Though champagne can be consumed year round, most of us turn to the bubbly stuff when December pushes its last seconds through the hourglass. We all love a bit of effervescence to ring in the new year, and champagne is certainly a festive drink. As I pour myself a cold flute of the golden liquid my mind turns to the more technical aspects of this spectacular drink. It’s time to investigate the physics of champagne!
To begin: what is champagne? Champagne is a sparkling wine produced from a northeastern region in France (the champagne region). The bubbles, obviously, set it apart but it isn’t the only sparkling wine on the market. In order to make wine bubble and fizz you have to initiate a secondary fermentation. Yes, regular wine undergoes one phase of fermentation (the phase that takes grape juice through vinegar and into alcohol). But then things get interesting. Once the wine is fermented, a bit of yeast and sugar are added. This, then, begins the second fermentation. As the yeast consumes the sugar, it produces carbon dioxide (yay, bubbles!).
How, then, do you get a cork into something that is highly pressurized? Champagne corks are not mushroom shaped to begin with. They are born straight! Using a special tool, the corks are compressed and slipped into the neck of the bottle. Once there, they continue their regularly scheduled expansion and grow into the mushroom shape we associate with the special wine.
Most important are the bubbles. How and why do they form on the inside of a glass? In order for CO2 to break free from its liquid bonds, it needs something to hang onto. Since everything in nature is imperfect in some for or another, there are always tiny nucleation points inside glasses. To improve things, glassmakers often engrave microscopic lines into the bottom of a glass, providing ample imperfection for the CO2 to gather. Here’s what happens: dissolved gas (CO2) is not a stolid, slow thing. It moves. And as it moves, it collects into a vibrating bubble at the site of any imperfection. Once a bubble has begun to grow, more gas can collect quickly. As soon as the buoyancy of the bubble (i.e. air density) is stronger than the liquid surrounding it, the bubble will float to the surface where it pops.
For most connoisseurs the best way to open a bottle of champagne is to slip a towel over the cork and remove it with a hiss. But when life calls for celebration, there’s only one way to open your champagne: with a saber! This tradition dates back at least to Napoleon’s time ruling France, though as with most food history there are multiple stories surrounding the origin. Regardless, sabrage is the act of lopping off the top of a champagne bottle with a sword.
Champagne bottles are highly pressurized due to the aforementioned secondary fermentation inside the bottle that produces CO2. Bottles are made of thick glass to contain the strong liquid, but that glass has two weak spots. The lip creates a 90 degree angle against the neck, which is a stress concentration. And running vertically along the bottle is a faint line called the seam. This seam is a second stress concentration. Where these two stress concentrations meet, the strength of the bottle is reduced by more than 50%. Because of this imperfection, it’s possible to hit that intersection with enough force to propagate a crack all the way through the neck. Remember, glass is brittle which in chemistry means it will break, not bend, when force is applied.
Traditionally a short sword was used for this festive uncorking, but because we know the physics of a bottle, it can be done with nothing more than a regular spoon. Hold the bottle at a 45 degree angle, then run the spoon along the seam straight toward the lip with medium force. Be confident in your stroke and the top will come flying off. Make sure your guests stand back, and have glasses ready! The champagne will flow freely!