Champagne is distinct from wine because it undergoes a second fermentation (typical wine goes through one fermentation) that traps carbon dioxide gas, which then dissolves into the wine to form those beautiful lines of bubbles when it's uncorked.
What makes the carbon dioxide in the first place? During the second fermentation a bit of yeast is added. Yeast consumes the fructose and glucose in grape juice and converts them into carbon dioxide and ethanol. The carbon dioxide is trapped. After aging, the bottles are then turned slightly, either manually or by machine, so that the lees settles out in the neck of the bottle. The bottles are chilled until the neck is frozen and the cap is removed. The pressure in the liquid forces the frozen lees out, then it's quickly corked, securing the carbon dioxide.
An interesting sidebar note: Before insertion a champagne cork is about 50 percent larger the opening of the bottle. Originally corks are cylindrical and are compressed to fit into the bottle. Once stuck, the cork that is not in the bottle billows out forming that distinctive "mushroom" shape. So the age of the champagne can sometimes be determined by the cork's shape. The longer it's been in the bottle the less it will return to it's original cylindrical shape.
Champagne obeys Henry’s Law, which states that the pressure of a gas outside of a liquid must be proportional to the concentration of gas in the liquid. In unopened bottles of champagne the carbon dioxide within the liquid is in equilibrium with the gas in the space between the cork and the liquid. Uncorking the bottle releases the gas and of course throws off the equilibrium. The dissolved carbon dioxide leaves the champagne as tiny bubbles in an effort to adhere to Henry’s Law and restore equilibrium.
As the story is told, it was a French monk, Dom Pierre Perignon, who discovered champagne in the mid-1600s. Apparently he was ordered by his superiors to stop creating the "bubbles" because too many of the bottles burst in the wine cellar. Centuries later cellar workers wore iron masks to protect themselves from randomly exploding bottles.
Champagne has more than 600 chemical compounds apart from the carbon dioxide, that give it its unique aroma and flavor. Typically the grapes used in champagne are Pinot Noir, Chardonnay and Pinot Meunier.
As you are uncorking bottle after bottle this weekend, remember the best way to pour champagne is on an angle because studies have proven this retains twice as much carbon dioxide than when we pour straight down the middle of the glass. And we want to preserve the bubbles because it’s those bubbles that carry more of the hundreds of flavor compounds in the champagne.