The science (and art) of wine making nowadays is so advanced that it is almost impossible to churn out bad wine. The brief descriptions below are the procedure normally used in France.
Once the red grapes are picked they are rushed immediately to the winery where they are gently crushed to release the juice. The pulp and the juice (called the ‘must’) are fed into traditional wooden vats for fermentation. Fermentation is the chemical process to turn sugar content to alcohol, thus the juice to wine. It is necessary to stir often in order to push the red grape skins down to leach out the required colour and tannin. Yeast, sugar and other chemicals may be added to control the process. Once fermentation is finished the wine is blended with wines fermented from different grapes to arrive at the wine style of the region. However the wine is usually left to mature for a period from a few months to years (quality wine is aged in oak barrels). After maturation the red wine is ready to bottle.
The process is similar to that of making red wine except that the grape skins are taken out after crushing and pressing to leave the ‘must’ clear of colour. (Both red and white grapes can be used to make white wine.) Then fermentation begins with optional use of yeast, sugar, etc. Nowadays most white wines are fermented in huge stainless steel vats. Only the highest quality full-bodied whites are fermented in oak vats and then matured in oak barrels. The whites meant for early drinking are filtered and bottled for consumption within 6 months of harvest.
Making rosé is like half-way between making red and white wines. The red grape skins are allowed to stay in the juice for about 24 hours after crushing and pressing to result in a pinkish rose colour. The ensuing fermentation is similar to that of white wine. Bottling is immediate after without any maturation. French law does not allow rosé wine to be made by simply blending red wine with white as it is done in other countries (Rosé Champagne is the only exception).
The difference here is the application of a second fermentation after the first. In bottles of young still white wine is added a dosage of sugar and yeast. The carbon dioxide it emits is trapped as bubbles in the bottle to finish as sparkling wine. In France this traditional method of second fermentation in the bottle must be followed in all AOC sparkling wines including Champagne. However this method is expensive and time-consuming as shown by the prices of Champagne. Less expensive methods use vast tanks for the second fermentation or simply by pumping carbon dioxide into still wines but the resulting products are never the same.
Sweet wines, usually white require increased natural sugar content in the grapes. To achieve this they are deliberately left on the vine to ripe and dry out. The fermentation procedure is the same of that of white wine but at the desired point where the sugar, acid and alcohol levels are in harmony the fermentation is halted.
The best sweet wines, especially those from Bordeaux are made from grapes affected by the fungus Botrytis cinerea (the noble rot). It does not happen all the time but when the humidity and temperature are right the fungus would appear to attack and mould the grapes to ugly shrivels. The grapes are then picked and pressed and fermented. The best sweet wines such as Sauternes are almost always matured in oak barrels and some can last in maturation for over 20 plus years.
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