How Wine Is Made
Although the process of wine making may vary greatly in detail, there exists a basic procedure, whose central element is fermentation. Fermentation is a process in which sugar changes in a liquid into roughly equal parts of ethyl alcohol and the gas carbon dioxide. Wine production begins with the cultivation of grapes, whose crushing produces the liquid in which fermentation occurs. The wine is aged after fermentation and is finally bottled. To achieve a uniform taste and quality year after year, the wine maker may blend grapes of different varieties or different vineyards during crushing or fermenting. He may also blend wines of different years or different casks during the aging process. The blending of young and old wines maintains a certain freshness, or fruitiness, of flavor.
The type of grape that is planted in the vineyard depends mainly on climate, soil, and the kind of wine that is desired. Various types of Vitis vinifera grapes have traditionally been grown in the Old World in warm regions near the Mediterranean Sea and in certain river valleys. Vitis vinifera grapes were transplanted to Central America in the early 1500's and were carried northward to California by the late 1700's. In 1862 about 300 fine varieties of Vitis vinifera were brought from Europe to California, resulting in a great expansion of the wine industry in that state. In cooler areas of the United States, such as Michigan and New York, wines have traditionally been made from native grapes of the Vitis labrusca species.
Picking and Crushing
The vines in a vineyard are pruned each winter and carefully tended while they are growing. The grapes are picked each year when their ripening has produced a certain sugar content, which is higher for sweet wines than for the dry table wines. Harvest periods generally range from mid-August to November. At that time the bunches of grapes are cut from the vines by hand and are taken to the winery, where the grapes are crushed in a huge cylindrical container to release their juice. In the old-fashioned presses still used by a few Continental producers, workers crush the grapes by treading on them barefoot. In most wineries efficient mechanical crushers and presses are used. The juice of the crushed grapes is run off into vats or tanks for fermentation. In the making of white wines only the grape juice is put into the vats or tanks. In the making of red wines the pulp, seed, and color-bearing skins are mixed with the juice.
In the vats or tanks the liquid, called the must, begins to ferment almost immediately. Yeast, which comes from the grape skins broken in the pressing, makes contact with sugar from the inside of the grapes, and yeast enzymes convert the sugar to alcohol and carbon dioxide, which escapes into the air. Complete fermentation takes from a few days to a few weeks. It produces dry wines by converting all the grape sugar to alcohol. If fermentation is stopped before it is completed, some sugar remains in the must and the wine will be sweeter. To stop fermentation in making such sweet dessert wines as port, sherry, and muscatel, a little pure grape brandy is added to increase the alcohol content of the must to the desired amount. To stop fermentation in making such sweet dinner wines as Sauterne, sulfur dioxide is added to stop the action of the yeast enzymes. To make such sparkling wines as champagne, more sugar and yeast are added after the new wine has been transferred to bottles or to a tank. A second fermentation in the closed bottles or in the tank then builds up the bubble-producing carbon dioxide under pressure.
Aging and Bottling
After fermentation the wine is aged in large containers for months or even years. Chemical changes cause the various elements in the wine to blend and smooth and to produce the wine's distinctive flavor and aroma. Aging is traditionally done in wood casks, whose pores allow the wine the slight contact with air that promotes some of the chemical changes. Too much contact with air will spoil the wine. Many wineries now use lined concrete or steel tanks in the early part of the aging process.
During aging the wine must be periodically racked, or pumped into a new cask to separate it from the lees, or sediment, that collect at the bottom and sides of the old cask. Filtering is also employed to separate the wine from the leaves, as is fining, or adding an absorptive material to the wine to settle the sediment. Because wine ages best at cool even temperatures, aging was traditionally done in underground wine cellars. Much wine is now aged in large temperature-controlled warehouses.
When wine is aged to a peak of flavor, it is removed from the casks or tanks and is bottled at the winery. Sometimes, containers of wine are shipped to wholesalers for bottling. Special care is taken to keep the wine from contact with oxygen or foreign elements that might harm it. In many cases the wine is then stored for a further period before sale, since it continues to mature in the bottle.