How does the widget found in Draught beer cans work?

Draught beer cans contain a small plastic widget to enhance the drinking experience by creating a creamy head and a smooth pour that typically characterize draft beers. The widget works through the following mechanism:

1. Nitrogen Charging: Draught beer cans are filled with nitrogen gas instead of carbon dioxide, which is commonly used in regular beer cans. Nitrogen has smaller bubbles compared to carbon dioxide, resulting in a denser head that resembles the creamy foam found in draft beers served from a keg.

2. Widget Structure: Inside the can, there's a small, ball-shaped widget made of plastic. The widget contains a small hole at the bottom and is filled with nitrogen gas.

3. Pouring Mechanism: When the can is opened, the pressure inside the can pushes the beer upward. As the beer flows out of the can, it passes through the widget.

4. Nitrogen Diffusion: The small hole at the bottom of the widget allows a controlled release of nitrogen gas into the beer. The nitrogen bubbles interact with the beer, creating a cascading effect known as a nucleation reaction.

5. Creamy Head Formation: The nucleation reaction causes the nitrogen gas to form tiny bubbles that bond with the proteins and lipids in the beer. These bubbles act as nucleation sites, attracting more dissolved gas from the beer and leading to the formation of a dense, creamy, and stable foam head.

6. Smooth Pour: The widget also helps in achieving a smooth and controlled pour. The nitrogen gas provides a gentle push, allowing the beer to flow out of the can smoothly, preventing excessive foaming or splashing.

Overall, the widget found in draught beer cans works by utilizing nitrogen gas to create a creamy head and smooth pour, giving drinkers a draft-like experience from a regular beer can.