Beer 101 - Nitrogen capsules

Nitrogen capsules ("widgets")

The term widget can also be used to refer to a laser-etched pattern at the bottom of a beer glass which aids the release of carbon dioxide bubbles.^[2] The pattern of the etching can be anything from a simple circular or chequered design to a logo or text.

The widget in the base of a beer glass works by creating a nucleation point, allowing the CO₂ to be released from the liquid which comes into contact with it, thus assisting in maintaining head on the beer.

While glass widgets work on any carbonated beverage, the result is considerably less noticeable with bottled or canned drinks, with the best results produced in draught lager or cider. Czech and German glass makers would use beer to show how perfect their handblown glass was allowing very little imperfection to create this nucleation point for the CO_2.

Guinness introduced the nitrogen capsule, commonly known as the widget, in cans of Guinness Stout in the late 1980s. Subsequently, this device has caused many shirts and shoes to be soaked with beer as people discover for themselves the magic of nitrogen draft flow systems. Guinness served on draft acquires its creamy head when nitrogen bubbles are flushed through the beer at the time of serving. The widget is a small plastic capsule containing pressurized nitrogen gas that rushes out of a pinhole when the can is opened and the internal pressure is lowered. Widgets have now found their way into bottles as well as cans and have jumped species from Irish stouts to other ales, though not necessarily with the same levels of critical acclaim.

Why Nitrogen?

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. It is important that oxygen be eliminated from any process developed as this can cause flavour deterioration when present.

The presence of dissolved nitrogen allows smaller bubbles to be formed thereby increasing 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 is then poured out, 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