Napa Valley, California


Crush and the Making of Wine

Most grapes are picked by hand with a special knife.

Grape knife

The grape picker's tool of choice.

The grapes are picked one or more clusters at a time, and put into crates or bins, then dumped into open containers called gondolas, which are then taken to the winery.

Some vineyards now use mechanical harvesters. The harvester is particularly useful in large vineyards in flat areas, although smaller versions can be used on rather steep hills.

Mechanical grape harvester

Not all grapes are picked by hand. Mechanical harvesting is becoming more common in some areas.

The harvester gently shakes the trunk or cordon of the vine, causing the grapes to fall from the vine into a catcher, which then moves them into a waiting gondola or other container.

However the grapes are picked, once they arrive at the winery, they are put into a destemmer/crusher, which removes the leaves and stems and crushes the grapes. Crushing doesn't mean pulverizing; it's done as gently as possible. Just enough to break the skins and allow the juice to come out.

Grape stemmer crusher

The grapes arrive at the winery and immediately go into the stemmer crusher. (Photo courtesy of Wine Institute.)

The destemmer is a perforated, rotating drum. The juice and skins drop through the holes in the drum, while the leaves and stems are too big to fit through the holes so they continue on out of the crusher and into waiting trucks to be returned to the vineyard as compost.

The crushed grapes and juice, called must, are pumped into the winery.

Some winemakers may skip the crushing and destemming and move the grapes directly to a press for whole berry or whole cluster pressing. Or they may do carbonic maceration in which the weight of the grapes themselves gently crushes the grapes, releasing the juice.


Red Wine

The juice, skins and seeds from most red grapes (actually called "black" grapes by growers) go into large stainless steel fermentation tanks for primary fermentation, where yeast is added that breaks down the natural grape sugars into ethyl alcohol and carbon dioxide (CO2). Fermentation is done at a temperature of approximately 85° Fahrenheit for four to six days.

Black (red) grapes

Red wine grapes are referred to as "black", and usually aren't either color. (Photo courtesy of Wine Institute.)

After fermentation, red wines are pressed, and the grape skins and seeds are then separated from the wine. The skins, seeds and dead yeast cells are called "pomace", and can be used as compost.

White Wine

White grapes (which are actually green in color) are not immediately fermented but go first to a "press".

White (green) grapes

Grapes for white wine are actually green in color. (Photo courtesy of Wine Institute.)

A wine press is a stainless steel cylinder containing an inflatable rubber bladder. The must is poured into the cylinder and the bladder is inflated with air. The bladder gently squeezes the skins against the sides of the cylinder, forcing the juice out. The press juice then goes to fermentation tanks. White wine is frequently fermented at around 60° for 12 to 18 days, although fermentation temperatures can range from 5° to 75° white wine takes longer because fermentation is slower at lower temperatures.

Sometimes white wines such as Chardonnay are fermented in oak barrels rather than stainless steel tanks. This is referred to as barrel fermentation.


Settling and Aging

After fermentation, most red and white wines go into large stainless steel tanks, where settling takes place. After the skins, seeds, yeast and other particles settle to the bottom of the tank (creating the lees), the clearer wine is pumped out and put into small (55-60 gallon) oak barrels for barrel aging.

Wine fermentation tanks

Stainless steel tanks are used for settling. Skins, seeds and yeast sink to the bottom, clarifying the wine. (Photo courtesy of Wine Institute.)

Most reds are barrel-aged to impart the oaky taste that many people find desirable. Many wineries also barrel-ferment Chardonnay. Lighter white wines, such as Sauvignon Blanc or Johannisberg Riesling are seldom, if ever, barrel-aged. An exception is Fumé Blanc, which is a barrel-fermented Sauvignon Blanc. Barrel aging can last from three to ten months for white wine, and anywhere from six months to three years for red wine.

Some red wines are subjected to malolactic fermentation. The winemaker adds a specific bacterium to the wine that breaks down the malic acid in the wine into lactic acid. This secondary fermentation can give the wine a creamy, buttery taste and texture. It is frequently done for red wines, and often for Chardonnay.


During barrel aging, most wines "throw" sediments so that the wine must be "fined" and/or "filtered" to give it the clarity desired by most American wine drinkers. Filtration can also stabilize the wine, making sure that it does not continue to ferment in the bottle, by removing all yeast from the wine.

Several methods of fining are used. Traditionally in Europe, oxblood was poured on top of the vat and allowed to settle down to the bottom. As it settled, it attracted the sediment (yeast, seeds, and bits of skin) in the wine and pulled it down to the bottom of the vat.

Since blood passing through their wine is not something that appeals to most Americans—even though it didn't remain in the wine after the treatment—this method was long ago discontinued.

These days gelatin and egg whites, also traditional methods, are frequently used to fine the wine. Also, if the wine is run through a filtration machine, diatomaceous earth or filter pads are used in the filter to help remove very fine sediment.

Some winemakers prefer not to clarify their wines, subjecting the wines to as little physical treatment as possible.

After clarification, the wine is then bottled, corked and labeled. Some wines are then ready to drink; others, particularly heavier red wines, may undergoing aging in the bottle for as long as three years before being made available to consumers. Once sold to the customer, most wines are ready to drink, but some will still improve with age if the customer has the space and patience (and money) to store them.

Sparkling Wine

Sparkling wine (not referred to as Champagne, because that type of sparkling wine comes only from the Champagne district of France) is primarily made from Chardonnay and Pinot Noir grapes.

Grapes for sparkling wine (sparklers) are picked earlier in the season when sugar content is lower, usually starting in late July. Fermentation almost always takes place in stainless steel tanks over a period of two to three weeks.

After five months or so, selected wines are blended to form the cuvee that will be the basis for the final wine. After blending, the wine goes into its permanent bottle, and the tirage is added, which is a blend of sugar, wine and live yeast that will begin the wine's second fermentation. The bottle is then sealed with a temporary cap like that on a soft drink bottle.

Secondary fermentation takes place in the bottle. Because it is sealed, the carbon dioxide bubbles produced by fermentation remain in the bottle. This continues for at least a year.

During aging, the bottles are riddled. Riddling is the process of separating the clear wine from the sediment (primarily dead yeast cells) that forms in the bottle. The bottles are very gently shaken and twisted to allow the sediment to gradually settle at the top of the bottle. Riddling was historically done by hand, but today in most large sparkling wineries it is done by a machine that gently mimics the hand process.

When ready, the tops of the bottles are dipped into a solution to freeze the liquid and sediment in the bottle neck, but not in the rest of the bottle. The temporary bottle cap is removed and the pressure of the carbon dioxide forces out the frozen sediment. This is referred to as disgorgement.

The resulting empty space in the bottle is filled with a blend of wine and sugar called dosage. The bottle is then recorked, and the traditional cage and foil are placed over the top. Once sealed, the sparkling wine rests for additional months before it's made available for sale.

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