Winemaking

Winemaking, wine-making, or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. There is evidence that suggests that the earliest wine production took place in Georgia and Iran around 6000 to 5000 B.C. The science of wine and winemaking is known as oenology. A winemaker may also be called a vintner. The growing of grapes is viticulture and there are many varieties of grapes.

Winemaking can be divided into two general categories: still wine production (without carbonation) and sparkling wine production (with carbonation – natural or injected). Red wine, white wine, and rosé are the other main categories. Although most wine is made from grapes, it may also be made from other plants. (See fruit wine.) Other similar light alcoholic drinks (as opposed to beer or spirits) include mead, made by fermenting honey and water, cider ("apple cider"), made by fermenting the juice of apples, and perry ("pear cider"), made by fermenting the juice of pears, and kumis, made of fermented mare's milk.

There are five basic stages to the wine making process which begins with harvesting or picking. After the harvest, the grapes are taken into a winery and prepared for primary ferment; at this stage red wine making diverges from white wine making. Red wine is made from the must (pulp, including the juice) of red or black grapes and fermentation occurs together with the grape skins, which impart color, flavor and tannins to the wine through the process of maceration. White wine is made by fermenting juice which is made by pressing crushed grapes to extract a juice; the skins are removed and play no further role. Occasionally, white wine is made from red grapes. This is done by extracting their juice with minimal contact with the grapes' skins. Rosé wines are either made from red grapes where the juice is allowed to stay in contact with the dark skins long enough to pick up a pinkish color (maceration or saignée), or (less commonly) by blending red wine with white wine. White and rosé wines extract little of the grape tannins contained in the skins. Orange wine (a.k.a. skin-contact white wine) is wine made with maceration in the manner of rosé or red wine production, but using white wine grape varieties instead of red.

To start primary fermentation, yeast may be added to the must for red wine, or may occur naturally as ambient yeast on the grapes (or in the air). For white wine, yeast may be added to the juice. During this fermentation, which often takes between one and two weeks, the yeast converts most of the sugars in the grape juice into ethanol (alcohol) and carbon dioxide (which is lost to the atmosphere).

After the primary fermentation of red grapes, the free run wine is pumped off into tanks and the skins are pressed to extract the remaining juice and wine. The press wine is blended with the free run wine at the winemaker's discretion. The wine is then kept warm and the remaining sugars are converted into alcohol and carbon dioxide.

The next process in the making of red wine is malolactic conversion, a bacterial process which converts "crisp, green apple" malic acid to "soft, creamy" lactic acid, softening the taste of the wine. Red wine is characteristically transferred to white oak barrels to mature for a period of weeks or months; this practice imparts oak aromas and some oak tannins to the wine. The wine must be settled or clarified and adjustments made prior to bottling.

The time from harvest to drinking can vary from a few months for Beaujolais nouveau wines (made by carbonic maceration) to over twenty years for wine of good structure with high levels of acid, tannin or sugar. However, only about 10% of all red and 5% of white wine will taste better after five years than it will after just one year. Depending on the quality of grape and the target wine style, some of these steps may be combined or omitted to achieve the particular goals of the winemaker. Many wines of comparable quality are produced using similar but distinctly different approaches to their production.

Variations on the above procedure exist. With sparkling wines such as Champagne and Methodé Champenoise (sparkling wine that is fermented in the style of champagne but is not from the Champagne region of France), an additional, "secondary" fermentation takes place inside the bottle, dissolving trapped carbon dioxide in the wine and creating the characteristic bubbles. Bottles then spend 6 months on a riddling rack before being disgorged to remove any sediment that has accrued. An expedited technique using sealed tanks to contain carbon dioxide is known as the bulk Charmat method. Other sparkling wines, such as prosecco, are fermented using force-carbonation — a faster process that involves using machinery to manually add CO₂ and create bubbles. Sweet wines or off-dry wines are made by arresting fermentation before all sugar has been converted into ethanol and allowing some residual sugar to remain. This can be done by chilling the wine and adding sulphur and other allowable additives to inhibit yeast activity, or sterile filtering the wine to remove all yeast and bacteria. In the case of sweet wines, initial sugar concentrations are increased by harvesting late (late harvest wine), freezing the grapes to concentrate the sugar (ice wine), allowing or encouraging Botrytis cinerea fungus to dehydrate the grapes or allowing the grapes to raisin either on the vine or on racks or straw mats. Often in these high sugar wines, the fermentation stops naturally as the high concentration of sugar and rising concentration of ethanol retard the yeast activity. Similarly in fortified wines, such as port wine, high proof neutral grape spirit (brandy) is added to arrest the ferment and adjust the alcohol content when the desired sugar level has been reached. In other cases, the winemaker may choose to hold back some of the sweet grape juice and add it to the wine after the fermentation is done, a technique known in Germany as süssreserve.