When beer is stored in large quantities—in the cool cellar of a bar or pub, for example—it can be retained in the casks in which it was delivered, where its continued fermentation improves the taste and strength of the drink. When the cask beer is eventually drawn out by a pump, it mixes with nitrogen in the air and gains its characteristic texture and head. Guinness Irish s-tout is unusual in that its distinctive head is caused by special taps that ensure a precise mix.
When brewers started putting beer in bottles so that it could be drunk away from the cask, they found that the fermentation in bottles caused a much higher level of carbonation. All this carbon dioxide is good because it leaves no room for oxygen in the bottle, which would sour the beer, but it creates a much fizzier drink. Without the taps to pour the beer, the texture of the beer is significantly different also.
Beer was first sold to the public in cans in 1935.However, many drinkers, perhaps even the majority, prefer the taste and texture of draft beer to the canned product. And if people demand that, then companies such as Guinness want to sell it to them. Guinness has therefore spent a fortune in finding a way to transfer the taste, texture, and head of their stout into cans.
In the 1980s Alan Forage and William Byrne found a way to simulate the nitrogen mix that a Guinness tap gives the beer. A small ball full of nitrogen and beer called a "widget" is put in the can along with the beer. When the can is opened, the internal pressure suddenly drops, and the nitrogen escapes into the beer, giving it the required texture and head.
