A widget is a device placed in a container of beer to manage the characteristics of the beer's head. The original widget was patented in Ireland by Guinness. The "floating widget" is found in cans of beer as a hollow plastic sphere, approximately 3 centimetres (1.2 in) in diameter (similar in appearance to a table tennis ball, but smaller) with two small holes and a seam. The "rocket widget" is found in bottles, 7 centimetres (2.8 in) in length with the small hole at the bottom.[1]
Method
Some canned beers are pressurized by adding liquid nitrogen, which vaporises and expands in volume after the can is sealed, forcing gas and beer into the widget's hollow interior through a tiny hole—the less beer the better for subsequent head quality. In addition, some nitrogen dissolves in the beer which also contains dissolved carbon dioxide. Oxygen is generally excluded as its presence can cause flavour deterioration.
The presence of dissolved nitrogen allows smaller bubbles to be formed, which increases the creaminess of the head. This is because the smaller bubbles need a higher internal pressure to balance the greater surface tension, which is inversely proportional to the radius of the bubbles. Achieving this higher pressure would not be possible with just dissolved carbon dioxide, as the greater solubility of this gas compared to nitrogen would create an unacceptably large head.
When the can is opened, the pressure in the can quickly drops, causing the pressurised gas and beer inside the widget to jet out from the hole. This agitation on the surrounding beer causes a chain reaction of bubble formation throughout the beer. The result, when the can's content is then poured, is a surging mixture in the glass of very small gas bubbles and liquid.
This is the case with certain types of draught beer such as draught stouts. In the case of these draught beers, which before dispensing also contain a mixture of dissolved nitrogen and carbon dioxide, the agitation is caused by forcing the beer under pressure through small holes in a restrictor in the tap. The surging mixture gradually settles to produce a very creamy head.
