January 5, 2018 – It’s always a celebratory moment when we hear a Champagne cork pop but exactly why it happens is probably something most of us have not spent a lot of time thinking about. Leave it to physicist Helen Czerski, a specialist in the physics of bubbles, to give us the lowdown. As an oceanographer, as well as physicist whose research focuses on the physics of the ocean surface, especially the bubbles formed by breaking waves, she is an internationally recognized bubbles specialist. That sounds like fun.
Writing in The Wall Street Journal Review section last weekend, Dr. Czerski explains the amazing things that happen, in just milliseconds, when we open a bottle of bubbles.
If you’ve ever toured a Champagne or sparkling wine facility (and if you haven’t, you should put it on your bucket list) you learn that a bottle of Champagne packs pressure about three times the pressure in your tires, which is why the bottles are very heavy glass and the cork is encased in a wire cage. It’s not to make it look pretty or some ancient ritual. It is for safety. Dr. Czerski says removing the cage is like “priming a cannon”. In fact the cork can blast out of the bottle at 20 miles an hour, which is why the bottle should always be pointed away from yourself and other people. It is also why people who open a bottle with great gusto end up dousing themselves and anyone standing nearby. Ease the cork out slowly and you won’t waste a drop.
So where does all this pressure come from? It is caused by the carbon dioxide that results from fermentation. Since the carbon dioxide is trapped in the bottle, and there’s very little room for it in the space between the top of the wine and the bottom of the cork, the wine in the bottle is full of dissolved carbon dioxide. Using high-speed photography, Dr. Czerski was able to see the pop happening. As the carbon dioxide in the neck of the bottle whooshes out, a vacuum is formed and air is sucked back in. This air oscillates in and out creating a sound wave. All of this takes about 50 milliseconds. There are one thousand milliseconds in a second so no wonder we can’t see what is going on. That’s the short version. There are more interesting details in her article.
It’s the carbon dioxide that causes the bubbles in sparkling wine and how that happens is also fascinating. Physicist Gérard Liger-Belair of the University of Reims describes champagne bubbles as “a fantastic playground for fluid physicists”. One of the more interesting pieces of information is that carbon dioxide molecules collect on bits of dust or lint in the Champagne flute. When the bubble becomes buoyant it detaches from the dust and floats to the top causing another bubble to form in its place. That’s how the delightful train of bubbles we love to admire is formed. All these processes happen in split seconds and are affected by temperature, glass shape and other things that are quite amazing and something to ponder. However, pondering is not a normal preoccupation when anticipating that first sip of bubbly, unless you are a physicist.
Which leads to the most asked question in any sparkling wine tasting room or cave tour: How many bubbles are in my glass? About a million.