How is sparkling wine made?
Sparkling wines are wines with carbonic acid that has been produced by a second fermentation. The pressure must be at least 3 bar, for quality sparkling wine(Sekt) at least 3.5 bar; the maximum value is 6 bar in each case. If the carbonic acid is artificially added to a still wine, it must be described as "sparkling wine with added carbonic acid".
For the second fermentation, a mixture of sugar and yeast, the so-called tirage liqueur, is added to the base wine (a finished still wine). The yeast then converts the sugar into alcohol and carbon dioxide, making sure that this time the carbon dioxide does not escape - as is usual in the first fermentation - but that it dissolves in the liquid as carbonic acid.
During the Bottle fermentation the bottle is hermetically sealed with a crown cork after the tirage liqueur has been added. The bottles are then stored horizontally in so-called riddling trays. Over a period of several months, they are turned around an eighth of a circle at regular intervals, each time with the neck of the bottle pointing downwards(remuage). In this way, the yeast sediment (the dead yeast after completion of the second fermentation) collects in the bottle neck directly below the crown cork. The longer the sparkling wine lies on the yeast, the finer and more differentiated it becomes in aroma and texture. The riddling can be done by hand or by machine in so-called gyropalettes (computer-controlled riddling racks). Once the riddling and yeast storage are complete, the sparkling wine bottles are disgorged: Upside down, they travel through a cold bath that freezes the part of the liquid with the yeast residues. When the grain cork is then removed, the carbonic acid pressure in the bottle expels 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 possibly also 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.
With the transvasation method, disgorging is omitted: After completion of the second fermentation, the bottles are opened and emptied into large tanks with the lees. These are then cooled down to minus degrees so that the carbonic acid 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 lees are stirred regularly. Finally, the tank is cooled down and the sparkling wine is filtered and bottled.