
Walk into any pub and order a pint of Guinness, and you’ll witness a mesmerizing ritual. The bartender pulls the tap, fills the glass two-thirds full, then sets it aside to settle before topping it off with that iconic creamy head. But crack open a can of Guinness at home, and something magical happens without any theatrical waiting period. Pour it out, and you get that same cascading foam effect that made the beer famous.
But how is it done? It’s all thanks to a tiny little device that is affectionately known as The Widget.
Beer Engineering

In 1959, draught Guinness diverged from other beers. The pints served from the tap at the pub were charged with a combination of nitrogen gas and carbon dioxide, rather than just carbon dioxide alone. Nitrogen is less soluble in beer than carbon dioxide, and low temperatures and higher pressures are required to get it to stay in the fluid. Charging the beer in this way, and then forcing it through a tap with a restrictor plate with many fine holes, allows the pouring of a beer with small, fine bubbles. This is what gives Guinness its signature smooth, creamy texture and characteristic dense head. The lower carbon dioxide level also contributes to the flavor, removing some of the sharp taste present in regular carbonated beers.
When Guinness started using the nitrogenation method, it quickly gained popularity and became the default way to serve the draught beer. The problem was that it wasn’t initially practical to do the same for bottled Guinness. Without being poured through the fine holes of a special tap under pressure, it wasn’t possible to create the same foamy head. Bottled Guinness thus remained carbonated in the traditional manner, and it was thus very much unlike the draught beer served at the pub. The desire was to produce a better version—”bottled draught Guinness” was a term often bandied about. The company experimented with a variety of methods of serving nitrogenated Guinness from a bottle or can. It even sold some bottles with a special “initiator” syringe to generate head in select markets, but it was all too clumsy to catch on with the beer drinking public. A better solution was needed.

The modern widget was developed as the technological solution to this fundamental problem in beverage physics. Guinness tackled this challenge by essentially putting a tiny pressure vessel inside the larger pressure vessel of the can itself. The widget is a small plastic sphere, hollow inside, with a tiny hole on the surface. The widget and beer are placed inside the can on the production line. Liquid nitrogen is then added, before the can’s lid is sealed. The can is then inverted as the liquid nitrogen quickly boils off into a gas. This effectively fills the widget with gaseous nitrogen under pressure, often along with a small amount of beer. It’s a charged pressure vessel lurking inside the can itself.
The magic happens when the beverage is served. When you crack open the can, the pressure inside drops rapidly to atmospheric pressure. The nitrogen under pressure in the widget thus wants to equalize with the now lower-pressure environment outside. Thus, the nitrogen sprays out through the tiny hole with tremendous force, creating countless microscopic bubbles that act as nucleation sites for the rest of the nitrogen dissolved in the surrounding beer. As the beer is poured into a glass, a foamy head forms, mimicking the product served fresh from the tap at the local pub.
Today’s widget, first marketed in 1997, is the floating sphere type, but the original version was a little different. The original widget launched in 1989 was a flat disc, which was mounted in the bottom of the can, but fundamentally worked in the same way. However, it had a tendency to cause rapid overflowing of the beer if opened when warm. The floating spherical widget reduced this tendency, though the precise engineering reasons why aren’t openly explained by the company. The fixed widget actually had a surprise return in 2020 due to COVID-19 supply chain issues, suggesting it was still mostly fit for purpose in the brewery’s eyes.
The key to the widget’s performance is in the filling and the construction. It’s important to ensure the widget is filled with pressurized gas, hence the inversion step used in the filling process. If the pressurized nitrogen was allowed to simply sit in the empty space in the top of the can, it would just vent out on opening without making any head. The orifice size on the widget is also critical. Too large, and the pressure equalizes too quickly without creating the necessary turbulence. Too small, and insufficient gas and beer volume flows through to generate adequate nucleation. The widget as it stands today is the result of much research and development to optimize its performance.

Further different widget designs have emerged over the years. The company had mastered draught Guinness in a can, though it needed to be poured into a glass to be drank properly. The company later looked to create draught Guinness that could be drank straight from the bottle. This led to the creation of the “rocket widget.” It worked largely in the same way, but was designed to float while remaining in the correct orientation inside the neck of the bottle. Fins ensured it wouldn’t fall out of the bottle during drinking. It would charge the beer with bubbles when first opened, and continue to boost the head to a lesser degree each time the bottle was tilted for a sip.
Guinness could have left this problem unsolved. It could have remained a beautiful tap-based beer, while selling its lesser carbonated products in bottles and cans for home consumption. Instead, it innovated, finding a way to create the same creamy tap-poured experience right out of the can.
The next time you crack open a widget-equipped can and watch that mesmerizing cascade of bubbles, you’re witnessing a masterpiece of beverage engineering that took years to perfect. It’s a reminder that sometimes the most elegant engineering solutions hide in the most ordinary places, waiting for someone clever enough to recognize that a tiny plastic ball could revolutionize how we experience beer outside the pub.
This articles is written by : Nermeen Nabil Khear Abdelmalak
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