Foamy CO2

• Placed inside the can just before sealing, the plastic widget serves as a vessel that delivers a burst of gas into the beer upon opening. This burst results in a release of CO2 -- carbon dioxide gas -- which is responsible for giving draft beer its foamy head. Without the widget, an open can of beer has some carbonation bubbles, but relatively little foam.

Atomic Number Seven

• Inside the widget is nitrogen gas, which assists in the creation of a thick head. When the can is sealed and pressurized, beer enters the widget through a small hole, compressing the nitrogen gas. Opening the tab results in a drop in pressure, forcing the beer and nitrogen to escape the widget and enter the surrounding beer. This rush of beer and gas causes the CO2 to escape the liquid and becomes the free gas that forms the foam.

Chilly Widgets

• Opening up a warm beer proves quite messy when the can is equipped with a widget. Gases are less soluble in warm liquids; combine this with a widget that increases free gas and you have an increased amount of CO2 flowing from an open can of beer. In other words, the warmer the beer, the more likely the foam is to overflow from the can. Chilling the beer prior to opening ensures a more controlled head.

Widget Woes

• Despite its ability to mimic draft beer, the widget it not well-received by all beer drinkers. In fact, some find the plastic device more of a nuisance than a benefit. The sight of the widget floating makes the beer less unappetizing for some consumers. Others find the widget an unnecessary eyesore. For this reason, some manufacturers have removed the widgets from their beers. Some manufacturers state that the beer is widget free on the packaging label.