Bubbles in Champagne
What causes more bubbles in a champagne glass? A taller glass? An older vintage? A dirtier glass?
Answer: the more bubbles there are in your champagne, the dirtier your glass is!
In a luxurious a palace, a glass of champagne sits upon a white tablecloth, strings of tiny bubbles gently trailing up to the surface. This immaculate and perfect décor, however, hides a little secret – the bubbles in this elegant drink are associated with impurities on the surface of the glass. In fact, every string of bubbles is caused by either a defect in the glass or a piece of dust or grime stuck to its surface. These imperfections trap the air when the champagne is poured, and then act as minuscule launching pads for the bubbles.
Carbon dioxide is dissolved in champagne because it is pressurized. The dissolution depends upon the pressure, and can be described in physics using Henry’s law. When the cork is popped, the pressure decreases and the champagne becomes saturated with carbon dioxide. The 10g of CO2 dissolved in a closed 75dl champagne bottle would occupy a volume of nearly five liters at ambient pressure. So why are dust particles needed for strings of bubbles to form in the glass? Every roughness or impurity on the surface of the glass imprisons a tiny pocket of air when the champagne is poured. The CO2 still trapped in the liquid is sucked into these air pockets, where it is liberated into a gas form. The bubble grows as more gas is added to it, until eventually it detaches and rises to the surface, leaving behind a small pocket of gas on the imperfection that acts as a new nucleus, relaunching the process. Thus a string of tiny bubbles ensues from a single point. Over time as the CO2 escapes to the surface, the saturation diminishes, and thus there are fewer bubbles.
The shape of the glass has little influence on the process. The age of the vintage, however, is generally associated with the size of the bubbles. Corks are not completely airtight, and over long periods of time, some CO2 will escape. This is why older champagnes form tinier bubbles; the lower pressure doesn’t allow them to create bigger ones. Since the best champagnes are the ones stored for several years, popular wisdom has it that the small bubbles are an indication of the quality of the vintage.
Champagne enthusiasts don’t stop at just tasting their object of their passion; they also describe its bubbles. They wax eloquent about their size, the trains they form, the patterns they form on the surface. So keep this in mind the next time you serve champagne on a special occasion, and don’t worry about getting every last speck of dust out of your champagne glasses!
Source: École polytechnique fédérale de Lausanne (A university in Switzerland)