What does the widget do in a Guinness beer?
After pouring a can of Guinness, you may notice something rattling inside the empty can. This device is known as a “widget”. The widget is a small plastic sphere with a small amount of the beer inside of it. When the can is opened and the pressure inside is relieved, the beer inside the widget squirts out of small holes in the sides of the widget, acting like small jets of beer. These jets create nucleation sites in the beer for CO2 and Nitrogen to rapidly come out of solution and form the familiar dense head.
