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Im just guessing here.. But maybe its because of centripetal force? When you stir it it kinda has a small current and that pushes the nucleation sites to the middle.. And if you didnt stir it, when you poured it would have swirled around anyway so its pretty much the same thing..Correct me if in wrong..
Stephen Fry on Qi, Re: bubbles in champagne:-"No, what it is, is . . . In absolutely pure . . . say, pure distilled water, er, the exact amount of carbon dioxide, that, say, produces the supposed quarter of a billion bubbles per bottle of champagne, would just dissolve invisibly in the water. But the impurities in . . . from the glass: bits of dirt; any flake . . . like . . . like . . . like a . . . you know, a pearl from an oyster . . . it needs that, and it's called a "condensation nucleus". And about those tiny, invisible specks, each bubble just forms."http://www.freewebs.com/qitranscripts/310.htmA microscopic fragment of grape is more likely than "dirt", a flaw in the glass would also suffice.
Hi Neilthis is all about surface tension and bubble nucleation. Water is a very sticky molecule because it forms electrical interactions between adjacent molecules called hydrogen bonds. This makes it very difficult for a nascent (newly forming) bubble to prise the water molecules apart sufficiently to allow the bubble to remain in existence. This collapsing force is the surface tension.This means that bubble formation will tend to occur where there is naturally already an imperfection in the way the molecules of liquid are interacting with each other. So a slightly rough or sharp region of the glass wall in a champagne flute for example. Here the bubbles find it slightly easier to form, so they originate at this point preferentially. Once a small bubble has formed then gas can move out of the drink very readily to join and swell the newly formed bubble, which rises to the surface and pops.Chris
As stated already its mainly due to minute particles of dust etc. stuck to the glass and sometimes due to imperfections in the glass that cause the bubbles to stream. Mainly the former as glass tends to have a fairly smooth regular tough finish.A friend who works in a pub says its forbidden to pour beer and fizzy drinks into wet glasses as it stops most bubbles from forming and stops beer getting a head.Try it yourself and pour a fizzy drink into a freshly washed wet glass and see the lack of bubbles.
Dry ice - frozen CO2 ? - boy that will produce one cold drink (-60C)!
Stirring the lemonade knocks most of the bubbles out of it. BTW, did you know that the only reason I have ever heard of for ordering a Guinness shandy was to wind up the bar staff?