No Matter How Big the Bubbles, Size Isn’t Everything

Sparkling wines have long been judged by drinkers and critics, at least in part, by the size of their bubbles. Fine bubbles, coarse bubbles, persistent bubbles — from the finest sparklers, say some, emerge a million pinpricks of air, offering more foam or mousse than a gurgling fish tank.  

The cheap stuff manages only miserable and pathetic lumpen orbs, so large as to bring Atlas to his knees.

Or maybe it’s all nonsense.

Age before beauty

“The size of bubbles provides precious information about the age of the wine — not its quality,” says Professor Gérard Liger-Belair, a chemical physicist at the University of Reims Champagne-Ardenne, who specializes in bubbling phenomena in sparkling beverages. He is the author of Uncorked: The Science of Champagne.

He explains that the growth rate of bubbles ascending a wine glass is directly correlated with the amount of dissolved carbon dioxide found in the wine. The more carbon dioxide that is dissolved in a wine, the higher the growth rate, and therefore the bigger the bubbles. The lower the dissolved CO2, the smaller the bubbles.  

Young Champagnes or sparkling wines hold about eleven grams per liter of dissolved carbon dioxide, says Professor Liger-Belair.

During the aging process, he explains, which can last several years or even several decades for the most prestigious cuvées, carbon dioxide escapes from the sealed bottles, either through the cork or through the cap used to seal the bottle. In other words, the amount of dissolved CO2 progressively decreases over time.

This means when a drinker uncorks an old Champagne or sparkling wine, bubbles will be smaller simply because there is less dissolved carbon dioxide in the wine, whatever the wine’s intrinsic quality. “If you buy a very poor quality, three-dollar bottle of sparkling wine, and if you forget it in your cellar for 10 years, the bubbles will be fine and elegant in your glass, but the wine will be evidently undrinkable,” he says.

“If you buy a very poor quality, three-dollar bottle of sparkling wine, and if you forget it in your cellar for 10 years, the bubbles will be fine and elegant in your glass, but the wine will be evidently undrinkable,” he says.

Birth of bubbles 
                                                                                                       
Dissolved carbon dioxide comes from a wine’s second alcoholic fermentation.
 

Gérard Liger Belair studying bubbles. Photo by Emmanuel Goulet.

The traditional method — sometimes called the classic method or Champagne method, named for the region in which it was established and continues to be used — sees the second fermentation occurring in the very sealed bottles that a wine drinker will buy at the store. Yeast and sugar are added to the bottle of blended still wine. This triggers the second fermentation. Because the carbon dioxide byproduct of the second fermentation itrapped in the bottle, it dissolves in the wine until pouring, which happens much later; three years, minimum, from the Champagne region of France, but oftentimes double that or more.

Not all winemakers follow Méthode Champenoise.                                                                                                                                                                
Winemakers using the Charmat, or tank, method initiate the second fermentation in a large, pressurized tank. The wine is added to bottles after the fermentation is complete or halted.

Sparklers are also made using various other methods, some of which involve rebottling, multiple tanks, and even, in the case of pétillant naturel, bottling before the first fermentation is complete.

Very cheap sparkling wines can be given fizz in the same method as soda water. That method is called carbonation and involves an artificial infusion of carbon dioxide into a liquid using pressure; this is not a method used by any quality producer.

No matter the method, the interior forces of a Champagne bottle can be intense: about 90 pounds per square inch, or three times that of a car tire. Those forces are holding the carbon dioxide molecules dissolved in sparkling wine at bay.  

To make a cuvée with finer bubbles, says Professor Liger-Belair, “the simplest thing to do is to put less sugar in the bottle to promote the second alcoholic fermentation and therefore produce a reduced amount of dissolved CO2.” 

The glassware matters

The stemware used to drink a sparkling wine can also affect the experience.

The act of pouring Champagne generates turbulence. The taller the glass, the greater the turbulence, the more carbon dioxide bubbles produced. Those bubbles are blasting aroma compounds to the surface of the wine. 

Which brings up the problem with wine flutes: their shape, which is so perfect for showcasing bubbles on the march, also concentrates the carbon dioxide in the headspace above the glass. That can lead to an unpleasant carbonic bite on the nose. 

Alternately, the problem with coupes — those saucer-shaped glasses wielded by old-time stars in vintage movies — include both aesthetics and dilution. The aromatic compounds released from sparkling wine poured in a coupe are diffused and hard to capture. Research by Professor Liger-Belair, in which a gas chromatograph and an infrared imager were used on stemware bearing Champagne, confirms this.

His findings suggest the ideal stemware compromise is the tulip-shaped wine glass, which is curved inward and shorter than a traditional flute.

Musical bubbles

Researchers have also succeeded in empirically measuring the size of bubbles in sparkling wine. Dr. Kyle Spratt, a former researcher at the University of Texas at Austin, and presently an Austin-based independent contractor specializing in audio signal processing, performed experiments using a hydrophone — an underwater microphone — in glasses of sparkling wine and Champagne.
 

Photo by Pixabay

“When the bubbles that form in sparkling wine break off the glass and start to rise, they vibrate, and this vibration emits sound in the liquid,” he says. “The frequency of vibration — think of this as the musical pitch of the sound — is determined by the size of the bubble.” 

Larger bubbles emit lower pitches than smaller bubbles. By listening to the sounds present in sparkling wine using a special submerged microphone, Spratt was able to gather information about the size and quantity of the bubbles. 

He and fellow researchers used two wines: Moët & Chandon, and a bottle of Cook’s California Champagne.

“We wanted one to be an actual Champagne, and so Moët & Chandon seemed like the obvious choice. To contrast that with a less expensive sparkling wine, we ended up using Cook’s simply because it was sold at the convenience store across the street from the mechanical engineering department,” he explains.

Analysis of the acoustic recordings revealed that the bubbles in the Moët were smaller than in the Cook’s, and that bubble creation was also much more vigorous in the Champagne versus the California creation. 

“That information itself is clear enough just by looking at the two different glasses of sparkling wine,” says Dr. Spratt. “So in a sense it wasn’t telling us anything that we didn’t already know. But the results showed that a simple acoustic recording could be used as a means to conveniently gather quantitative information about the bubble size and quantity in these wines, which is really what we were looking for.”

The findings at the University of Texas are consistent with Professor Liger-Belair’s work in Reims. 

Bubbles are not a metric for measuring a wine’s quality, or lack thereof. The size of bubbles in sparkling wine can be an indicator of craftsmanship, but is not the cause or invariable result. Like glittering diamonds, towering mountains, and stars in the sky, fine, foamy bubbles are a function of time and pressure. It just so happens that some of the best wines require both.

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