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|A Toast to Surface Tension|
As you rung in the New Year and popped the
cork on a bottle of Dom Perignon, you probably didn't think much about
surface tension. Neither did the winemakers of northeast France in the
5th century where sparkling wine was born. In fact, until recently, the
art of making a superior champagne was mostly a trial and error effort.
Part of the magic of champagne is the impact it has on your senses. The bubbling and rising is visually captivating. The resulting mist is an aromatic wonder. The bubbly taste is appealing but only part of the overall sensation experience.
Effervescence occurs when the champagne meets the glass. Bubbles develop as the result of nucleation, a process that is facilitated by microscopic airborne fibers and those left behind by the drying process and which cling to the inside of the glass due to electrostatic forces. Since champagne has a low surface tension (about 30% less than water) and high viscosity (about 50% more than water), the microbubbles trapped inside the fibers when the liquid is poured into the glass release as shown in the graphic below. As long as the diameter of the microbubble is at least 4 microns, CO2 will begin to fill the bubble. By the time the bubble increases in size to between 10 and 50 microns in diameter, it will detach from the fiber and travel to the surface picking up speed as it increases in size. By the time it reaches the surface (which can take one to five seconds) it will be as large as 1mm in diameter. Bubbles release at a rate of 30 per second per fiber. Over the past few years Dr. Liger-Belair and his colleagues have thoroughly characterized the formation and motion of gas bubbles in a glass of sparkling wine.1
Since it's difficult to control nucleation an artificial method is often used which involves etching the surface of the inside of the champagne glass. A laser is used to engrave patches, typically at the bottom of the glass, that promote more controlled and predictable nucleation.
A good champagne will produce up to 400 bubbles per second. That's about three times the rate of beer. As the bubbles rise to the surface and pop the resulting mist creates an aromatic fragrance. The resulting bubbling, rising, popping, and fizz are the result of a two-step fermentation process. Yeast and sugar are mixed with a base wine. It's the second fermentation that is caused when the yeast consumes the sugar that results in about five liters of CO2 for a 0.75 liter bottle. Over three quarters of the gas is lost when the bottle is uncorked - which often results in the notorious bubbly shower...when not done properly. Even so, there is enough CO2 left over to produce about 20 million bubbles per (0.1 liter) glass.
By understanding pressure, surface tension, and viscosity, scientists have not only unlocked the mysteries of the bubbly drink but are developing ways to improve and control something as ephemeral as effervescence.
1 Liger-Belair, G.
2004. Uncorked: the Science of Champagne. Princeton: Princeton
On a similar note, surface rheological properties can be measured using the oscillatory axisymmetric bubble shape method to quantify specifically surface dilatational elasticity and viscosity.1 ramé-hart instrument company provides a tool for taking these measurements. It's our Model 100-28 Oscillator.
This device (shown above) sits inline between the Automated Dispensing System and the dispensing tip which could be a needle or bubble adapter. An experiment is created and the oscillation volume and frequency is controlled while measurements are taken. For a detailed technical explanation of the Oscillator, its controls, and the output format, please consult our November 2008 Newsletter.2
1 Fromyr, T.;
Hansen, F. K.; Kotzev, A.; Laschewsky, A.; Adsorption and Surface
Elastic Properties of Corresponding Fluorinated and Nonfluorinated
Cationic Polymer Films Measured by Drop Shape Analysis, Langmuir 2001,