I know the actual result of the Widget, a fine, rich froth. I know the basic mechanism, pressurized gas escaping when the whole can depressurizes, and pushing the beer out from the widget. I still don't understand how this whole "activation" process works.
What physical processes occur in the liquid that result in this particular effect. as opposed to, say, big, coarse big bubbles as would blowing air through a straw into beer create?
Widgetized beers are packaged with liquid nitrogen, and the widget, which contains a small hole. The liquid nitrogen warms, turns to a gas inside the sealed can, which forces gas and beer into the widget through the hole.
When the can is opened, the pressure inside drops suddenly, causing the contents of the widget to be shot into the beer, agitating the beer, producing the foam.
If this were tried with a regularly carbonated beer, you'd end up with foam erupting out of the can. Hence, beers packaged with a widget have only about 1/3 the carbon dioxide dissolved than regular beers, plus the nitrogen, which creates a smooth mouthfeel and dense foam. Due to the requirements of reduced carbon-dioxide, the widget is used almost exclusively with Stouts, Bitters and Irish Red ales - styles that can be served with lower volumes of carbon-dioxide.
see
