Grapes into Wine
Turning Grapes into Wine: Vinification
Vinification, or the process of turning grapes into wine, is responsible for many of a wine's characteristics. Like grape-growing, the wine-making process involves the same basic steps for all wines, although the details of the process can vary widely. The decisions involved in the making of wine begin with the harvesting of the grapes, which can be done either by machine or by hand.
Some vineyards produce their own wine from their own grapes; others sell their grapes to wineries that will produce wine. Once grapes are harvested, they are crushed to split the skins and destemmed—it is up to the winemaker to determine what percentage of stems get removed at this stage. White wines are then pressed, to separate the grape skins and seeds from their juice, and then fermented; red wines are first fermented and then pressed (fermenting the grapes with their skins contributes to a wine's red color).
After fermentation, the wine is transferred to ageing vessels, then may undergo racking, fining, filtration, or stabilization processes before it is eventually bottled. Decisions are made at every step of the way—about which equipment and processes to use, the length of time each step will take, whether to use additives, whether to skip or undertake certain steps altogether—and these decisions ultimately influence the character and quality of the wine.
The wine maker's choices determine the following about the wine:
Type of wine:
A winemaker can opt to produce still wine, fortified wine, or sparkling wine. The majority of wines produced are still wine, which follows the basic fermentation process. Fortified wines such as sherry, port, and Madeira, have alcohol added to the wine. Sparkling wines, such as Champagne, Cava, and Prosecco, do not allow carbon dioxide—a natural by-product of fermentation—to escape the wine.
A winemaker's decisions regarding which grapes to use and when to separate the skins from the juice partly determines the wine's color. White wines have skins removed immediately after pressing, while red wines are fermented while the skins, stems, and seeds from some or all of the grapes are still intact. Rosé wines have the skins left on for just a brief amount of time.
Fermentation will naturally cease when all of the sugar in a wine is converted to alcohol (among other conditions). However a wine maker may opt to halt the fermentation process sooner, leaving some residual sugar in the wine. The decision of when to stop fermentation combined with the amount of natural sugar in the grapes determines whether a wine will be dry, off-dry, semi-sweet, or sweet.
Wines can vary from less than 8% to over 15% alcohol by volume. This percentage is largely determined by the winemaker, who may halt fermentation sooner to create low alcohol wines, or prolong it to achieve higher alcohol wines. Winemakers can also add additional sugars (known as enrichment) to be converted to alcohol, thus increasing the alcohol content of the wine.
While the natural acidity in grapes will largely determine the acidity of a wine, the wine maker can adjust or alter this acidity. Acidification and deacidification are both common in winemaking, particularly in unusually warm or cool climates. Maloactic fermentation, a second fermentation process that most red wines and some white wines go through, decreases the acidity of a wine.
Tannins are present in grape skins, stems, and seeds, as well as in oak. The wine maker's decisions regarding when to de-stem grapes, when to separate them from their skins, as well as whether and how long to age or ferment the wine in oak determines the level of tannins in the wine.