Champagne bubbles: the science

As you uncork this bottle and raise your glass, take some time to toast physics and chemistry with the New Year

In a laboratory in the heart of the French vineyard, a group of researchers carefully positions an ultra-fast camera. Like many good scientists, they are dedicated to the practice of unraveling the secrets of the universe, seeking to describe the material world in the language of mathematics, physics, and chemistry. The object of their study: champagne bubbles.

The chemical physicist Gérard Liger-Belair, head of the eight-member “Effervescence & Champagne” team at the University of Reims Champagne-Ardenne, may know more about champagne bubbles than anyone on the planet. Since his doctoral thesis in 2001, Liger-Belair has focused on the sparkling effervescence inside and above a glass. He has written over 100 technical papers on the subject, including a 2021 deep dive into champagne and sparkling wines in the Annual review of analytical chemistry and a popular book ( Opportunity: The Science of Champagne).

“When I was a child, I was fascinated by the breath and the observation of soap bubbles,” recalls Liger-Belair. This fascination has persisted, alongside a lot of more practical work: there are plenty of good reasons to be interested in bubbles, well beyond the pleasures of sparkling wine. Liger-Belair has helped show which aerosols are thrown into the sky by tiny bubbles bursting in the spray, affecting the ocean’s role in cloud formation and climate change. He even helped determine that some mysterious light spots in Saturn’s Titan moon radar scans could be centimeter-sized nitrogen bubbles bursting on the surface of its polar seas.

But Liger-Belair has had the pleasure of focusing the last 20 years of its work on champagne bubbles and other carbonated drinks, including cola and beer. His lab studies all the factors that affect bubbles, from the type of cork and the ingredients in the wine to the way the drink is poured. They wonder how these carbon dioxide bubbles affect taste, including the size and number of bubbles and the aromatics thrown into the air above the glass.

In search of answers, they turned to gas chromatography and other analytical techniques – and, along the way, took some striking photos. Others too, around the world, have turned their gaze to bubbles, even inventing robots to produce cohesive pouring and focusing on the psychology of how we enjoy bubbly.

Champagne from grape to glass

It is often said that Dom Pierre Pérignon, a monk appointed cellar master of an abbey in Champagne, France, drank the very first accidental sparkling wine and exclaimed, “I drink the stars! It turns out that this is probably fiction. The first sparkler probably came from another French abbey, and the first scientific paper on the subject came from the Englishman Christopher Merret, who presented the idea to the newly established Royal Society of London in 1662, years before. that Pérignon does not get his post.

The traditional method of producing champagne involves a first fermentation of the grapes to produce a base wine, which is supplemented with cane or beet sugar and yeast and left to ferment a second time. The double-fermented wine then rests for at least 15 months (sometimes decades) so that the now dead yeast cells can alter the flavor of the wine. This dead yeast is removed by freezing it in a stopper in the neck of the bottle and squeezing out the frozen mass, losing some of the gas from the drink along the way.

The wine is recapped, sometimes with the addition of sugars, and a new balance is established between the air layer and the liquid in the bottle which determines the final quantity of dissolved carbon dioxide. (There are equations to describe the gas content at each stage, for those who are curious to see the calculations.)

The taste of the final product of course depends a lot on the starting ingredients. “Grapes are central to wine quality,” says Kenny McMahon, a food scientist who studied sparkling wines at Washington State University before setting up his own winery. It also depends a lot on the amount of sugar added in the final step. In the Roaring Twenties, the champagnes introduced to the United States were really sweet, says McMahon; modern tastes have changed and vary from country to country.

But bubbles are also extremely important: the proteins in wine, including those from burst dead yeast cells, stabilize the smaller bubbles that froth the desired ‘froth’ atop a champagne glass and a sharper pop. in the mouth. According to Sigfredo Fuentes of the University of Melbourne, most of a sparkling wine lover’s impressions come from an unconscious assessment of bubbles.

“Basically you like or dislike a champagne or sparkling wine by the first reaction, which is visual,” says Fuentes, who researches digital agriculture, food, and the science of wine. This high is so powerful, he found, that people will highly rate a still, inexpensive wine that has been made sparkling by exploding it with sound waves just before pouring it. People were even prepared to pay more for sound bubble wine. “It went, for really bad wine, to $ 50,” he laughs.

As a general rule, a bottle should contain at least 1.2 grams of CO2 per liter of liquid to give it the desired luster and bite of carbonic acid. But there is too much: more than 35.5% CO 2 in the air in a glass will irritate the nose of the drinker with an unpleasant tingling sensation. The potential for irritation is greatest in a flute, where the concentration of CO 2 above, the liquid is almost double that of a larger French coupe, and lower if poured from a chilled bottle than from a lukewarm bottle.

The Liger-Belair team discovered that a good cap (made up of small particles stuck together with a lot of glue) will retain gas in a cylinder for at least 70 years; after that the drink will be disappointing flat. Such was the fate of champagne bottles found in a shipwreck in 2010 after 170 years under water.

Liger-Belair and his colleague Clara Cilindre received a few precious milliliters of this elixir to study. The wines had interesting properties, they reported with their colleagues in 2015, including an unusually high percentage of iron and copper (likely from nails in barrels used to age wine, or even pesticides on grapes) . They also contained a lot of sugar and surprisingly little alcohol, possibly due to fermentation late in the year at cooler temperatures than usual. While Liger-Belair and Cilindre unfortunately didn’t get a chance to sip their samples, others who have tasted them have described it using terms such as “wet hair” and “cheesy.”

For a more common sparkling bottle, even the pouring method has an impact on the bubbles. If 100 milliliters (approximately 3.4 fluid ounces) of champagne are poured directly into a vertical flute, Liger-Belair calculates that the glass will contain approximately one million bubbles. But a smoother “pouring beer” on the side of a glass will increase that by the tens of thousands. There are “huge losses of dissolved CO2 if it’s done badly, ”he said. Rough spots on the inside of a glass can also help to form bubbles; some glassmakers engrave shapes on the inside of the glasses to facilitate this process. And to avoid introducing surfactants that cause bubbles to burst, some people even go so far as to wash their glasses without soap, McMahon says.

Champagne tasting test

All of the science has “direct implications for how best to serve and taste champagne,” says Liger-Belair. McMahon, too, is convinced that the industry has fine-tuned the protocols to align with the scientific findings, although he cannot name any specific wineries that have done so. There are many university departments focused on wine, and there’s a reason for that, he says – their work finds fruitful and financially beneficial applications. Fuentes says he knows that some sparkling wine producers (although he doesn’t name them) add egg protein to their wine to produce a small bubble foam that can last up to an hour.

Fuentes pursues another angle of commercial application: his team created the FIZZeyeRobot – a simple robotic device (the prototype was made from Lego bricks) that performs a consistent casting, uses a camera to measure the volume and duration of life of the foam on top of the glass and has metal oxide sensors to detect CO levels2, alcohol, methane and more in the air above the glass. The team uses artificial intelligence-based software to use these factors to predict the aromatics in the drink itself and, most importantly, the taste. (Much of this research is done on beer, which is cheaper and faster to make, but it also applies to sparkling wine.)

“We can predict the acceptability by different consumers, whether they are going to like it or not, and why they are going to like it,” says Fuentes. This prediction is based on the team’s own datasets of tasters reported preferences, as well as biometrics, including body temperature, heart rate, and facial expressions. One way to use this information, he says, would be to determine the optimal time for any sparkling wine to rest with the dead yeast, in order to maximize the pleasure. He expects the system to be commercially available in 2022.

Of course, human palates vary and can be fooled. Numerous studies have shown that the tasting experience is deeply influenced by the psychological expectations determined by the appearance of the wine or the setting, the company one keeps with the room lighting and the music. Nonetheless, Liger-Belair has, through decades of experience, formed a personal preference for aged champagnes (which tend to contain less CO 2), poured gently to keep as many bubbles as possible, at a temperature close to 12 ° Celsius (54 ° Fahrenheit), in a large tulip glass (more traditionally used for white wines) with generous headroom.

“Since becoming a scientist, a lot of people have told me that I seemed to have landed the best job in all of physics, since I built my career around bubbles and work in a lab filled with premier champagne. order, ”he said. . “I would be inclined to agree.” But his real professional pleasure, he adds, “comes from the fact that I still have the same childish fascination with bubbles as when I was a kid.” This love of bubbles has yet to explode.

This article originally appeared in
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