FEATURE ARTICLE
Bubbles and Flow Patterns in Champagne
Is the fizz just for show, or does it add to the taste of sparkling wines?
Guillaume Polidori, Philippe Jeandet, Gérard Liger-Belair
The Champagne Method
Fine sparkling wines and Champagne result from a two-step fermentation process. After completion of the first alcoholic fermentation, some flat Champagne wine (called base wine) is bottled with a mixture of yeast and sugar. Consequently, a second fermentation starts inside the bottle as the yeast consumes the sugar, producing alcohol and a large amount of carbon dioxide (CO2). This is why Champagne has a high concentration of CO2 dissolved in it—about 10 grams per liter of fluid—and the finished Champagne wine can be under as much as five or six atmospheres of pressure.
As the bottle is opened, the gas gushes out in the form of tiny CO2 bubbles. In order for the liquid to regain equilibrium once the cork is removed, it must release about five liters of CO2 from a 0.75 liter bottle, or about six times its own volume. About 80 percent of this CO2 is simply outgassed by direct diffusion, but the remaining 20 percent still equates to about 20 million bubbles per glass (a typical flute holds about 0.1 liter). For Champagne connoisseurs, smaller bubble size is also a measure of quality.
For consumers and winemakers as well, the role usually ascribed to bubbles in Champagne tasting is to awaken the sight sense. Indeed, the image of Champagne is intrinsically linked to the bubbles that look like “chains of pearls” in the glass and create a cushion of foam on the surface. But beyond this visual aspect, the informed consumer recognizes effervescence as one of the main ways that flavor is imparted, because bursting CO2 bubbles propel the aroma of sparkling wine into the drinker’s nose and mouth.
One cannot understand the bubbling and aromatic exhalation events in Champagne tasting, however, without studying the flow-mixing mechanisms inside the glass. Indeed, a key assumption is that a link of causality may exist between flow structures created in the wine due to bubble motion and the process of flavor exhalation. But the consequences of the bubble behavior on the dynamics of the Champagne inside the glass and the CO2-propelling process are still unknown. Quantifying the exhalation of flavors and aromas seems a considerable challenge, something that is difficult to control experimentally, but this constitutes the aim of our current work.
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