The méthode champenoise, or traditional method, is the process that gives Champagne its natural effervescence and fine bubbles. After an initial classic alcoholic fermentation, the still wine is bottled with a liqueur de tirage (a mixture of sugar and yeasts). A second fermentation then takes place directly in the bottle, generating CO₂ that dissolves into the wine. The bottles are subsequently stored on laths for a minimum of fifteen months (thirty-six months for vintage wines), then subjected to progressive riddling to gather the yeast deposits in the neck. Finally comes disgorgement, which removes this deposit, before the addition of the dosage liqueur (liqueur d'expédition), which determines the final dosage level, and therefore the style — Brut, Extra-Brut, or Demi-Sec — of the cuvée.