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How Wine is Made

by winenews on Oct.23, 2008, under Articles, Tips & Terms

The quality of a wine depends largely on the quality of the grapes used.  The goal of the production process is to maximize this quality.  Wine is produced through a biochemical process called fermentation, initiated by the yeast added. During this process the sugar contained in the must (the fresh grape juice) is transformed into alcohol along with the output of carbonic gases that escape into the environment. Yeast is only able to fulfill its task between -3°C and 36°C, and the wine maker can therefore regulate the temperature of the steel vats according to their needs. Fermentation stops completely when the sugar is completely transformed, but may also be stopped artificially. Enzymes are destroyed over 65°C allowing for pasteurization. For finer wines this is known as flash-pasteurization, which subjects the wine to temperatures up to 80°C for thirty to sixty seconds.

One needs to distinguish between red and white wine. In the production of red wine, fermentation takes place at approximately 28°C and includes marc (grape skins, stems and seeds). White wine is usually fermented at 18°C and without the marc. The grape skins give the color to the wine. White wine can be made with red grapes if the marc is removed before the color passes into the liquid.

Fermentation and maturation can be completed in steel or oak containers. The advantages and disadvantages for the two types are as follows:

  Steel vat Oak Barrel
Cost for production Low High (4x to 10x)
Duration of container Long Short
Temperature controllability High Low
Respiratory capacity of container No Yes
Maintaining the cleanliness of container Easy Difficult
Vanillin extract passed to wine No Yes
Variation of Tannin content of wine No Yes

During the production process, the wine is racked. Racking is the process of draining the clear wine off the sediment into another vat or cask. Some wines exist, such as the Muscadet, which are never racked. Fining agents are also used to clarify and may even be used prior to the fermentation, and sulfur dioxide is used to control the oxidation of wines.

RED WINE

After the harvest that takes place in September or October, the grapes are crushed and de-stemmed. Some stems remain since these contain vital tannins.

The fermentation then begins in a fermentation vat (casks or stainless-steel tank). The grape skins tend to float at the top of the vat forming a cap or manta. To mix the must with the skins it has to be pumped up from the bottom of the tank. To control the fermentation the vats are held at a constant temperature of 28/30°C and at this stage selected yeasts are added (the grapes already contain an amount of natural yeast).

The fermentation period lasts from a few days, for lighter wines and up to 30 days for stronger wines. The longer the contact of the juice with the skins is maintained, the stronger the color and tannin content of the wine becomes. This can give the wine a fuller body and potentially a longer life span in the form of age reachable. Too much tannin can, however, ruin a wine. At this point the wine is separated from the skins and begins the aging process in barrels and later bottles. After a period of fining in bottles it is sold on the market.

WHITE WINE

White wine differs from red not only in terms of color. Traditionally they are fermented without maceration, have lower tannin content, a lighter body, a higher acidity and a shorter aging time compared to red wines. A white wine usually has less alcohol but a greater fruit and floral characteristic. White wines tend not to need decanting or opening before serving and are best served at about 8° with lighter dishes.

The fermentation process is usually more complex and involves a higher level of technology. The grapes are crushed or pressed, immediately separating the skins. After this the juice is cleansed and purged. Today the grapes are sometimes crushed and macerated in a “vinimatic” for anything from 12 to 48 hours. This is to extract the aromas contained in the skins. This process results in a “free-run wine” and musk which will need a further press.

Fermentation is usually at a temperature of about 18°C. Yeasts are often used when producing white wine from red grapes because the contact with the skins is shorter and therefore many natural yeasts are lost. Aging in barrels is not common but is more commonly used today than in the past.

ROSÉ WINE

Rosè wine can be produced by one of 3 methods: bleeding, pressing or limited maceration. The latter is the most used and is exactly the same as the vinification process of red wine, differing only in the maceration time. Rose wine has a shorter maceration time.

SPARKLING WINE

In the basic production of a sparkling wine, the carbonic gases produced by the alcoholic fermentation are not allowed to escape but instead are dissolved into the wine.

Champagne is produced through a second fermentation and is sold in the very same bottle. Dom Perignon, a monk of the 17th century, is credited to have invented Champagne by mistake. The system is known as the ‘Champenois method’, since it originated in the Champagne region in France . This method of adding of sugar and new yeasts to a wine and bottling it immediately is also used in other regions of the world but is then no longer to be mistaken for Champagne . A different process, called ‘Charmat’, refers to wines that undergo this second fermentation in a tank and not in the actual bottle. In some cases sparkling wine is even be produced artificially. Carbonic gases are inflated into the wine. However, this method is not necessarily a sign of quality for a wine.

DESERT WINE

This is usually produced from white wine where the grapes have been allowed to wilt. This means that both the percentage of sugar and the amount of contact with oxygen has been allowed to increase (due to the fact that the liquid tends to decline). The wines produced tend to be gold or amber in color and are sweeter than classical white wines.

MATURING AND AGING

White wines are usually ready to be drunk the spring after the harvest. Nowadays, many whites are aged for 6 to 18 month in barrels, to add more character and body to the wine. Dessert wines, such as the Italian Vinsanto or Vino Santo may even be aged up to 10 years before being sold.

Red wines usually benefit by aging in barrels, and in some cases a long maturing phase is necessary to obtain the optimum wine. Wines suitable for aging tend to have a minimum of 12% alcohol, have a higher content of acid and are rich in tannins. For example the Italian Nebbiolo (used for Piedmont Barolo or Barbaresco) has the characteristics suitable to undergo a long aging process.  Not all grape varieties produce a wine suited to aging. The optimal maturing period changes from wine to wine and sometimes from harvest to harvest. It is very important to age the wine in the best woods and in a correct cellar. Temperatures should be between 10-15°c with humidity around 70%. The cellar should be clean, dark, and aired.

In the past few years it has become very fashionable to use oak barrels in the production of wine. These contain 225litres, and are also referred to as barriques (often made from French forest oak wood). These barrels tend to last up to 7 or 8 years but are often only used for just a couple of years before being replaced. Wines suited best for the maturing in barrique are usually rich in polyphenols such as Cabernet Sauvignon, Sangiovese, Merlot and Pinot Noir.


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