Bubbles, bubbles, everywhere

There are many reasons to love the movie, Charlie and the Chocolate Factory (I’m referring to the Gene Wilder version). While the film is a delight of cinematic wonder and bon mots, there’s a line in there that always stuck with me “Bubble, bubbles everywhere but not a drop to drink”. This is a riff on a line from “The Rime of the Ancient Mariner”, “water, water every where but not a drop to drink”. I’m not entirely sure why this line stuck with me all these years. Besides the obvious reason of everyone loving bubbles, it’s an especially memorable quote from the movie. The reason may not be as important as the result, not only do I love soap bubbles, I love champagne bubbles. I thought for a festive, New Year’s Eve version of my “explaining the science behind things I love” series, I’d dive into the world of champagne bubbles.

I’ve always (since I’ve been 21 of course) like 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. However, 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 branding champagne to be as associated with celebrations as it is now. 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 and not above ruining a good magical moment with a scientific fact, I set out to see what I could find about what makes champagne bubbles so special.

First, let’s get the question of the glass out of the way. In the articles that I had access to, i.e. the ones I didn’t have to pay to read, there wasn’t a consensus on which champagne glasses provide the best drinking experience. In this relatively non-scientific survey done by the Wine and Spirit Education Trust (https://www.wsetglobal.com/knowledge-centre/blog/2019/october/18/whats-the-best-glass-for-champagne/), they made a slight case for a tulip flute or white wine glass since those allow more of the aroma to be taken while drinking. However, there is some room for personal preference in there and some difference based on the champagne. I’m going to through my hat in the ring for tulip flutes myself.

That’s not to say that the shape of the glass doesn’t impact the bubbles, it most certainly does. Fairly recently, glass manufacturers introduced laser etching into champagne and beer glasses to improve the bubble flow in both liquids. The lasers etch a ring on the bottom of the glass that leads to the formation of bubbles, leading to the characteristic effervescence (a continuous stream of bubbles flowing upwards in the glass). (1) So the shape and make-up of a glass can impact bubbles but where do they come from and why are they important?

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 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. The really interesting thing is that the bubbles don’t only bring CO2 to the surface, they also bring dissolved volatile organic compounds. 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) There is a significant body of research using infrared thermography imaging (images generated from thermal cameras) and particle image velocimetry (an optical method of flow visualization) to research the relationship between flow patterns of the bubbles and release of CO2 from the champagne surface. It’s hoped that further understanding the fluid dynamics of the bubbles and how to influence their formation and flow could lead to better tasting experience for champagne lovers.

One research article that I found particularly interesting relating to champagne bubbles was written by Elisabethe Ghabache et al (2). These researchers compared champagne bubbles to sea spray and set out to further characterize the bubbles. It turns out that sea spray is also used to transport dissolved gases, salts, surfactants and biological materials to the atmosphere (2). This spray (and most other bubbling liquids) are made of two types of droplets; 1) film droplets, which are smaller and form as the film of the emerged bubble disintegrates; and 2) jet droplets, which are larger and formed as the cavity collapses and ruptures (2). A series of experiments was set up using a syringe pump and 5 types of liquids (de-gased champagne, demineralized water and 3 hydro-alcoholic solutions) to characterize the bubbles in champagne. An array of methods, including extreme close-up, ultra-fast imagery, high-speed digital cameras and fluid dynamics modeling was used to measure various aspects of the bubbles in the different liquids.

So what did they find? Amazingly, 300-500 bubbles per second burst at the top of the champagne glass. That’s quite a rate of exchange! It turns out that champagne contains no film droplets and only jet droplets so the comparison to sea spray and how that works is not 100% accurate. They also found that the aerosols from the top evaporated 10x faster in champagne than still liquid surfaces. What that means for us is that the fizz in champagne (and other sparkling beverages) is a crucial part of the flavor experience. Since more bubbles equals more exchanges of gases and volatile organics, that’s more chances for your nose to pick up on all those amazing aromas and have those scents round out how you taste the champagne. What was also interesting about this article is that they found that larger bubbles created more aroma diffusion. This is contrary to the popular opinion that smaller bubbles are better in champagne. (2)

How cool is all this?! I love finding out a little bit about the science behind the things I love. It’s a process that has always enhanced my experiences in life. And when I was doing my research I found an in-depth and entertaining review article about bubbles in general and their importance in the world at large (3). As we saw with the champagne example, bubbles are great for mixing, in nature this mixing capacity is used for oxygenation and other iterations of stirring things up. You see this especially with bodies of water but it can also be observed in biofermentors and artificial environments too. (3) 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 bioreactors. 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”. (3) Seeing how these sometimes abstract sciences work together in nature is fascinating for me.

I could on and on about bubbles but there are party hats to don, crackers to get ready and of course, bubbles to drink (all with our nuclear families only of course). I hope you all have a happy, healthy and safe New Year. I’m off to go chill a bottle of champagne.

References:

  1. 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.
  2. Ghabache, E, et. al. Evaporation of droplets in a Champagne wine aerosol. Sci Rep. 2016; 6: 25148
  3. 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.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s