Dear Matthew Alice: Recently, as I lay sipping fine champagne and playing snugglebunnies with my latest female conquest, my visions of carnal delights-to-be were constantly interrupted by one niggling query: Why do champagne bubbles appear to continuously emanate in a stream from a sole source on the crystal flute's inner wall, in perfect cadence, and never varying in diameter more than .001 surface profile? This is very unlike soda bubbles that appear to follow a sort of Brownian effervescence theory. — Hurricane Jim, Encinitas
While you’ve been out seducing half of North County, ’Cane, the French have been diligently developing bubble- and foam-analyzing machines for your edification. And here’s what they’ve learned so far. Which actually isn’t a lot. The biggest difference between the two is the stability of the CO2 in each. The bubbles in champagne (and beer and cider) are a natural byproduct of fermentation; soft drinks have the CO2 forced in artificially.
If bubbles are to form at all, in any kind of liquid, they require a nucleation site, some irregularity on the surface of a glass (or ice or whatever) around which the CO2 molecules can accumulate. The density of the liquid determines how big the bubble must be before it is buoyant enough to release from the glass and rise. The bubbles themselves then act as nucleation sites, attracting CO2 and growing as they float upward. Because the bubbles are spherical, their buoyancy (volume) increases proportionally faster than their drag (surface area), so the bubbles speed up as they rise. Champagne is carefully cultured to produce the finest bubbles and just the right amount of foam, something soft drink bottlers don’t particularly care about. The French now suspect the quality of the bubbles is also affected by certain chemical components in the surrounding liquid, but exactly how is not precisely known.
Champagne yields a “wet” foam; a film of wine still clings to each bubble after it surfaces so it doesn’t cling directly to its neighbor. This creates a thin layer of round or dome-shaped bubbles around the rim. Beer generates “dry” foam; natural surfactants cause the brew to slide off the bubbles, and they stick together reshaped into polyhedrons, like soap bubbles, and maintain a head. Happy now? Bottom’s up, Jim.