In the process of fermentation the sugar of the grape is transformed into alcohol with other various congeneric substances, and into carbon dioxid, commonly known as carbonic acid gas. When the process of fermentation is in full vigor the liquor in the fermenting tank boils as if heat had been applied thereto. This boiling is due to the escape of the carbon dioxid. In the making of still and sparkling wines the first or principal fermentation is the same in both cases. In the making of still wines there is no attempt made at any time of the fermentation to confine the gas which is allowed to escape in the manner just described. In the making of a sparkling wine, the subsequent fermentations following the first partial fermentation are conducted in the bottle in which the wine is to be sold. This bottle is stoppered in such a way as to confine the gas so that it becomes dissolved in the liquid contents of the bottle. When the cork is removed from a bottle of this kind the gas which has been kept under pressure immediately begins to escape, producing the boiling or foam, or frothing, which is characteristic of carbonated beverages.

The general term "sparkling wines" is applied to the products manufactured as just described.