There are three main methods to produce sparkling wine: they all have in common the first step a primary fermentation to turn the grape juice into still wine, called base wine. The following steps are different depending on the method.
Wine & Food Magazine
The traditional method, called metodo classico in Italy, metode champenois in France, is widely recognised as producing the highest quality product. The base wine goes through a secondary fermentation in bottle: the winemaker instigates the fermentation by adding yeast and sugar to the base wine. The yeast convert the sugar into alcohol and CO2 bubbles as natural product of the transformation. The wine rest in the cellar for several month, depending on the winemaker's choice or on the disciplinary. After the yeast is removed by riddling and the bottle topped up and sealed with cork and wire hood.
In the bulk method or Charmat, the secondary fermentation occurs in pressurized tank where yeast and sugar are added to the base wine. After the fermentation the wine is cooled, clarified and the bottled under pressure. Widely used for aromatic and semi aromatic grape varieties. It is less expensive in space time and labour than the previous one.
Finally the aeration method consists in dissolving carbon dioxide into the base wine in pressurized tank to trapp the bubbles in the wine. The aeration tecnique is used for unexpensive wine, since the production is very quick and cheap.