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How is sparkling wine made?
Sparkling wines are carbonated wines that have undergone a second fermentation. The pressure must be at least 3 bar, for quality sparkling wine(Sekt) at least 3.5 bar; the maximum value in each case is 6 bar. If carbon dioxide is artificially added to a still wine, it must be labelled as "sparkling wine with added carbon dioxide".
For the second fermentation, a mixture of sugar and yeast, the so-called tirage, is added to the base wine (a finished still wine). The yeast then converts the sugar into alcohol and carbon dioxide, ensuring that the carbon dioxide cannot escape this time - as is usual during the first fermentation - but that it dissolves in the liquid as carbonic acid.
The second fermentation can take place either in a pressurised tank(Méthode charmat) or in the bottle(Méthode champenoise or Méthode classique). The transvasation process combines both methods.
With the Bottle fermentation the bottle is sealed airtight with a crown cork after the filling dosage has been added. The bottles are then stored horizontally in so-called riddling vats. Over a period of several months, they are turned around an eighth of a circle at regular intervals, each time placing them at a slight angle with the neck of the bottle facing downwards(remuage). In this way, the lees (the yeast that has died after completion of the second fermentation) collects in the neck of the bottle directly below the crown cork. The longer the sparkling wine lies on the lees, the finer and more differentiated its flavour and texture become. The riddling can be done by hand or mechanically in so-called gyropallets (computer-controlled riddling racks). Once the riddling and yeast storage are complete, the sparkling wine bottles are disgorged: Upside down, they pass through a cold bath that freezes the part of the liquid containing the yeast residue. When the grain cork is then removed, the carbon dioxide pressure in the bottle drives out the yeast plug, leaving behind the finished, clear sparkling wine. The missing amount of liquid is then compensated for by the so-called shipping dosage. The shipping dosage is a mixture of (base) wine, sugar and, if necessary, brandy; it determines the residual sugar content of the sparkling wine. The bottle is then sealed with a cork and agraffe. This process is used in particular in the production of champagne.
In the transvasation process, disgorging is omitted: Once the second fermentation is complete, the bottles are opened and emptied into large tanks with the lees. These are then cooled down to sub-zero temperatures so that the carbon dioxide remains bound before the sparkling wine is filtered and bottled.
In tank fermentation, the entire process takes place in temperature- and pressure-controlled large tanks. The carbon dioxide produced during the second fermentation is dissolved in the wine and the yeast sediment is stirred regularly. Finally, the tank is cooled down and the sparkling wine is filtered and bottled.