How Does the Beer Can Widget Work?

The Guinness Widget. Note the cavity near the center of the ball, the tiny hole is located within the cavity.
The Guinness Widget. Note the cavity near the center of the ball, the tiny hole is located within the cavity.

To answer this question first we need to discuss what makes beer fizzy and how a head forms.

Most beers are carbonated with carbon dioxide (CO2). When the beer is in the can some of this CO2 is dissolved in the beer and some is at the top of the can. The CO2 that is dissolved in the beer is what makes it fizzy. When the can is closed the pressure inside is higher than the pressure outside, so that when you open the can the sudden drop in pressure and the agitation of pouring causes some of the CO2 to bubble out of solution, forming a head on your beer.

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A stout like Guinness has a creamier, longer lasting head than a canned lager beer. In addition, Guinness is less fizzy than a regular lager beer. Guinness is canned with a mixture of carbon dioxide and nitrogen. Nitrogen is not absorbed into the beer nearly as well as carbon dioxide, so even though a can of Guinness may be at the same pressure as a can of lager, it contains less CO (and is therefore less fizzy) because the nitrogen makes up some of the pressure.

Because a beer like Guinness contains less dissolved CO2, if you poured it from a can with no widget, the head not be very thick because most of the CO2 would stay dissolved.

The purpose of the widget is to release the CO2 from some of the beer in the can to create the head. The widget is a plastic, nitrogen-filled sphere with a tiny hole in it. The sphere is added to the can before the can is sealed. It floats in the beer, with the hole just slightly below the surface of the beer.

Just before the can is sealed a small shot of liquid nitrogen is added to the beer. This liquid nitrogen evaporates during the rest of the canning process and pressurizes the can. As the pressure increases in the can, beer is slowly forced into the sphere through the hole, compressing the nitrogen inside the sphere.

When you open the can, the pressure inside immediately drops, the compressed gas inside the sphere quickly forces the beer out through the tiny hole into the can. As the beer rushes through the tiny hole, this agitation causes the CO2 that is dissolved in the beer to form tiny bubbles that rise to the surface of the beer. These bubbles help form the head.

Originally Published: Aug 16, 2000

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Beer Widget FAQ

What beers have a widget?
Though this list is not all-inclusive, some of the most popular beers that have a widget are Old Speckled Hen, Boddingtons Pub Ale, Murphy's Stout, and Guinness.
Who invented the beer widget?
Although it was patented in Ireland by Guinness in 1969, the beer widget was invented by John Lunn, Master Distiller. The beer widget didn't appear in the United States until around 1990.
Does Guinness still use a widget?
Yes, though what kind of widget has changed a bit. Guinness has been using a floating widget since 1997, but switched back to a fixed widget system in 2020 due to supply issues caused by COVID-19. They have plans to bring back the floating widget in 2021, barring any further challenges.
What does a widget accomplish?
A beer widget creates a taste in a can that's close to a real draft. British, Irish, Scottish and Welsh beer is not as heavily carbonated as American beer, so when their brews are bottled, there's no head when poured. This is also why these countries are the only ones who use this technology.
Do beer glasses have widgets?
Some beer glasses have a nucleation point or an etched pattern on the inside bottom of the glass, which helps release the beer's dissolved CO2 in the form of bubbles. This makes for better head retention — the foam on top of a glass of beer.