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Winemaking requires a series of
steps. Decisions made by the winemaker during each step influence
the final character of the wine. A
winemaker must first decide which grapes to use and when to harvest
them. After the grapes are crushed, the juice is converted into wine
through a process called fermentation. Wine is then aged
until it is ready for drinking. Grape growers harvest their crop as
soon as the grapes have ripened, usually in late summer to early
fall, with the exception of late harvest wine grapes, which are used
to produce dessert wines. Winemakers commonly measure ripeness by
the amount of sugar in the grapes. They may also consider the
grapes' acid content, flavor, and aroma. Workers usually pick the
grapes by hand. The grapes then go to the winery for processing. The
grape harvest is sometimes called the vintage. In some years,
a favorable climate produces grapes of especially high quality.
Those vintage years are considered to be superior.
At the
winery, a machine called a crusher breaks the grape berries
and removes them from their stems. The crushed grapes and their
juice are called must. The length of contact between the
juice and the skin influences the color of the red wine, and the
taste of all wine.
To make
white wine, winemakers separate the skins and pulp from the juice.
The juice them enters a tank or barrel for fermentation. In making
red wine, the seeds and skins go into the fermentation tank with the
juices. Stirring the mixture from time to time ensures that the
color is extracted from the skins.
Fermentation is the chemical change in which yeast converts the sugar
in grapes into alcohol. Some yeast grows naturally on the skins of
the grapes. Some European winemakers allow this yeast to conduct
this fermentation. In the United States and most other countries,
winemakers add selected yeasts to the must to begin fermentation.
During the fermentation, the yeast grows and changes sugars called
glucose and fructose into the ethanol, a type of alcohol,
and carbon dioxide gas. The carbon dioxide is released as bubbles.
The yeast also produces various by-products that may add to the
wine's flavor and aroma.
Fermentation also releases heat. Most wineries refrigerate the must to
keep its' temperature constant during fermentation. Winemakers
usually ferment juice for white wine at about 59°
Fahrenheit and red wine juice at about 86° Fahrenheit. The
temperature of the must influences the rate of fermentation, the
retaining of grape aromas, and the formation of yeast by-products.
It also determines the rate at which the color and flavor of the
grape skins transfer into the wine. The fermentation of red wine
takes from 4-6 days and 12-18 days for white wine.
Most red table wines and some white table
wines undergo a second fermentation, by bacteria. This fermentation,
called the malolactic fermentation, lowers a wine's
acid content by converting a substance called malac acid into
lactic acid.
A new wine appears cloudy after
fermentation. Winemakers clarify (clear) by removing particles of
yeast and other unwanted substances. Such particles may be filtered
out, allowed to settle naturally, or separated from the wine
by a machine called a centrifuge. Wine may be further
clarified, or fined, by adding certain solutions that reduce
the content of unstable or unpleasant components.
After clarification, wine goes into
wooden barrels or stainless steel tanks for aging. Wooden
barrels contribute their own flavor to the wine. The size of the
barrel, the age of wood, the storage temperature and humidity, and
the length of storage time all influence the extent of the aging
process. Many wineries hold wine at a temperature close to freezing
for one or more days so that a salt called potassium bitartrate will
precipitate (separate) out of the wine. This prevents the salt from
forming crystals in the wine after bottling.
Although some wines are soon ready for
drinking, others must age a few years to soften harsh flavors and
allow desirable flavors to develop. Wine is bottled after some
aging, and it continues to age slowly in the bottle.
Fortified wines, such as port and sherry,
are made by adding brandy to fermenting must. The wine that results
generally is sweet. Drier fortified wines are achieved by adding
brandy near or at the end of fermenting. Sparkling wines are usually
made by a second fermentation of the table wine. This fermentation
may take four to eight weeks. The bubbles of carbon dioxide produced
by the fermentation are trapped in the wine. |
