time a barrel is used). The barrels used by California winemakers may be made in America or imported from France or Eastern Europe. They are very expensive and can be used for only a few years. In recent years, wineries have begun using “concrete eggs” (egg-shape fermenting tanks made out of concrete), mostly to make white wines. Bigger than a barrel but smaller than most stainless tanks, the eggs, like barrels, are porous enough to “breathe,” but unlike wood don’t impart flavors or tannins to wines. Some winemakers believe concrete can increase the minerality and the feel in the mouth of wines such as Sauvignon Blanc or Chardonnay. The egg shape is thought to aid in fermentation, because as the wine is fermenting it becomes hotter and starts to bubble like water boiling in a pan. Some winemakers believe that the flavors mix better at this stage than they do in other fermenters. The notion of fermenting wines in concrete receptacles may sound new-fangled, but their use dates back to the 19th century (and some say even further).

When the wine has finished fermenting, whether in a tank or a barrel, it is generally racked—moved into a clean tank or barrel to separate it from any remaining grape solids. Sometimes Chardonnay and special batches of Sauvignon Blanc are left "on the lees"—atop the spent yeast, grape solids, and other matter that were in the fermenting tank—for extended periods of time before being racked to pick up extra complexity. Wine may be racked several times as the sediment continues to settle out.

After the first racking, the wine may be filtered to take out solid particles that can cloud the wine and any stray yeast or bacteria that can spoil it. This is especially common for whites, which may be filtered several times before bottling. Most commercial producers filter their wines, but many fine-wine makers don't, as they believe it leads to less complex wines that don't age as well.

White wine may also be fined by mixing in a fine clay called bentonite or albumen from egg whites. As they settle out, they absorb undesirable substances that can cloud the wine. As with filtering, the process is more common with ordinary table wines than with fine wines.

Winemakers typically blend several batches of wine together to balance flavor. Careful blending gives them an extra chance to create a perfect single-varietal wine or to combine several varietals that complement each other in a blend. Premium vintners also make unblended wines that highlight the attributes of grapes from a single vineyard.

New wine is stored in stainless-steel, oak, or concrete containers to rest and develop before bottling. This stage, called maturation or aging, may last anywhere from a few months to more than a year. Barrel rooms are kept dark to protect the wine from both light and heat, either of which can be damaging. Some wineries keep their wines in air-conditioned rooms or warehouses; others use long, tunnel-like caves bored into hillsides, where the wine remains at a constant temperature.

If wine is aged for any length of time before bottling, it will be racked and perhaps filtered several times. Once it is bottled, the wine is stored for bottle aging. This is done in a cool, dark space to prevent the corks from drying out; a shrunken cork allows oxygen to enter the bottle and spoil the wine. In a few months, most white wines will be ready for release.

Red Wines

Red-wine production differs slightly from that of white wine. Red-wine grapes are crushed in the same way, but the juice is not separated from the grape skins and pulp before fermentation. This is what gives red wine its color. After crushing, the red-wine must—the thick slurry of juice, pulp, and skins—is fermented in vats. The juice is "left on the skins" for varying amounts of time, from a few days to a few weeks, depending on the type of grape and on how much color and flavor the winemaker wants to extract.

Fermentation also extracts chemical compounds such as tannins from the skins and seeds, making red wines more robust than whites. In a red designed for drinking soon after bottling, tannin levels are kept down; they should have a greater presence in wine meant for aging. In a young red not ready for drinking, tannins feel dry or coarse in your mouth, but they soften over time. A wine with well-balanced tannin will maintain its fruitiness and backbone as its flavor develops. Without adequate tannins, a wine will not age well.

Creating the oak barrels that age the wine is a craft in its own right. At Demptos Napa Cooperage, a French-owned company that employs French barrel-making techniques, the process involves several elaborate production phases. The staves of oak are formed into the shape of a barrel using metal bands, and then the rough edges of the bound planks are smoothed. Finally, the barrels are literally toasted to give the oak its characteristic flavor, which will in turn be imparted to the wine.

Red-wine fermentation occurs at a higher temperature than that for whites—about 70°F to 90°F (21°C to 32°C). As the grape sugars are converted into alcohol, large amounts of carbon dioxide are generated. Carbon dioxide is lighter than wine but heavier than air, and it forms an "aerobic cover" that protects the wine from oxidation. As the wine ferments, grape skins rise to the top and are periodically mixed back in so the wine can extract the maximum amount of color and flavor. This is done either in the traditional fashion by punching them down with a large handheld tool or by pumping the wine from the bottom of the vat and pouring it back in at the top.

At the end of fermentation, the free-run wine is drained off. The grape skins and pulp are sent to a press, where the remaining liquid is extracted. As with white wines, the winemaker may blend a little of the press wine into the free-run wine to add complexity. Otherwise, the press juice goes into bulk wine—the lower-quality, less expensive stuff. The better wine is racked and then perhaps fined; some reds are left unfined for extra depth.

Next up is oak-barrel aging, which takes from a half year to a year or longer. Oak, like grapes, contains natural tannins, and the wine extracts these tannins from the barrels. The wood also has countless tiny pores through which water slowly evaporates, making the wine more concentrated. To make sure the aging wine does not oxidize, the barrels have to be regularly topped off with wine from the same vintage.

New, or virgin, oak barrels impart the most tannins to a wine. With each successive use the tannins are diminished, until the barrel is said to be "neutral." Depending on the varietal, winemakers might blend juice aged in virgin oak barrels with juice aged in neutral barrels. In the tasting room you may hear, for instance, that a Pinot Noir was aged in 30% new oak and 70% two-year-old oak, meaning that the bulk of the wine was aged in oak used for two previous agings.

The only way even the best winemaker can tell if a wine is finished is by tasting it. A winemaker constantly tastes wines during fermentation, while they are aging in barrels, and, less often, while they age in bottles. The wine is released for sale when the winemaker's palate and nose say it's ready.

Sparkling Wines

Despite the mystique surrounding them, sparkling wines are nothing more or less than wines in which carbon dioxide is suspended, making them bubbly. Good sparkling wine will always be fairly expensive because a great deal of work goes into making it.

White sparkling wines can be made from either white or black grapes. In France, Champagne is traditionally made from Pinot Noir or Chardonnay grapes, whereas in California sparkling wine might be made with Pinot Blanc, Riesling, or sometimes other white grapes. If black grapes are used, they must be picked very carefully to avoid crushing them. The goal is to minimize contact between the inner fruit (which is usually white) and the skins, where the purplish-red color pigments reside. The grapes are rushed to the winery and crushed very gently, preventing the juice from coming in contact with the pigments and turning red. Even so, some sparklers have more of a pink tinge to them than the winemaker intends.

The freshly pressed juice and pulp, or must, is fermented with special yeasts that preserve the characteristic fruit flavor of the grape variety used. Before bottling, this finished "still" wine (without bubbles) is mixed with a liqueur de tirage, a blend of wine, sugar, and yeast. This mixture causes the wine to ferment again—in the bottle, where it stays for up to 12 weeks. Carbon dioxide, a by-product of fermentation, is produced and trapped in the bottle, where it dissolves into the wine (instead of escaping into the air, as happens during fermentation in barrel, vat, or tank). This captive carbon dioxide transforms a still wine into a sparkler.

New bottles of sparkling wine are stored on their sides in deep cellars. The wine now ages sur lie, or "on the lees" (the dead yeast cells and other deposits trapped in the bottle). This aging process enriches the wine's texture and increases the complexity of its bouquet. The amount of time spent sur lie has a direct relation to its quality: the longer the aging, the more complex the wine.

The lees must be removed from the bottle before a sparkling wine can be enjoyed. This is achieved in a process whose first step is called riddling. In the past, each bottle, head tilted slightly downward, was placed in a riddling rack, an A-frame with many holes of bottleneck size. Riddlers gave each bottle a slight shake and a downward turn—every day, if possible. This continued for six weeks, until each bottle rested upside down in the hole and the sediment had collected in the neck, next to the cork. Simple as it sounds, this process is actually very difficult. Hand-riddling is a fine art perfected after much training. Today most sparkling wines are riddled in ingeniously designed machines called gyro palettes, which can handle 500 or more bottles at a time, though at a few wineries, such as Schramsberg, the work is still done by hand.

After riddling, the bottles are disgorged. The upside-down bottles are placed in a very cold solution, which freezes the sediments in a block that attaches itself to the crown cap that seals the bottle. The cap and frozen plug are removed, and the bottle is topped off with a wine-and-sugar mixture called dosage and recorked with the traditional Champagne cork. The dosage ultimately determines the sparkler's sweetness.

Sparkling wines with 1.5% sugar or less are labeled brut, those with 1.2% to 2% sugar are called extra dry, those with 1.7% to 3.5% are called sec (French for "dry"), and those with 3.5% to 5% are demi-sec (half dry). Sparkling wines labeled doux (sweet) have more than 5% sugar. Most sparkling-wine drinkers refuse to admit that they like their bubbly on the sweet side, and this labeling convention allows them to drink sweet while pretending to drink dry. It's a marketing ploy invented in Champagne at least a century ago. A sparkling wine to which no dosage has been added will be bone dry (and taste sour to some) and may be called natural or extra-brut.

Most sparkling wines are not vintage dated but are assembled (the term sparkling-wine makers use instead of blended) to create a cuvée, a mix of different wines and sometimes different vintages consistent with the house style. However, sparkling wines may be vintage dated in particularly great years.

Sparkling wine may also be made by time- and cost-saving bulk methods. In the Charmat process, invented by Eugene Charmat early in the 20th century, the secondary fermentation takes place in large tanks rather than individual bottles. Basically, each tank is treated as one huge bottle. After the bubbles have developed, the sediments are filtered out and the wine is bottled. This comes at a price: although the sparkling wine may be ready in as little as a month, it has neither the complexity nor the bubble quality of traditional sparklers. In the United States, sparkling wine made in this way must be labeled "Bulk Process" or "Charmat Process." Sparkling wines made in the traditional, time-consuming fashion may be labeled "Méthode Traditionelle" or "Wine Fermented in This Bottle."

Rosé Wines

Rosé or blush wines are made from red-wine grapes, but the juicy pulp is left on the skins for a matter of hours—typically from 12 to 36—rather than days. When the winemaker decides that the juice has reached the desired color, it is drained off and filtered. Yeast is added, and the juice is left to ferment. Because the must stays on the skins for a shorter time, fewer tannins are leached from the skins, and the resulting wine is not as full flavored as a red. You might say that rosé is a lighter, fruitier version of red wine, not a pink version of white.

Rosé has gotten a bad rap in recent years, perhaps because it's sometimes confused with inexpensive, sickly sweet white Zinfandels that are a similar hue, but the French have been making excellent dry rosés for decades. Many California vintners have jumped on the rosé bandwagon, and it seems like almost every tasting room features at least one of these refreshing wines. The range of tastes and textures is remarkable. Depending on how it’s made, Rosé of Cabernet Sauvignon, for instance, can have a velvety and almost savory taste, while Rosé of Pinot Noir or Syrah can might have a crisp and mineral taste.

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