Open a bottle of champagne, pour yourself a glass and watch what happens. Bubbles everywhere, springing up from thousands of different spots on the inside of the glass, floating off and then joining together to form elegant streams rising to the surface like so many tiny hot air balloons.Bend your ear to the glass. Can you hear the soft crackling of the bubbles as they burst at the surface and can you feel the myriad tiny droplets that tickle your nose as you raise the glass?
Regardless of whatever other characteristics a champagne may have experts will judge a champagne on its bubbles. The beads that spiral upwards in the glass as well as the cordon or crown of bubbles at the surface, are the distinguishing marks of the wine. Although there’s no scientific basis for linking the quality of a champagne to the size of the bubbles, champagne lovers are nevertheless quick to assert that “the smaller the bubbles, the better the champagne.”This is partly a matter of aesthetics; tiny bubbles rise more slowly than large ones and therefore create a long, lingering effervescence that lends a certain delicacy to the wine. More objectively, older champagnes (which are often judged to be of superior quality) lose some of their CO2 as they age and so the bubbles will inevitably be smaller when the bottle is finally opened. Over time this phenomenon has developed into a firm correlation between small bubbles and higher quality in the minds of champagne drinkers.Above all, when you’re opening a bottle of champagne don’t forget that, even though it’s undoubtedly a festive drink, shooting the cork out with a loud pop is not good for the taste of the champagne. It’s always better to take out the cork gently even though some people may think that you don’t know what you’re doing. If you absolutely must make a big noise with the cork remember that a flying cork can travel at a speed of up to 50 km/hour and if it were to hit someone in the eye, that romantic evening you had planned could end up in a visit to the hospital emergency ward.
The gas responsible for creating the bubbles is carbon dioxide (CO2) which is produced by the yeast inside the sealed bottles. Henry’s law states that a balance must exist between the molecules of gas dissolved in the liquid and the molecules of the same gas present in the small space between the cork and the wine. Before the bottle is opened the pressure of gas beneath the cork is about 6 atmospheres. The amount of gas in suspension is about 12 grams per litre of champagne.A 75cl bottle of champagne will release about 5 litres of CO2 (or about 0.7 litres for a standard 10cl glass). It’s possible to get an idea of the number of bubbles this represents by using the fact that the average diameter of a bubble is 0.5 millimetres. This means that in order for the liquid to find its balance some 11 million bubbles need to escape from each glass: that’s more than the population of Paris and all its suburbs.However not all the dissolved CO2 escapes in the form of bubbles.
There are two ways in which CO2 can escape from the wine:
1) through the formation of bubbles
2) directly and invisibly from the surface of the liquid
Recent experiments have shown that only 20% of the CO2 in champagne is released in the bubbles. The other 80% escapes via the surface of the wine in the glass.
So, if you resist the temptation to drink your glass of champagne until all the fizz has gone, about 2 million bubbles of CO2 will have escaped from your glass.But where have they gone?
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Gérard LIGER-BELAIR Edition Odile JACOB