What Causes Champagne To Bubble?

In order to produce the bubbling and sparkling epithet of champagne, it is made to ferment two times.  The first fermentation takes place in wooden casks.  Once that fermentation stops for a short, ephemeral time in the first winter, it is transferred to strong bottles, after being blended and sampled by experienced connoisseurs of champagne.  

The second fermentation occurs in those bottles.  For the first three months, the wine is gradually moved and tipped by hand, making the bottles stand upside down.  This is done to make all the impurities settle at the bottom of the cork.  The same position of the bottle is retained for at least six months and sometimes even years.  The 'bubbly foam' is produced by the yeast that introduces carbon dioxide into the wine, which is achieved by putting the bottles under pressure upside down.