After primary fermentation and bottling, a second alcoholic fermentation occurs in the bottle. This second fermentation is induced by adding several grams of yeast and several grams of rock sugar.

According to the Appellation d'Origine Contrôlée a minimum of 1.5 years is required to completely develop all the flavour but most houses age for longer - sometimes much longer. For years where the harvest is exceptional, a millesimé is declared.

This means that the Champagne will be very good and has to mature for at least 3 years. During this time, the Champagne bottle is sealed with a crown cap similar to that used on beer bottles. After ageing, the bottle is manipulated, either manually or mechanically, in a process called remuage, so that the lees settle in the neck of the bottle.

After chilling the bottles, the neck is frozen, and the cap removed. The pressure in the bottle forces out the ice containing the lees, and the bottle is quickly corked to maintain the carbon dioxide in solution. Some syrup (le dosage) is added to maintain the level within the bottle.