The addition of
liqueur de tirage provokes a second
alcoholic fermentation within the wine, a process known in French as ''''. During this phase, the yeast metabolizes the sugar, producing
alcohol and
carbon dioxide (CO). The winemaker's goal is to keep this gas dissolved in the liquid; when the bottle is eventually opened, the pressurized gas expands to return to a gaseous state, creating the wine's characteristic bubbles (mousse). This method contrasts with the
ancestral method (used for
Gaillac and
Blanquette de Limoux) and the Dioise method (used for
Clairette de Die), where carbonation is achieved by bottling wine that has not yet completed its primary fermentation, utilizing the natural residual grape sugar rather than an added liqueur.
Liqueur de tirage should not be confused with
liqueur de dosage, which is added later in the process to adjust the sweetness of the wine. == Composition and regulation ==