Why Does Guinness Have That Little Ball Rattling In Its Cans?

The rattling sound in an empty can of Guinness is caused by a small, white plastic ball, called a widget. It serves to mimic the appearance of Guinness served right from the tap.

Each can of Guinness has beer, a widget, and nitrogen. When the liquid nitrogen evaporates in the sealed can, the gas can only go into the widget through a small hole on its side.

Now, once the can is opened, all the pressure inside the can is released. The gas and beer trapped inside the widget then come bursting out through the hole.

The sudden surge of activity creates cascading bubbles, a nice foamy head, and a whooshing sound, all of which give your canned Guinness the look of a freshly poured draft beer.