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LuxeSci Show Notes: S1E6: Champagne

Hello again!  Welcome back to the LuxeSci Podcast, a podcast to re-ignite your wonder by exploring the intersection of science and luxury. I’m Dr. Lex, PhD, infectious disease expert, podcast host and champagne obsessive. This is the third in my trio of holiday episodes and although its coming out after the New Year’s Eve festivities, I personally don’t need an excuse to bust out some bubbly.  I've always (since I've been 21 of course) liked a good sparkling wine or champagne, though my penchant for bellinis and mimosas has grown into a more mature appreciation for a very dry Brut. /my interest in the process behind champagne making piqued with a gift of a book. My husband happens to be particularly adept at gifting books. A few years ago, he gifted me the biography of Barbe-Nicole Ponsardin Cliquot, otherwise none as the Veuve Cliquot, "veuve' meaning widow in French. Though her husband Philippe started the champagne house, she took over after his early death and built it into the powerhouse brand it is today. She also had a hand in bringing about the association that champagne currently has with celebrations. She was truly a magnificent woman, well ahead of her time and with a mind like a steel trap. Though the company Veuve Cliquot no longer has a woman at its head, I gravitated to this excellent champagne, which also happens to have a uniquely feminist background. (There are also many excellent small grower/vintner champagne producers now run by women. You can find a few here: https://fatcork.com/pages/growers). There's always been, for me, something special and intoxicating about the sparkle in champagne, those tiny little bubbles that seem to tickle your nose and add a bit of celebration into one sip. Since I'm at heart a curious person (hence this podcast) and not above ruining a good magical moment with a scientific fact, let’s dive into a bubbly glass of champagne to see what it’s all about.


Background:

  • First things first, what is champagne.  Champagne has two criteria: 1) it is a sparkling wine made in the Champagne region of France and 2) it is made under the rules of appellation.  Appellation is something that the French (and others) take very seriously. It is a “legally defined and protected geographical indication, primarily used in wines”.  Appellation can have other requirements associated with and for champagne to be call the champagne, the vineyards producing the grapes not only have to be in a specific area but they need to follow specific practices around growing, harvesting and pressing the grapes and the secondary fermentation of the wine but be done in the bottle.

  • This may all seem a little fussy, and it is.  It also protects unique agricultural and food production processes around the world, not just champagne.

  • If you get a bottle of bubbly from outside of the champagne region of France but it was produced using the same methods then you will likely see Methode champagnoise on the label

  • There are several different types of champagnes:

  • Prestige cuvee - blended wine (most champagnes today are blended) that is considered the top tier by the producer.  Examples include Moet and Chandon’s Dom Perignon and Louis Roederer’s Cristal (fun fact, Cristal was made as early as 1876 but was exclusively for the Russian Tsar’s consumption)

  • Blanc de noirs - white wine from red or black grapes. This produces a white wine with a slightly more yellow color

  • Blanc de blancs - made from Chardonnay (or rarely Pinot blanc) grapes

  • Rose champagne - produced from either leaving the clear juice from dark grapes to macerate in the skins for a brief time or by adding still red wine to sparkling wine.

  • One important taste aspect of champagne is the dosage - this is refers to the amount of sugar (and wine) that is added to adjust the overall levels of sugar in the Champagne when bottled for sale.  While sweet Champagne is currently out of fashion, the dosage is used to balance the perception of acidity in the wine. Terms such as Extra brut, brut, extra dry, sec, etc are used to denote how much dosage is used.  Extra brut being the least and Doux being the most

  • History

  • The champagne region of France has a long history of providing celebratory wines.  In 496 AD, Clovis was baptised in the Reims Cathedral and crowned the first King of France and champagne wines were used in the ceremony

  • Starting in 896, all French kings were coronated in Reims and the wines of the region were served at the celebrations and soon took on international acclaim

  • The oldest record of sparkling wine is from a Benedictine monastery near Carcassonee in 1531 by bottling before the fermentation ended.

  • In the 1600s, an English scientist and physician (Christopher Merret) published the addition of sugar to the wine to create the secondary fermentation (well before Dom Perignon) and English glass makers developed glass bottles that could withstand the internal pressure

  • There were many other innovations around sparkling wine over the centuries with the 1800s being the banner century for champagne production as we know it now

  • There are many extremely fascinating historical facts about champagne but we’re here for the science and what says champagne more than bubbles!!


The Bubbles:

  • First, let’s get the question of the glass out of the way.  In a survey done by the Wine and Spirit Education Trust, with wine tasters, there was a preference for the tulip-shaped glasses but it seemed that was because the tasters thoughts so

  • This may have some underlying scientific truth to it as a tulip glass pairs the glass length of a champagne flute (essential for good bubble speed and distribution at the surface) with the wide head space of a coupe, better for sticking your nose in to get those levely aromas

  • There also may be a slight edge for different-shaped glasses for different champagnes

  • Overall - go with the glass you like.  Personally, i’m either a flute or tulip glass kind of person.  I’m too much of a clutz to have a coupe glass around

  • However, that steady stream of tiny bubbles flowing up from the bottom of a champagne glass, whatever the shape, is the defining feature of a good champagne To help this process along, glass producers introduced laser-etched glass. In laser-etched glasses, bubble nucleation is most often triggered at the bottom of the glass with a ring-shaped structure made with adjoining laser beam impacts.

  • This leads to a vertical stream of bubbles that is seemingly endless

  • So the shape and make-up of the vessel that champagne is in can impact the nature of the bubbles but where do the bubbles come from

  • Bubbles

  • For champagne, or beer, or any other naturally carbonated beverage, the bubbles arise from the CO2 that's generated as a byproduct of secondary fermentation. 

  • These fermentations are done in sealed containers (like a champagne bottle) so the released CO2 dissolves into the liquid. 

  • When the cork is popped, some CO2 is released into the air immediately, but a good portion remains in the liquid and forms bubbles (1). 

  • CO2 also diffuses at the air/wine interface of the glass but that is imperceptible to us.

  •  The really interesting thing is that the bubbles don't only bring CO2 to the surface, they also bring dissolved volatile organic compounds. (remember that vocab word?  VOCs are responsible for aroma). When the bubbles burst, they release those organics and we inhale them. 

  • This process enhances the aroma of champagne and the overall tasting experience. (1)

  • Beaumont et al researched the impact of glass construction on champagne bubbles using 2-D and 3D computational fluid dynamic modeling of the flow of the bubbles and published it in the Journal Food (my kind of journal)

  • Surprisingly, they found a two phase flow of the bubbles in a single glass of champagne.  The two flows were a toroidal (fancy, scientific was of saying donut-shaped) along the ascending column of bubbles and surface eddies that interact with that column flow

  • Since this modeling predicted the flow of the bubbles (which was later validated looking at the actual champagne) this could be a tool for glass makers to determine the optimal shape and etching for champagne glasses to achieve maximum bubble and a better tasting experience (remember bubbles = VOCs = taste)

  • So how do bubbles contribute to the flavor experience from champagne?

  • A team lead by Elisabethe Ghabache set out to characterize the bubbles in champagne with the hypothesis that they would be akin to the bubbles in sea spray.

  • Sea spray is also used to transport dissolved gases (VOCs), salts, surfactants and biological materials to the atmosphere.  

  • This spray is made of up of two types of droplets:

  • Film droplets - smaller and form as the film of the emerged bubble disintegrates

  • Jet droplets - larger and formed as the cavity of the bubble collapses and ruptures

  • The scientists set up a series of experiments using a syringe pump and 5 different types of liquids (de-gased champagne, demineralized water and 3 hydro=alcohol solutions) 

  • Using an array of methods including extreme close-up photogorapy, ultra-fast imagery, high-speed digital cameras and fluid dynamic modeling they measure various aspects of the bubbles in different liquids

  • It turns out that 300-500 bubbles per second burst at the top of a champagne glass (thats a lot of fizz!). 

  • Champagne is comprised only of the larger jet droplets (as opposed to sea spray, which is mostly film droplets).  This disproved the researchers hypothesis but that’s OK.  a disproved hypothesis still means useful info

  • All those jet droplets mean that aerosol from the top of a champagne glass evaporate 10X faster than from the surface of still liquids

  • Right here is the crux of the whole champagne situation.  The fizz (i.e. the bubbles bursting) equals more exchanges of gases and volatile organics and that’s more chances for your nose to pick up on all those amazing aromas and those scents round out how you taste the champagne

  • One interesting fun fact from this research was that larger bubbles created more aroma diffusion and thus, one would think a better champagne tasting experience. However, smaller bubbles have always been prized in champagne making.  Wonder what that’s all about?

  • Other bubbles

  • Now i know this episode is about champagne but while i was putting it together i got so excited about bubbles in general and other roles they play in our lives

  • Walls et al wrote a great review (yep, those again) about the interaction between bubbles and microorganisms

  • In nature, bubbles are formed across all natural bodies of water whenever the surface is broken and air is introduced into the water (rainfalls, snowfalls, breaking waves)

  • One cool example is whitecaps - whitecaps are a myriad of small bubbles rising to the surface

  • Bubbles can also be artificially introduced by aeration

  • Which ever way bubbles are made - the fluid around them is not stagnant but instead flows over the bubble-generating area (like the toroids and eddies of champagne)

  • Bubbles have many desirable characteristics - such as aeration and transport of biomaterial and chemicals and some deterimental affects such as outbreaks of disease (they can carry microorganisms)

  • In fact, while a formed bubble is rising, it is also mixing. There is ambient fluid formed in the wake of the bubble and it is shedding vortices that can spread laterally and provide passive transport for microorganisms and particles (3). As we've seen with champagne, when a bubble reaches the surface, the thin film that defines it's path leads to a hole and the retraction of that film. This causes the bubble to burst and its contents to be exposed to the air. This mixing (or aeration) performed by bubbles is crucial to life in the water and in bioreactor

  • Bubbles even live on after they have burst by creating smaller bubbles that themselves mix and burst or by releasing pathogen or particle-filled droplets (3). All of this from a humble result of surface tension, pressure and fluid dynamics. In the paper, the authors state that "bubbles deeply connect physics to biology through subtle interfacial fluid dynamics"

  • Final fun fact

  • In a paper published in 2002 in the journal Anesthesia, Pemberton et al looked at the angle of cranio-cervical extension (i.e. neck bend) involved in drinking from various types of glasses 

  • They found that: The mean [95% confidence intervals] extension from the neutral position required to drain each glass was: narrow flute 40 degrees [35-44]; wide flute 22 degrees [19-25]; wine glass 26 degrees [24-29]; champagne saucer 0 degree [-1-2]. Drinking from the narrow rimmed champagne flute required significantly more extension than the other types of glass (p < 0.001), and 73% of the total available cranio-cervical extension. 

  • So many do some neck stretches before a night of champagne drinking if you favor a narrow champagne flute

  • And if you’re thinking about what to pair with champagne, Schmidt et al proposed a umami pairing model in a 2020 article in Sci Rep which looks at the free glutamate and free nucleosides and their action on the umami receptors on our tongue to pair foods (eggs and bacon, ham and cheese)

  • Glutamate - amino acid most commonly found as a neurotransmitter

  • Nucleosides - nucleotides without the phosphate group

  • Looking at the umami compounds in champagne in oysters, the scientists hypothesize that pairing is so good due to the free glutamate in the champagne and the free glutamate and 5-nucleosides in the oysters all hitting those umami receptors on your tongue

  • They even measured the amounts in different champagne and oysters to find the optimal pairing

  • Aged champagnes with long yeast contact and the European oyster (Ostrea edulis) rather than a Pacific oyster (Crassostrea gigas)

  • I absolutely love this idea of a scientific approach to food pairings.  Although, without setting up a chemistry lab in the shed, i don’t know if it’s practical for everyday life

Vocab

  • Fermentation - the chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of heat.

  • Fluid dynamics - subdiscipline of fluid mechanics that describes the flow of fluid

  • Film droplets - smaller and form as the film of the emerged bubble disintegrates

  • Jet droplets - larger droplets and formed as the cavity of the bubble collapses and ruptures

  • Glutamate - amino acid involved in neurotransmission

  • Nucleosides - akin to nucleotides but without the phosphate group

Thanks for listening to this episode of LuxeSci.  A very special thank you to my audio engineer, Dimos.  Our theme music is Harlequin Moon by Burdy. If you have a correction, comment or suggestion for a topic, you can reach me at: drlex@luxesci.com.  We’re on Twitter and Instagram at luxescipod and our website is luxesci.podcastpage.io.  If you like us, please subscribe.   Please also leave us a review where ever you listen to podcasts.  See you again in 2 weeks!



  Beaumont, F, et. al. Computational Fluid Dynamics (CFD) as a Tool for Investigating Self-Organized Ascending Bubble-Driven Flow Patterns in Champagne Glasses. Foods 2020, 9(8), 972.

  Ghabache, E, et. al. Evaporation of droplets in a Champagne wine aerosol. Sci Rep. 2016; 6: 25148

  Walls, P., et. al. Moving with Bubbles: A Review of the Interactions between Bubbles and the Microorganisms that Surround them. Integrative and Comparative Biology, Volume 54, Issue 6, December 2014, Pages 1014–1025.


Professor Gerard Liger-Belair at the University of Reims


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