The basic principle for producing wine is very simple. Grapes are collected from vineyards and pressed in order to obtain grape juice. There are two contributing factors that add to fermentation: sugar and yeast (the first is in the grape itself and the second is flowing in the air). Grape juice is already rich in glucose and fructose, and therefore there is no need to add extra amounts of sugar. Yeast is normally in the air but is not abundant- though present -in grape juice, and it is convenient to add cultured yeast in order to ensure fermentation. For red wines, fermentation temperature is typically 22 to 25 degrees Celsius, and for white wines 15 to 18 °C. For every gram of sugar that is converted, about half a gram of alcohol is produced, so a 12% alcohol wine requires about 24% sugars.
This primary fermentation results in ethanol and carbon dioxide- which becomes fizz. Once all the sugar has been turned into alcohol and carbon dioxide, grape juice is already wine. After primary fermentation, wine is usually fermented for a second time, in either large stainless steel vessels or oak barrels, depending on the variety of wine that wants to be produced. During secondary fermentation- which takes three to six months -wine is kept under an airlock to be protected from oxidation. Wines may be left to develop in aging barrels or may be matured without contact with wood. Some varieties of wine do not need aging, but are preferably consumed young. Cabernet Sauvignon, for instance, is one of the grape varieties that need aging in order to better taste.
In order to obtain white wine, it is possible to use either white or red grapes, since most grapes have colorless juice. When producing this type of wine, experts press grapes immediately after harvest, and separate the juice from the skin before fermentation. As long as juice is separated from grape skin before fermentation, the resulting wine is white. This happens because the propriety of coloring wine is in the skin of red grapes and not in its juice.
Red wine, on the contrary, cannot be made from white grapes, but only from red or black ones. After being pressed, red grapes are left to ferment together with skin. There are times when skin may not be removed until the wine has been already matured, since the components that give this wine its color are released both when juice is fermented and when wine is matured.
Rosé is a type of wine that is made from red grapes. To obtain rosé, grapes are pressed and left to ferment with skin only for a short time. Then the skin is removed and the juice keeps on fermenting. Another less frequent method to obtain rosé is to mix red wine with white wine.
Sparkling wine can be made following different methods. It is characterized by its bubbles, which are the released in the form of bubbles due to its level of carbon dioxide. The most usual method of making this type of wine is by adding carbon dioxide into the wine and bottling it under pressure. The oldest method is the one known as méthode ancestrale, which is still used in some parts of France. It consists of bottling wine before fermentation is completed, and it produces wine that is slightly sparkling and, sometimes, slightly sweet and with the lees.
Sweet wine is made by adding hard liquor- commonly brandy – to partially fermented wine. Liquor interrupts fermentation and wine is stabilized. Depending on the stage of fermentation in which liquor is added, the resulting wine differs in taste. When liquor is added to grape juice that has not been fermented, the result is a very sweet type of wine- such as Pineau des Charentes or Muscat Vins de Liqueur. If it is added to partially fermented juice, the result is a sweet wine- such as Port. And if the liquor is added to wines that are already fermented, the resulting wine is dry –Sherry, for instance.
An important factor, especially during fermentation, is temperature. Most white wines are fermented at low temperatures, using refrigeration methods in order to maintain its aroma. Red wine, on the contrary, is fermented at higher temperatures, usually at ambient temperature. It is said that the best temperature for white wine fermentation is between 9ºC and 18 °C, and for red wine between 20ºC and 30 °C. Wine can be refrigerated before being bottled in order to let it stabilize.
The type of container in which it has been kept also affects wine flavor. Some types of container, such those made from stainless steel, produce wine of neutral flavor. If, on the contrary, wine is meant to have a woody flavor, it will be left to develop in a container mad of oak or other type of wood. French oak barrels produce subtle flavor and vanilla-like aromas, while those wines stored in American oak vessels will have the aroma and flavor of resin. Another factor that contributes to flavor is time. Most types of wine are deteriorated soon after being bottled, and the sooner they are consumed the better their flavor becomes. Expensive wine, on the contrary, betters its quality when it is laid down, especially after it has been bottled.
Wine production is possible wherever the climate is template. Especially in Europe, geographical origin was a traditional means of distinguishing between different wine varieties. During the last decades, however, the development of new vineyards outside Europe meant that wine started to be distinguished by the type of grape from which it is made rather than by the geographical location of its vineyard. The main reason for this change is that grape varieties indicate the style and flavor of a certain wine.
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